Microstructure and mechanical properties of laser fusion welded Al/steel joints using a Zn-based filler wire

Laser fusion welding technique was used for lap joining of Q235 steel to AA5052 aluminum alloy using a flux-cored Zn-22Al filler wire. The influence of laser power on the microstructure and mechanical properties of laser Al/steel joints was investigated. A fusion welded region and a brazed region were formed at the fusion zone/steel interface: Fe₂Al_5−xZn_x and FeZn₁₀ were formed at the both regions, while a new FeAl IMCs with much lower hardness and brittleness was observed in the welded region. The phase constitutions at the both regions were unvaried with the change of laser power, while the phase morphologies were slightly changed. The tensile-shear testing results showed that the joint fracture load first increased then decreased with the rising laser power and the maximum value reached 1225 N at laser power of 2800 W. The joint fractured at the fusion zone/steel interface when the laser power was less than 2800 W and it changed into fusion zone when the laser power reached 3000 W. The change of joint fracture load and fracture behavior was mainly attributed to the change of morphology of IMC and interfacial bonding length.