Solid-state amorphization induced high-performance 5A06 Al alloy and 304 stainless steel dissimilar FSWed joint

Dissimilar joints of lightweight aluminum alloys and stainless steels are essential for advanced structural applications. However, the interfacial brittle intermetallic compounds under conventional welding profoundly limits the performances of dissimilar Al/steel joints. Here, a low heat-input friction stir welding (FSW) strategy with the effect of solid-state amorphization enabled an exceptional tensile strength of 266.8 MPa for 5A06/304SS dissimilar joint. Solid-state amorphization led to the development of a nanoscale amorphous interfacial layer comprising discontinuous Al₁₈Cr₂Mg₃, Al-Fe-Ni amorphous structures, and dispersed Al₅₇Mn₁₂ nanoparticles. The inherent severe plastic deformation of FSW and rapid cooling method introduced structural defects and elevated the system free energy beyond the critical threshold required for solid state crystallization to promote amorphous transition. The low heat-input inhibited the formation of deleterious intermetallic compounds during FSW. This work establishes a nanoscale amorphous layer and second phase nanoparticle strengthening as synergistic mechanisms for strengthening Al/steel joints, providing a viable pathway to overcome long-standing challenges in joining dissimilar alloys.