The effect of process parameters on mullite-based plasma electrolytic oxide coatings

Thick, mullite-based plasma electrolytic oxide (PEO) coatings, designed for a combination of wear-protection and thermal protection, have been produced on 6082 aluminium alloy substrates under various conditions (electrolyte, processing time, current density) and their growth rate, hardness, Young's modulus and microstructure have been studied. The final coating thickness depends predominantly on the processing time and the applied current density. The concentration of silicate in the electrolyte has reasonable effect on the resulting coating thickness, composition or porosity. The hardness and Young's modulus decrease slightly with an increase of the concentration of silicate. A through-thickness variation in the composition of the coating is observed.