Formation of black ceramic layer on aluminum alloy by plasma electrolytic oxidation in electrolyte containing Na 2WO 4

Abstract

The formation of black ceramic layer produced by plasma electrolytic oxidation (PEO) coating has been investigated as a function of coating time. A series of PEO coatings was carried out on aluminum alloy sample in a phosphate electrolyte containing sodium tungstate (Na 2WO 4) with four different coating times, i.e., 20, 100, 200 and 300 s. As the coating time increased, the amount of tungsten element in the ceramic layer increased, resulting in the black ceramic layer. This phenomenon was discussed based on the electrochemical reaction assisted by micro sparks to form WO 3 compounds in the ceramic oxide layer. © 2012 The Japan Institute of Metals.