Effect of equal channel angular pressing as the pretreatment on microstructure and corrosion behavior of micro-arc oxidation (MAO) composite coating on biodegradable Mg-Zn-Ca alloy

摘要

To improve the mechanical properties and control the long-term corrosion properties of biodegradable Mg4.71Zn-0.6Ca (wt%) alloy, a composite coating was fabricated on the Mg-4.71Zn-0.6Ca alloy by using micro-arc oxidation (MAO) under the pretreatment of equal channel angular pressing (ECAP). Experimental results showed that ECAP treatment refined the microstructure of Mg-4.71Zn-0.6Ca alloy with an average grain size of 1.6 mu m, and made the mechanical properties improve from 206 MPa to 290 MPa. The phase composition of MAO coatings includes the alpha-Mg matrix phase, Mg2SiO4, MgO, and HA, and the ECAP/MAO coating is denser with a smaller pore size than the as-cast/MAO coating. The electrochemical and immersion test results indicated that the corrosion resistance of the ECAPed sample is better than that of the as-cast sample, and the MAO processing can significantly increase the corrosion resistance of both as-cast and ECAPed samples. The corrosion rate of ECAP/MAO treated Mg-4.71Zn-0.6Ca alloy is the lowest, and the ECAP pre-treatment improves the long-term corrosion properties of the MAOed Mg alloy. Besides, the bioactivity of Mg-4.71Zn-0.6Ca alloy was enhanced by the hybrid ECAP/MAO treatment as well.