Influence of samarium content on microstructure and mechanical properties of recycled die-cast YL112 aluminum alloys

The influence of Sm(Samarium) content on microstructure and mechanical properties of recycled die-cast YL112 aluminum alloys was investigated.The results show that many small Sm-rich particles form in the recycled die-cast YL112 alloys with Sm addition.At the same time,the secondary dendrite arm spacing in the YL112 alloys modified with Sm is smaller than that of the unmodified alloy.The eutectic Si of recycled diecast YL112-xSm alloys transforms from coarse acicular morphology to fine fibres,Mechanical properties of the investigated recycled die-cast YL112 aluminum alloys are enhanced with Sm addition,and a maximal ultimate tensile strength value(276 MPa) and elongation(3.76%) are achieved at a Sm content of 0.6wt.%.Due to the modification of eutectic Si by Sm,numerous tearing ridges and tiny dimples on the fractures of tensile samples are observed.

Low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys

Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys.To feature their mechanical aspect of fatigue behavior,the low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys at room temperature was investigated.The experimental results show that both permanent mold cast and die-cast Al-Si-Cu-Mg alloys mainly exhibit cyclic strain hardening.At the same total strain amplitude,the die-cast Al-Si-Cu-Mg alloy shows higher cyclic deformation resistance and longer fatigue life than does the permanent mold cast Al-Si-Cu-Mg alloy.The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior,and can be described by the Basquin and Coffin-Manson equations,respectively.

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied.The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined.The defects investigated are gas and shrinkage porosity.In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid (GISS) technique.Then, the slurry was transferred to the shot sleeve and injected into the die.The die and shot sleeve temperatures were kept at 180 °C and 250 °C, respectively.The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure.From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process.In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

Friction self-piercing riveting(F-SPR)of aluminum alloy to magnesium alloy using a flat die

Friction self-piercing riveting(F-SPR)process based on a pip die has been invented to solve the cracking problems in riveting high-strength and low-ductility light metals,such as magnesium alloys,cast aluminum,and 7 series aluminum alloys.In this paper,in order to solve quality issues caused by the misalignment between rivet and pip-die in F-SPR,a flat-die based F-SPR process was proposed and employed to join 1.27 mm-thick AA6061-T6 to 3 mm-thick AZ31B.The results indicate that a 1.0 mm die distance is effective to avoid rivet upset and insufficient flaring.As the feed rate increases,the heat input in the whole process decreases,resulting in a larger riveting force,which in turn increases both the bottom thickness and interlock amount.Besides,solid-state bonding,including Al-Mg intermetallic compounds(IMCs),Al-Mg mechanical mixture,and Al-Fe atom interdiffusion was observed at the joint interfaces.The upper Al layer was softened,but the lower Mg layer was hardened,and both sheets exhibited a narrowed affected region with the increase of feed rate,while the rivet hardness shows no obvious change.Three fracture modes appeared accompanying the variations in lap-shear strength and energy absorption as the feed rate increased from 2 mm/s to 8 mm/s.Finally,the F-SPR process using a flat die was compared to those using a pip die and a flat bottom die to show the advantage of flat die on coping with the misalignment problem.

Strengthening technology and mechanism for semi-solid die casting of aluminum alloy

Combined with theoretical evaluation, an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail, then, the semi-solid die castings and liquid die castings were heat treated with the optimized process. The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings, especially the strengthening degree of heat treated semi-solid die castings is much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10%, and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings. The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase（Mg2Si） and formation of GP Zone.

Strength and ductility optimization of HPDC AlSi8MgCuZn2 alloys by modifying pre-aging treatment

Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.

Machining studies of die cast aluminum alloy-silicon carbide composites

Metal matrix composites （MMCs） with high specific stiffness, high strength, improved wear resistance, and thermal properties are being increasingly used in advanced structural, aerospace, automotive, electronics, and wear applications. Aluminum alloy-silicon carbide composites were developed using a new combination of the vortex method and the pressure die-casting technique in the present work. Machining studies were conducted on the aluminum alloy-silicon carbide （SiC） composite work pieces using high speed steel （HSS） end-mill tools in a milling machine at different speeds and feeds. The quantitative studies on the machined work piece show that the surface finish is better for higher speeds and lower feeds. The surface roughness of the plain aluminum alloy is better than that of the aluminum alloy-silicon carbide composites. The studies on tool wear show that flank wear increases with speed and feed. The end-mill tool wear is higher on machining the aluminum alloy-silicon carbide composites than on machining the plain aluminum alloy.

Opportunities and challenges of Chinese die-casting market

The present status and perspectives of Chinese die-casting market were commented. In 2003, the total output of die castings in the whole country was 708000 tons, in which the outputs of Al-alloy, Zn-alloy, Mg-alloy, Cu-alloy die castings were 474600 tons, 222000 tons, 5800 tons, 5600 tons, respectively, each accounted for 67%, 31.35%, 0.85%, 0.8% of the total. The annual sale volume of die-casting machines was approximately 1800. And the gross output value of dies approached RMB 38 billion, in which die-casting dies accounted for about 10%. In the die-casting industry of the entire country, the foreign capital enterprises, public-run enterprises, township and village enterprises, private enterprises accounted for over 80% of the total die-casting enterprises. Super huge die-casting groups are forming.

