Study on Electroless Copper Plating on Magnesium Alloy MAO Layer Prepared by Tetrahydroxypropyl Ethylenediamine （THPED）/Sodium Citrate Dual Complexation System

In order to improve the electrical conductivity of micro-arc oxidation（MAO） layer of magnesium alloy, the electroless copper plating layer on the MAO layer of AZ31B magnesium alloy was prepared by using sodium hypophosphite as reducing agent, sodium citrate as complexing agent, and THPED as additive. The microstructure, phase composition,conductivity and reaction process of the composite film were studied by SEM, XRD, EDS, electrochemical experiments and four-probe test. The results show that the deposition rate of copper plating layer increases first and then decreases with the increase of THPED proportion. The best ratio of complexation agent is sodium citrate of 16 g/L and THPED of 4g/L, and the copper coating is tightly bonded with MAO layer with a resistivity of 4.89×10^-3mΩ·cm. The electrochemical results show that the addition of nickel ions promote the reduction reaction of copper ions,a small proportion of THPED can promote the reduction reaction, but when the THPED proportion exceeds 4 g/L, it can inhibit the reduction reaction.