Preparation of Phytic Acid Conversion Coating on AZ91D Magnesium Alloy Surface

The optimized process for preparing phytic acid conversion coating on AZ91D Mg alloy was determined based on orthogonal tests,and phytic acid conversion coating with good corrosion resistance was prepared.The morphology and composition of the conversion coating were analyzed by means of scanning electron microscopy and energy dispersive spectrometry.The corrosion resistance of the phytic acid conversion coating was evaluated by conducting dipping test and measuring polarization curve and electrochemical impedance spectrum.Results show that as-prepared phytic acid conversion coating consists of Mg,Al,O,P,C and Na.The coating was able to greatly increase the corrosion resistance of the Mg alloy,reducing the corrosion current of Mg alloy by three orders of magnitude.The size of cracks on the surface of the conversion coating had no effect on the corrosion resistance of the coating.Process factors influenced the corrosion resistance of the coating could be ranked as pH valuephytic acid concentrationcoating-forming timecoating-forming temperature.