This paper concerns the effects of Mg content on keyhole behaviours during the laser welding process of 5754, 5083 and 5A06 Al-Mg alloys. The features of the vapour plume and keyhole area are extracted from high-speed images with image processing methods. The increase of Mg content leads to the increase of hydrodynamic pressure caused by metal evaporation and decrease of surface tension acting on the keyhole wall. The strong metal evaporation and decrease of surface tension help the formation of keyhole, which both result in a large size of keyhole with deep penetration and low frequency of keyhole collapse. However, the impact of metal vapour could be enhanced by the increase of evaporation and the decrease of both surface tension and viscosity, which leads to the frequent generation of swelling at the rear weldpool and poor formation of the weld bead.

本文涉及5754、5083和5A06 Al-Mg合金激光焊接过程中Mg含量对锁孔性能的影响。利用图像处理方法从高速图像中提取出蒸气羽和锁孔区域的特征。Mg含量的增加导致由金属蒸发引起的流体动压的增加以及作用在锁孔壁上的表面张力的减小。金属的强烈蒸发和表面张力的降低有助于形成锁孔，这两者都导致锁孔尺寸大，穿透力强和锁孔塌陷的频率低。但是，金属蒸气的影响可以通过增加蒸发量以及降低表面张力和粘度来增强，