Reaction products formed at the welding interface of aluminium/steel can deteriorate mechanical properties. It would therefore be quite beneficial to analyse the mechanism of crack propagation to obtain strong joints. In this study, we directly observed the fracture process of the aluminium/steel sample by in situ scanning electron microscopy. In situ observation revealed that the crack propagated in the reaction layer and aluminium, and that crack propagation was arrested by the interface between the reaction layer and steel.
