镁合金厚板激光焊缝组织及抗拉强度研究

Tensile strength and microstructure of laser welding of AZ31 magnesium alloy thick plates

为了提高镁合金激光焊接认识程度,采用高功率CO_2激光焊接了10mm厚AZ31镁合金,并对焊缝微观组织和接头抗拉强度进行了研究。在高温作用下,因为镁元素的高温蒸发与烧损,焊缝表面会形成难以克服的凹坑缺陷。在实验条件下,焊缝熔合区微观组织为等轴枝晶,且随着焊接热输入的减少,晶粒细化。抗拉强度测试表明,表面凹坑和焊缝内气孔缺陷是影响接头抗拉强度的主要因素;在表面凹坑缺陷存在时,接头抗拉强度最高仅为母材的74%,但是,通过补焊消除该缺陷后,接头抗拉强度达到母材的91%。焊缝气孔则是补焊接头表面凹坑缺陷消除后抗拉强度仍然低于母材的主要原因。结果表明,采用适当方法消除表面凹坑及气孔缺陷是提高厚板镁合金激光焊接接头力学性能的必要方法。

To deepen the understanding of laser welding of magnesium alloys, a high power CO2 laser was employed to join AZ31 magnesium alloy in 10mm thick. Its microstructure and tensile strength of laser welds were studied. Obvious concaves appeared on the welding surface because of serous burning-lost of magnesium at high temperature. Under the experimental conditions, the mierostructure of the welding zone was equiaxed dendrites and the grains were refined with the decrease of the welding heat. The tensile test results showed surface concaves and porosities were two main factors affecting the tensile strength. The maximum tensile strength was only 74% of the substrate metal if the surface including concaves. However, it reached 91% of the substrate metal after surface concaves were eliminated by laser repair welding. Besides, the porosities were the main affecting factor inducing the tensile strength of laser repair weld is lower than that of the substrate metal. The results show it is necessary, to eliminate the surface concaves and weld porosities in order to increase the mechanical property of laser welding joints.