Effect of Magnesium Carbonate and Phosphoric Acid Concentration on Microstructure and Corrosion Behavior of Magnesium Phosphate Coating

In this investigation, the effect of variations of phosphating bath (magnesium carbonate and phosphoric acid) concentration was studied on the properties of magnesium phosphate coating. The formation of the coating and morphological evolution were examined by XRD and SEM, respectively. The coating thickness was measured using a magnetic thickness gauge. Potentiodynamic polarization curves were used to investigate corrosion behavior. The findings revealed that optimizing both the phosphoric acid and magnesium carbonate concentration affects the nucleation and growth of the phosphate crystals and considerably affects the coating thickness and porosity. Therefore, optimizing these constituents is essential to decrease the corrosion rate. The heaviest coating thickness, lowest porosity and the lowest corrosion rate were observed at 23 mL/L of phosphoric acid and 9 g/L of magnesium carbonate concentrations. Variations of magnesium carbonate concentration was a more effective factor than the phosphoric acid.