Microscopic bonding mechanism of welding interface with molten Cu–4Zn deposited on solid-state steel

An initial characterization was carried out on the heat affected zone between a 30CrMnSi steel and a Cu–4Zn (wt.%) alloy formed from a novel welding technique involving induction melting of a Cu alloy over a steel substrate at 1100 °C. A very thin (∼ 20 nm) reaction interface between the steel substrate and the Cu alloy is shown to play a key role in effecting these joints. This reaction interface is an Fe–Cu rich discrete phase with a FCC structure and substantial coherence to both the steel substrate and the Cu alloy layer. This reaction interface is expected to form under highly non-equilibrium conditions and provides a bridging effect for the join. This is proposed as the major reason for the strength and mechanical integrity of the weld.