Study on Characteristics and Generation Mechanism of YAG Pulsed Laser Welding Cracks of AZ31B Magnesium Alloy

Due to poor metallurgical weldability of magnesium alloy, laser welding crack is still one of the main defects. The generations of welding crack seriously affected the weld quality and reduce the mechanical properties of welded joints which have become a bottleneck of the magnesium alloy products widely used in the structure materials. In this paper, AZ31B magnesium alloy sheet with 2mm thickness was used for this investigation. The forming reason and extending characteristics of the welding cracks were investigated during the Nd:YAG pulsed laser welding. The results show that welding cracks are mainly solidification crack which were always present in the weld centers. Few welding hot cracks appear multiple furcation phenomenons, and main and branch cracks were intercrystalline crack. The partial branch crack was mixed intercrystalline and transgranular extension. In addition, few cracks in the weld were caused due to irregular shape porosity and inclusion. The delayed crack weren't observed in the weld after deposited 48 hours. In the pre-process on the basis, the characteristics and generation mechanism of YAG pulsed laser welding cracks of magnesium alloy were analyzed further.