Investigation Of Stannate Chemical Conversion Coatings On AZ91D And AZ31Magnesium Alloy

Magnesium alloy chemistry, high electrochemical activity and poor resistance corrosion is the main reason of resistance of magnesium alloy using. The corrosion of magnesium and magnesium alloys is very sensitive, especially in the salt spray environment, serious impact on magnesium and magnesium alloys in industrial applications. AZ91D, AZ31 as the most widely used cast magnesium alloy and deformation magnesium alloy, surface protection to improve their using life and to expand the applications is very important.This method of protective film will be used to improve the corrosion resistance of magnesium alloy. Using stannate chemical conversion method, Conversion of AZ91D, AZ31 magnesium alloys, analysis factors of magnesium stannate conversion, the effect factors of corrosion rate are concentration of salt solution,temperature, pH value, conversion time and the matrix a (Mg) phase, P (Mg17Al12) in the group phase and the magnesium alloy elements. Determine the process conditions of the AZ31, AZ91D stannate conversion, Using optical microscopy, scanning electron microscopy (SEM), energy spectrum analysis (EDS), the corrosion weight loss and other methods, conversion coatings on magnesium alloy surface.the morphology, chemical composition, phase structure and corrosion resistance were measured and analyzed.Corrosion data is available based on two main concentration of magnesium alloy into liquid 40g/L,50～55℃, PH value 3.5～4,50min, the condition is good corrosion resistance, pH value of 7.0 is the second corrosion resistance,the worst corrosion resistance is in the pH value is 12.0.Thus, AZ91D magnesium alloy into solution under acidic condition for the transformation of the conversion coating has a certain degree of protection. The detection of conversion film is amorphous structure, surface uniformity, main components are divided into Mg, Al, Sn, O. these elements is formed of Oxides, hydroxide, MgO, Mg(OH)2, MgAl2O4, Al2O3, Al(OH)3,MgAl2O4, Al2O3 matrix can play a good protection. Corrosion resistance of conversion coatings on AZ91D magnesium alloy is better than AZ31 magnesium alloy, after transformation of uneven surface film, no rough treatment that the organic coating can provide a good base.