Effect of Na2WO4 in electrolyte on mechanical properties of oxide layer on Al alloy via plasma electrolytic oxidation

Abstract

This paper investigates with the mechanical properties of Al alloy samples coated by plasma electrolytic oxidation (PEO) using a phosphate electrolyte with a Na2WO4 solution. Under an A Ccondition of 60Hz, PEO coatings were applied for 300 seconds at a current density of 100mA/cm(2). Microstructural observations of the PEO-coated samples revealed that the size and fraction of the micro-pores remained nearly constant while WO3 and W were additionally in corporated in the oxide layer using the Na2WO4 solution. During PEO coating, the Na2WO4 solution dissociated into Na+ and WO42- and the high dielectric voltage exceeding the ignition voltage activated the electrochemical reactions of WO42- in the anode, leading to the formation of WO3 and W. The incorporation of WO3 and W is expected to lead to enhancement of the hardness and wear resistance of the PEO-coated Al sample.