Characteristics and formation mechanisms of defect bands in vacuum-assisted high-pressure die casting AE44 alloy  

真空压铸镁合金AE44缺陷带的组织特征及形成机理

作　　者：Ying-ying HOU Meng-wu WU Bing-hui TIAN Xiao-bo LI Shou-mei XIONG 侯莹滢;吴孟武;田冰辉;李晓波;熊守美(武汉理工大学现代汽车零部件技术湖北省重点实验室,武汉430070;清华大学材料学院,北京100084)

机构地区：[1]Hubei Key Laboratory of Advanced Technology for Automotive Components,Wuhan University of Technology,Wuhan 430070,China [2]School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China

出　　处：《Transactions of Nonferrous Metals Society of China》2022年第6期1852-1865,共14页中国有色金属学报（英文版）

基　　金：the financial supports from the the National Natural Science Foundation of China (No. 51805389);the Natural Science Foundation of Hubei Province, China (No. 2018CFB210);the “111” Project, China (No. B17034)

摘　　要：The microstructure in vacuum-assisted high-pressure die casting(HPDC) Mg-4Al-4RE(AE44) alloy was studied. Special attention was paid to the characteristics of defect bands and their formation mechanisms. Since double defect bands are commonly observed, the cross section of die cast samples is divided into five parts with different grain morphologies and size distributions. The inner defect band is much wider than the outer one. Both the defect bands are solute segregation bands, resulting in a higher area fraction of Al;RE;phase than that in the adjacent regions. No obvious aggregation of porosities is observed in the defect bands of AE44 alloy. This may be due to a narrow solidification temperature range of AE44 alloy and a large amount of latent heat released during the precipitation of intermetallic phases. The formation of the defect bands is related to the shear stress acting upon the partially solidified alloy, which can lead to collapse of the grain network. However, the generation mechanisms of shear stress in the outer and inner defect bands are quite different.研究真空压铸镁合金AE44的显微组织,重点关注缺陷带的组织特征及形成机理。实验中普遍观察到的双缺陷带将压铸试样横截面划分为5个部分,各部分的晶粒形态与尺寸分布存在较大差异。心部缺陷带显著宽于表层缺陷带。双缺陷带均为溶质偏析带,Al;RE;相面积分数均高于周围区域。压铸镁合金AE44缺陷带内未观察到明显的孔洞聚集现象,这是由镁合金AE44较窄的凝固温度区间以及金属间化合物相析出过程中释放出大量的潜热造成的。缺陷带的形成与作用于半固态合金的剪切应力有关,剪切应力会导致半固态区域晶粒骨架崩塌。然而,表层及心部缺陷带处的剪切应力形成机制大不相同。

关 键 词：high-pressure die casting magnesium alloy AE44 microstructure defect band 

分 类 号：TG249.2[金属学及工艺—铸造]