Effect of Alloying Elements of Al Alloy on the Interfacial Microstructure and Fracture Behaviour of Al Alloy/Steel Inertia Friction Welded Joint: A Comparative Study

The present study highlighted the effect of alloying elements in Al alloy on the interfacial microstructure, and the corresponding fracture behaviour of the Al alloy/steel inertia friction welded joint by selectively adopting two types of Al alloys. A strong texture of <111>//radial direction was formed on the Al alloy side in both types of joints, while no obvious changes were identified on the steel side. Different types of intermetallic compounds (IMCs) were formed at the weld interface. In the Al-Mg-Si alloy/steel joint produced at a low heat input, the interfacial microstructure was composed of a nanoscale amorphous layer and partially crystallised layer, while it turned into a fully crystallised Fe2Al5 phase with Si enriched when the heat input was enhanced. In the Al-Cu alloy/steel joint, Cu was enriched at the weld interface, with the possible formation of Fe-Al-Cu based IMCs. Moreover, a two-layered structure of IMC with different compositions of Cu appeared when the joint was prepared at a high heat input. Such distinct interfacial microstructure caused different fracture behaviours of joints. An interfacial reaction layer less than 130 nm thick led to the failure of Al alloy rather than the weld interface which easily happened at a thicker IMC.