Improved laser-induced dynamic wetting behavior and spreading mechanism of non-reactive Mg/steel systems with the assistance of Cu coating

A Cu coating was introduced on the steel surface by electroplating, and the wetting and spreading behavior of Mg alloys on Cu-coated steel substrates during the laser machining process was investigated. Wetting behavior, microstructure, diffusion kinetics, and thermodynamic calculations were conducted to comprehend the role of the Cu coating in the wetting process. The contact angle decreases first followed by an increase with the increased Cu coating thickness. The interfacial reaction is enhanced by the combination of Mg atoms with Fe atoms, transitioning the primary wetting mechanism from reaction control to adsorption/desorption processes. The introduction of Cu elements promoted the creation of a loosely structured Mg + Mg₂Cu phase at the solid–liquid interface between Mg and steel. It significantly increased the wetting of Mg droplets on the steel surface. The results showed that the wetting behavior in this material system was synergistically governed by reactions, surface energy, and thermodynamic driving forces. These findings provided a foundational understanding for enhancing the joining of dissimilar Mg/steel materials under non-isothermal processing conditions.