Improving the phosphating process for Ca-P coating on ZK21 biomedical magnesium alloy

Abstract The optimization study of the phosphating process was conducted on the surface of ZK21 biomedical magnesium alloy using the chemical conversion technique to fabricate Ca-P coating. The findings reveal that the optimal concentrations of the three additives in the phosphating solution, Ca(CH 3 COO) 2 , C 6 H 4 O 5 NSNa, and Na 2 MoO 4 , are 12 g/L, 2 g/L, and 0.5 g/L, respectively. Under these specified conditions, the resulting Ca-P coating appears compact and uniform. An optimal quantity of Ca(CH 3 COO) 2 can enhance the concentration of Ca 2 + in the solution. C 6 H 4 O 5 NSNa accelerates the rate of membrane formation, whereas Na 2 MoO 4 facilitates the creation of nucleation sites, consequently bolstering membrane formation even further. Analysis through EDS and XRD confirmed that the predominant compound in the Ca-P coating is CaPO 3 (OH) 2 ·2H 2 O (DCPD).