Potentiostatic preparation and in vitro characterization of functional hazenite conversion coatings on AZ31 magnesium alloy

Abstract

A functional hazenite coating was deposited on AZ31 Mg alloy by polarization at −0.8 V in a deaerated phosphate solution containing 0.1 M K2HPO4 and 0.1 M Na2HPO4 with pH 9. The growth process of the coating was determined by analyzing its morphological and composition evolution. The roughness, hydrophilicity, long-term protectiveness, bioactivity and bio-compatibility of the coating were characterized. The stress corrosion cracking (SCC) susceptibility of the coated AZ31 Mg alloy was also investigated. The results showed that the coating consisted of crystallized Mg(OH)2, MgHPO4·3H2O, KMgPO4·6H2O and KNaMg2(PO4)2·14H2O. The latter three compounds were transformed into hydroxyapatite, improving the bioactivity of AZ31 Mg alloy. The coating increased the roughness and hydrophilicity and significantly stimulated the proliferation of rabbit bone marrow stem cells, enhancing the biocompatibility of AZ31 Mg alloy. Additionally, the coating reduced the degradation rate of AZ31 Mg alloy by more than two orders of magnitude and the hydrogen volume by 50.9 % and showed good long-term protectiveness. Moreover, the coating decreased the SCC susceptibility indexes IUTS and Iε of AZ31 Mg alloy by 41.9 % and 44.9 %, respectively.