Comparison of Corrosion Resistance of Biological Ceramic Coatings Prepared on Magnesium Alloy by Micro-Arc Oxidation with Different Phosphorous Sources

Biological ceramic coatings with rich Ca and P were prepared on the surface of AZ31B Mg alloy by micro-arc oxidation.The morphology,phase composition,Ca/P atomic ratio,thickness and corrosion resistance of the oxide films were analyzed using a scanning electron microscope,an X - ray diffractometer,an X - ray fluorescence spectrometer,a coating thickness gauge and an electrochemical workstation.The effects of five kinds of P-containing compounds(P sources) on the microstructure and corrosion resistance of as - prepared ceramic oxide films were investigated.Results show that Na_3PO_4 and Na_4P_2O_7 can not serve as P sources for micro - arc oxidation of the Mg alloy,while ceramic coatings with micro - porous structure can be obtained when NaH_2 PO_2?H_2O,(NaPO_3)_6 and Na_2 HPO_4 are used as the P sources.The micro-arc oxide coating obtained with NaH_2 PO,? H_2O as the P source had micro - cracks on the surface, showing the smallest thickness.The coating prepared with (NaPO_3)_6 as the P source had the maximum thickness and showed unevenly distributed interlocked micro - pores on the surface. The coating fabricated with Na,HPO_4 as the P source contained uniformly distributed micro - pores on the surface and had the maximum Ca/P ratio.As - prepared ceramic oxide coatings were mainly composed of MgO and MgAl_2 O_4,and Ca and P in the coatings existed in the form of amorphous compounds.In one word,micro-arc oxidation contributed to greatly improved corrosion resistance of the Mg alloy.The oxide coating obtained with NaH_2 PO_2? H_2O as the P source possessed the worst corrosion resistance,while the one prepared with(NaPO_3)_6 as the P source had the best corrosion resistance.