Thèses sur le sujet « Al-Si-Cu ALLOY »

Dissertation submitted in fulfilment of the requirements for the degree Master of Technology: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology
Aluminium alloys has seen recent increase usage in the automotive industry. This is due to the global obligation towards carbon emission reduction and fuel efficiency in the transport sector. The good strength-to-weight ratio offered by Al-Si-Cu alloys showed promising results towards the compliance of these environmentally friendly criteria. The enhanced mechanical properties is obtained when the alloy is subjected to the T6 heat treatment process, which cause microstructural changes due to the evolution of intermetallic phases. The process involves solution heat treatment, for dissolving soluble Cu- and Mg-containing phases, the homogenization of alloying elements, and the spheroidisation of eutectic Silicon. It is followed by quenching, for maximum precipitation hardening particle retention in solution, and a further artificial ageing process with the aim to acquire a uniform distribution of small precipitates, for strength improvement. The heat treatment schedule applied in this study was conducted as follows: Solution heat treatment at a temperature of 525°C for 6h Quenching in water of temperature 50°C; Artificial ageing for 8h at a temperature of 175°C, and then after left inside furnace to cool down to room temperature. This is higher than the 520°C, but shorter than the 8-12h, observed in literature. Also, quenching is done at a lower temperature rather than 60°C, and artificial ageing at a higher temperature, rather than the 155°C. This was done to be able to draw a comparison between the MAGMASOFT® simulation, which has this non-adjustable schedule, and the experimental results. The simulated and experimental results were comparable and similar outcomes, but with some discrepancies. Such as the porosity was far more visible and intense in the experimental, than what was predicted by the software. The as-cast and heat treated microstructure revealed the expected evolution of intermetallic particles, such as dissolving of the Al2Cu and the spheroidisation of the eutectic Si phases. Another phase that was identified was the insoluble AlFeSi and other possible Fe-containing phases, which due to the higher solution heat treatment temperature, showed partial fragmentation and dissolution. The study provided practical data about the effect of heat treatment on microstructural evolution and how it affects the properties of the Al-Si-Cu alloy. It also brought to the attention and understanding of how critical pouring temperature is, as it affect the initial nucleation, and cooling rate, and therefore the micro and macro properties.

У 2004 р були опубліковані перші роботи, присвячені створенню і дослідженню нового класу матеріалів, так званих високоентропійних сплавів (ВЕС), що можуть включати в себе до 13 основних елементів, в концентраціях від 5 до 35%. У даній роботі за допомогою вібраційного магнітометра досліджені магнітні властивості ВЕС Al0.5CuFeNi та CuFeNiSi0.5 у литому стані. При цьому встановлено, що обидва сплави є феромагнетиками із питомою намагніченістю MS відповідно 28 А·м2/кг та 37 А·м2/кг. Підвищене значення MS для сплаву CuFeNiSi0.5 вочевидь пояснюється наявністю у ньому ОЦК фази, сформованої на основі феромагнітного α-заліза.

In this work, we have investigated the internal stress contribution to the flow stress for a commercial 6xxx aluminium alloy (AA6111). In contrast to stresses from forest and precipitation hardening, the internal stress cannot be assessed properly with a uniaxial tensile test. Instead, tension-compression tests have been used to measure the Bauschinger stress and produce a comprehensive study which examines its evolution with i) the precipitation structure and ii) a wide range of applied strain. A large set of ageing conditions was investigated to explore the effect of the precipitation state on the development of internal stress within the material. It is shown that the Bauschinger stress generally increases with the applied strain and critically depends on the precipitate average radius and is thus linked to the shearable/non shearable transition. Further work in the case of non-shearable particles shows that higher strain eventually lead to particle fracture and the Bauschinger stress then rapidly decreases. Following the seminal work of Brown et al, a physically based approach including plastic relaxation and particle fracture is developed to predict the evolution of the internal stress as a function of the applied strain. Knowing the precipitation structure main characteristics –such as the average precipitate radius, length and volume fraction– allows one to estimate accurately the internal stress contribution to the flow stress with this model.

Among the commercial aluminum alloys, aluminum 319 (Al-7wt%Si-4wt%Cu) type alloys are popularly used in automobile engine parts. These alloys have good casting characteristics and excellent mechanical properties resulting from a suitable heat treatment. To get a high strength in the 319 type alloys, grain refining, reducing the porosity, solid solution hardening, and precipitation hardening are preferred. All experimental variables such as solidification condition, composition, and heat treatment are influence on the precipitation behavior; however, precipitation hardening is the most significant because excess alloying elements from supersaturated solid solution form fine particles which act as obstacles to dislocation movement. The challenges of the 319 type alloys arise due to small size of precipitate and complex aging response caused by multi components. It is important to determine the chemical composition, crystal structure, and orientation relationship as well as precipitate morphology in order to understand the precipitation behavior and strengthening mechanism. In this study, the mechanical properties and microstructure were investigated using transmission electron microscopy and three dimensional atom probe tomography. The Mn and Mg effects on the microstructure and mechanical properties are discussed with crystallographic study on the iron intermetallic phases. The microstructural evolution and nucleation study on the precipitates in the low-Si 319 type aluminum alloys are also presented with sample preparation and analysis condition of TEM and 3DAP tomography.

AA6061 Al alloys modified with addition of Mn, Cr and Cu were homogenized at temperatures between 350 ºC and 550 ºC after casting. STEM experiments revealed that the formation of α-Al(MnFeCr)Si dispersoids during homogenization were strongly affected by various factors such as heating rate, concentration of Mn, low temperature pre-nucleation treatment and homogenization temperature. Through analysis of the STEM results using an image software Image-Pro, the size distributions and number densities of the dispersoids formed during different annealing treatments were quantitatively measured. It was revealed that increasing the heating rate or homogenization temperature led to a reduction of the number density and an increase in size of the dispersoids. The number density of dispersoids could be markedly increased through a low temperature pre-nucleation treatment. A higher Mn level resulted in the larger number density, equivalent size and length/width ratio of the dispersoids in the alloy. Upsetting tests on two of these Mn and Cr-containing AA6061 (Al-Mg-Si-Cu) Al alloys with distinctive Mn contents were carried out at a speed of 15 mm s-1 under upsetting temperature of 450 ºC after casting and subsequent homogenization heat treatment using a 300-Tone hydraulic press. STEM experiments revealed that the finely distributed α-Al(MnFeCr)Si dispersoids formed during homogenization showed a strong pinning effect on dislocations and grain boundaries, which could effectively inhibit recovery and recrystallization during hot deformation in the two alloys. The fractions of recrystallization after hot deformation and following solution heat treatment were measured in the two alloys with EBSD. It was found that the recrystallization fractions of the two alloys were less than 30%. This implied that the finely distributed α-dispersoids were rather stable against coarsening and they stabilized the microstructure by inhibiting recovery and recrystallization by pinning dislocations during deformation and annealing at elevated temperatures. By increasing the content of Mn, the effect of retardation on recrystallization were further enhanced due to the formation of higher number density of the dispersoids. STEM and 3-D atom probe tomography experiments revealed that α-Al(MnFeCr)Si dispersoids were formed upon dissolution of lathe-shaped Q-AlMgSiCu phase during homogenization of the modified AA6061 Al alloy. It was, for the first time, observed that Mn segregated at the Q-phase/matrix interfaces in Mn-rich regions in the early stage of homogenization, triggering the transformation of Q-phase into strings of Mn-rich dispersoids afterwards. Meanwhile, in Mn-depleted regions the Q-phase remained unchanged without segregation of Mn at the Q-phase/matrix interfaces. Upon completion of α-phase transformation, the atomic ratio of Mn and Si was found to be 1:1 in the α-phase. The strengthening mechanisms in the alloy were also quantitatively interpreted, based on the measurements of chemical compositions, dispersoids density and size, alloy hardness and resistivity as a function of the annealing temperature. This study clarified the previous confusion about the formation mechanism of α-dispersoids in 6xxx series Al alloys. Four-point bend fatigue tests on two modified AA6061 Al alloys with different Si contents (0.80 and 1.24 wt%, respectively) were carried out at room temperature, f = 20 Hz, R = 0.1, and in ambient air. The stress-number of cycles to failure (S-N) curves of the two alloys were characterized. The alloys were solution heat treated, quenched in water, and peak aged. Optical microscopy and scanning electron microscopy were employed to capture a detailed view of the fatigue crack initiation behaviors of the alloys. Fatigue limits of the two alloys with the Si contents of 0.80 and 1.24 wt% were measured to be approximately 224 and 283.5 MPa, respectively. The number of cracks found on surface was very small (1~3) and barely increased with the applied stress, when the applied stress was below the yield strength. However, it was increased sharply with increase of the applied stress to approximately the ultimate tensile strength. Fatigue crack initiation was predominantly associated with the micro-pores in the alloys. SEM examination of the fracture surfaces of the fatigued samples showed that the crack initiation pores were always aspheric in shape with the larger dimension in depth from the sample surface. These tunnel-shaped pores might be formed along grain boundaries during solidification or due to overheating of the Si-containing particles during homogenization. A quantitative model, which took into account the 3-D effects of pores on the local stress/strain fields in surface, was applied to quantification of the fatigue crack population in a modified AA6061 Al alloy under cyclic loading. The pores used in the model were spherical in shape, for simplicity, with the same size of 7 μm in diameter. The total volume fraction of the pores in the model were same as the area fraction of the pores measured experimentally in the alloy. The stress and strain fields around each pore near the randomly selected surface in a reconstructed digital pore structure of the alloy were quantified as a function of pore position in depth from the surface using a 3-D finite element model under different stress levels. A micro-scale Manson-Coffin equation was used to estimate the fatigue crack incubation life at each of the pores in the surface and subsurface. The population of fatigue cracks initiated at an applied cyclic loading could be subsequently quantified. The simulated results were consistent with those experimentally measured, when the applied maximum cyclic stress was below the yield strength, but the model could not capture the sudden increase in crack population at UTS, as observed in the alloy. This discrepancy in crack population was likely to be due to the use of the spherical pores in the model, as these simplified pores could not show the effects of pore shape and their orientations on crack initiation at the pores near surface. Although it is presently very time-consuming to calculate the crack population as a function of pore size and shape in the alloy with the current model, it would still be desirable to incorporate the effects of shape and orientation of the tunnel-shaped pores into the model, in the future, in order to simulate the fatigue crack initiation more accurately in the alloy.

