Dual-rotation friction stir welding of Al/steel: Suppressing intermetallic compound growth for enhanced joint performance

To solve the performance degradation caused by brittle intermetallic compound (IMC) layers at the interface of Al/steel dissimilar lap joints, this study employs dual-rotation friction stir lap welding (DR-FSLW) to join 2 mm-thick 5083 aluminum alloy with 1.4 mm-thick DP780 dual-phase steel for the first time. Independent pin rotation regulation enables partitioned thermomechanical control: high shoulder rate (600 rpm) ensures material flow adequacy, while low pin rate (300 rpm) induces low-temperature interfacial deformation, suppressing IMC growth. The results demonstrate that the DR-FSLW process reduces the IMC layer thickness from 2.9 μm under conventional process to 280 nm—a 90% reduction—and transforms the IMC composition from brittle Al-rich IMC to tougher Fe-rich IMC. Concurrently, the grain size decreased from 20 μm to 11 μm, with notable increases in hardness in the nugget zone. The DR-FSLW joint exhibits a tensile shear strength of 420 N/mm, representing a 121% increase over the conventional process, and an enhancement in fatigue strength from 60 N/mm to 90 N/mm, a 50% improvement. This study proposes a novel processing method for Al/steel dissimilar welding, demonstrating significant potential for lightweight applications in transportation.