Investigation on a Non-cyanide Plating Process of Ni-P Coating on Magnesium Alloy AZ91D

摘要

In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO_4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO_4-6H_2O 20 g/L, NaH_2PO_2-H_2O 20 g/L and C_6H_8O-2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95 deg C, respectively. The present process flow is composed of ultrasonic cleaning-- >alkaline cleaning-5-acid pickling- >activation- >double immersing zinc- >electroplating zinc- > electroless nickel plating-passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.