The Effect of Potassium Oxalate and Nickel Oxide as Additives on The Structure, Corrosion Resistance and Abrasion Properties of Manganese Phosphate Coating

During this research, the formulation of manganese phosphate bath was designed to create layers on the surface of low carbon steel alloys (St 37) to enhance corrosion, abrasion and friction resistance. At the first, a basic solution of the manganese phosphate bath was prepared by optimizing the concentration of each components of the bath. Then, the effects of potassium oxalate and nickel oxide additives on coating properties such as thickness, unit weight of surface (With optimal value of 1± 0.1 gr/l nickel oxide, the weight of the coating 39.8 ± 0.2 gr/m was obtained and optimal value of 0.5±0.1 gr/l potassium oxalate, the weight of the coating 48.99±0.3 gr/m2 was obtained), morphology, corrosion and abrasion resistance were investigated and finally, the best coating determined.The results of various experiments showed that the major phase of manganese phosphate coating is Hureaulite, which is in the form of cubic crystals in the basic solution that does not contain any additives, of course, with the addition of additives, the shape of the crystals is changed and the particle size becomes smaller and denser. The highest corrosion resistance obtained during the salt spray test (98 hours) and electrochemical impedance spectroscopy (EIS) (with Polarization 77983±253) is related to phosphate coating containing nickel oxide. According to the results of the Pin on disk test the specimens which were phosphated and soaped reduced the coefficient of surface friction from about 0.6 (for uncoated steel) to about 0.15, and this indicated the anti-abrasion and friction properties of these coatings.