Microstructural evolution, bonding mechanism, and fracture behavior of 6061-T4 Al/Q355B steel dissimilar joints fabricated by inertia friction welding

Abstract

This study explores the inertial friction welding (IFW) of 6061-T4 Al alloy with Q355B steel, with a focus on the evolution of the joint interface microstructure and its influence on mechanical properties. The bonding mechanism and fracture behavior are elucidated as well. The findings reveal the formation of an intermetallic compounds (IMCs) at the weld joint, including Al₂Fe, Fe₂Al₅, Mg-rich Al₂O₃, and the Al matrix. Uneven distribution of heat, force, and friction states at the welding interface results in heterogeneous distributions of grain size, recrystallization degree, dislocations, and texture. The Brass {011} <211> texture shows a moderate Schmid factor and Taylor factor, whereas the P {011} <122> texture has a high Schmid factor and low Taylor factor. Grain refinement, dislocation motion inhibition, grain boundary strengthening, and the Brass {011} <211> texture enhance the joint performance. Conversely, the build-up of deformed grains, the presence of oxides, and the development of the P {011} <122> texture decrease the joint's ductility. The brittle IMC layers and Mg-rich Al₂O₃ trigger crack initiation, serving as the primary fracture mechanism. The development of the P {011} <122> texture, coupled with sparse dislocations that initiate and propagate cracks, serves as the secondary fracture mechanism of the joint. The Schmid factor is linked to frictional heat, while the Taylor factor is associated with grain deformation and the formation of IMCs.