Microstructure and Mechanical Properties of Laser Welded Magnesium Alloy/Steel Joint Using Cu-Si Composite Interlayer

Abstract

In this study, Cu-Si composite powder was used as the interlayer to carry out laser lap deep penetration welding of AZ31B magnesium alloy and DP590 dual-phase steel. The effects of Cu-Si composite powder on the weld formation, microstructure, and mechanical properties of magnesium alloy and steel joint were studied. The results show that the addition of Si can improve the laser absorption rate of the interlayer and increase the melting depth at the magnesium side. In addition, the Cu-Si composite interlayer hindered the diffusion of Al, and reduced the thickness of reactive layer at the magnesium alloy and the steel interface. After adding Si into the interlayer, the reactive layer changed from Fe3Al+α-Mg to Fe-(Al, Si) +α-Mg and the content of intermetallic compounds in the reactive layer decreased, which improved the plastic deformation capacity and the ductility of the reactive layer. As a result, the tensile shear force firstly increased and then decreased with the Si increase. The maximum tensile shear force of 86.2 N/mm was achieved when the Si content was 5%, which was 20.4% higher than that of the Cu interlayer. Plus, the fracture location changed from near the steel side to near the magnesium side weld.