Composition and process for the treatment of metal surfaces

Abstract

A method of forming a conversion layer on a metallic surface and a composition usable in the method are provided. The composition is an aqueous solution comprising a source of tungstate ions and a soluble material comprising zirconium. The method provides a conversion coating on a surface that can then be painted or otherwise treated. The conversion coatings of the present invention are minimally affected by heating and / or baking, unlike chromate conversion coatings of the prior art.

Description

field of invention

[0001] The present invention relates to a composition and method for producing conversion coatings on metal surfaces. The conversion coatings of the present invention are generally chrome-free and improve the corrosion resistance of the treated surface as well as the adhesion of dry organic varnishes to the treated surface. Additionally, the conversion coatings of the present invention are less affected by subsequent heating and / or baking steps. The invention is particularly suitable for the treatment of zinc, zinc alloys, aluminum and aluminum alloys, although steel and other metals can also be treated. Background technique

[0002] In order to protect the metal against corrosion and as a substrate to improve the adhesion of subsequently applied dry organic varnishes, various conversion coatings have been suggested in the prior art for the purpose of forming coatings suitable for metal surfaces. The conversion coating is produced by treating the metal s...