压铸AZ91D镁合金激光重熔区氢气孔的形成机制

摘要

In order to investigate the mechanism of pore formation in fusion welding zone of die cast Mg alloys,local re-melting of die cast magnesium alloy AZ91D of 6mm thickness and hot extruded AZ71 Mg alloy of 2.2mm utilizing CO2 laser have been conducted.Base metal microstructure and pore morphology have been observed by adopting SEM.The size of pores has been measured by particle size analysis software Nano measure 1.2.The results indicate that large pores have irregular shape and hackly inner wall of obvious traces scoured by metal,and these pores are developed by shrinkage blowhole of base metal; Small pores,resulted from hydrogen,have smooth inner wall and upside down broadening formation.The formation mechanism of hydrogen induced pores was analyzed,a model of hydrogen induced pores' formation was established.Furthermore,the model was compared with the experimental photographs,which could be used to explain the formation of hydrogen induced pore.%为研究压铸镁合金熔化焊接气孔的形成机理,对厚度为6mm的AZ91D压铸镁合金和厚度为2.2mm的AZ71热挤压镁合金进行CO2激光局部重熔.采用扫描电子显微镜(SEM)观察气孔形貌,利用粒径分析软件Nano measure 1.2测量气孔的尺寸.结果表明:压铸镁合金重熔区气孔问题突出,少数粗大的宏观气孔形状不规则,内壁粗糙,具有明显的金属冲刷痕迹,均来源于母材预存微观气缩孔；多数微观气孔内壁光滑、呈倒喇叭形,属于氢致气孔.分析了氢致气孔的形成机制,建立了氢气孔形成过程的模型,并同实验照片进行了比较,发现所建立的模型能够很好地用来解释氢致气孔的形成过程.