Effect of Concentration of Sodium Acetate on Stannate Conversion Coatings of AZ91D Magnesium Alloy

A process for preparing stannate conversion coating on Mg alloy was established by using sodium acetate as the major component.Thus stannate conversion coatings were obtained on AZ91D Mg alloy by immersing in the conversion fluids containing sodium acetate of various concentrations.The microstructure and corrosion resistance of the conversion coatings were analyzed by means of scanning electron microscopy,X-ray diffraction and full immersion tests.Results show that as-prepared conversion coatings are composed of Mg(α phase plus β phase) and MgSnO3·3H2O.The peak of weight of the conversion coatings increased with increasing concentration of sodium acetate in the conversion fluids,but the peak of weight decreased when the concentration of sodium acetate reached 40 g/L.Moreover,the conversion coating prepared from the conversion fluid containing 20 g/L sodium acetate had the best corrosion resistance.