Influence of zincate pretreatment on adhesion strength of a copper electroplating layer on AZ91 D magnesium alloy

Cu was electrodeposited on AZ91 D Mg alloy with zincate pretreatment in an alkaline plating bath, and the effect of zincate pretreatment on adhesion strength of the Cu layer was investigated. Scanning electron microscopy results showed that Zn was mainly deposited on the α-phase surface, and ultrasonic agitation at the initial stage of the zincate pretreatment improved the coverage of the Zn layer even on the β-phase surface, resulting in enhancement of the adhesion strength of the Zn layer and the successive Cu layer to the substrate. Adhesion tests revealed that the plating layer peeled off at the mixed layer of Zn and Cu deposits formed at the interface between the zincated layer and the electrodeposited Cu layer. A smooth Cu surface was obtained in the plating bath containing H3BO3.