Effects of process parameters on morphology and distribution of externally solidified crystals in microstructure of magnesium alloy die castings

During the cold-chamber high pressure die casting(HPDC) process, samples were produced to investigate the microstructure characteristics of AM60B magnesium alloy. Special attention was paid to the effects of process parameters on the morphology and distribution of externally solidified crystals(ESCs) in the microstructure of magnesium alloy die castings, such as slow shot phase plunger velocity, delay time of pouring and fast shot phase plunger velocity. On the basis of metallographic observation and quantitative statistics, it is concluded that a lower slow shot phase plunger velocity and a longer delay time of pouring both lead to an increment of the size and percentage of the ESCs, due to the fact that a longer holding time of the melt in the shot sleeve will cause a more severe loss of the superheat. The impingement of the melt flow on the ESCs is more intensive with a higher fast shot phase plunger velocity, in such case the ESCs reveal a more granular and roundish morphology and are dispersed throughout the cross section of the castings. Based on analysis of the filling and solidification processes of the melt during the HPDC process, reasonable explanations were proposed in terms of the nucleation, growth, remelting and fragmentation of the ESCs to interpret the effects of process parameters on the morphology and distribution of the ESCs in the microstructure of magnesium alloy die castings.

Research advances of magnesium and magnesium alloys worldwide in 2022

More than 4600 papers in the field of Mg and Mg alloys were published and indexed in the Web of Science(WoS)Core Collection database in 2022.The bibliometric analyses indicate that the microstructure,mechanical properties,and corrosion of Mg alloys are still the main research focus.Bio-Mg materials,Mg ion batteries and hydrogen storage Mg materials have attracted much attention.Notable contributions to the research and development of magnesium alloys were made by Chongqing University(>200 papers),Chinese Academy of Sciences,Shanghai Jiao Tong University,and Northeastern University(>100 papers)in China,Helmholtz Zentrum Hereon in Germany,Ohio State University in the USA,the University of Queensland in Australia,Kumanto University in Japan,and Seoul National University in Korea,University of Tehran in Iran,and National University of Singapore in Singapore,etc.This review is aimed to summarize the progress in the development of structural and functional Mg and Mg alloys in 2022.Based on the issues and challenges identified here,some future research directions are suggested.

Heat Transfer between Casting and Die during High Pressure Die Casting Process of AM50 Alloy-Modeling and Experimental Results

A method based on die casting experiments and mathematic modeling is presented for the determination of the heat flow density （HFD） and interfacial heat transfer coefficient （IHTC） during the high pressure die casting （HPDC） process.Experiments were carried out using step shape casting and a commercial magnesium alloy,AM50.Temperature profiles were measured and recorded using thermocouples embedded inside the die. Based on these temperature readings,the HFD and IHTC were successfully determined and the calculation results show that the HFD and IHTC at the metal-die interface increases sharply right after the fast phase injection process until approaching their maximum values,after which their values decrease to a much lower level until the dies are opened.Different patterns of heat transfer behavior were found between the die and the casting at different thicknesses.The thinner the casting was,the more quickly the HFD and IHTC reached their steady states.Also,the values for both the HFD and IHTC values were different between die and casting at different thicknesses.

Latest research advances on magnesium and magnesium alloys worldwide

In the past two years,significant progresses have been achieved in high-performance cast and wrought magnesium and magnesium alloys,magnesium-based composites,advanced cast technologies,advanced processing technologies,and functional magnesium materials,such as Mg ion batteries,hydrogen storage Mg materials,bio-magnesium alloys,etc.Great contributions to the development of new magnesium alloys and their processing technologies have been made by Chongqing University,Shanghai Jiaotong University,Chinese Academy of Sciences,Helmholtz Zentrum Geesthacht,Queensland University,Brunel University,etc.This review paper is aimed to summarize the latest important advances in cast magnesium alloys,wrought magnesium alloys and functional magnesium materials worldwide in 2018–2019,including both the development of new materials and the innovation of their processing technologies.Based on the issues and challenges identified here,some future research directions are suggested,including further development of high-performance magnesium alloys having high strength and superior plasticity together with high corrosion resistance and low cost,and fundamental research on the phase diagram,diffusion,precipitation,etc.,as well as the development of advanced welding and joining technology.

Research advances of magnesium and magnesium alloys worldwide in 2021

More than 4000 papers in the field of Mg and Mg alloys were published and indexed in Web of Science(WoS)Core Collection database in 2021.The bibliometric analyses indicate that the microstructure,mechanical properties,and corrosion of Mg alloys still are the main research focus.Mg ion batteries and hydrogen storage Mg materials have attracted much attention.Significant contributions to the research and development of magnesium alloys were made by Chongqing University,Shanghai Jiaotong University,and Chinese Academy of Sciences in China,Helmholtz Zentrum Hereon in Germany,Ohio State University in the United States,the University of Queensland in Australia,Kumanto University in Japan,and Seoul National University in Korea,University of Tehran in Iran,etc..This review is aimed to summarize the progress in the development of structural and functional Mg and Mg alloys in 2021.Based on the issues and challenges identified here,some future research directions are suggested.

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like a-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, a-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in Cavity, microstructural segregation of unmelted a-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.

Grain Size Distribution and Interfacial Heat Transfer Coefficient during Solidification of Magnesium Alloys Using High Pressure Die Casting Process

The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCASTTM, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting, Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interracial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interracial heat transfer coefficient for different locations.

