Preparation of corrosion–resistant coating on Mg alloys and investigation of electrolytic components on coating formation

Although Mg alloys exhibit excellent application prospects in some areas where lightweighting is very critical, their poor corrosion resistance severely restricts their engineering applications. In this study, a near-neutral pH solution mainly containing hexamethylenetetramine (HMTA), sodium phytate, K 2 ZrF 6 , Na 2 B 4 O 7 and Na 3 PO 4 was selected and MAO coatings were successfully prepared on WE43 Mg alloys by micro-arc oxidation (MAO) under different constant voltages. The fabricated MAO sample under 520 V achieves good corrosion resistance and its i corr value is three orders of magnitude lower than that of Mg substrate. Then, the corrosion inhibition behavior and the underlying mechanism of electrolytic components on Mg alloys were systematically investigated. The results elucidate, for the first time, that before MAO treatment, Mg substrate is initially corroded and then the micro-corrosion areas are healed by the MAO solution through adsorption stage, chemical reaction stage and surface deposition stage. Before MAO treatment, all electrolytic components synergistically passivate the Mg substrate. Among four electrolytic components, the anticorrosive ability on WE43 Mg alloys is ranked as 360 g/L HMTA > 5 g/L Na 3 PO 4 > 2 g/L K 2 ZrF 6 > 12 g/L sodium phytate. These results will provide a basis for future screening of suitable electrolytes and the preparation of high corrosion-resistant coatings.