Effects of Na2WO4additive on properties of Plasma electrolytic oxidation coatings on 6061 Al alloy

Plasma electrolytic oxidation (PEO) ceramic coatings were prepared on 6061 aluminum alloy substrate in silicate based electrolyte with and without Na2WO4 additive with different pulse frequency. The composition, surface morphology and corrosion resistance of PEO coatings were investigated by means of SEM, XRD, potentiodynamic polarization and EIS measurement in a 3.5% NaCl solution. These results show that Na2WO4 can contributing to the transition from the metastable gamma-Al2O3 to a better thermal stability alpha-Al2O3, while has certain inhibitory effect on the deposition of SiO32- anion on the surface during the plasma discharge process. After adding Na2WO4 in the electrolyte, the surface layer of PEO coatings are more smoother and less distinctly discharge holes appear which leads to the PEO coatings have better corrosion resistance than those of samples coated in the electrolyte without Na2WO4 additive.