High power fiber laser arc hybrid welding of AZ31B magnesium alloy

High power fiber laser–metal inert gas arc hybrid welding of AZ31B magnesium alloy was studied. The fusion zone consisted of hexagonal dendrites, where the secondary particle of Al8Mn5 was found at the center of dendrite as a nucleus. Within hybrid weld, the arc zone had coarser grain size and wider partial melted zone compared with the laser zone. The tensile results showed the maximum strength efficiency of 5 mm thick welds was up to 109%, while that of 8 mm thick welds was only 88%. The fracture surface represented a ductile–brittle mixed pattern characterized by dimples and quasi-cleavages. On the fracture surface some metallurgical defects of porosity and MgO inclusions around with secondary cracks were observed. Meanwhile, a strong link between the joint strength and weld porosity were demonstrated by experimental results, whose relevant mechanism was discussed by the laser–arc interaction during hybrid welding.

► Fiber laser–metal inert gas arc hybrid welding of AZ31B Mg alloy was developed.
► The maximum tensile strength efficiency of 5 mm thick welds is up to 109%.
► Grain size of fusion zone and width of PMZ both increase with heat input.
► Hall–Petch relationship between microhardness and grain size is obtained.
► Strength difference between 5 mm and 8 mm thick welds is summarized and discussed.