AZ91D压铸镁合金激光局部重熔区气孔的形成机制

Pore Formation Mechanism in Laser Local Re-melted Areas of Die Cast Magnesium Alloy AZ91D

摘要:

为研究压铸镁合金熔焊过程气孔的形成机制，对厚度为6 mm的AZ91D压铸镁合金进行激光局部重熔。采用光学显微镜(OM)和扫描电子显微镜(SEM)观察母材组织和气孔形貌。利用粒径分析软件Nano measure 2.1测量气孔的尺寸，分析各类气孔的形成机制。结果表明: 随激光功率的增大，熔合区气孔率增大；微观气孔内壁光滑、呈倒喇叭形，属于氢致气孔；粗大宏观气孔形状不规则，内壁粗糙，具有明显的金属冲涮痕迹，是遗传于母材预存的气缩孔，建立了重熔区气孔体积同熔池气泡体积内在关联的数学模型

Abstract:

In order to study the pore formation mechanism of die cast magnesium alloy during fusion welding, local re-melting of die cast magnesium alloy AZ91D of 6 mm thickness utilizing laser has been conducted. Microstructure and pore morphology of base metal have been observed adopting OM and SEM. The size of pores has been measured by particle size analysis software Nano measure 2.1. The formation mechanism of various kinds of pores was analyzed. The results indicate that the porosity increases with the increase of laser power. Small pores, resulted from hydrogen, have smooth inner wall and inverted-trumpet shape. Large pores have irregular shapes and hackly inner wall with obvious traces scoured by metal. These pores are developed by shrinkage blowhole of base metal. Mathematical model on relationship of pore in re-melted zone associated with that in the molten pool was established