PROCESSES AND COMPOSITIONS FOR IMPROVING CORROSION PERFORMANCE OF ZIRCONIUM OXIDE PRETREATED ZINC SURFACES

摘要

A method of improving corrosion resistance of a metal substrate comprising a zinc surface coated with zirconium oxide conversion coating by, prior to conversion coating, contacting the zinc surface with a composition comprising: a) iron(III) ions, b) a source of hydroxide ion; c) at least one complexing agent selected from organic compounds which have at least one functional group -COOX, wherein X represents either a H or an alkali and/or alkaline earth metal; d) 0.0 to about 4 g/1 cobalt (II) ions; and optionally e) a source of silicate: wherein the composition has a pH of at least 10.