Dry sliding wear behaviour of magnesium oxide and zirconium oxide plasma electrolytic oxidation coated magnesium alloy

Abstract

Two types of PEO coatings, one consisting of magnesium oxide (MgO) and the other comprising zirconium oxide (ZrO2) as the main phase composition were produced on AM50 magnesium alloy from alkaline and acidic electrolytes, respectively. The ZrO2 coating was found to be spongy and thicker with a higher roughness, whilst the relatively more compact MgO coating was having contrasting features. In the dry sliding oscillating wear tests under two different loads viz., 2N and 5N, the ZrO2 coating exhibited a very poor wear resistance. The MgO coating showed an excellent resistance to sliding wear under 2N load; however, the load bearing capacity of the coating was found to be insufficient to resist the wear damage under 5N load. The higher specific wear rates of the MgO coating under 5N load and that of the ZrO2 coating under 2N and 5N loads were attributed to the poor load bearing capacity and a three-body-abrasive wear mechanism.