Effect of Welding Heat Input on the Microstructure and Mechanical Properties of MIG-Welded Dissimilar Magnesium Alloy Joints

Welding is one of the key joining routes for expanding the engineering applications of dissimilar magnesium alloys. However, after experiencing rapid non-equilibrium heating and cooling cycles, the heat-affected zone (HAZ) of a welded joint tends to undergo grain coarsening as well as dissolution or agglomeration of precipitates, and therefore becomes the region most susceptible to failure. In this study, 3 mm thick sheets machined from AZ61A and AZ80A magnesium alloy hollow sections were joined by metal inert gas welding (MIG). Different ranges of welding heat input were obtained by combining multiple sets of welding parameters, in order to further tailor the HAZ of dissimilar magnesium alloy joints and achieve sound weld quality. The results showed that the joint exhibited the best overall mechanical performance at 523 J·mm−1, with an ultimate tensile strength, yield strength, and elongation of 292 MPa, 172 MPa, and 5.4%, respectively. All fractures occurred in the HAZ on the AZ61A side. Under this condition, the second phases in the HAZ were more finely and uniformly dispersed, with a volume fraction of 3.19%, an average size of 2.51 μm, and a minimum average grain size of 23.65 μm.