THE EFFECTS OF INTERMETALLIC COMPOUNDS IN ULTRASONIC-ASSISTED Sn SOLDERING OF Mg/Al ALLOYS

The formation of intermetallic compounds (IMCs) affects the joint performance of Mg/Al. In this study, nickel (Ni) pre-plated AZ31 magnesium (Mg) alloy and 6061 aluminum (Al) alloy were joined by ultrasonic-assisted soldering using Sn-3.0Ag–0.5Cu (SAC) solder. The effects of Ni coating on the microstructure and mechanical properties of Mg/Al joints were systematically studied. The results show that the Ni coating could block the diffusion of the Mg element into the solder, thus inhibiting the formation of Mg 2 Sn IMC in the joint. With the increase in holding time, the joint strength increased first and then decreased. The shear strength of the joint reached 62.3[Formula: see text]MPa when held at 280 ∘ C for 10[Formula: see text]min, and the joint was broken at the Mg(Ni)/SAC interface. However, when the holding time increased to 20[Formula: see text]min, the blocky Mg 2 Sn IMC was precipitated in the solder, which indicated that the Ni coating could no longer prevent the diffusion of Mg into the solder. At this time, the shear strength of the Mg (Ni)/SAC/Al joint was reduced to 40.5[Formula: see text]MPa, and the Mg 2 Sn IMC became the main reason for the fracture of the joint. Pre-plating Ni is a feasible method to inhibit the formation of IMCs during the joining of dissimilar metals.