铝(镁)合金消失模铸造近净成形技术研究进展

阐述了铝(镁)合金消失模铸造技术的研究现状,着重介绍了铝(镁)合金消失模铸造在金属液充型、振动凝固、压力凝固以及消失模壳型铸造等技术方面的最新研究进展。研究表明,铝(镁)合金在消失模铸造过程中,需重点解决针孔、缩松等缺陷,提高液态合金的充型能力和铸件的力学性能;通过采用振动凝固和压力凝固的手段,可以提高金属液充型能力、细化组织、提高组织致密性,明显提高铸件力学性能。真空低压消失模壳型铸造技术,可以解决普通消失模铸造易于出现的孔洞和夹杂等缺陷以及浇不足和浇注温度高等问题,是一种生产复杂薄壁高质量铝、镁合金精密铸件的新方法。     

铝合金汽车转向节精密铸造工艺研究

目的 对某铝合金汽车转向节的精密铸造工艺进行设计与优化研究,以得到合格的铝合金汽车转向节的精密铸造工艺方案。方法 结合铝合金转向节铸件的结构特征、铸件材料特性和铸造经验,在转向节铸件主体部和鹅颈部各开设一个内浇口,设计了铝合金转向节初始浇注方案;通过在初始工艺方案中铸件缺陷较严重的区域设置补缩冒口、在铸件顶部增设排气道等措施给出了铝合金汽车转向节的优化浇注方案,基于ProCAST软件建立了铝合金转向节精密铸造2种浇注方案的有限元模型,对铝合金转向节精密铸造的充型过程、凝固过程及缩孔缩松特性进行了数值模拟与分析。结果 铝合金转向节铸件初始浇注方案的充型过程相对稳定流畅,铸件在凝固过程中有孤立液相区的形成,完全凝固后铸件中间部位存在大面积缩松缩孔缺陷;优化浇注方案能够控制金属液的流动、充型顺序及凝固特性,铸件的整个凝固过程基本呈中间对称分布,最后凝固区域位于补缩冒口内部,最大缩孔缩松率控制在2%以下。结论 优化浇注方案的设计合理且有效,能够有效地消除铝合金转向节铸件的缺陷。     

机械振动对AZ91镁合金充型能力的影响

为改善镁合金的铸造性能,研究机械振动对AZ91镁合金充型能力的影响,并探索了不同频率的机械振动增强充型能力的影响机制.结果表明:机械振动能够显著提高镁合金的充型能力,当振动频率为50 Hz时,螺旋形试样的平均长度相较于不振动来说增加了14%左右;机械振动通过枝晶破碎、减缓黏度增大的趋势、降低沿程阻力来增强充型能力.     

基于数值模拟缸体浇注系统的设计与优化

针对镁合金发动机缸体的结构特点设计了浇注系统,并用铸造分析软件对其充型和凝固过程进行了模拟。通过观察分析模拟结果,预测了充型时间、凝固时间以及铸件中可能存在的缩孔缩松缺陷的分布与尺寸,并设计了优化浇注系统。     

机械振动对A356合金充型能力影响的研究

将机械振动应用于A356合金浇注过程中,测量不同振动频率下合金的充型长度,通过多项式回归,建立充型长度与振动频率之间的数学表达式,来探索机械振动对合金充型能力的影响机理。实验结果表明,在A356铝合金充型过程中进行机械振动,使流动阻力减小,晶粒细化,改善了金属液充型能力,而使界面换热系数增加,阻碍了充性,因此振动频率对充型能力的影响不是单调的,振动f在20~50Hz之间存在一个频率,使A356铝合金的充型能力达到极大值,为35Hz,经过回归分析得出极大值点为f=39.05Hz,Lmax=823.89mm。     

静态条件下HP（MA—VAc—MMA）多孔载体固定化微生物的…

本文研究了ＨＰ（ＭＡ－ＶＡｃ－ＭＭＡ）多孔载体静态状况下固定化厌氧微生物的影响因素。结果表明，多孔高分子载体固定化微生物效果优于活性炭、活性污泥，固定化效果受单体组成、致孔剂、交联剂等的影响显著。当ＭＡ／ＶＡＣ／ＭＭＡ为４／５／１，用ＤＶＢ与ＥＧＤＡ混合物为交联剂，ＰＶＡＣ与ＢＡＣ混合物为致孔剂，用量分别为１０％，２０％，水解度大于３０％，粒径４０－６０目的多孔共聚物载体，固定化厌氧微生物效果优良     

