US 5,843,242 A · Compositions and processes for forming a solid adherent protective coating on metal surfaces

Abstract

An aqueous liquid chromate free primary composition for forming a protective coating on metals, particularly aluminum, is made by reacting cobalt(II) cations, carboxylate anions, at least one other type of coordinate complexing agent for cobalt(III) cations, and an oxidizing agent in an aqueous solution in which the molar ratio of carboxylate anions to cobalt(II) cations is from 0.10 to 6.8 and the aqueous solution contains no more than 1% of each of ammonia, ammonium ions, and nitrite ions. The primary layer formed by this or any other composition that forms a coating containing metal atoms and oxygen atoms on a metal substrate is advantageously sealed by further treatment with an aqueous solution of sodium ammonium decavanadate, optionally after an intermediate step of immersing in water for a few minutes between the primary treatment and the sealing treatment.

Claims20

Dependent claims

A process for improving the corrosion protection afforded to an underlying metal substrate selected from a group consisting of aluminum or any aluminum alloy containing at least 45% aluminum by an adherent primary coating containing cobalt oxide and aluminum oxide formed over the metal substrate, said process comprising the steps of

(I) contacting the adherent primary coating, for a time effective to improve the resistance to corrosion in a salt spray test of the underlying metal substrate after completion of the process, with an aqueous sealing composition consisting essentially of water, dissolved vanadate anions, and dissolved counterions for the vanadate anions, containing not more than about 0.030M in total of tungsten in any anionic form, and containing at least 0.007 moles per liter of vanadium atoms from the vanadate anions;
(II) discontinuing the contacting performed in step (I) and drying the surface of the metal substrate at a temperature not greater than about 100.degree. C.

A process for improving the corrosion protection afforded to an underlying metal substrate, said process comprising steps of:

(i) forming on the metal substrate an adherent primary conversion coating containing cobalt and oxygen atoms;
and
(ii) contacting the adherent primary conversion coating, for a time effective to improve the resistance to corrosion in a salt spray test of the underlying metal substrate after completion of the process, with an aqueous sealing composition comprising dissolved vanadate in one or more anionic forms, and, optionally, also comprising dissolved tungsten in one or more anionic forms;
and
(iii) discontinuing the contacting performed in step (I) and drying the surface of the metal substrate at a temperature not greater than about 100.degree. C.,
wherein the improvement comprises utilizing an additional intermediate step, between steps (i) and (ii), of contacting the adherent primary conversion coating with purified water, optionally containing an oxidizing agent, for a period of at least 1 minute.

3 more elements

Dependencies are inferred from the claim text.

Compositions and processes for forming a solid adherent protective coating on metal surfaces

Life of this patent

Compositions and processes for forming a solid adherent protective coating on metal surfaces

Life of this patent

Abstract

Claims20