Friction stir solid–liquid spot welding of Cu to Al assisted by Zn interlayer

Abstract

The relatively low joint performance restrains the application of Cu/Al dissimilar metals welding structure. In order to obtain a high-quality Cu/Al joint, the friction stir solid–liquid spot welding was proposed. At the same time, the Zn interlayer was used and three probes with different lengths were adopted. The assisted Zn interlayer improved the joint quality by regulating the interfacial microstructure. The IMCs layers at the bonding interface of Cu/Al were composed of Al4.2Cu3.2Zn0.7 layer and Al2Cu layer or αAl + Al2Cu eutectic layer. The long probe produced more heat, larger pressure and stronger material flow at the lap interface, while the thickness of IMCs layer reached the maximum under the 1.3 mm-length probe because of the most residual liquid phase. Under the 1.3 mm-length probe, the maximum tensile shear load of the Zn-added joint was 6.64 kN, and this value was 0.51 kN bigger than that of conventional joint. The joints all fractured at the lap interface, but the fracture modes in micro-level were diversified. The hole and crack defects at the bonding interface influenced the micro-fracture mode fracture.