Mechanical properties and microstructures of hybrid laser MIG welded dissimilar Mg-Al-Zn alloys

Bead shape, microstructure changes and mechanical properties of laser metal inert gas (MIG) welded dissimilar Mg-Al-Zn alloys (from AZ31B to AZ61) are studied. The results show that heat ratio of arc to laser (HRAL) and welding speed are dominant parameters for achieving good tensile strength efficiency and elongation property. From AZ31B to AZ61, microstructure changes are observed as cellular dendrites to equiaxed dendrites and fish bone dendrites in the upper part of hybrid weld. Besides, at weld centreline, the solidification structure of lower part is finer than that of upper part. In this study, the maximum tensile strength efficiency and elongation reached 97.6 and 7% respectively. When the HRAL matches welding speed well, the joint achieves higher tensile strength with 45 degrees shearing fracture at heat affected zone because of fewer defects. However, when utilising too low HRAL or fast welding speed, the joints show lower tensile strengths with nearly vertical fracture at fusion zone.