Effect of reaction time on the microstructure and properties of in-situ hopeite chemical conversion coatings formed by self-corrosion on zinc alloy

Zinc (Zn) and its alloys are considered as promising biodegradable metals due to its suitable degradability and important physiological functions. However, in the process of degradation, excessive release of Zn ions (Zn2+) will significantly affect the cytocompatibility and antibacterial properties. Surface modification technology can not only control the corrosion behavior of biodegradable metals but also improve its biocompatibility and antibacterial properties according to clinical requirements. In this study, an in-situ hopeite (HP, Zn3(PO4)2·4H2O) coating was prepared on Zn alloy by phosphate chemical conversion (PCC) method using Zn2+ provided by self-corrosion of the substrates. And the effect of phosphating time on the microstructure, phase composition, corrosion resistance, and wettability of HP coatings was investigated. The results showed that a complete HP coating was formed on the Zn alloy after reaction for 1 min, even if Zn2+ were supplied by self-corrosion without an additional Zn source. It also revealed that the reaction time had a marked impact on the morphologies and microstructures of the HP coating. The electrochemical test results proved that the prepared HP coatings had obvious protection on the Zn alloy and could regulate the corrosion rate of the substrate. Meanwhile, the Zn alloy modified by the PCC method also possessed excellent hydrophilicity. These primary findings might support new opportunities in the exploration of controllable coatings on biomedical Zn alloys.