A preliminary study of calcium containing plasma electrolytic oxidation coatings on AM50 magnesium alloy

摘要

An experimental study of calcium containing plasma electrolytic oxidation (PEO) coatings on AM50 magnesium alloy was reported. Specimens of size 15 mm × 15 mm × 4 mm of a cast AM50 magnesium alloy were used as substrate for the PEO processing. They were ground successively with 500, 800, 1200 and 2500 grit emery sheets and cleaned with acetone before the PEO treatment. The temperature of the electrolytes was always kept at 10 ± 2°C by a water cooling system. Electrochemical impedance spectroscopy (EIS) tests were carried out using a Gill AC potentiostat/frequency response analyser with a three electrode cell setup. It can be observed that both the KOH electrolyte coating and the Ca(OH)_2 electrolyte coating were constituted with MgO and Mg_3(PO_4)_2 phases. There was no macroscopic corrosion damage on the surface even after 150 h of exposure to the corrosive environment, as can be observed from the optical macrograph.