铝合金端盖件压铸工艺的数值模拟

运用铸造模拟软件Procast对一模四腔的A356铝合金压铸零件进行数值模拟,分析铸件的充型凝固过程,预测缺陷。结果显示：在压射速度为2．5m／s,浇注温度为650℃,模具温度为240℃的条件下四腔同时充填,充型平稳,排气良好,得到充型完整、无缩松缩孔、气孔倾向小的铸件。     

柴油机铝合金活塞铸造工艺数值模拟研究

目的优化柴油机铝合金活塞的砂型重力铸造工艺。方法采用MAGMASOFT铸造仿真软件对ZL109铝合金活塞铸造工艺进行了仿真预测,分析了铸件充型凝固过程的速度场和温度场,并预测了缩孔、缩松等铸造缺陷,在此基础上优化了浇注系统和铸造工艺参数。结果铸件充型过程中内浇道金属液流速最高,液面沿铸件外壁平稳上升,整体充型过程平稳有序,铸件整体温度分布为从下到上依次降低;凝固过程铸件自下而上顺序凝固,但冒口部分凝固速度过快,导致铸件顶部和右上部出现缩松、缩孔缺陷;通过增设冒口、降低浇注速度等工艺措施后,实现了铸件的顺序凝固,补缩效果明显,铸件可能发生缩孔、缩松缺陷的位置已由顶部转至顶冒口和侧冒口等区域。结论利用铸造仿真软件预测铸件工艺上的缺陷,对铸造工艺进行优化及改进,能有效预防铸件缺陷的产生,提高铸件的工艺出品率,降低生产成本。     

抽拉速率对铝合金定向凝固热裂形成的影响

在半连续真空定向凝固设备上进行了Ａｌ－０．６ｗｔ％Ｃｕ和Ａｌ－２．０ｗｔ％Ｃｕ两种铝合金的热裂试验，结果表明，两种成分铝合金试样的热裂程度随抽拉速率的提高而增大，理论分析认为，抽拉速率的提高，增加了合金凝固后期的收缩速率，因而造成热裂程度的增加。     

nNA与PMMA的溶混特性

研究了间硝基苯胺（ｍＮＡ）与聚甲基甲酯（ＰＭＭＡ）的溶混特性，用非平衡方法制取ｍＮＡ在ＰＭＭＡ中均匀混合的透明薄膜，通过工艺参数优化将透明薄膜中ｍＮＡ的含量提高到５０ｗｔ％。     

Cyclic deformation behaviour and fatigue crack propagation in AZ91HP and AM50HP

Abstract

The purpose of the present work was to investigate room temperature cyclic deformation and crack propagation behaviour in the most widely used die casting magnesium alloy AZ91HP with different heat treatments. In addition, examination of the low cycle fatigue properties of solid solution treated alloy AZ91HP-T4 was emphasised in comparison with AM50HP. Obvious cyclic strain hardening was found in low cycle fatigue tests, especially for AZ91HP-T4 at high cyclic strain amplitudes. Nevertheless, it was very difficult to evaluate differences in low cycle fatigue behaviour between die casting alloy AZ91HP-F, artificially aged alloy AZ91HP-T6, solution treated alloy AZ91HP-T4, and AM50HP(-F) because of the scatter of test data. However, it may be concluded that the last two alloys had greater plastic strain components during cyclic deformation, and AZ91HP-T4 exhibited a longer fatigue life than that of AM50HP at the highest strain amplitude. According to results of tests carried out on AZ91HP compact tension (CT) specimens, it was concluded that solution treatment could reduce the fatigue crack propagation rate, and plasticity induced crack closure was considered to have a predominant effect on fatigue crack propagation.     

