Effect of Homogenized IMCs on mechanical properties of Al/steel oscillating laser brazing joints via small punch testing

In laser weld-brazing Al/steel dissimilar joints, intermetallic compounds (IMCs) critically govern joint strength through their compositional characteristics. Four distinct oscillating laser scanning patterns (non-oscillating, rectangular, circular, and infinite trajectories) were implemented to fabricate Al/steel dissimilar joints, with subsequent characterization of interfacial morphology, microstructural development analysis revealed that the oscillating laser significantly reduced the thickness of the IMC layer at the joint interface, resulting in a more homogeneous IMC distribution. The circular scanning mode demonstrated superior interfacial control, generating an optimally refined IMC layer with enhanced phase homogeneity. The results of the corresponding mechanical evaluations showed that the highest tensile strength and bending angle were obtained for the circular path specimens. SPT specimens with varying IMC compositions were then prepared using the oscillating laser and finite element simulations were also employed to investigate the effects of IMC composition on fracture toughness, and fracture energy. The results showed that the joint with a 2–3 μm thick τ₅-Fe₂Al₈Si interface exhibited the best fracture toughness and fracture energy, demonstrating exceptional fracture resistance and ductility. Furthermore, this joint exhibited the lowest tensile stress during the SPT. The 2–3 μm thick τ₅-Fe₂Al₈Si composition was identified as the ideal IMC target for Al/steel dissimilar joints. Future studies will focus on optimizing the formation of homogeneous 2.3 μm τ₅-Fe₂Al₈Si compositions under oscillating laser conditions to further enhance the safety and reliability of these joints.