Mould filling ability and microstructure of aluminum alloy under electromagnetic die casting

In order to solve the mould filling problem of large thin walled aluminum alloy castings effectively, a new casting technology called electromagnetic die casting has been developed. Emphasis has laid on studying the mould filling ability and microstructure under the mentioned method. The results show that the mould filling ability of A357 is increasing continually with the increasing of the input voltage, that is, the magnetic induction intensity. The pressure head of the molten metal increases from the lowest one at the input of the mould to the highest one at the end of the mould while in a conventional mould the pressure head depends invariably on the sprue height. Under electromagnetic die casting, the grains of A357 alloy are refined, and the pattern of eutectic silicon of alloy changes from rough plate to smooth strip.

Comparative Analysis of the Effects of Pressure on the Mechanical Properties and Microstructure of Die Cast Aluminum Alloys

A study of the effects of pressure on the microstructure and mechanical properties of two aluminum alloys (A1350 and A380) was carried out and subsequent analysis made. Pressure was regulated at various levels in the die cast machine. Samples of both alloys were cast under varying regulated applied pressure. The mechanical properties of both alloy casts were tested and microstructure analysis done and the results compared for both alloys. The results obtained show that hardness, tensile strength, yield strength and impact strengths for both alloy cast samples followed similar pattern in the casting process. The hardness values increased with applied pressure but not too significantly in both alloy casts as pressure rose in the casting process. The yield strength of both alloy casts also increased with applied pressure. The impact strength and elongations also increased with applied pressure in both alloy casts. Also the microstructure analysis carried out on both alloy casts showed similar pattern of structural changes in the morphologies of both alloy casts as grains became fine as pressure rose from 350 to 1400 kg/cm2. Models were developed for the results and for all the models developed, a close relationship with the experimental results were underlying in view of the small errors generated by them and can be used to predict the experimental values.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Mechanism of die soldering during aluminum die casting

Soldering is a unique casting defect associated with die casting or metal mold casting of aluminum alloys. It occurs when molten aluminum sticks or solders the surface of the die steel and remains there after the ejection of the casting, causing a surface defect and dimensional inaccuracy of the castings and increased machine downtime. Soldering occurs easily when a bare die steel mold is used for die casting of aluminum alloys. When molten aluminum comes in contact with the die steel at a temperature higher than a critical temperature, the iron and aluminum atoms diffuse into each other, forming a series of intermetallic phases and a liquid aluminum-rich fcc phase. This liquid phase exists between intermetallic phases. On cooling, the liquid fcc phase solidifi es on the intermetallic phases and grows into the casting, resulting in soldering. The critical temperature is the eutectic temperature near the aluminum corner of the phase diagram. If the die is protected using a nonreactive ceramic coating, soldering starts at locations where local coating failure occurs. Molten aluminum comes into contact with die steel through the coating failure locations and eats into the steel matrix, forming small pits. As these small pits grow, the coating is gradually removed and soldering becomes more severe. Details of die soldering step on a bare steel die and on a coated die material are discussed.

Semi-solid near-net shape rheocasting of heat treatable wrought aluminum alloys

Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commercial 2024, 6082 and 7075 wrought aluminum alloys.Tensile properties were measured for the above mentioned rheocast wrought aluminum alloys in the T6 condition.The results showed that tensile properties were close to or even in some cases exceeded the minimum specifications.The yield strength and elongation of rheocast 2024-T6 exceeded the minimum requirements of the wrought alloy in the T6 condition but the ultimate tensile strength achieved only 90% of the specification because the Mg content of the starting alloy was below the commercial alloy specification.The strengths of rheocast 6082-T6 exceeded all of the wrought alloy T6 strength targets but the elongation only managed 36% of the required minimum due to porosity, caused by incipient melting during solution heat treatment, and the presence of fine intermetallic needles in the eutectic.The yield strength of rheocast 7075 exceeded the required one and the ultimate tensile strength also managed 97% of the specification; while the elongation only reached 46% of the minimum requirement also due to incipient melting porosity caused during the solution heat treatment process.

Effects of process parameters and die geometry on longitudinal welds quality in aluminum porthole die extrusion process

By using the rigid-visco-plasticity finite element method,the welding process of aluminum porthole die extrusion to form a tube was simulated based on Deform-3D software.The welding chamber height(H),back dimension of die leg(D),process velocity and initial billet temperature were used in FE simulations so as to determine the conditions in which better longitudinal welding quality can be obtained.According to K criterion,the local welding parameters such as welding pressure,effective stress and welding path length on the welding plane are linked to longitudinal welds quality.Simulation turns out that pressure-to-effective stress ratio(p/σ) and welding path length(L) are the key factors affecting the welding quality.Higher welding chamber best and sharper die leg give better welding quality.When H=10 mm and D=0.4 mm,the longitudinal welds have the best quality.Higher process velocity decreases welds quality.The proper velocity is 10 mm/s for this simulation.In a certain range,higher temperature is beneficial to the longitudinal welds.It is found that both 450 and 465 ℃ can satisfy the requirements of the longitudinal welds.

