Influence of electroless plating on the deterioration of the corrosion resistance of MAO coated AZ31B magnesium alloy

A composite bi-layer film is prepared on AZ31B Mg alloy for corrosion protection by means of micro arc oxidation (MAO) and electroless Ni-P plating. The electroless plating of Ni-P on MAO coated Mg alloy is accomplished based on a St-co-NIPAAm/Pd nanoparticles activator. The structure and corrosion protection are characterized by scanning electron microscopy (SEM), electron probe X-ray micro -analyzer, potentio-dynamic polarization measurements in 3.5 wt% NaCl solution and salt spray tests. A compact and continuous bi-layer coating on Mg alloy substrate can be formed via MAO for 10 min and electroless plating coating for 40 min. However, our results show that the bi-layer coating exhibited a much worse corrosion resistance than that of the Mg alloy with a single MAO coating. After a systematical investigation in corrosion behaviors, a possible mechanism for the deterioration of corrosion resistance is proposed in this study. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.