Influence of zinc-dipping on electroless nickel coating on magnesium alloy

Abstract

In this paper, the effect of zinc dipping pretreatment on corrosion resistance of electroless nickel plating on magnesium alloy was studied. The results showed that the corrosion resistance of nickel coating was influenced greatly by the complexing agent and main salt in the zinc dipping solution, and the formula and technological conditions of zinc dipping were optimized by the orthogonal test. The optimum formulation and process conditions were as follows: C₄H₆O₅ 40 g L⁻¹, ZnSO₄·7H₂O 40 g L⁻¹, NaF 4 g L⁻¹, pH 9, temperature 90°C, time 10 min. The corrosion resistance, morphology and phase composition of the nickel coating prepared under the optimum conditions were analysed by SEM, XRD and electrochemical workstation. The results showed that the self-corrosion potential of the nickel coating is 0.87 V higher than the magnesium alloy substrate, the self-corrosion current reduces by two orders of magnitude and the magnesium alloy substrate is completely covered. The corrosion resistance of magnesium alloy was effectively enhanced.