Microstructure and Mechanical Properties of Friction Stir Weld of Dissimilar Ti6Al4V Titanium Alloy to AA2024 Aluminum Alloy

Dissimilar Ti6Al4V titanium alloy and AA2024 aluminum alloy sheets with a thickness of 3 mm were friction stir welded successfully, and the microstructure and mechanical properties of the butt joints were investigated. The results show that: the stirred zone (SZ) exhibits a mixture structure, which is characterized by fine recrystallized grains of aluminum alloy and titanium particles. Unfilled defects are observed among titanium particles in SZ. Moreover, at the aluminum side the thermal-mechanically affected zone (TMAZ) and the heat affected zone (HAZ) appeared like in the traditional FSW-joints. But, at the titanium side, a recrystallization band with a width of 6–10 μm and a layer with fibrous structures are found at the joint interface. Also, the Ti–Al compounds layer with some micro-cracks is presented in the fibrous structure. The hardness distribution of the joint along the cross-section centerline varies significantly due to the existence of different broken titanium particles. The ultimate tensile strength (UTS) of the joint reached 83% of aluminum base metal and the joint failed with a ductile–brittle fracture mode.