Effect of heat input on interfacial microstructure, tensile and bending properties of dissimilar Al/steel lap joints by laser Welding-brazing

Laser welding-brazing technique was used for lap joining of Q235 steel to AA5052 aluminum alloy using a flux-cored Zn-22Al filler wire. The influence of heat input on microstructure, joint strength and bending property of laser Al/steel joints was investigated. The results showed that the types of interfacial intermetallic compounds (IMCs) were kept unchanged with the different laser powers, i.e., Fe₂Al_5-xZn_x phase and FeZn₁₀; while the thickness and morphology of IMC layer changed significantly. This was mainly ascribed to the large increase of the interfacial temperature with the rising laser power, which led to an intensified diffusion reaction. The fracture load first increased and then reached a plateau with the increasing laser power. However, the laser power had very limited influence on the joint bending property because of the formation of dispersed tough FeZn₁₀. Numerical simulation indicated that the interfacial temperature along the interfacial region varied, decreasing from the weld root to weld toe. The peak temperature increased by 700 ℃ and liquid–solid reaction time increased 3.41 s with the increased laser power, which was responsible for the change of IMCs layer.