Morphology, composition and properties of PEO coatings formed in tartrate-based electrolytes on aluminum alloy AMg61

The study results of the morphology, composition, electrochemical and mechanical properties of coatings formed by plasma electrolytic oxidation (PEO) on aluminum alloy AMg61 in tartrate-based electrolytes of two compositions: 20 g/l tartaric acid and 6 g/l potassium hydroxide; 20 g/l potassium tartrate and 0.6 g/l sodium fluoride. The presence of sodium fluoride in the electrolyte causes the formation of γ-modification of aluminum oxide(III) in the form of microtubules (visible porosity of 23%), while a low-porous layer of γ-Al2O3 is formed in the electrolyte with potassium hydroxide (visible porosity of 3%). A sample with a PEO coating formed in an electrolyte containing 20 g/l tartaric acid and 6 g/l potassium hydroxide has the best electrochemical and wear-resistant properties. Applying such a coating to the AMg61 alloy reduces the corrosion current density of the sample by more than an order of magnitude (Ik = 1.4·10–9 A/cm2) compared with the value of this parameter for the uncoated sample (Ik = 4.8·10–8 A/cm2). The scalar impedance at low frequency |Z|f = 0.01 Hz for such coating increases by three orders of magnitude (|Z|f = 0.01 Hz = 2.51·108 ohms·cm2) compared with this parameter for an uncoated sample (|Z|f = 0.01 Hz = 1.94·105 ohms·cm2). Reduction by 2 times of the coefficient of friction (μ = 0.10–0.12) and decrease in the wear rate by half an order (4.8·10–4 mm3/(N·m)) compared with the values of these parameters for a sample treated in an electrolyte with 20 g/l potassium tartrate and 0.6 g/l NaF (1.1·10–3 mm3/(N·m) at μ = 0.23–0.26) are caused by the morphology and phase composition of the oxide layer.The article was prepared using the results of the work carried out with the financial support of the Russian Science Foundation No. 23-23-00372 “Protective composite coating of aluminum alloys operated in marine conditions”.