Process parameter optimization and bonding mechanism in dissimilar S45C/A6061 joints via novel sacrificing-sheet linear friction welding

• Novel SSLFW method was developed and effectively utilized to join S45C/A6061 alloy. • Joint efficiency of ∼ 96% relative to the A6061 Al alloy after post-aging. • Evaluation of the effect of key process parameters to optimize welding conditions. • Extremely thin IMC of ∼ 100 nm through process parameter optimization. • Optimized joint revealed a fracture towards Al alloy side. Sacrificing-sheet linear friction welding (SSLFW) is a novel solid-state joining technique developed to address the challenges of dissimilar welding between S45C steel and A6061 aluminum alloy, which are difficult to join using conventional linear friction welding (LFW). In this method, a S45C center sheet is linearly oscillated while the two base materials, i.e., S45C and A6061, are pressed against it using a center-driven, double-sided LFW system. The center sheet acts as a sacrificial sheet, which is progressively expelled from the joint interface during welding owing to thermomechanical effect from each side, thereby enabling direct joining between the base materials. This study investigates the effects of key process parameters on mechanical properties and interfacial microstructure, and clarifies the bonding mechanism of SSLFW. Optimum welding conditions with 2 mm upset length, 300 MPa applied pressure toward A6061, 1 s preheat time, and 50 MPa preheat pressure produced sound, defect-free joints with a thin, continuous intermetallic compound (IMC) layer of approximately 100 nm. These conditions enabled simultaneous plastic deformation of both base materials through sacrificing role of center sheet and effective suppression of unbonded regions. The resulting as-welded joint achieved a peak tensile strength of ∼235.3 MPa, corresponding to a joint efficiency of ∼73% with respect to the A6061 base metal. Post-weld artificial aging significantly exhibited hardness recovery on the A6061 side, enhancing the joint strength to ∼307 MPa and increasing joint efficiency to ∼96%. These results demonstrate the high potential of SSLFW for sound dissimilar metal joining.