Zinc phosphate coating on 316L-type stainless steel using hydrothermal treatment

Parkerizing or zinc phosphatizing, a kind of zinc phosphate coating is utilized for mild steel to acquire a protective layer against a corrosion reaction. Although this method is useful for mild steels, it is not possible for 316L-type stainless steels (316L SS) because of their lower chemical reactivity. In order to investigate the possibility of preparing zinc phosphate coating on 316L SS, substrates were subjected to hydrothermal treatment in zinc phosphate solution at different temperatures and duration times. SEM observation with EDX analysis showed that the zinc phosphate coating layer was successfully prepared at 200 °C for 24 h. Besides, XRD results indicated that the crystal phase of the coating layer was assigned to zinclipscombite (ZnFe3+2(PO4)2(OH)2). Adhesive test indicated that the coating layer was strongly attached on the 316L SS substrate (more than 12.0 ± 1.4 MPa).