Comparative study between novel magnesium phosphate and traditional zinc phosphate coatings

In this study, novel magnesium phosphate as well as traditional zinc phosphate coatings were applied on low carbon steel substrate. The coatings were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. In addition, magnetic thickness gauge was used to determine the thickness of the coatings. The results showed that after 20 min of phosphating, magnesium phosphate coating (MP) was about 3 times thicker than zinc phosphate coating (ZP). It was also noticed that MP endured salt spray atmosphere for more than 2 times longer than ZP without any sign of red rust.

► A novel phosphate coating “secondary magnesium phosphate” was applied on carbon steel.
► Magnesium phosphate coating was achieved by the combination of magnesium carbonate and phosphoric acid.
► A dense and uniform coating was achieved after 20 min at 80 °C and the pH of 4.3.
► Magnesium phosphate coating endured the salt spray atmosphere for about 2.5 times more than zinc phosphate coating without any signs of corrosion.