Influence of process parameters on growth behaviour and properties of coatings obtained by plasma electrolytic oxidation (PEO) on AA 6061

摘要

Plasma electrolytic oxidation coating is obtained on AA6061 alloy using positive uni-polar pulsed DC in a sodium silicate-based electrolyte. The effect of process parameters such as solution concentration, process time, average current density, pulse frequency and positive on-time is investigated systematically and the corresponding voltage-time response is correlated with the coating growth rate. Surface morphology of the coatings is studied using scanning electron microscopy and the elemental distribution on the coating is investigated using energy dispersive X-ray spectroscopy. The concentration of sodium silicate in the solution is found to play a key role in determining the morphology and composition of the coating. X-ray diffraction studies indicate a transition from crystalline to amorphous nature of the coating with increase in silicate content of the electrolyte. Effect of pulse frequency on the voltage-time response and the corresponding coating growth rate is highly dependent on the solution concentration.