Bonding interface morphology of keyholeless friction stir spot welded joint of AZ31B Mg alloy and DP600 galvanized steel

Because the bonding interface of dissimilar metal joint between AZ31B Mg alloy and DP600 galvanized steel by keyholeless friction stir spot welding (KFSSW) is permanent bonding, the interface morphology cannot be directly observed. If the joint is separated by external force, the original features of bonding interface of joint will be destroyed, which has influence on the accuracy for observation and analysis of the result. In this paper, the coordinates of the key point at the interface of every cross-section at intervals of 0.2 mm were measured and connected into an outline. The outline of all interfaces makes up the three-dimensional morphologies of bonding interface between AZ31B Mg alloy and DP600 steel by KFSSW, which was constructed by Solidworks software to restore the real mechanical bonding state of joint. Combined with the microhardness analysis of cross-section and results of in-situ tensile test, the unique bonding state and morphology of Mg and steel in the welded joint were confirmed.