Structure and Properties of Plasma–Electrolytic-Oxidation Coatings Obtained on Д16Т Alloy under Different Electrical Parameters and Prior Ultrasonic Impact Treatment

Abstract

The surface of the aluminium Д16Т alloy is modified using plasma– electrolytic oxidation (PEO) at different current densities і and electrolyte-flow rates v. Taking the maximum microhardness and minimum wear of the PEO coating into account, the optimal process parameters are determined (і = 4 A/dm2 and v = 80 cm/s). With these parameters, a combined surface treatment of the Д16Т alloy is carried out with preliminary ultrasonic impact treatment (UIT) and finishing PEO. The total porosity, pore size, and their distribution over the thickness of the PEO coatings are investigated using the scanning electron microscopy method, depending on the applied current densities, electrolyte feed rates, and UIT. As shown, the increase in microhardness HV (≅ 22 GPa) and the decrease in wear W (≅ 0.18 g) of the UIT + PEO coating amount to ≅ 3–5% as compared to those for the PEO coating produced without UIT. This is associated with a decrease in the porosity of the coating-surface layer of 40 µm thick (by 3.5 times) and the layer near the interface between the coating and the Д16Т-alloy specimen surface (by 4.5 times), as well as a decrease in the size and more uniform arrangement of pores.