Microstructural Evolution, Intermetallic Formation, and Mechanical Performance of Dissimilar Al6061–Ti6Al4V Static Shoulder Friction Stir Welds

Abstract

The present study focuses on achieving microstructural uniformity in dissimilar Al–Ti joints through static shoulder friction stir welding (SSFSW). This method restricts material mixing at the Al–Ti interface due to reduced shoulder action, resulting in peak temperatures of 317 °C (SSFSW) and 491 °C in conventional friction stir welding (CFSW). This reduction in heat input during SSFSW leads to decreased mechanical mixing, resulting in a thinner 2.169 μm intermetallic layer at interface of SSFSW compared to 5.485 μm in CFSW. The resulting weld nugget (WN) microstructure reveals the presence of Ti particles, intermetallic compounds, and fine Al‐associated grains. Rearrangement of dislocations through slip‐and‐climb mechanisms, along with distinct recrystallization processes in SSFSW, significantly reduces grain size within WN. The kernel average misorientation map highlights the presence of nonuniform dislocation concentrations at the interface of CFSW, attributed to the large Ti particles that impede the mobility of dislocations. As a result, the interface of CFSW is found to be the weakest among all the zones, eventually leading to the failure of the CFSW joint near the Ti interface after reaching an ultimate tensile strength of 259 MPa. In contrast, SSFSW welds achieve a higher tensile strength of 289 MPa.