This thesis systematically investigates the effects of a recently developed modified ageing procedure of aluminium alloys, termed the T6I6 temper, on the microstructural development and mechanical properties of the Al ??? Mg ??? Si - Cu alloy 6061. For the T6I6 temper, a conventional single stage T6 temper is interrupted by an ageing period at a reduced temperature (65??C) to facilitate secondary precipitation, before resuming the final ageing at the temperature of the initial T6 treatment. The T6I6 temper was found to cause simultaneous increases in tensile properties, hardness, and toughness as compared with 6061 T6. Al ??? Mg ??? Si ??? Cu alloys are medium strength alloys widely used in the automotive industry and their further improvement is underpinned by stringent demands for weight reduction placed on the transportation industry in recent years. The potential for further improvement of the mechanical properties was found in the control of secondary precipitation that may take place even in some fully aged alloys when exposed to reduced temperatures. The overall improvement in the mechanical properties of 6061 T6I6 was attributed to the formation of finer and more densely dispersed precipitates in the final microstructure. The refinement of precipitates was facilitated by control of the precipitation processes and gradual evolution of the microstructure throughout each stage of the T6I6 treatment. The results indicated that the concentration and the chemical environment of the vacancies controlled the precipitation processes in this alloy. Findings also show that the proportion of the different precipitate phases present in the final microstructure, as well as the amount of the solute in these precipitates, can be controlled and modified utilizing secondary precipitation. A number of analytical techniques were used in this study. The evolution of the microstructure was studied using Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and Three Dimensional Atom Probe (3DAP). Vacancy-solute interactions were studied using Positron Annihilation Lifetime Spectroscopy (PALS) and 3DAP. The distribution of the solute was studied using 3DAP and Nuclear Magnetic Resonance (NMR). Differential Scanning Calorimetry (DSC) was used to identify precipitation reactions and to determine the stability of vacancy-associated aggregates.

Environmental savings can be made by increasing the use of aluminium alloys in the automotive industry as the vehicles can be made lighter. Increasing the knowledge about the heat treatment process is one task in the direction towards this goal. The aim of this work is to investigate and model the heat treatment process for Al-Si casting alloys. Three alloys containing Mg and/or Cu were cast using the gradient solidification technique to achieve three different coarsenesses of the microstructure and a low amount of defects. Solution treatment was studied by measuring the concentration of Mg, Cu and Si in the α-Al matrix using wavelength dispersive spectroscopy (WDS) after various times at a solution treatment temperature. A diffusion based model was developed which estimates the time needed to obtain a high and homogenous concentration of alloying elements for different alloys, temperatures and coarsenesses of the microstructure. It was shown that the yield strength after artificial ageing is weakly dependent on the coarseness of the microstructure when the solution treatment time is adjusted to achieve complete dissolution and homogenisation. The shape and position of ageing curves (yield strength versus ageing time) was investigated empirically in this work and by studying the literature in order to differentiate the mechanisms involved. A diffusion based model for prediction of the yield strength after different ageing times was developed for Al-Si-Mg alloys. The model was validated using data available in the literature. For Al-Si-Cu-Mg alloys further studies regarding the mechanisms involved need to be performed. Changes in the microstructure during a heat treatment process influence the plastic deformation behaviour. The Hollomon equation describes the plastic deformation of alloys containing shearable precipitates well, while the Ludwigson equation is needed when a supersaturated solid solution is present. When non-coherent precipitates are present, none of the equations describe the plastic deformation well. The evolution of the storage rate and recovery rate of dislocations was studied and coupled to the evolution of the microstructure using the Kocks-Mecking strain hardening theory.

