Effects of anodizing biodegradable Mg-Zn-Zr alloy on the deposition of Ca-P coating

To improve the poor binding force between Ca-P coating and Mg-Zn-Zr alloy, the anodization of Mg-Zn-Zr alloy has been employed prior to the deposition of Ca-P coating. Firstly, different anodizing conditions were studied and a two-step anodizing method (current density 8mA/cm² for 10min+current density 16mA/cm² for 10min) was suggested. Then, Ca-P deposition process was investigated to determine the optimized immersion time. Finally, compared with the direct deposition, the improvement of Ca-P coating by anodization was proved. The microstructures of anodizing films and Ca-P coatings have been analyzed by SEM, the binding forces between anodizing films and Ca-P coatings determined by scratch tester, and the corrosion potentials measured by electrochemical workstation. The results show that as the current density increases, anodizing films tend to have larger pores and lower binding force with Mg alloy. The deposition of Ca-P coating on anodized Mg-Zn-Zr alloy for 24h leads to an optimal morphology. Anodization as the pretreatment can make the Ca-P coating denser, remarkably increase the binding force with Mg alloy, at the same time shift the corrosion potential to a higher range.