Protection of an AZ91D substrate by an intermediate Zn layer for Al plating from an AlCl3-NaCl-KCl molten salt bath

An intermediate protective layer of Zn was formed on the AZ91D surface to prevent dissolution of the substrate surface and to obtain a uniform deposition layer of Al in an electroplating process from a molten salt bath. Simple zincate treatment did not result in the formation of a Zn layer with sufficient thickness and coverage for substrate protection. Electrodeposition of Zn was thus conducted after the zincating process to thicken the Zn layer. A Zn layer of a few μm in thickness sufficiently protected the AZ91D substrate. A uniform Al layer was then electrodeposited on Zn-protected AZ91D without degradation of the substrate. Since the Mg alloy surface and Zn surface were not sufficiently active for Zn deposition and Al deposition, respectively, Cu-nanoparticle predeposition was applied to each surface before the electrodeposition processes.