Orientador: Eugênio José Zoqui
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho tem como objetivo avaliar a tixoconformabilidade de ligas Al-Xwt%Si- 2,5wt%Cu abrangendo todas as etapas do processo: obtenção das ligas tixofundidas, caracterização microestrutural, caracterização do comportamento viscoso e processo de tixoforjamento em dois conjuntos de equipamentos diferentes, a saber, prensa excêntrica e prensa pneumática. As ligas Al-2,0wt%Si-2,5wt%Cu, Al-3,0wt%Si-2,5wt%Cu, Al-4,0wt%Si- 2,5wt%Cu, Al-5,0wt%Si-2,5wt%Cu e Al-7,0wt%Si-2,5wt%Cu foram produzidas via lingotamento estanque com agitação eletromagnética e com técnica de ultra-refino (adição do refinador Al-5,0wt%Ti-1,0wt%B). As ligas foram submetidas a tratamentos térmicos de globularização pelos tempos de 0s, 30s, 90s e 210s, para duas condições de frações sólidas, 45% e 60%; foram realizados ensaios de viscosidade sob as mesmas condições e ensaios de tixoforjamento com a fração sólida de 45% e com todos os tempos de tratamento. Por fim, foram avaliadas as propriedades mecânicas, via ensaios de tração, das peças tixoforjadas. Os tratamentos térmicos promovem a globularização das partículas de fase primária, de forma que os melhores resultados de viscosidade foram alcançados para ligas submetidas às frações sólidas de 45%: todas as ligas apresentaram resultados de viscosidade aparente na faixa de 106 (Pa.s), segundo a literatura, materiais que se encontram nesta faixa de viscosidade possuem o comportamento similar ao do vidro fundido e demonstram alta conformabilidade, mostrando-se viáveis ao processo de tixoconformação. As peças tixoforjadas apresentaram boa conformabilidade preenchendo toda a matriz e reproduzindo sua geometria. Apresentaram boas propriedades mecânicas através dos ensaios de tração e quando submetidas ao tratamento de solubilização apresentaram propriedades mecânicas superiores, ou seja, houve um aumento do limite de escoamento em todas as ligas em torno de 50MPa, aumento no alongamento em torno de 2 a 3 vezes e o aumento do limite de resistência a tração em todas as ligas em torno de 80MPa
Abstract: The goal of this work was to evaluate the thixoformability of Al-Xwt%Si-2,5wt%Cu alloys, including all the stages process: obtaining the thixocasting, characterization in terms of microstructural, characterization of the rheological behavior, and the thixoforging process in two different sets equipment, ie., eccentric press and pneumatic press. The Al-2,0wt%Si-2,5wt%Cu, Al-3,0wt%Si-2,5wt%Cu, Al-4,0wt%Si-2,5wt%Cu, Al-5,0wt%Si-2,5wt%Cu e Al-7,0wt%Si- 2,5wt%Cu alloys were produced by direct casting with electromagnetic stirring and by ultrarefining (addiction of Al-5,0wt%Ti-1,0wt%B). The alloys were submitted to re-heating treatment for 0s, 30s, 90s and 210s in two conditions of solid fraction, 45% and 60%; had been realized tests of viscosity under the same conditions and thixoforging tests with solid fraction of 45% and with all re-heating treatment times. Finally, had been the mechanical properties, by tensile tests, of the thixoforged pieces. Re-heating treatment times promote the solid phase particles globularization, from that the best results of viscosity been reached for alloys treated with solid fractions of 45%: all the alloys presented resulted of apparent viscosity of 106 (Pa.s), literature according to materials that if find in this index of viscosity possess the similar behavior the casting glass and demonstrate high conformability, revealing viable the process thixoforming. The thixoforged piece presented good conformability, total fulfilling of the matrix and reproducing geometry. Showed good mechanical properties by tensile tests and subjected to solubilization treatment had superior mechanical properties, ie, an increase in the yield strength in all alloys about 50MPa, elongation increased approximately 2 to 3 times and increasing the limit of tensile strength in all leagues around 80MPa
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica

One of the serious problems encountered in the use of various materials in technology is the occurrence of fatigue phenomena as an undesirable material damage under cyclic mechanical load. For aluminium alloys this issue is of extremely high importance in case of their utilisation for aircraft purposes, e.g., where a very wide spectrum of frequencies occur. Moreover, the cyclic loading may be joined by the presence of specific electrolyte media. Therefore, the material candidates must be thoroughly examined in view of their sensitivity to fatigue as well as to corrosion fatigue. Usually, the Cu-containing alloy EN-AW 2024 T3 is applied besides 7075 T6 in Airbus aircrafts, but the weldable alloy 6013 T6 is considered to be a potential alternative. Referring to former investigations on the environmental sensitivity (ES) in the fatigue behaviour /1-6/ this paper brings up experimental findings as well as expanded considerations about damaging mechanisms and modelling. The situation with the alloy 6013 T6 is emphasized. The propagation of cracks under cyclic load in different environments, such as vacuum, air or aqueous media, is described by means of fracture mechanics. This enables discrimination in view of the influence of environmental factors and, hence, the participation of corrosion processes.

One of the serious problems encountered in the use of various materials in technology is the occurrence of fatigue phenomena as an undesirable material damage under cyclic mechanical load. For aluminium alloys this issue is of extremely high importance in case of their utilisation for aircraft purposes, e.g., where a very wide spectrum of frequencies occur. Moreover, the cyclic loading may be joined by the presence of specific electrolyte media. Therefore, the material candidates must be thoroughly examined in view of their sensitivity to fatigue as well as to corrosion fatigue. Usually, the Cu-containing alloy EN-AW 2024 T3 is applied besides 7075 T6 in Airbus aircrafts, but the weldable alloy 6013 T6 is considered to be a potential alternative. Referring to former investigations on the environmental sensitivity (ES) in the fatigue behaviour /1-6/ this paper brings up experimental findings as well as expanded considerations about damaging mechanisms and modelling. The situation with the alloy 6013 T6 is emphasized. The propagation of cracks under cyclic load in different environments, such as vacuum, air or aqueous media, is described by means of fracture mechanics. This enables discrimination in view of the influence of environmental factors and, hence, the participation of corrosion processes.

Стабильная икосаэдрическая ψ-фаза (Al[6]Cu[2]Fe), обладающая уникальными свойствами, была обнаружена в системе Al–Cu–Fe. Несмотря на широкое внимание к новому классу квазикристаллов, фазовая диаграмма системы Al–Cu–Fe при легировании Si и B в области существования икосаэдрической фазы не достаточно определена. Влияние легирующих элементов на структуру сплавов Al–Cu–Fe остается спорным. Поэтому целью работы является изучение влияния Si и B на фазовый состав сплавов Al–Cu–Fe.

Alloy castings are usually solidified with a coarse columnar grain structure under normal casting conditions unless the mode of the solidification is carefully controlled. It is desirable for the grain structure to be fine and equiaxed to improve their mechanical performance as finished castings. It is possible to develop a fine and equiaxed grain structure either by increasing the number of nucleation sites or by grain multiplication. Immiscible alloys with a microstructure in which a soft phase is dispersed homogeneously in a hard matrix have significant potential applications in advanced bearing systems, especially for the automotive industry. Despite considerable efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desired immiscible microstructure of alloys. Experimental results on Al-Sn-Cu immiscible alloys have confirmed that intensive shearing using melt conditioning by an advanced shearing technology (MCAST) unit, is an effective way to achieve a fine and uniform dispersion of the soft phase without macro-demixing, and that such a dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm for 60 s will be adequate to produce a fine and uniform dispersion of the Sn phase, and that a higher shearing speed and prolonged shearing time can only achieve further minor refinement. A study of Al-Si hypoeutectic and hypereutectic alloys presents the effects of the processing temperature and intensive shearing on the microstructural and mechanical properties which have been investigated systematically. Attempts have been made to explain the solidification mechanism with intensive melt shearing. The sheared melt was cast into tensile test samples by high pressure die caster (HPDC) to examine the microstructures and mechanical properties. The experimental results reveal that significant grain refinement and uniformity of grains was achieved by the intensive shearing and also a considerable increase in mechanical properties with pouring temperature by changing intermetallic particles morphology, the position of defect band and reduced microscopic defects.

The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today are limited in types. The main purpose of this Ph.D. project is to understand what makes an alloy suitable for SSM processing on both aspects of thermodynamics and kinetics. This research started with a fundamental study of binary alloys based on Al-Si, Al-Cu and Al-Mg systems (wt%): Al-1Si, Al-5Si, Al-12Si and Al-17Si; Al-1Cu, Al-2Cu and Al-5Cu; Al-0.5Mg, Al-3Mg and Al-5.5Mg. These are representative of Si, Cu and Mg contents in commercial alloys used for SSM processing. The Single-Pan Scanning Calorimeter (SPSC) and Differential Scanning Calorimeter (DSC) were used to investigate the liquid fraction changes during heating and cooling of these binary alloys. Thermo-Calc and DICTRA (DIffusion-Controlled TRAnsformations) software have been used to predict the fraction liquid versus temperature taking into account both thermodynamics and kinetics. Comparison of the predictions with experimental data revealed that the simulation results show the same pattern with experimental results in the fraction liquid-temperature relationship. However, the SPSC results are closer to the prediction than DSC curves are, even with the relatively large sample size associated with SPSC. This is potentially a significant result as predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing remains one of the challenges. The results also suggest that the fraction liquid sensitivity to time should be identified as a critical parameter of the process window for semi-solid processing in addition to the fraction liquid sensitivity to temperature. For microstructure investigation, microanalysis techniques, including Scanning Electron Microscopy (SEM) and micro-indentation testing, have been used on polished sections, and compared to theoretical predictions. In addition, some parts of this project are in cooperation with General Research Institute for Nonferrous Metals (GRINM), which aims to design and develop high performance semi-solid alloys. Thermodynamic analysis (both predictions and experiments) were carried out on thixoformed 319s (2.95Cu, 6.10Si, 0.37Mg, wt%) and 201 (4.80Cu, 0.7Ag, wt%) aluminium alloys. SEM techniques and Transmission Electron Microscopy (TEM) were used for the microstructural characterisation. The results showed that the DSC curves were sensitive to microsegregation in SSM alloys and resulted in a lower liquid fraction than the cast alloys calculated through the integration method from the DSC results. Al2Cu phase in SSM alloys 319s and 201 can be dissolved into matrix up to 0.4 % before melting temperature under 3K/min heating rate when compared with 10K/min heating rate. The DSC scan rate should be carefully selected as higher heating rate can inhibit dissolution of the intermetallic phases during heating leading to less accurate liquid fractions predictions.

