Multi-scale Characterization and Simulation of Dissimilar Friction Stir Lap Welding Between Al/Al_0.1CoCrFeNi Alloys

Dissimilar friction stir lap welding (FSLWing) of Al and high entropy alloy (HEA) systems presents significant challenges in terms of complex interfacial reactions and diffusion-driven phase transformations. This study investigated the atomic-scale mechanisms governing the interfacial behavior between 1060-O Al and Al_0.1CoCrFeNi HEA through a multiscale approach combining finite element (FE) simulation and molecular dynamics (MD). The FE model accurately predicted the thermal profile, revealing a peak temperature of 527ºC in the stir zone. This FE-informed thermal field was used as input for MD simulation to investigate the atomic interdiffusion behavior near the Al/HEA interface. Mean square displacement analysis confirms that Cr atoms exhibit the highest atomic mobility and diffusion coefficient among all elements. Radial distribution function and cohesive energy analyses demonstrate strong chemical affinity and thermodynamic favorability for Al–Ni atomic pairs, promoting the selective formation of Al₃Ni and Al₄Ni₃ intermetallic compounds at the weld interface. Conversely, weak Al–Cr affinity limits Cr incorporation into these intermetallics. The agreement between simulation and experimental results provides mechanistic insight into atomic transport and intermetallic evolution during dissimilar welding of immiscible alloys, offering valuable guidance for the tailored design of Al/HEA joints.