An experimental study on the energy absorption capacity of thin-walled castings

The energy absorption potential of high-pressure die cast (HPDC) components made of magnesium alloys AM20, AM50, AM60, AZ91 and the aluminium alloy A356 is investigated using a shear–bolt principle. Both quasi-static and dynamic tests have been performed. In addition, single cast plates of AM60 and A356 alloy with different thickness have been tested in order to investigate the effect of plate thickness on the shear–bolt mechanism. It is found that this deformation principle gives an approximately constant average force during the deformation process. Therefore, thin-walled HPDC components can be suitable as energy absorbing components when using the shear–bolt principle. A simple empirical model for prediction of the average shearing force as a function of plate thickness and bolt diameter is proposed.     

An investigation on hot-crack mechanism of Ca addition into AZ91D alloy

In automotive components, there is a significant weight saving potential in converting to magnesium alloys. Adding Ca element is one of the most effective ways to improve the temperature and mechanical properties of magnesium alloy. However, as hot-cracks often appear in such materials, Ca addition will thus encumber the development of this magnesium alloy. There are few reports on the hot-crack mechanism of magnesium alloy with Ca. This paper focused on the investigations as why to results in the hot-crack phenomenon of Ca addition. These results indicated that Ca addition affects the solidification process of AZ91D alloy, such as elevating the tendency of divorce eutectic and forming the new temperature of Al₂Ca phase. In addition, the Ca-contained phase distributed as the net-shape forms on grain boundary and results in lower boundary strength of the liquid film. Both of the above reasons would deteriorate filling capacity of the melt and the hot-crack resistance during solidification stage, resulting in the worst hot-crack property of this alloy.     

Bio-corrosion behavior of magnesium-fluorapatite nanocomposite for biomedical applications

Recent studies indicate that there is a high demand for designing magnesium alloys with adjustable corrosion rates and precipitation ability of bone-like apatite layer on the surface of magnesium alloys in body. An approach to this challenge might be the application of nanocomposites based on magnesium alloys. The aim of this work was fabrication and bio-corrosion evaluation of a nanocomposite that was made of magnesium alloy AZ91 as matrix and fluorapatite (FA) nano particles as reinforcement. Magnesium-fluorapatite nanocomposite (AZ91-20FA) was made via the blending-pressing-sintering method. In vitro corrosion measurements were performed for characterization of initial materials and produced composite. The results showed that the addition of FA nano particles to magnesium alloy as reinforcement can reduce the corrosion rate and accelerate the formation of bone-like apatite layer and in turn provide better protection for matrix alloy. It is suggested that the formation of bone-like apatite layer on the surface of magnesium alloy might contribute to the good osteoconductivity of magnesium alloys.     

Thermal analysis and solidification pathways of Mg–Al–Ca system alloys

Mg–Al–Ca alloys are creep resistant magnesium alloys with high application potentials. The solidification pathways and microstructure formation in this alloy system are still under discussion. In this paper, the solidification behavior of AZ91 and AM50 with Ca addition (AZC91x and AMC50x alloys) was investigated by a computer-aided cooling curve analysis (CA-CCA) system. Microstructure and phase identification were carried out by SEM and EDX analysis. The results show that the Ca-containing phase formation mainly depends on Ca content and Ca/Al ratio. With increasing the Ca/Al ratio these phases transform from Al₂Ca to (Mg, Al)₂Ca and Mg₂Ca. Moreover, Ca addition decreases the liquidus temperature of Mg–Al alloys, but influences the solidus temperature in a more complex way. Increasing the Ca content also decreases the solid fraction at which dendrite coherency occurs. The relationship between solidification interval, dendrite coherency point, formation of Ca-containing phases and hot tearing is also discussed.     

Mikrostrukturelle Veränderungen von Magnesium‐Druckgusslegierungen nach langzeitiger thermischer Beanspruchung

Microstructural Changes of Pressure Die Cast Magnesium Alloys after Long‐Term Thermic Loading The expansion of the application of pressure die cast magnesium alloys for automobiles requires the development of new alloys and the comprehensive assessment of available alloys on aggravated conditions, too. Such conditions are also given at higher temperatures, which can cause the creep of the material and lead to the component failure. Because the microstructural stability decisively depends on the thermic loading, this paper deals with the change of the microstructure and the hardness of the alloys AZ91, AM50 and AE42 after a long‐term annealing at 150 °C and 200 °C in comparison to the pressure die as‐cast condition. The results reveal clear differences of the microstructural stability of the alloys AZ91 and AM50 on the one hand and the alloy AE42 on the other hand. Due to the long‐term annealing at 150 °C the alloys AZ91 and AM50 show chiefly an intense precipitation of Mg₁₇Al₁₂ from the Al‐rich eutectic α‐phase. Furthermore at 200 °C, it is observed the coagulation and coarsening of these precipitates, too. The last appearances are connected with a weakening of the material. Regarding the alloy AE42, the changes of the precipitation state are not so intensely and do yet not lead to a microstructural weakening.     