镁合金及其成型技术综述

简要介绍了镁合金的特点、分类以及镁合金在汽车、3C和自行车行业的应用,并举例说明了各自的现状;通过大量相关资料,对现阶段国内外镁合金的成型技术进行了系统的论述,其中包括镁合金铸造成型、塑性成型、连接成型,对它们各自的工艺特点和应用范围进行对比分析,发现镁合金的成型技术现在主要是压铸成型,其他的成型工艺的应用还比较少.同时分析了我国镁合金发展的现状,找出与国外的差距,为我国镁合金的进一步发展提出一些建议,预测了它的发展方向和前景.

镁合金压铸件在汽车上的应用

介绍了镁合金构件的主要特性，综述了镁合金压铸件在全球汽车业中的应用现状及镁铸件用量增长情况，镁合金的发展状况和目前应用的镁合金压铸工艺及防腐蚀表面处理技术。

镁合金铸造成形技术的发展

本文综述了镁合金的主要成形技术及其最新发展。镁合金成形技术的进一步发展将主要体现在现有技术的改进 ,新成形技术的研究 ,不同成形技术的结合三个方面。不同成形技术的结合可充分发挥各种成形技术的优点 。

真空压铸工艺参数对AM50镁合金力学性能的影响规律

采用阶梯试验模具及AM50合金,进行了系统的真空压铸试验,实测了不同厚度的阶梯试样在不同工艺条件下的密度及力学性能,研究了高真空压铸工艺参数对AM50镁合金力学性能的影响规律。结果表明,随着型腔真空压力的降低,铸件密度、抗拉强度和伸长率均随之提高;铸造压力对力学性能的影响在真空压铸和常规压铸中遵循基本相同的规律,即增大铸造压力可以使铸件的致密程度、抗拉强度、屈服强度和伸长率得到提高;随着高速速度的增大,薄壁铸件的抗拉强度、屈服强度和伸长率均表现出明显的增加,这一点与常规压铸的规律相反。结合高真空和高速工艺,可以使薄壁铸件的抗拉强度和伸长率得到较为明显的提升。

原镁直接熔炼生产镁合金压铸件的工艺进展

简述了我国镁合金压铸件生产现状,分析了从原镁到镁合金压铸件的工艺过程及存在的问题;讨论了全封闭式熔化及浇注集成化方法、合金化阻燃技术和半固态成形技术等三种工艺优化方法。

AZ91D镁合金壳形件真空压铸充型和凝固过程的数值模拟

运用有限元模拟仿真软件对镁合金AZ91D壳形件进行多组正交试验真空压铸过程的数值模拟,找出最佳的压铸工艺参数。通过模拟结果表明:最佳压铸工艺参数为浇注温度655℃、冲头压射速度3m/s、模具初始温度200℃。在这组优化的工艺参数下,通过对液态合金充型及凝固过程的可视化观察,有效的预测铸造缺陷产生的部位及原因,从而在实际生产中采取相应的措施避免缺陷的产生,优化铸造过程。

AZ91D半固态流变压铸成形的研究

采用双螺杆机械搅拌方式制备半固态浆料;研究了AZ91D镁合金半固态浆料的流变压铸成形工艺。结果表明:压射压力在40～50MPa,压射充型速度在10～15m/s内,固相率在10%～60%的浆料都能流变压铸成薄壁圆形铸件;半固态流变压铸成形比液态压铸成形的强度、伸长率分别提高37%、44%,并可施以热处理,进一步提高性能,易于实现"净近成形"。

镁合金汽车座椅骨架浇注系统的设计优化

采用有限元数值模拟技术,对镁合金坐椅骨架压铸件充型过程、凝固过程进行仿真分析,预测了压铸件可能出现缺陷的位置,提出了浇注系统的优化设计方案。对比优化前后工艺方案表明,优化后的浇注系统使镁合金压铸过程中的卷气及缩孔缩松倾向明显减小,压铸件的品质得到提高,从而有效改善了传统压铸工艺和模具设计的潜在风险,缩短了生产周期。

镁合金成形性能和加工技术综述

简述了镁合金的特点、物理性能,重点分析了镁合金的成形性能和压铸成形、半固态成形、锻造等加工技术,并展望了未来镁合金加工技术的发展趋势。

压铸工艺对镁合金组织性能影响的研究

论述了压铸工艺条件下镁合金的凝固过程及特点,结合最近的研究进展,分析了压铸工艺对镁合金凝固组织及缺陷形成的影响,并探讨了压铸镁合金组织与性能之间的关系。

飞速发展的压铸技术——第二届中国国际压铸会议评述

介绍了“第二届中国国际压铸会议”概况 ;根据会议宣读的论文 ,分压铸工艺、压铸设备、镁合金压铸、锌合金压铸、计算机在压铸中的应用等五个方面 。

镁合金挤压铸造成形的研究

采用间接冲头式方法,研究了AZ91D镁合金的挤压铸造成形工艺,试生产了圆形铸件。结果表明:用N2或Ar气排除挤压模具型腔中的空气,能防止镁合金液在挤压成形流动过程中产生氧化及夹杂;挤压模具的加热,特别是挤压活塞及定量室外套的加热,对镁合金的挤压成形影响很大;挤压压力、保压时间和挤压速度等挤压工艺参数与铸件的结构密切相关。

半固态AZ91D镁合金压铸过程的数值模拟

采用机械搅拌方式研究了半固态AZ91D合金的流变特性,并根据实验数据,拟合出剪切速率为238s-1时,半固态AZ91D合金的固相体积分数和表观粘度之间的关系式。从流体力学的角度,采用数值技术对半固态AZ91D镁合金的压铸过程进行了研究。数值模拟结果表明,半固态浆料温度为550℃、模具温度为300℃、压铸速度为1m/s时,该文所设计的压铸件的压铸过程能很好地进行。同时,该研究工作能为分析压铸成形过程提供有益的信息。