一类硅铝合金HPDC工艺过程的研究分析

采用高压压铸(HPDC)方法制造的铸件力学性能受铸造缺陷影响很大,而铸造缺陷的产生过程具有较高的随机性,其产生机理尚未明确。提出了一种基于有限元铸造软件ProCAST的HPDC数值模拟方法,将其应用于铝合金铸件拉伸试验试样的制造过程模拟。通过仿真分析得到HPDC各阶段(浇注、注射、冷却)流体流动、凝固和缺陷的形成过程,预测了铸件内部空气滞留和孔隙度分布情况。将所得结果与温度测量值、孔隙度以及固体分布情况进行了比较,结果表明熔体的湍流度和压铸过程与实际情况相符。

型腔背压条件下的压铸数值模拟及缺陷分析

压铸过程中金属液充型行为受型腔残余气体背压影响,为准确模拟金属液充型过程,需考虑背压条件。通过引入背压控制方程,计算了某汽车用铝合金滤清器压铸充型过程,并以计算结果为依据提出了改进方案。引入背压条件预测气孔缺陷位置与实际情况一致。通过调整排气口位置能够改变局部型腔背压,进而改变金属液充型行为,从而消除了铸件缺陷。

模具充型过程中光滑粒子流体动力学模拟(英文)

讨论了基于光滑粒子流体动力学(SPH)的压铸充型模拟的实施过程。建立了一种区分流体粒子和入流粒子的入流边界条件。对人工黏度和移动最小二乘法在处理压力振荡中的作用进行了对比。对最终模型在模拟压铸二维与三维的充型过程进行了验证。将SPH和有限差分的模拟结果与实验结果进行了对比研究。结果显示SPH与实验更为吻合,表明了SPH在描述充型过程流态方面的有效性与精度。

镁合金零件压铸过程裂纹成因及数值模拟(英文)

薄壁镁合金件裂纹缺陷制约着其应用,其成因受多方面因素影响。通过虚拟仿真技术,考察了某薄壁镁合金件压铸充型凝固过程的温度场,凝固过程中产生的热应力,及其对裂纹成因的影响。通过数值分析得出AZ91D铸件裂纹的产生与铸件孔洞类缺陷及凝固收缩不一致产生的应力有关,分析结果与实验一致。以数值分析结果为依据,提出了改进方案。

短周期热处理在A356合金铸件中的应用及力学性能分析

制作了不同的A356合金试样,包括半固态金属(SSM)高压压铸(HPDC)试样和熔模铸造试样。试样经过不同的热处理,比较了不同试样不同状态的维氏硬度值和拉伸性能参数,主要研究了A356合金短周期热处理工艺。结果表明,半固态高压压铸(SSM-HPDC)得到的球晶微观结构的试样与熔模铸造得到的树枝晶微观结构试样的硬度值和拉伸性能相近;A356合金短周期热处理能够取代长周期热处理。

一种采用气冷搅拌杆流变压铸工艺制备的Al-8Si合金的组织与性能（英文）

报道了一种新颖、高效的采用气冷搅拌杆制备半固态浆料的工艺,该工艺通过将压缩空气不断注入到搅拌杆内腔来冷却熔体。采用该工艺制备了一种新近研发的高导热Al-8Si合金半固态浆料,并将该工艺与高压铸造机结合生产出一种无线基站用薄壁散热壳体件。研究了气体流量对初生晶粒的形貌、流变压铸件的力学性能及导热系数的影响。结果表明:当气体流量超过3 L/s时,采用该工艺可以制备出优质的半固态浆料。当气体流量为5 L/s时,流变压铸件的力学性能和导热系数最高,分别为抗拉强度261 MPa,屈服强度124 MPa,伸长率4.9%,显微硬度HV 99和导热系数153 W/(m·K)。相比于传统压铸件,采用气冷搅拌杆流变压铸工艺生产的铸件力学性能和伸长率大大提高,其抗拉强度、屈服强度、伸长率、显微硬度和导热系数的增长率分别为20%、15%、88%、13%和10%。

