Effects of beta phase on the growth behavior of plasma electrolytic oxidation coating formed on magnesium alloys

摘要

Plasma electrolytic oxidation (PEO) was carried out on AZ91 and WE43 Mg alloys in phosphate electrolyte. The effects of beta-phases on growth behaviors of PEO coatings formed on two Mg substrates were analyzed and compared. Results showed that PEO coatings developed heterogeneously in two Mg substrates due to the existence of beta-phases. Before discharge breakdown, conversion film initially grew on alpha-Mg matrix and spread to beta-phase (Mg17Al12) in AZ91 alloy, while it preferentially formed around beta-phase (Mg14Nd2Y) rather than alpha-Mg matrix in WE43 alloy. This was attributed to the different reactivity of beta-phases in two Mg alloys. After discharge breakdown, the micro-pores in PEO coatings grew on beta-phases were larger in size as compared with that on alpha-Mg matrix. With the treated time, the inhomogeneous growth of PEO coatings disappeared gradually and PEO coatings became uniform. Finally, beta-phases did not destroy the continuity of PEO coatings. (C) 2019 Elsevier B.V. All rights reserved.