Quaternary ammonium salts as a conversion coating or as anticorrosive additive in paints

Disclosed are quaternary ammonium salts containing non-halogen anions such as carbonates, bicarbonates, phosphates, glycolates and mixtures thereof as conversion coatings or additives imparting anti-corrosive properties to paints. Particularly disclosed is a one-step method for improving corrosion resistance and paint adhesion to the surface of a metal substrate, comprising contacting the substrate with a composition comprising an aqueous solution of at least one quaternary ammonium salt having the formula (I), wherein R1 is an optionally aryl-substituted C1-20 alkyl group, and R2 is an optionally aryl-substituted C1-20 alkyl group, R3 and R4 independently of each other are C1-4 alkyl groups, Xn- is an anion selected from the group consisting of hydroxide, carbonate, bicarbonate, phosphates, phosphites, hypophosphite, nitrate, sulfates, borates, anions of saturated and unsaturated acyclic C1-20 monocarboxylic acids, anions of saturated and unsaturated acyclic C2-20 dicarboxylic acids and anions of hydroxy-substituted carboxylic acids, and n denotes the appropriate number of negative charges of said anion. The disclosure relates to a method for inhibiting the corrosion of metal surfaces by applying a composition containing one or more quaternary ammonium carbonate or bicarbonate. The description also relates to anti-corrosive coatings containing these compounds for inhibiting the corrosion on metal surfaces, and to metal substrates having these anticorrosive coatings.