固溶处理对AM60B＋xRE及AZ9lD＋xRE镁合金性能的影响

研究了添加少量富铈混合稀土的AM60B xRE及AZ9lD xRE合金(x＝0．4、0．8、1．2、1．6和2．0％，质量分数)固溶处理后的显微组织与机械性能．结果表明，添加混合稀土能显著提高合金的抗拉强度σb和屈服强度σ0.2，固溶处理明显提高AZ9lD xRE合金的强度；AM60B xRE及AZ9lD xRE合金的铸态组织由α(Mg)固溶体、杆状Al11RE3相、颗粒状Al10Ce2Mn7相以及网状Mg17Al12相组成，经过固溶处理后，网状Mg17Al12相完全溶解，只剩下热稳定性较高的Al11RE3相和Al10Ce2Mn7相，随固溶时间的延长，其形态略有改变．AM60B xRE合金拉伸试样断口呈带局部韧窝的准解理断裂形式，而AZ9lD xRE合金则呈现沿晶断裂 解理断裂的混合断口形态．     

In-vitro degradation behaviour of WE54 magnesium alloy in simulated body fluid

Rare earths containing magnesium alloy, WE54, exhibited a marginally higher in-vitro degradation resistance than that of pure magnesium. Heat-treatment procedure had an influence on the degradation behaviour. However, comparing with AZ91 magnesium alloy the in-vitro degradation resistance of WE54 magnesium alloy was significantly lower, which suggests that the passivating capacity of rare earths is inferior to that of aluminium under in-vitro condition.     

Nd对AZ91镁合金显微组织和耐腐蚀性能的影响

用金相显微镜、扫描电镜和静态质量损失法对AZ91-xNd镁合金(x=1.1%,1.4%,1.9%)的微观组织和腐蚀性能进行表征,研究了Nd对AZ9l镁合金显微组织和耐腐蚀性能的影响.结果表明:稀土Nd的添加明显细化了合金的组织,使半连续网状β(Mgl7Al12)相变为细小的长条状,且分布更加均匀.在合金中还生成了颗粒状...     

Nanoparticle interactions with the magnesium alloy matrix during physical deformation: Tougher nanocomposites

This study is aimed at understanding the toughness enhancing function of nanoparticles in magnesium nanocomposites, focussing on experimentally observed nanoparticle–matrix interactions during physical deformation. Al₂O₃ nanoparticles were selected for reinforcement purposes due to the well known affinity between magnesium and oxygen. AZ31/AZ91 (hybrid alloy) and ZK60A magnesium alloys were reinforced with Al₂O₃ nanoparticles using solidification processing followed by hot extrusion. In tension, each nanocomposite exhibited higher ultimate strength and ductility than the corresponding monolithic alloy. However, the increase in ductility exhibited by ZK60A/Al₂O₃ (+170%) was significantly higher than that exhibited by AZ31/AZ91/Al₂O₃ (+99%). The previously unreported and novel formation of high strain zones (HSZs, from nanoparticle surfaces inclusive) during tensile deformation is highlighted here as a significant mechanism supporting ductility enhancement in ZK60A/Al₂O₃ (+170% enhanced) and AZ31/AZ91/Al₂O₃ (+99% enhanced) nanocomposites. Also, ZK60A/Al₂O₃ exhibited lower and higher compressive strength and ductility (respectively) compared to ZK60A while AZ31/AZ91/Al₂O₃ exhibited higher and unchanged compressive strength and ductility (respectively) compared to AZ31/AZ91. Here, the previously unreported nanograin formation (recrystallization) during room temperature compressive deformation as a toughening mechanism in relation to nanoparticle stimulated nucleation (NSN) ability is also highlighted.