Influence of Conversion Time on Phytic Acid Conversion Coating on AZ31B Magnesium Alloy

Phytic acid conversion samples were formed on AZ31B magnesium alloy at different times. The anticorrosive performance, morphology and composition of the conversion samples were studied by hydrogen evolution method, Tafel analysis, SEM and EDS. The results indicated that the conversion time had obvious influence on the properties of the phytic acid conversion coating. The anticorrosive performance of the samples increased with increasing the conversion time when the conversion time was short. When the conversion time was 40 min the conversion sample had the best anticorrosive performance. After this time, the anticorrosive performance of the samples reduced with the increase of conversion time. The main elements of the coating were Mg, Al, Zn, O and P. The conversion coating also had a few cracks, and a thin coating was formed on the crack. Furthermore, hydrogen evolution method, Tafel analysis and kinetics analysis showed that the phytic acid conversion sample had better corrosion resistance than untreated sample.