Electroless Ni-P plating on AZ91D magnesium alloy from a sulfate solution

Direct electroless Ni-P plating on the AZ91D magnesium alloy from a plating bath containing sulfate nickel was investigated in the paper. The nucleation mechanism of Ni-P deposits on the AZ91D magnesium alloy was studied by using XRD and SEM. The electroless Ni-P deposits were preferentially nucleated on the β-Mg17Al12 phase and extended to the primary and eutectic α phases of the AZ91D magnesium alloy. The effect of the acid pickle treatment time of the AZ91D magnesium alloy substrate on the electroless Ni-P plating was also investigated. With prolonging the acid pickle treatment time, the cluster of electroless Ni-P deposition became smaller and the deposits were found to be more compact. The deposition rate of electroless Ni-P plating was proportional to the acid pickle treatment time. The hardness values of the Ni-P coatings were about 660 VHN and were not influenced by the pretreatments.