Ni Pre-Plating on the Liquid Metal Embrittlement Behavior of Zn-Al-Mg Coated Dual-Phase Steel during Resistance Spot Welding

The liquid metal embrittlement (LME) susceptibility of Zn-1.5Al-1.5Mg coated dual-phase (DP) steel with Ni pre-plating was investigated during resistance spot welding. Microstructural analysis revealed primary Zn phases with binary and ternary eutectic structures, where Mg and Al were selectively distributed. The Ni pre-plating layer (~2.5 mm) promoted the formation of Fe-Ni-Zn and Ni-Fe intermetallic compounds, which were associated with LME crack initiation. Diffusion-assisted phase evolution, combined with thermal and mechanical stresses, is suggested to degrade interfacial integrity. These findings highlight the role of Ni pre-plating in LME susceptibility and provide insights into the detrimental role of Ni pre-plating in Zn-Al-Mg systems and suggest careful consideration in coating design.