Using Post-supercritical CO2-assisted Method to Deposit Ni-P Alloy Coating on the Micro-arc Oxidation Layer of AZ31 Magnesium Alloy and its Corrosion Behavior Analysis

Abstract

In this study, a Ni-P alloy coating was deposited on the micro arc oxidation (MAO) layer of AZ31 magnesium alloy to improve its corrosion resistance. The MAO layers were prepared under different operated voltages from 300 to 400 V. The results indicated that the optimize operated parameters for MAO layer is at 350 V, the MAO coatings had the most compact microstructure and superior corrosion resistance. In order to improve the corrosion resistance of MAO coating, this study chose to deposit Ni-P alloy coating on the surface of MAO coating via the post supercritical CO2-assisted electroless plating (PSC-CO2-EP) process. The results presented that a MAO/Ag/PSC-CO2-NiP sandwich-structured composite coating was successfully prepared and had the best corrosion resistance which icorr value is approximately at 8.60 pound 10<inverted exclamation>7 A/cm2. Moreover, the results of the alternating hot and cold salt spray test in seawater showed that cracks appeared in the coating, and corrosion products could be observed at the crack interface, which indicated that the coating had a corrosion reaction.