Experimental and numerical simulation study of magnesium/aluminium dissimilar metal swing laser welding

Abstract

In this study, AZ91/6061 joint were successfully prepared by using the swing laser welding process, and the process, microstructure, mechanical properties, and temperature field distribution of swing laser welding were investigated. During welding, the laser beam is always in the transverse swing state, which has a stirring effect on the liquid molten pool, optimizing the size and distribution of Mg-Al intermetallic compounds in the weld, forming mechanical interlocking structure, which is beneficial to reducing the hazardous effects of intermetallic compounds on the joint properties. The microstructure results show that the Mg/Al reaction interface mainly consists of (α-Mg+Al12Mg17) eutectic structure, and Al12Mg17, and the different compounds form a wave-shaped mechanical interlocking structure. Orthogonal test results show that the laser power has the greatest influence on the joint performance, when the laser power is 900 W, the shear strength of the joint is 40.72 MPa, the fracture occurs in the mechanical interlocking zone, and the fracture mode is brittle fracture. In this case, the strengthening mechanism is the mechanical interlocking structure that prevents crack extension and the stirring effect of the swing laser beam on the liquid molten pool that avoids the formation of continuously distributed bulk Mg-Al intermetallic compounds. Numerical simulation results show that the centre zone of the heat source moves from side to side with the swing of the laser beam, resulting in a more uniform temperature distribution in the joint.