Orientador: Eugenio Jose Zoqui
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Este trabalho teve co:mo objetivo avaliar a tixoconformabilidade de ligas Al-Xwt%Si2,5wt%Cu-0,5wt%Mg, abrangendo desde a obtenção das ligas tixofundidas até sua completa caracterização em termos de macro e microestrutura e comportamento viscoso. Ligas Al-1,Owt%Si-2,5wt%Cu-0,5wt%Mg, Al-2,Owt%Si-2,5wt%Cu-0,5wt%Mg, Al-4,Owt%Si2,5wt%Cu-0,5wt%Mg e Al-7,Owt%Si-2,5wt%Cu-0,5wt%Mg foram produzidas via ultra-refino de grãos utilizando o refinador Al-5,Owt%Ti-l,Owt%B. Os materiais foram submetidos a tratamentos térmicos de reaquecimento pelos.tempos de Os, 30s, 90s e 21Os, para duas condições de frações sólidas, 45% e 60%. As ligas contendo 1,Owt%Si, 2,Owt%Si e 4,Owt%Si mostraram-se. bastante próximas em termos de viscosidade aparente, no entanto, a liga com 4,Owt%Si apresentou melhor desempenho em termos de globularização, expressa pelo RQI. Já a liga contendo 7,Owt%Si mostrou-se dendrítica para todas as condições estudadas, o que dificulta sua aplicação nos processos de tixoconformação Os tempos de tratamento térmico agem no sentido de promover a globularização das partículas de fase primária, de forma que os melhores resultados de viscosidade foram alcançados para ligas submetidas aos tempos de 21 Os. As frações sólidas de 45% e 60% não apresentaram diferenças significativas em termos de RQI, porém as ligas contendo menor fração sólida apresentaram melhor desempenho em termos de viscosidade aparente, da ordem de 105Pa.s
Abstract: The goal of this work was to evaluate the thixoformability of Al-Xwt%Si-2.5wt%CuO.5wt%Mg alIoys, including the thixocasting of all alloys and their complete characterization in terms of macro and microstructures and rheological behavior. Al-l.0wt%Si-2.5wt%CuO.5wt%Mg, Al-2.0wt%Si-2.5wt%Cu-0.5wt%Mg, Al-4.0wt%Si-2.5wt%Cu-0.5wt%Mg and Al-7.0wt%Si-2.5wt%Cu-0.5wt%Mg alloys were produced by ultra-refining by addiction of Al5.0wt%Ti-1.0wt%B master alIoy. The materials were submitted to re-heating treatment for Os, 30s, 90s and 2l0s in two conditions, 45% al!d 60% of solid fraction. 1.0wt%Si, 2.0wt%Si and 4.0wt%Si alloys showed very similar results for apparent viscosity, however the 4.0wt%Si alloy showed better performance in terms of globularization, measured by RQI. Thixocast 7.0wt%Si alloy presented dendrictic structures for alI conditions analyzed, making its application too difficult for thixoforming processes. Re-heating treatment times promote the solid phase particles globularization, so that the alloys treated during 210s achieved better results for apparent viscosity. Both 45% and 60% solid fractions did not show significant differences in terms of RQI, but the alloys containing lower solid fraction showed better performance for apparent viscosity, in the order of 105Pa.s
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

Orientador: Eugênio José Zoqui
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O objetivo para este trabalho foi avaliar a tixoconformabilidade de ligas Al¿Si¿Cu produzidas via refino de grão, abrangendo desde a obtenção das ligas tixofundidas até sua completa caracterização em termos de metalografia colorida e convencional no comportamento viscoso. Ligas Al¿2,0wt%Si¿2,5wt%Cu, Al¿3,0wt%Si¿2,5wt%Cu, Al¿4,0wt%Si¿2,5wt%Cu e Al¿7,0wt%Si¿2,5wt%Cu foram produzidas via ultra-refino de grãos utilizando o refinador Al¿5,0wt%Ti¿1,0wt%B. Os materiais foram submetidos a tratamentos térmicos de reaquecimento pelos tempos de 0s e 210s, para duas condições de frações sólidas, 45% e 60%. As ligas contendo 2,0wt%Si, 3,0wt%Si, 4,0wt%Si e 7,0wt%Si mostraram-se bastante próximas em termos de viscosidade aparente, no entanto, a liga com 4,0wt%Si apresentou melhor desempenho em termos de globularização. Já a liga contendo 7,0wt%Si mostrou-se dendrítica para todas as condições estudadas, o que dificulta sua aplicação nos processos de tixoconformação
Abstract: The target for this work was the analyses to evaluate the thixoformability of Al¿Si¿Cu alloys produted by grain refining, including the thixocasting of all alloys and their complete characterization in terms of color metallography and conventional on rheological behavior Al¿2.0wt%Si¿2.5wt%Cu , Al¿3.0wt%Si¿2.5wt%Cu , Al¿4.0wt%Si¿2.5wt%Cu and Al¿7.0wt%Si¿2.5wt%Cu alloys were produced by ultra-refining by addiction of Al¿5.0wt%Ti¿1.0wt%B master alloy. The materials were submitted to pre-heating treatment for 0s and 210s in two conditions, 45% and 60% of solid fraction. 2.0wt%Si, 3.0wt%Si, 4.0wt%Si and 7.0wt%Si alloys showed very similar results for apparent viscosity; however the 4.0wt%Si alloy showed better performance in terms of globularization
Mestrado
Materiais e Processos de Fabricação
Mestra em Engenharia Mecânica

Orientadores: Amauri Garcia, Ivaldo Leão Ferreira
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: As ligas de alumínio para fundição possuem propriedades de grande interesse industrial, como: baixa massa especifica, boa resistência a corrosão, elevadas condutibilidade térmica e elétrica, boas combinações de propriedades mecânicas, boa trabalhabilidade em processos de usinagem e conformação mecânica. Atualmente, essas ligas são produzidas em vários sistemas e dezenas de composições. A literatura apresenta vários estudos tanto teóricos quanto experimentais focando na evolução microestrutural de ligas binárias a base de alumínio. Leis de crescimento celular e dendritico experimentais e teóricas foram propostas e devidamente validadas. As analises de macrossegregação e formação de poros de ligas binárias de alumínio também foram contempladas em vários estudos recentes. Entretanto, são escassos os estudos abordando importantes famílias de ligas multicomponentes a base de alumínio. Nesse sentido, o presente trabalho se propôs a analisar ligas da família Alumínio-Silício-Cobre (A319.1 e A333.1) [Al-5,5%Si-3,0%Cu e Al-9,0%Si-3,0%Cu] no que diz respeito a evolução da microestrutura dendrítica, macrossegregação e formação de porosidade na solidificação. Para a produção das ligas ternárias foram utilizados Alumínio e Silício comercialmente puros e Cobre eletrolítico. A macrossegregação de soluto e a formação de microporosidade são investigadas tanto experimentalmente quanto por meio de simulações numéricas. A microestrutura dendrítica e quantificada através de seus espaçamentos primários, secundários e terciários, que são devidamente correlacionados com os parâmetros térmicos da solidificação. Os perfis de macrossegregação de soluto, densidade teórica e densidade aparente são apresentados ao longo dos comprimentos dos lingotes. Os perfis de segregação de soluto experimentais foram obtidos através da técnica de espectrometria de fluorescência de raios-X e para a simulação foram calculados levando-se em conta transformações de fase secundarias que ocorrem ao longo da solidificação. As medições de microporosidade foram realizadas utilizando-se a técnica de picnometria...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance, high thermal and electrical conductivities, good combination of mechanical properties, good workability in machining processes and mechanical forming. Currently, these alloys are produced in various systems and dozens of compositions. The literature presents several studies, both theoretical and experimental, focusing on the microstructural evolution of binary aluminum base alloys. Theoretical and experimental cellular and dendritic growth laws have been proposed and validated. Macrosegregation and pore formation during solidification of binary alloys of aluminum have been the focus of several recent studies. However, there are few studies in the literature addressing important families of multicomponent aluminum base alloys. Accordingly, this study aims to analyze Aluminum- Silicon-Copper alloys (series: A319.1 and A333.1) [Al-5.5wt%Si-3.0wt%Cu and Al-9.0wt%Si- 3.0wt%Cu] with respect to the evolution of the dendritic microstructure, porosity formation and macrosegregation during solidification. For the production of the ternary alloys commercially pure aluminum and silicon and electrolytic copper have been used. Solute macrosegregation and microporosity formation are investigated both experimentally and through numerical simulations. The dendritic microstructure is quantified by their primary, secondary and tertiary arm spacings, which are correlated with solidification thermal parameters. The solute macrosegregation profiles, theoretical and apparent densities have been determined along the castings lengths. The solute segregation profiles were obtained by X-ray fluorescence spectrometry and the simulations were performed taking into account secondary phase transformations that occur during solidification. Microporosity measurements were carried out by the picnometry technique...Note: The complete abstract is available with the full electronic document
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica

