Comparison of corrosion resistance and biocompatibility of magnesium phosphate (MgP), zinc phosphate (ZnP) and calcium phosphate (CaP) conversion coatings on Mg alloy

• Published in: Surface & coatings technology 2020-09, Vol.397, p.125919, Article 125919
• Main Authors: Zai, Wei, Zhang, Xiaoru, Su, Yingchao, Man, H.C., Li, Guangyu, Lian, Jianshe
• Format: Article
• Language: English
• Subjects: Biocompatibility; Calcium phosphates; Conversion coatings; Corrosion mechanisms; Corrosion resistance; Corrosion resistant alloys; Corrosion tests; Electrochemical measurements; Hydrogen evolution; Immersion tests (corrosion); Magnesium alloy; Magnesium base alloys; Magnesium phosphate; Phosphate conversion coating; Protective coatings; Substrates; Toxicity; Zinc phosphate
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.125919

Seven different conversion coatings (which can be classified into three types: MgP, ZnP and CaP) were prepared on Mg alloy substrates to compare the corrosion resistance and biocompatibility of these coatings. Biocompatibility and cytotoxicity of different coated samples and bare Mg alloy were studied using the CCK-8 test. The corrosion resistance of different conversion coatings was comparatively studied by electrochemical tests (OCP, EIS and PDP) and long-term immersion test in Hanks' solution. Based on the experimental results, the corrosion mechanism of different types of conversion coatings and Mg alloy substrate was proposed and investigated. [Display omitted] •In this work, seven kinds of conversion coatings (which can be classified into three types of MgP, ZnP and CaP) were prepared by changing the content of Mg2+, Zn2+ and Ca2+ ions in conversion solutions.•The conversion coating generation priority was proposed: ZnP type > CaP type > MgP type.•The anti-corrosion performance of different coated samples are systematically investigated in Hanks' solution, and corrosion mechanisms different coatings are proposed from the perspective of filiform and pitting corrosion.•The biocompatibility and biodegradability of different conversion coatings and bare Mg alloy were investigated.•A “time constant shielding (TCS)” effect was proposed to explain the interaction between conductive loops and inductive loops in the EIS plot.