Investigation of Zn alloy coating with submicron phases on magnesium alloy by the novel hot-dip process

A Zn alloy coating with submicron phases was fabricated on magnesium alloys by a novel hot-dip process, exhibiting excellent corrosion resistance. The microstructure and phases of coatings were characterized and their correlation with the corrosion performance was investigated. The results indicated that the coating immersed in Zn-3Mg molten bath for 4 s primarily consisted of submicron dot-like Zn phases with well-ordered distribution, while the coating immersed in Zn-3Mg molten bath for 7 s mainly comprised rod-like compact MgZn2 phases with a scattered distribution of Zn phase. The presence of these fine phases of coatings effectively impeded ion permeation in corrosive environments, leading to a significant enhancement in corrosion resistance. Notably, the exceptional corrosion resistance of the coating immersed for 4 s can be attributed to the submicron Zn phase with a grain size of 0.51 mu m, resulting in a 62-fold increase in low-frequency impedance value compared to the AZ31 alloy, and a 22-fold decrease in corrosion rate compared to the AZ31 alloy.