Hardness measurements and Three-Dimensional Atom Probe (3DAP) were used to characterize the early stages of precipitation in three different Al-Mg-Si alloys (Al-0.50 wt%Mg-1.00 wt%Si) with different Cu contents (0.03 wt%, 0.15 wt%, or 0.80 wt% Cu). Heat treatments were chosen to simulate an industrial production line for car body-sheet material and included natural ageing (NA), pre-ageing at 80 °C (PA), paint-bake ageing at 180 °C (PB) and 10 second ageing at 180 °C (spike). The Cu content and the chosen heat treatments were found to influence the microstructural evolution of the alloy considerably. Based on the determined microstructures and matrix solute concentrations, mechanisms for the effect of NA, PA and Cu additions were proposed. NA had a deleterious effect on the PB hardening response, which was delayed dramatically after 20 minutes NA or longer. When the NA time was 1 minute, β" precipitates were formed within 30 minutes PB resulting in high hardness of the alloy. The delay with NA time was caused by a decrease in the nucleation rate of elongated precipitates during the subsequent PB. This decrease was thought to be due to a combination of a decrease in the matrix solute concentrations and clusters acting as vacancy sinks. PA before NA improved the PB response due to the formation of a high density of short elongated precipitates. Small Mg-Si clusters were detected after both NA and PA. Clusters formed during PA were found to be, on average, Mg-richer and larger than those formed during NA. Larger clusters were found to be more stable during PB and, upon PB, to grow into nucleation sites for elongated precipitates. Application of a spike before PA resulted in faster growth of clusters during PA. Growth of clusters and nucleation of short elongated precipitates during PB was found to be enhanced with increasing Cu content when no PA was given. Cu was found to be present in all precipitates and clusters in the alloy with the highest Cu content. These precipitates were thought to be precursors to the Q' phase.

Application prospects in the automotive industry have led to increasing studies on Al-Mg- Cu-Si alloys. In this thesis, nine Al-(1-3)Mg-(0-0.4)Cu-0.15Si-0.25Mn (in wt%) alloys with potential applications in packaging and automotive industries have been investigated. By means of mechanical testing, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), several mechanisms was identified that influence the final strength of cold rolled alloys during ageing: solid solution, work hardening, recovery and precipitation. Microstructure analyses revealed the formation of undissolved particles consuming the small Si addition, which influences age hardening behaviour of the alloys. Tensile testing was performed to evaluate the strength and work hardening. The integrated experimental results showed that for cold worked samples, b² (Mg2Si) contributes to age hardening of Cu-free alloys, whilst both b² and S (Al2CuMg) contribute to that of Cu-containing alloys. According to the experimental findings, a yield strength model has been developed to elucidate the relation between processing and the final strength. It consists of three main components: i) dissolution of intermetallic phase Mg2Si; ii) precipitation of two strengthening phases b² and S; iii) strengthening contributions from solution strengthening, dislocation strengthening and precipitation hardening due to the strengthening phases. The model was calibrated and tested using separate tensile data and was applied to predict the yield strength evolution of cold worked samples during ageing. An accuracy of 8.6 MPa (about 4% of the total range of strengths) has been achieved. Based on the analysis of the relation of work hardening with cold work, composition and ageing time, three primary findings were obtained: i) cold worked samples usually have the lowest work hardening rate (WHR); ii) WHR increases after 30-minute ageing due to recovery and iii) WHR increases with decreasing level of cold work and increasing Mg and Cu contents. Work hardening models based on the Kocks-Mecking (KM) model and the Kocks-Mecking-Estrin (KME) model have been utilized to explain the main trends. The modelling results showed that the KM model is able to predict the work hardening behaviour of cold worked samples reasonably well. However, the KME model is insufficient to fully describe that of cold-worked-and-aged samples.

Nous avons analysé par microscopie électronique à transmission et par diffraction des neutrons les alliages quasicristallins suivants: Ti2Fe, Al65Cu20Fe15, Al71Pd19Mn10, Al65Cu20Fe10Cr5, Al65Cu17,5 et Al63Cu17,5Si2. Toutes ces études abordent deux aspects différents de ces alliages : les phases quasicristallines et leurs approximants cristallins. Dans le premier aspect, nous avons étudié la structure et la formation des phases icosaédriques Ti-Fe, Al-Cu-Fe et Al-Pd-Mn. Les mécanismes de croissance ont été identifiés. Les vitesses de croissance de ces quasicristaux sont très faibles par rapport à celles des cristaux. En ce qui concerne le deuxième aspect, nous nous sommes attachés à l'étude des approximants de la phase décagonale dans les alliages Al65Cu20Fe10Cr5 et Al63Cu17,5Co17,5Si2. Nous avons pu relier la phase décagonale à ses approximants en mettant en évidence les mêmes types d'unités structurales. Nous avons aussi mis l'accent sur la phase de type CsCl qui peut être la structure de base pour toutes les structures quasicristallines et cristallines étudiées dans ce travail

The aim of this thesis is to investigate the influence of ageing process on the microstructure and mechanical properties of aluminium-silicon alloys. The investigation was carried on Al-9%Si-3%Cu and Al-9%Si-0.4%Mg. To obtain different DAS with low content of oxide films and micro shrinkage, gradient solidification has been used. The specimens were treated according to T6 heat treatment.

In this thesis it has been shown that solidification rate has great influence on mechanical properties since it controls microstructure. To reach peak level of mechanical properties different times of artificial ageing were used depending on the alloy.

In peak value condition Yield’s Strength of alloys was 197MPa for Al-Si-Cu alloy and 243MPa for Al-Si-Mg one. These results can be compared to these presented in other papers concerning aluminium silicon alloys. Such comparison shows that when talking about potential of alloy, these results are more or less the same as in other articles in this field.

The work was conducted within 10 weeks and for this reason not all the necessary data was collected. Further work will be conducted to obtain missing results, like overaged state for Al-Si-Cu alloy.

