ZK21镁合金激光焊接缺陷分析及防治措施

Defects Analysis and Control Measures for Laser Beam Welding for ZK21 Mg Alloy

采用高功率激光对ZK21镁合金板材进行焊接,表征接头中存在的缺陷,分析其产生原因和防治措施。结果表明:结晶裂纹和表面凹坑是恶化接头质量的主要原因。结晶裂纹易产生于焊缝的末端及焊接速度较高的工艺条件下,焊接时,应使用同材质引弧板且不推荐采用导致熔池冷却速率过高的焊接工艺;表面凹坑是由高能量密度激光束加热下熔体的蒸发和烧损所致;半熔化区易发生的晶界液化并存在开裂风险,其主要原因与该合金凝固温度区间过宽有关;熔合线附近和焊缝上表面是气孔的高发区域,适当降低焊接速度或增大激光功率有利于抑制焊缝气孔的产生。

ZK21 alloy plates were welded by high energy laser beam. The defects in welded joints were characterized, and then, the formation mechanisms and remedy methods were investigated. The results show that the pits in the face of welds and solidification cracking are the main defects which can deteriorate the quality of the welded joints. The solidification cracking tends to occur at the end of weld or too fast welding speeds. For avoiding it, the end tab with same material is preferred and the welding parameters resulting in high cooling rate for weld pool are not recommended. The pits in the face of weld are caused by the evaporation and losing of molt metal under the heating of high power density laser beam. Th grain boundaries in the partially melted zone （PMZ） are liquefied and risk to crack during the welding which are caused by wide solidification temperature range of the base metal. The pores and porosities often appear near the fusion boundary and under the surface of the weld seam, which can be reduced by lowering welding speed or enhancing the laser power properly.