Synergistic regulation mechanism of interfacial microstructure and properties in aluminum/steel welds using laser beam oscillation with a Cu interlayer

The joining of steel/aluminum composite components is a critical technology for achieving lightweight design in modern manufacturing. However, the uncontrolled formation of brittle intermetallic compounds (IMCs) at the Al/steel interface during fusion welding severely deteriorates the joint's mechanical properties, representing a critical obstacle to its widespread application. To address this issue, this study proposes a synergistic control strategy that combines laser beam oscillation with a copper interlayer, aiming to reconfigure the interfacial structure and optimize the thermodynamic behavior of the welding process. It was revealed that this synergistic process successfully suppressed the formation of the thick, tongue-like brittle FeAl₃ and Fe₂Al₅ phase, constructing a layered composite interface composed of a thin (Fe, Cu)₄Al₁₃ ternary IMC layer and extensive regions of a ductile α-Al + CuAl₂ eutectic structure. This unique interfacial architecture resulted in a 125% increase in the peak tensile load compared to the directly welded joint and transitioned the failure mode from brittle cleavage along the interface to ductile fracture within the weld seam. Finite element modeling reveals that while the synergistic thermal buffering from laser oscillation and the Cu interlayer mitigates thermal shock and reduces the cooling rate, the required high heat input still generates substantial residual stress. However, optimizing the process by reducing the Cu interlayer thickness lowered the overall von Mises stress by 19.1% and, more importantly, reduced the peak longitudinal residual stress responsible for cracking by 30.7%. This work provides a new paradigm for achieving high-performance dissimilar metal joining through interfacial structural design.