Towards a compact coating formed on Al6061 alloy in phosphate based electrolyte via two-step PEO process and K2ZrF6 additives

In this work oxide coatings were prepared on Al6061 aluminum alloy using one and two-step plasma electrolytic oxidation (PEO) process. Under various conditions K2ZrF6 was added to the phosphate based electrolyte solution which was used to prepare one and two-step PEO coatings. Microstructure and phase composition of the final coatings were examined using SEM and XRD. The investigation revealed that that the solo use of K2ZrF6 caused the formation of highly rich ZrO2 and pseudo craters based coatings, however with damaged inner layer structure. By using a combined solution of K2ZrF6 and Na3PO4 (film formation agent), the coating growth and structural density were highly improved. Further enhancement in the coating properties such as high corrosion resistance ~ 7.63 × 105 Ω·cm2 and hardness were obtained by applying two step processes in the combined K2ZrF6 - Na3PO4 solution.