Microstructural and mechanical evolution of aluminium–steel joints during cold roll

This study, a multilayer aluminium system, consisting of an AlSn40Cu core enclosed by two thin 1050–Al sheets, was joined to steel through a single-pass rolling operation. Specimens prepared with P80 belt grinding exhibited markedly superior adhesion compared with those treated by wire brushing. The P80 –ground surfaces required roughly 20% less deformation to initiate bonding and ultimately produced bond strengths nearly 48% higher. This improvement arises from two concurrent mechanisms: mechanical anchoring generated by the textured surface profile and metallurgical bonding activated when the hardened surface layer (HSL) fractures. However, an optimal condition was identified in which the substrate retains sufficient strength to prevent separation, –even as cracks form, allowing the joint to reach or surpass the intrinsic strength of the aluminium alloy. Under ideal rolling conditions, the bonding process evolves through four characteristic stages: (i) an initial state with no adhesion; (ii) gradual development of interfacial strength; (iii) a rapid rise in bonding as fresh metallic surfaces are exposed; and (iv) a final regime where the joint strength approaches the tensile strength of the aluminium layer.