Tensile properties and microstructure of rheo-diecast 7075 alloy prepared by serpentine channel process

A semisolid slurry of 7075 aluminum alloy was prepared by means of a serpentine channel process (SCP) and rheo-diecasting. The influences of pouring temperature during slurry preparation, the injection pressure and die preheat temperature on the mechanical properties and microstructure of a rheo-diecast 7075 aluminum alloy were investigated. The results show that the as-cast strength and elongation of the tensile samples were 210-260 MPa and 0.2%-1.7%, respectively, with an injection pressure of 130 MPa, a pouring temperature of 700-720℃, a preheat temperature of 280-350℃, and a plunger speed of 0.5 m·S^-1. The results also show that the aged strength and elongation of the tensile samples were 420-453 MPa and 1.0%-1.4%, respectively, when the alloy solution was treated at 470℃ for 12 h and aged at 120℃ for 24 h. The substantial shrinkage porosity in the 7075 aluminum alloy tensile samples was the main cause of low elongation.

ISOTHERMAL PRECISION FORGING PROCESS OF ALUMINUM ALLOY CYLINDRICAL HOUSING

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铸造增压压力对汽车用AlSi9Mg铝合金组织和力学性能的影响

通过改变低压铸造过程中不同增压压力来研究其对AlSi9Mg合金显微组织与力学性能的影响。结果表明,在高增压压力制备的AlSi9Mg合金样品具有更加致密的显微组织及更接近球形的共晶Si颗粒。同时,由于具有更好的填充能力,高增压压力下合金的气孔缺陷大大减少,合金具有更优异的力学性能。在90、150、210 kPa3种不同级别的增压压力下,晶粒尺寸呈逐渐减小的趋势,对应的合金晶粒尺寸和二次枝晶臂间距分别为246、197、149μm,44.9、37.3、31.1μm;3种增压压力对应的密度和孔隙率分别为2.656、2.659、2.674 g/cm^(3),0.96%、0.79%、0.38%;AlSi9Mg合金的抗拉强度、屈服强度和伸长率分别为238.76、174.68 MPa和3.14%;252.43、177.47 MPa和4.61%;256.10、178.81 MPa和6.85%,分别提高了7.26%、2.36%、118.15%。

基于球形底模的铝合金自冲铆接工艺多元回归模型

针对低延展性铝合金薄板材料自冲铆接成形过程易出现裂纹问题,提出了一种基于球形底模的自冲铆连接工艺.针对7075铝合金材料,采用Box-Behnken Design响应面试验方法,开展自冲铆接头工艺试验研究,确定最优工艺参数.以铆钉长度,冲头速度和冲头行程作为输入变量,接头的失效载荷和能量吸收值为响应值,建立基于球形底模的自冲铆接工艺多元非线性回归模型,并进行试验验证.结果表明,采用球形底模在保证接头强度下有效抑制自冲铆接头机械内锁区裂纹的产生;应用回归模型得到的理论预测值与试验值之间的相对误差较低,回归模型具有较高的可靠性;同时,单因素分析表明,铆钉长度对接头静力学性能的影响最大;交互作用分析中,铆钉长度和冲头行程的交互作用对失效载荷和能量吸收值的影响最为显著.最后通过NSGA-Ⅱ遗传算法确定最优工艺参数组合.

基于ProCAST的一模多腔YL112铝合金压铸件数值模拟及工艺优化

针对YL112压铸铝合金一模多铸产品的组织性能均一性需求,采用ProCAST软件对典型一模多铸工艺进行模拟,比较了两种不同充型顺序的压铸方案。结果表明:基于顺序凝固一模多腔压铸件由于充型与凝固过程的温度场分布不均,导致近浇口端铸件出现明显缩松缩孔缺陷,造成铸件性能均一性差。后续采用等流程浇注系统,实现一模多腔铸件同时充型凝固过程,改善了铸件温度场分布,减少了工艺缺陷。经过实际生产验证,获得了组织性能均一性好的压铸件。

6061铝合金自润滑热锻条件下工件和模具摩擦磨损特性

基于热锻条件,使用销-盘摩擦设备对6061热锻铝合金和H13钢基自润滑模具材料进行了高温对磨实验,通过电子探针和能谱仪分析了不同工况下工件和模具的磨损机理。结果表明,随着载荷的增加,工件和模具之间的摩擦因数与磨损率先降低后升高;随着转速的增加,工件和模具之间的摩擦因数增大,磨损率呈倍数增加;当载荷为12 N、转速为100 r·min^(-1)时,工件和模具之间的摩擦因数最小,其值为0.416,磨损率仅为24.591 mm 3·N^(-1)·m^(-1);随着转速和载荷的增加,工件和模具之间的粘着磨损加重并且逐渐出现磨粒磨损和氧化磨损。