Influence of surface pretreatment of steel substrate on the interfacial microstructure and tensile properties of laser Al/steel joints

•The influence of surface pretreatments of steel on Al/steel joints was investigated.•The fracture energy of SMed joints increased by 126% compared to UTed ones.•AMed joints significantly improve fracture energy by 232% compared to UTed joints. The influence of surface-pretreatments, viz., subtractive manufactured (SMed), additively manufactured (AMed), and untreated (UTed) steel substrates on dissimilar laser aluminum (Al)/steel joints were comparatively investigated, for the first time, in terms of the interfacial microstructure and mechanical properties. Compared to the UTed joints, the interfacial microstructure of SMed joints remained unchanged with both composing of Fe-Al-Si and Fe-Al IMCs, but the joint fracture energy increased from 1.89 kJ to 2.39 kJ. Differently, the interfacial microstructure changed to a composite structure consisting of a high entropy alloys (HEAs) skeleton and reaction regions, and the joint fracture energy further increased to 4.38 kJ in the case of AMed joints. The mechanisms of the altered interfacial microstructure and tensile properties were also investigated.