METHOD OF MAKING PROTECTIVE COATINGS ON VALVE METALS AND ALLOYS THEREOF Russian patent published in 2019 - IPC C25D11/02 

FIELD: technological processes.

SUBSTANCE: invention relates to plasma-electrolytic coating of valve metals and their alloys and may find application in various industries, in engineering, instrumentation for work in friction units and to protect products and structures from atmospheric and electrochemical corrosion. Method includes plasma-electrolytic oxidation for 40–50 minutes in the bipolar mode with an effective current density of 20–180 A/dm² in alkaline electrolyte containing, g/l: sodium fluoride NaF 0.6–3.0, potassium tartrate C₄H₄O₆K₂⋅0.5 H₂O 25–50, sodium silicate Na₂SiO₃⋅2H₂O 25–50, sodium borate Na₂B₄O₇⋅10H₂O 10–30, sodium molybdate Na₂MoO₄⋅2H₂O 1–10, and during the first 5 minutes the anode voltage is raised from 30 V to the initial formation voltage, which is 460–470 V for aluminum and its alloys and 260–270 V for titanium and its alloys, form the coating, increasing the voltage to 480–490 V at a speed of 0.6 V/min for aluminum and its alloys and at a speed of 6.0 V/min for titanium and its alloys, after which they complete the formation, reducing the voltage for 6–7 min up to 400–420 V for aluminum and up to 220–230 V for titanium, the density of the cathode current during the formation of the coating is increased to 50–75 A/dm² and reduce to 10 A/dm² within 6–7 minutes at the completion of the formation of the coating simultaneously with a decrease in the anode voltage.

EFFECT: increasing the corrosion resistance of the resulting coatings, increasing the hydrophobicity and improving the mechanical properties.

3 cl, 4 dwg, 6 ex