Friction stir welding (FSW) was used to fabricate AA6061-T6 aluminum/DP590 dual-phase steel dissimilar butt joints under controlled heat-input conditions. The influence of thermomechanical flow on interfacial intermetallic compound (IMC) evolution, aluminum microstructure gradients, and joint performance was investigated using synchronized process monitoring (temperature, torque, and axial force) combined with multi-scale characterization (OM/SEM-EDS, XRD, EBSD), hardness mapping, tensile testing, and electrochemical evaluation in 3.5 wt. % NaCl. Optimized conditions produced defect-free joints with full-thickness interfacial continuity and a thin, uniform Fe-Al reaction layer (~3-6 μm), whereas insufficient heat input caused interfacial discontinuities and excessive heat input led to flash formation and IMC thickening (~10-15 μm). EBSD revealed pronounced grain refinement near the interface (~7-8 μm) and a corresponding hardness peak (~135-140 HV0.2), while the aluminum heat-affected zone exhibited softening (~60-70 HV0.2) that governed tensile localization. The optimized joint achieved ~250 MPa ultimate tensile strength (~80-85% joint efficiency) with failure in the aluminum-side HAZ. The electrochemical results showed improved corrosion resistance under controlled IMC growth. Maintaining a stable thermomechanical processing window enables balanced interfacial bonding and durability in dissimilar Al/steel FSW. • Established a stable thermomechanical processing window for AA6061-T6/DP590 dissimilar FSW. • The quantitatively controlled Fe–Al interfacial IMC thickness was within ~3-6 μm to suppress brittle failure. • Achieved ~250 MPa tensile strength (~80-85% joint efficiency) with HAZ-governed failure. • Correlated EBSD-derived grain refinement (3-8 μm) and strain gradients with hardness evolution.
Zhou et al. (Sun,) studied this question.