影响铝合金缸体与铸铁缸套结合性能因素的分析

为了解决发动机铝合金缸体和铸铁缸套的结合问题,需要制定出能全面正确反应界面结合程度的评价方法用以控制产品质量。文中研究了不同铸造工艺下缸套的结合情况,并对结合间隙进行了对比、分析。结果表明:压力铸造下缸套的结合质量明显优于重力铸造,凝固压力是影响结合程度的主要因素;重力铸造时铝液和铸铁的润湿性能影响结合,润湿性能好能够改善结合效果;铸造工艺的控制、缸套的外壁形状对结合性能有直接影响。

大体积流变浆料制备与压铸成形一体化工艺及其应用

目的研究气体流量对ACSR流变压铸Al-Si-Fe合金组织的影响,同时研究与对比流变压铸与传统压铸合金的组织性能。方法通过改变气体流量制备流变压铸Al-Si-Fe合金,采用光学显微镜、扫描电子显微镜、电子探针、万能试验机等研究了合金的微观组织与拉伸性能。结果随着气体流量由0提高至6 L/s,流变压铸合金中α1-Al平均尺寸由35.6μm下降到23.9μm,形状因子由0.71上升到0.82;与传统压铸合金相比,流变压铸合金的抗拉强度和伸长率分别提高了15%和75%。结论 ACSR流变压铸工艺可以制备出组织细小圆整且力学性能高的铸件。

Interfacial heat transfer behavior at metal/die in finger-plated casting during high pressure die casting process

Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).

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.

Effect of vacuum on porosity and mechanical properties of high-pressure die-cast pure copper

Pure copper tensile bars were produced by conventional die casting(HPDC) and vacuum-assist die casting(VADC) processes. Porosity and mechanical properties were investigated by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray computed tomography(XCT) and tensile tester. Results show that porosities including gas porosity and shrinkage porosity could be observed in copper castings. Since the application of vacuum could reduce filling related gas entrapment and facilitate solidification due to the increased heat transfer between metal and die, both number and size of the entrapped gases, as well as shrinkage porosities were significantly reduced in vacuum-assist die castings of pure copper. The porosity fraction decreased from 2.243% to 0.875% compared with that of the conventional die casting. Besides, mechanical properties were improved significantly, i.e., by 15% for ultimate tensile strength and three times for elongation.

Study on interfacial heat transfer coefficient at metal/die interface during high pressure die casting process of AZ91D alloy

The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today's manufacturing industry. In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC) was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger, and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified, when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.

Different aging behaviors at surface layer and central region of a die-casting A380 alloy during heat treatment

Microstructural and hardness evolutions of a vacuum-assistant die-cast A380(Al-8.67 wt.%Si-3.27 wt.%Cu) alloy during heat treatment were investigated. Isothermal DSC test at 200 °C revealed that the precipitation reaction in the surface layer was faster than that in the central region. This corresponded with the hardness evolution that the surface layer hardened faster. The hardness increment in the surface layer was higher than that in the central region. Further experimental evidences indicated that the differences were due to the different amounts of heterogeneous nucleation sites for precipitation in the two parts. The influence of the characteristic as-cast microstructure on the artificial aging process is analyzed and discussed in detail.

Wear of semi-solid rheocast SiC_p/Al metal matrix composites

Rheocasting of plates in Al alloy 359 reinforced with SiC at 11%,27% and 50%(volume fractions) exhibits the capability of the council for scientific and industrial research-rheocasting system(CSIR-RCS) in rheo-processing and high pressure die casting of SiC metal matrix composites.The metal matrix consisting of nearly spherical proeutectic α(Al) globules was produced.Spheroidization of fibrous eutectic silicon took place upon heat treatment of the as-cast metal matrix composites(MMCs).Hardness increases as the volume fractions of SiC increases.Wear rates of the MMCs in the F and T6 heat treatment conditions were assessed with a metallographic preparation machine.It is found that the 11% SiC MMC wear rate is higher on SiC abrasives compared with the 50% SiC MMC wear rate due to wear of the aluminum matrix.This trend is reversed on diamond abrasives due to pull-out of the irregular shaped composite particles.The 50% SiC MMC suffers from composite particle fracture porosity after high pressure die casting(HPDC).

