Interface characteristics and formation mechanism of plasma arc welding-brazing aluminum alloy/ultrahigh-strength steel joint

Abstract

A butt welding-brazing joint of 5A06 aluminum alloy and DP1180 ultrahigh-strength steel was carried out by using plasma arc welding (PAW) with Al-Si welding wire. Interface characteristics, formation mechanism and mechanical properties of the joint were investigated. The results showed that the dissimilar joint contained bond zone, weld zone and Al/steel interface zone. During PAW, the inter-diffusion of Fe and Al and the interfacial reaction occurred, and the double-layer structure intemtallics (IMCs) composed of Fe4Al13 layer and Fe2Al5 layer were produced in the interface zone. The thickness and morphology of both IMC layers depended on different positions in the interface zone. The Fe2Al5 layer thickness decreased obviously and its morphology changed from continuous layer to discontinuous layer with the decrease of welding heat input. The average tensile strength of the joint was 88\u2009MPa and the joint fractured at the Al/steel interface zone with the highest hardness (524 HV). The interface zone IMCs were the main factor of affecting the mechanical properties of aluminum alloy and ultrahigh-strength steel PAW joint.