The enrichment of Fe during aluminium recycling increases the quantity of Fe-rich intermetallics formed, particularly β-Al5FeSi, limiting the usage of recycled Al in many fatigue-sensitive applications. In this study, fast synchrotron x-ray tomography was used to investigate microstructure evolution and defect formation in a commercial A319 alloy (Al-7.5Si-3.5Cu, wt.%) with differing Fe-levels (0.2-0.6 wt.%Fe) during in situ solidification and isothermal uniaxial tensile deformation. The captured dynamic changes were quantified using novel image analysis techniques and analysed using computational fluid dynamics. Together these provide new insights into the mechanisms of intermetallic nucleation and growth, and their influence on flow blockage and defect formation. First, time-resolved qualitative and quantitative characterisation revealed that plate-like β-intermetallics nucleate both off the primary aluminium dendrites in the bulk of the specimen as well as off the oxide skin on the specimen surface. Second, β-intermetallic formation is largely complete before the formation of the Al-Si eutectic. Third, β-intermetallics are geometrically complex, demonstrating fast lateral growth and an ability to grow around and in between the primary dendrite arms. Last, direct impingement and potential branching are observed at a wide range of contact angles, indicating that the growth interaction might not be crystallographically related. The presence of β-intermetallics contributes to several factors that influence defect formation. They block interdendritic flow, increase pore tortuosity and reduce permeability. Pores were observed to grow preferentially along the solid surface of intermetallics, suggesting that β-intermetallics may reduce the gas-solid interfacial energy and thus facilitate the pore growth. However, they do not nucleate the porosity. The results also show that failure under mild uniaxial semi-solid tension, simulating hot-tearing, displays a much more brittle-like failure mechanism when large β-intermetallics are present, compared to the more ductile behaviour of the base alloy with unresolved β-intermetallics.

Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.
Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.

Orientadores: Amauri Garcia, Ivaldo Leão Ferreira
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: As ligas fundidas de alumínio vêm desempenhando um papel importante no crescimento da indústria metal-mecânica. Hoje, essas ligas são produzidas em vários sistemas e dezenas de composições. Destacamos as ligas do sistema ternário Al-Cu-Si que apresentam excelente fluidez, alta resistência mecânica e baixo peso, o que as tornam uma escolha adequada como ligas de fundição, sendo amplamente aplicadas na indústria automotiva e aeroespacial. Tais características e o elevado grau de destaque dessas ligas no campo científico e tecnológico têm despertado o interesse de pesquisadores para o desenvolvimento de trabalhos que visam a investigação da evolução microestrutural, formação de macrossegregação e porosidade na solidificação. Neste trabalho, a caracterização e quantificação microestrutural e suas correlações com os parâmetros térmicos da solidificação de ligas Al-Cu-Si são investigadas juntamente com a macros segregação e formação de porosidade tanto através de simulações numéricas quanto através de experimentos de solidificação direcional em regime transitório. A microestrutura dendrítica foi caracterizada por técnicas tradicionais de metalografia para as ligas Al6Cu1Si e Al6Cu4Si e a quantificação dos espaçamentos dendríticos realizada por metodologias consagradas na literatura. Os resultados mostram que a adição de silício na composição da liga diminui os espaçamentos dendríticos primários e secundários quando comparados com a liga binária Al-Cu de mesmo teor de cobre. São propostas leis experimentais de evolução dos espaçamentos dendríticos como função da taxa de resfriamento ( ? ) e da velocidade de deslocamento da isoterma liquidus (VL), na forma 'lambda IND. 1' = C ( ? )-0,55, 'lambda IND. 2' = C ( ? )-0,33 'lambda IND. 3' = C ( ? )-0,55 para os espaçamentos primários, secundários e terciários respectivamente. Os valores experimentais dos espaçamentos dendríticos secundários foram comparados com o único modelo teórico de crescimento dendrítico existente na literatura para ligas multicomponentes. O diagrama de fases ternário, bem como os caminhos de solidificação de ambas as ligas analisadas, e propriedades termofísicas necessárias para simulações numéricas foram determinadas através do software Thermo-Calc. Os perfis experimentais e numéricos de macrossegregação, bem como as densidades teóricas e aparentes são apresentados em função do comprimento dos lingotes. Os perfis de soluto durante a solidificação unidirecional transitória das ligas foram calculados levando-se em conta transformações de fase secundárias que ocorrem ao longo do referido sentido de solidificação. A microporosidade foi obtida experimentalmente através de um procedimento picnométrico. Também é mostrado que o uso de uma chapa molde de aço carbono induz um aumento atípico na fração de poros próximos à superfície resfriada do lingote, o que é causado por uma maior concentração de ferro provocada pelo fluxo difusivo deste elemento da chapa molde para a superfície do lingote
Abstract: Aluminum alloys castings had a fundamental role in the growth of the metal-mechanics industry. Nowadays these alloys are supplied in a wide range of chemical compositions. We highlight the Al-Cu-Si ternary system because of particular outstanding properties such as high mechanical strength, low weight and very good fluidity. These qualities make them a good choice for applications in the automotive and aerospace industry. The potential of such alloys has attracted much attention of researchers with a view to investigating the microstructure evolution, and the formation of macrosegregation and porosity during the solidification process. In the present work, the microstructures of Al-Cu-Si alloys are characterized and correlated with solidification thermal parameters. The evolutions of macrosegreation and porosity during transient solidification are also examined both experimentally and by numerical simulations. The dendritic microstructure has been characterized using current metallographic techniques for both Al6Cu1Si e Al6Cu4Si alloys and the interdendritic spacings were measured by methods found in the literature. The results have shown that the addition of silicon to the alloy composition decreases the primary and secondary dendritic spacing when compared with those of an Al6Cu alloy. Experimental laws describing the evolution of dendritic spacings with the cooling rate ( ? ) and the velocity of the liquidus isotherm (VL) are proposed, i.e., 'lambda IND. 1' = C ( ? )-0,55, 'lambda IND. 2' = C ( ? )-0,33 and 'lambda IND. 3' for the primary, secondary and tertiary dendritic spacings, respectively. The experimental results of secondary dendritic spacings have been compared with the predictions of the only theoretical model existing in the literature for dendritic growth of multicomponent alloys. The Thermo-Calc software has been used to yield the tertiary phase diagram, thermophysical properties and the solidification path for both alloys. The experimental and numerical macrosegregations profiles, as well as the theoretical and apparent densities are presented as a function of the castings lenghts. The solute profiles that occur during the transient unidirectional solidification were simulated taking into account the formation of secondary phases during solidification. The microporosity was determined using a pyknometry procedure. The work also shows that the use of a carbon steel chill plate induces an abnormal increase in porous fraction at regions close to the casting cooled surface caused by a higher iron content, due to diffusive flux of iron from the chill steel plate toward the casting surface
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica

La caractérisation 2D/3D et l’analyse d'images ont permis d’estimer les changements microstructuraux liés à : différents taux de Fe, Mn et Sr, au procédé de moulage (Coulée coquille par Gravité vs. Procédé à Modèle Perdu, PMP) et au traitement thermique de mise en solution d’un alliage A319. L'évolution de la microstructure avec les éléments d'addition a aussi été étudiée par analyse thermique. La microstructure est constituée d'inclusions dures (Si eutectique, intermétalliques au Fe et phases Al2Cu) et de pores. L'effet sur les propriétés mécaniques a été évalué par dureté Vickers et essais de traction. L’observation de l’endommagement en surface d’alliages A319 avec différentes teneurs en Fe est effectuée in situ au cours de l'essai de traction afin de suivre l'évolution et la localisation de la déformation et des fissures. La corrélation d’images numériques et la fractographie ont mis en évidence le rôle des intermétalliques au Fe dans l'amorçage et la propagation des fissures. Des essais de traction sur des échantillons A319 PMP avec deux conditions de traitement thermique ont été effectués in situ sous tomographie de laboratoire. Les mesures de déformation par corrélation de volumes numériques et les mécanismes d'endommagement observés montrent que les fissures s’amorcent aux inclusions dures dans les zones de concentration de contraintes, surtout autour des pores, et se propagent souvent par la rupture des phases Al2Cu, des intermétalliques au Fe, et du Si eutectique, plutôt que par leur décohésion de la matrice
2D and 3D characterization and image analysis have been performed to measure the microstructural changes associated with: different Sr, Fe and Mn levels, the casting process (Gravity Die Casting vs. Lost Foam Casting, LFC) and the solution heat treatments in A319 alloy. The evolution of microstructure in Al-Si-Cu alloy with different alloying elements addition was also studied by thermal analysis. The microstructure consists of hard inclusions, i.e. eutectic Si, iron-intermetallics and Al2Cu phases, and pores. The effect on mechanical properties of the alloys has been monitored by Vickers hardness measurement and tensile tests. Surface damage observations are performed on A319 alloys with different Fe content during in-situ tensile test, which allows following the development and localization of the deformation and cracks. Digital image correlation measurement and fractography highlighted the role of iron-intermetallics in the cracks initiation and propagation. Tensile tests on LFC A319 samples with two different heat treatment conditions were performed in-situ under Laboratory Computed Tomography. Strain measurements from digital volume correlation and observed damage mechanisms show that cracks initiate at hard inclusions in the areas with sufficient stress concentrations, which are mainly provided by large pores, and often propagate through the fracture of Al2Cu, iron-intermetallics, as well as through Si particles rather than by their decohesion from the matrix

