Microstructure and mechanical properties of 2195/5A06 dissimilar joints made by resistance spot welding

Abstract

AA2195-T8 aluminum–lithium (Al Li) and 5A06 Al alloys were joined using resistance spot welding process for the first time. The macrostructure, microstructure, elemental distribution, precipitated phases, microhardness distribution, and tensile shear properties of spot welded joints were investigated. The 2195/5A06 spot welded joints were divided into the fusion zone (FZ), partially melted zone (PMZ), and heat-affected zone (HAZ) based on their microstructure. The FZ was composed of all fine equiaxed spherical grains, which were formed by the heterogeneous nucleation of Zr and Li elements. Elemental distribution results indicated the presence of Cu segregation and the eutectic θ ʹ (Al 2 Cu) phase. Transmission electron microscopy results showed that most precipitates dissolved during welding, and that the FZ contained reduced amounts of δ ′ (Al 3 Li) and β ' (Al 3 Zr) phases. In addition, the FZ exhibited lower microhardness than the base material due to the dissolution of the main strengthening T 1 phases. The tensile shear fracture morphologies of the 2195/5A06 spot welded joints exhibited the characteristics of ductile–brittle hybrid fracture. • The 2195 AlAl Li alloy and 5A06 Al alloy were first joined using resistance spot welding. • Fusion zone of weld nugget was found to be composed of all fine equiaxed spherical grains. • The fracture of 2195/5A06 spot welded joint exhibits a ductile-brittle hybrid fracture.