STUDY ON PHYTIC ACID CONVERSION COATINGS FOR MAGNESIUM ALLOY I.Formation Mechanism and Corrosion Resistance of Phytic Acid Conversion Coatings

The corrosion resistance of phytic acid conversion coatings on AZ91D magnesium alloy surface was studied by electrochemical methods.Morphology,composition and functional group of coatings were investigated by SEM,EDAX and FTIR,respectively.The formation mechanism of phytic acid conversion coatings was also discussed.Results show that the corrosion resistance of AZ91D magnesium alloy is improved by phytic acid coatings evidently.The conversion coatings formed under optimal processing parameters are found of high coverage and no cracks.The main elements of the conversion coatings are Mg,Al,O,P,and C.The FTIR results indicate that the coatings contain hydroxyl and phosphate radicals.