Investigation of interfacial microstructure and connection mechanism of magnetic field-assisted magnesium/aluminum laser welding joint

Abstract

Variable process experiments to prepare hybrid joints of AZ31 magnesium (Mg) and 6061 aluminum (Al) alloys by magnetic field-assisted laser welding were performed in an overlap Mg-on-Al configuration with the addition of titanium (Ti) foil. Temperature field and flow field of molten pool including chemical potential of each element were also calculated. It is shown that at the optimal welding parameters, the shear force of joint reaches 887.79 N, which is 83.4 % higher than that of no-added joint. In the case of external magnetic field, the improved mechanical properties of joints largely depend on the diffusional barrier effect of Ti foil, which benefits from the enhanced energy absorption and flow of molten pool leading to the enlargement of interface connection area and the formation of Ti-Al compounds such as TiAl3 at Mg/Al interface. Meanwhile, the grains refines due to the magnetic field, which reduces the strain at the joint and enhances the uniformity of the interface microstructure. However, under the condition of excessive magnetic field strength, the enhanced stirring effect of molten pool will cause Ti foil break and the direct interaction between Mg and Al, which deteriorates the joint properties.