Blue and Green Phosphate Coatings Formed on Steel without Heating

Phosphating is one of many methods of obtaining protective films on steel products at low temperatures. Phosphate coatings are obtained from solutions based on Mazev Salt containing Mn(H₂PO₄)₂∙2H₂O and iron phosphates (the proportion of phosphoric acid, in terms of P₂O₅, 46–52%; the mass fraction of manganese is not less than 14%; the mass fraction of iron is not more than 0.5%). To accelerate phosphating and carry out the process without heating, the solution contains metal nitrates and nitrites. To obtain blue and green colored phosphate coatings, it is proposed procyon olive green and methylene blue dyes are introduced in an amount of 8 g/l into phosphating solutions. Unlike conventional gray phosphate films, coatings from solutions with dyes are deposited unevenly on the steel surface. The thickness of the phosphate coatings was estimated from micrographs of the cross-sections; its value was 3–4 microns. When assessing the heat resistance of phosphate films, it was found that they continue to exhibit protective properties when heated to 100 °C, and when heated to 200 °C, the protective ability is low. Colored phosphate films have a low coefficient of friction, which does not allow them to be recommended as wear-resistant coatings. In colored phosphate coatings, the breakdown voltage is 180–200 V, which characterizes a low electrical insulation ability.