Proučavane su koroziona postojanost i tendencija lepljenja različitihmaterijala u kontaktu sa tečnom Al–Si–Cu legurom. Ispitivanjem suobuhvaćeni čelik za rad na toplo, plazma nitrirani čelik i dupleksslojevi sa CrN, TiAlN, TiAlSiN i CrAlN prevlakama, različitog nivoapovršinske hrapavosti. Za ispitivanja pomenutih fenomenaprimenjena je metoda izvlačenja, koja je unapređena kako bi se povećalenjena tačnost i verodostojnost simulacije procesa livenja. Korozioniefekti su pojačani tako što su uzorci osim kratkog kontakta sa odlivkomzadržavani i u dužim periodima u kontaktu sa tečnom legurom (5 i 20min). Uprkos opštim stavovima, za ispitivane materijale jeustanovljeno da su sile izvlačenja uzoraka iz Al–Si–Cu odlivakanezavisne od njihovog hemijskog sastava. Uticaj hrapavosti je izraženkod uzoraka sa prevlakama kod kojih pri smanjenju hrapavosti dolazi dopovećanja sile izvlačenja. Sve ispitane prevlake su sklone mehaničkomlepljenju Al–Si–Cu legure za svoje površine, ali sa aspekta korozije utečnom metalu značajno prevazilaze performanse čelika i plazmanitriranog sloja. Duži kontakt livene legure sa površinama prevlakauzrokovao je niže vrednosti sila izvlačenja, što je posledicaoksidacije površina prevlaka. Ustanovljeno je da su ispitivaneprevlake inertne ka tečnoj leguri aluminijuma. Međutim, dolazi dooksidacije i korozije materijala podloge kroz greške rasta koje suprisutne u prevlakama. Stečena znanja o identifikovanimmehanizmima habanja i propadanja zaštitnih slojeva prevlakaposlužiće daljem razvoju dupleks slojeva namenjenih za zaštitu alataza livenje pod pritiskom.
Corrosion resistance and soldering tendency of different materials in moltenAl–Si–Cu alloy were studied. Hot-working tool steel, plasma nitrided steel andduplex layers with CrN, TiAlN, TiAlSiN and CrAlN top coatings, which wereproduced to various degree of surface roughness, were covered by the study.An ejection test was employed for investigation of the concerned phenomena.The ejection test was improved in order to increase its accuracy and thereliability of process simulation. Samples were examined in both short andextended periods of contact (5 and 20 min) with liquid casting. Castingsolidification was extended in order to intensify the corrosion effects. Contraryto common findings, it was found that the ejection force of the investigatedmaterials does not depend on their chemical composition. For the coatedsamples, a pronounced dependence of the ejection force on the surfaceroughness was found. The ejection force increases with decrease in surfaceroughness. All investigated coatings are prone to mechanical soldering by Al–Si–Cu alloy. Still, their corrosion resistance substantially exceeds the corrosionresistance of steel and plasma nitrided layer. Longer exposure of coatedsamples to cast alloy induced lower ejection forces, which is a consequenceof coatings oxidation. It was found that the investigated coatings are inert toliquid aluminium. However, the underlying material undergoes oxidation andcorrosion through coating growth defects. The findings concerning the wearmechanisms of protective layers support further development of duplex layersintended for die casting tools protection.

L'objet de cette these est l'etude des composes fermions lourds supraconducteurs cecu#2si#2 et upd#2al#3 sous pression dans leur phase normale et supraconductrice par resistivite electrique (p#a#c) et par susceptibilite magnetique alternative (#a#c). Les mesures ont ete effectuees en conditions quasi-hydrostatiques (steatite) et hydrostatiques (#4he). Les mesures par resistivite electrique se sont effectuees sous champ magnetique : un diagramme hc#2(t) a ete etabli sous pression pour les deux composes. Pour cecu#2si#2, l'etude sur monocristal en resistivite electrique sous champ magnetique et sous pression (b,t)#- a montre une augmentation drastique du champ critique dans le regime ii avec hc#2(o)5 t contre 2,1 t a pression nulle. Les ajustements du champ critique dans un modele de supraconducteur en limite propre et couplage faible indiquent une anisotropie liee sans doute a la surface de fermi non spherique (coefficient gyromagnetique <1) tandis que ceux en limite sale et couplage fort indiquent une changement de comportement net entre les regimes i et ii. La pente varie fortement sous pression : 25 k/t dans le regime i et 12 k/t dans le regime ii. Pour upd#2al#3, une etude en susceptibilite magnetique sous pression #a#c- sur polycristaux caracterises en transport a permis d'etablir : un diagramme t#c(p) montrant une forte diminution de la supraconductivite apres 6 gpa. On constate en resistivite sous champ et sous pression le maintient du regime de liquide de fermi. On constate peu de variation du champ critique sous pression : la masse effective liee a la pente a t#c presente un faible maximum autour de 5 gpa avant de diminuer fortement a partir de 6 gpa. Ces deux composes presentent deux aspects de l'interaction entre supraconductivite non conventionnelle et magnetisme : competition pour cecu#2si#2 et coexistence pour upd#2al#3.

碩士
國立雲林科技大學
機械工程系
107
ABSTRACT In the research,Al-Si-Cu base aluminum alloy brazing filler metals with Ge、Sn or Zn were used to join 6061 aluminum alloy/Ti6Al4V and 6061 aluminum alloy/SUS304.The effect of Al-Si-Cu alloy on the joint properties of titanium alloy/aluminum alloy and stainless steel/aluminum alloy. Was also discussed adding 5% Ge into Al-Si-Cu alloy can decrease the liquidus temperature about 32°C. Adding 5% Sn to Al-Si-Cu alloy can decrease the liquidus temperature about 21°C and adding 10% Zn to Al-Si-Cu alloy can decrease the liquidus temperature about 26°C. The metallographic microstructure of Al-Si-Cu-X filler alloy is mainly Al2Cu phase and Al phase.The results of vacuum brazing showed that the shear strength of Ti6Al4V joints using Al-Si-Cu-Zn filler metal were higher than using the other two filler alloys.The best joint strength was 37.27MPa.The shear strength of SUS304 joints using Al-Si-Cu-Ge filler alloy was higher than the other two filler alloys.The best joint strength is 21.52MPa.The result showed the feasibility of thermal spraying for brazing. No intermetallic compound layer was observed. Due to non-uniform of the thermal spraying layer, so the jointability was reduced.The shear strength with thermal spraying coating was about 10MPa lower than that without spraying. Therefore, although thermal spraying coating can be used to braze, the coverage of thermal spraying and the selection of the base material were still the main factors of the bonding efficiency. Keywords：Aluminum brazing fillers, 6061 aluminum alloy, Ti6Al4V, SUS304

In modern age of technology Aluminium alloys have extensive application in industries. The range of physical properties that can be imparted to them is remarkable. Addition of Silicon and copper to Aluminium helps to increase their strength and wear resistance. Al-Si-Cu alloys can be extensively used in industrial applications due to better tribological properties. In the present work, an attempt has been made to study the tribological properties of Aluminium as-cast alloy sample i.e. Al alloy and and pure Aluminium. Wear tests were conducted using a pin-on-disc wear test rig as per ASTM specification G99. The operational parameters were normal load and sliding velocity of pin with respect to rotating disk at room temperature. The medium used were dry and wet lubrication. The amount of wear has been reduced significantly in aluminium alloy comparative to pure aluminium. Dry condition testing of samples showed a lot of noise and relatively more amount of wear for both aluminium and aluminium alloy.The coefficient of friction for aluminium alloy in wet condition was approximately constant up to the load the applied load of 2kg and then decreased with further application of load while coefficient of friction for pure aluminium was increasing continuously with the load.

