Interfacial Characterization and Mechanical Properties of Friction Stir Welding Dissimilar Joint Between Al Alloy and Advanced Ultrahigh-Strength Steel

Effectively joining Al alloy to advanced ultrahigh-strength steels (AUHSSs, the strength over 1 GPa) shows the considerable potential in lightweight design with the increase in the application of these two materials. However, there is currently a lack of research on butt welding Al alloys to AUHSSs. In the present study, friction stir butt welding was performed to join 5182Al alloy to DP1180 AUHSS. Intimate metallurgical combination without observable defects was formed at the interface of the Al-AUHSS butting joint, which consisted of a thin intermetallic compound (IMC) layer and a mixed layer. The IMC layer was comprised of nanoscale Al₁₃Fe₄ phases while the mixed layer was composed of the steel–IMCs intercalated structure. Ultrafine Al grains and tiny particles can be observed in the nugget zone. Benefited from the excellent metallurgical bonding interface and enhanced nugget zone, the Al-AUHSS joint failed at the Al side with the maximum tensile strength almost the same as the Al alloy.