An improved mathematical model to simulate mold filling process in high pressure die casting using CLSVOF method and CSF model

A 3D mathematical model was proposed to simulate the mold filling process in high-pressure die casting(HPDC) to improve accuracy considering the surface tension. Piecewise liner interface calculation(PLIC) and volume of fluid(VOF) methods were used to construct the pattern of the liquid interface. A coupled levelset and VOF method(CLSVOF) was proposed to capture the interface pattern and obtain its normal vector. A continuum surface force(CSF) model was used to consider the surface tension. Two water analogy experiments were carried out using the proposed model. Simulation and experimental results were analyzed and compared; and the effects of surface tension were also discussed. The simulation results agreed well with the experiments and the simulation accuracy was an improvement on interface geometries, liquid flows, and gas entrapments.

大型薄壁压铸材料Al-Si合金的组织和力学性能

针对大型薄壁压铸件的客户需求,采用模拟软件进行材料的热物性参数模拟和铸造过程的模拟,对产品研发过程中的成分设计、模具设计以及工艺设计进行了有效的指导。结果表明,试制铸件平均抗拉强度达到293.41MPa,平均屈服强度达到200.21MPa,平均延伸率达到5.37%,具有优良的综合力学性能,且产品的内部质量符合ASTM E505 A3级要求,产品品质满足客户需求。

AlSi12(Fe)(a)与AlSi10MnMg合金压铸件在长期热环境下的力学性能

长期热环境会影响AlSi12(Fe)(a)合金和AlSi10MnMg合金的力学性能。在相同的高压压铸工艺条件下制备合金。选择经过500h×120℃预处理的试样和普通试样进行力学性能测试。尽管预处理后AlSi12(Fe)(a)合金试样的力学性能发生了变化,但是没有衰减到材料标准值以下。预处理后AlSi10MnMg合金试样的抗拉强度与屈服强度有所提高,但伸长率降低,且低于材料的标准值。

凝固速率对压铸态AZ91-1.5Si-0.4Ca镁合金组织和性能的影响

以AZ91-1.5Si-0.4Ca为对象(以AZ91为参照),通过设计并压铸成型4种厚度的板状试样获得了4个凝固速率。首先对各壁厚试样的凝固速率进行了数值模拟,并对2种合金试样的显微组织、室温和180℃拉伸性能、拉伸断口形貌进行了对比研究。结果表明:AZ91-1.5Si-0.4Ca中的Si与Mg生成Mg_2Si,Ca主要以固溶的形式存在;Si和Ca有一定的晶粒细化效用。随着凝固速率增加,AZ91-1.5Si-0.4Ca中的Mg_2Si相由粗大的多边形及汉字状向细小的多边形颗粒及短棒转变。随着凝固速率增加,2种合金试样的室温和180℃力学性能提高,AZ91-1.5Si-0.4Ca室温和180℃强度受凝固速率影响大于AZ91,伸长率受凝固速率影响则小于AZ91。当壁厚小于2.5 mm时,AZ91-1.5Si-0.4Ca的180℃强度高于AZ91;当壁厚小于3 mm时,AZ91-1.5Si-0.4Ca的室温强度高于AZ91。

真空压铸对Al-Si-Cu合金固溶过程共晶硅的影响

对真空压铸Al-Si-Cu合金试样(500 mbar)和普通压铸Al-Si-Cu合金试样在500℃固溶处理0.5、2、4、6 h后,利用光学显微镜及相应软件研究了固溶处理过程共晶硅形貌的变化。结果表明:真空压铸可以得到更加细化的铸态共晶硅颗粒;在固溶处理过程中,真空压铸试样也可以得到球化效果更好的共晶硅颗粒,并在固溶处理4 h时达到最佳。