A356.2铝合金铸锭断口收缩区缺陷的研究

Defect Analysis of Shrinkage Zone on the Fracture Surface of A356.2 Alloy Remelt Ingots

对链式连续铸锭机生产的A356.2铝合金锭进行质检时发现少量铸锭断口有明显的收缩区,且收缩区颜色偏黑。采用金相显微镜和扫描电镜对铸锭断口及组织进行了观察和分析,结果表明,铸锭断口颜色较深位置对应最后凝固收缩区,其中存在大面积枝晶间缩孔;收缩区组织中发现了大量氧化膜,枝晶表面亦覆盖有氧化物、部分位置存在氯化物,同时发现了C、Na、Ca等杂质元素;铸锭收缩区存在大量非金属夹杂物是导致该区域颜色偏黑的主要原因。

Abnormal visual dark shrinkage zone was found on the fracture surface of some A356 aluminum alloy remelt ingots,which were produced on an open mold chain conveyor ingot casting machine.The fracture surface and microstructure of ingot were investigated by means of scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS)and optical microscopy(OM).The results indicate that there exist a lot of dendritic shrinkage porosity in the dark zone,and some dendrites surface covered by oxidized inclusions,chloride and carbides were confirmed by EDS.Oxide films with complex curve shape were also found in the optical microstructure.It’s believed that the gathered inclusions should be responsible to the dark visual of the shrinkage zone on the fracture surface of A356.2 alloy ingots.