碩士
國立雲林科技大學
機械工程系
107
In the research,three low-melting-point aluminum brazing filler metals based on Al-Si-Cu were developed. The low melting point fillers with quaternary alloys by adding different proportions of Zn, Ge or Sn elements in Al-Si-Cu alloys were used to join 6061 aluminum alloy. In the first experimental procedure, the melting temperatures of the filler metals were determined by DSC. The microstructure and phase composition of filler metals before and after brazing were analyzed with OM, SEM and EDS. The optimal brazing parameters were confirmed. Finally, using the microhardness tester and the tensile tester to understand the changes of mechanical properties of the joints. The results of the metallographic analysis showed that the microstructures of the Al-9.6Si-10Cu-10Zn filler metal included Al2Cu phase, Si phase and Al-rich phase of solid solution of Al and Zn. The solidius temperature was 495℃ and liquidius temperature was 546℃. The metallographic structure of Al-10.2Si-10Cu-5Ge filler had Al2Cu phase, Si-Ge phase, Al-Si eutectic structure and Al phase substrate. The solidus temperature was 490℃ and the liquidus temperature was 550℃. The metallographic analysis showed that the microstructures of the Al-10.2Si-10Cu-5Sn filler metal included Al phase substrate and Al2Cu phase, Si phase, Sn phase and Al-Si eutectic. The solidus temperature was 503℃ and the liquidus temperature was 554℃. The three filler alloys were brazed under the optimal brazing parameters. The hardness of the joint interface was higher than the base metal. The highest shear strength was about 28~33MPa. The fracture of the shear test appeared in filler center. In addition, the 6061 aluminum alloy was precipitation hardened aluminum alloy. After brazing, strength and hardness of the base material decreased. The mechanical properties were recoverded by T6 heat treatment.

Selective laser melting (SLM) is an additive manufacturing technology. In this thesis, a heat-treatable Al-3.5Cu-1.5Mg-1Si alloy and related materials (composites and hybrid materials) have been successfully fabricated by selective laser melting and characterized in terms of densification, microstructure, heat treatment, mechanical properties as well as tribological and corrosion behavior. Firstly, the fully dense SLM Al-Cu-Mg-Si alloy was fabricated by SLM successfully. The alloy shows a higher yield strength than SLM Al-12Si alloy, and lower wear resistance and corrosion rate than commercial 2024 alloy before and after T6 heat treatment. Secondly, with the aim of designing new alloy compositions and to examine the phases and microstructures of SLM Al-Cu alloys and to correlate their microstructures with the observed mechanical properties, Al-xCu (x = 4.5, 6, 20, 33 and 40 wt. %) alloys have been synthesized in-situ by SLM from mixtures of Al-4.5Cu and Cu powders. The results indicate that the insufficient Cu solute diffusion during the layer-by-layer processing results in an inhomogeneous microstructure around the introduced Cu powders. With increasing Cu content, the Al2Cu phase in the alloys increases improving the strength of the material. These results show that powder mixtures can be used for the synthesis of SLM composites but the reaction between the matrix and the second-phase should be considered carefully. Thirdly, the TiB2/Al-Cu-Mg-Si composite was also designed and fabricated successfully by SLM and it shows a higher strength than the unreinforced SLM alloy before and after T6 heat treatment. Finally, an Al-12Si/Al-3.5Cu-1.5Mg-1Si hybrid with a good interface was fabricated successfully. This hybrid alloy shows a good yield strength and elongation at room temperature, indicating an effective potential of selective laser melting in the field of hybrid manufacturing.

碩士
國立成功大學
材料科學及工程學系碩博士班
100
Communication connectors are almost manufactured by leaded brass. However, using lead easily causes environmental pollution, so developing substituted material is the big issue. Aluminum alloys have many advantages, such as light, low-cost, high specific strength, and environmental-friendly. Thus aluminum alloys are preferred for environmental-friendly material. The continuous chips easily disturb the cutting process. Hence chip segmentation is the important indicator for machinability. 　　4384 Al-Si-Cu-Ni-Mg aluminum alloy has excellent chip breakability in aluminum alloys as a result of many hard and brittle second-phases. In order to achieve the chip breaking standard of leaded brass, we use aging treatment to increase the chip breakability of 4384 Al-Si-Cu-Ni-Mg alloy. One part of this study probes effects of aging treatment to chip formation on 4384 Al-Si-Cu-Ni-Mg aluminum alloy. It shows that the artificial peak-aging treatment can supply the best chip breakability. For satisfying application, the other part of this study discusses that the feasibility of 4384 Al-Si-Cu-Ni-Mg aluminum alloy can apply in the communication connectors by comparing material characteristics of 4384 Al-Si-Cu-Ni-Mg aluminum alloy and C3604 leaded brass. 　　The α-Al hardness value of 4384 Al-Si-Cu-Ni-Mg aluminum alloy is directly proportional to chip breakability. When the deformation resistance of α-Al increase, working hardening layer decrease. In cutting process, α-Al is easy to break, which could reduce the cutting chip size, so the artificial peak-aging treated 4384 aluminum alloy has the best chip breaking factor in this material. 　　The material characteristics of 4384 Al-Si-Cu-Ni-Mg aluminum alloy enhance by artificial peak-aging treatment. The hardness, yield stress and chip breakability are more close to C3604 leaded brass. Weather resistance and electromagnetic shielding properties are even beyond C3604 leaded brass. Therefore, the artificial peak-aging treated 4384 Al-Si-Cu-Ni-Mg aluminum alloy is expected to replace the leaded brass and applied in communication connectors.

The microstructural evolution and mechanical properties at elevated temperatures of a recently fabricated fine-grained AA6xxx aluminium sheet were evaluated and compared to the commercially fabricated sheet of the same alloy in the T4P condition. The behaviour of the fine-grained and T4P sheets was compared at elevated temperatures between 350°C and 550°C, as well as room temperature. Static exposure to elevated temperatures revealed that the precipitate structure of the fine-grained material did not change extensively. The T4P material, however, underwent extensive growth of precipitates, including a large amount of grain boundary precipitation. At room temperature, the T4P material deformed at much higher stresses than the FG material, but achieved lower elongations. Deformation at elevated temperatures revealed that the fine-grained material achieved significantly larger elongations to failure than the T4P material in the temperature range of 350°C-450°C. Both materials behaved similarly at 500°C and 550°C. Above 500°C, the grain size was greatly reduced in the T4P material, and only a slightly increased in the fine-grained material. At temperatures above 450°C, the elongation to failure in both materials generally increased with increasing strain-rate. The poor performance of the T4P material at low temperatures was attributed to the precipitate characteristics of the sheet, which lead to elevated stresses and increased cavitation. The deformation mechanism of both materials was found to be controlled by dislocation climb, accommodated by the self diffusion of aluminium at 500°C and 550°C. The deformation mechanism in the fine-grained material transitioned to power law breakdown at lower temperatures. At 350°C to 450°C, the T4P material behaved similarly to a particle hardened material with an internal stress created by the precipitates. The reduction in grain size of the T4P material after deformation at 500°C and 550°C was suggested to be caused by dynamic recovery/recrystallization. The role of a finer grain-size in the deformation behaviour at elevated temperatures was mainly related to enhanced diffusion through grain boundaries. The differences in the behaviour of the two materials were mainly attributed to the difference in the precipitation characteristics of the materials.