Method for surface treatment of aluminum alloy

Abstract

A method for surface treatment of aluminum alloy to form a uniform and dense zinc phosphate coating, which has excellent corrosion resistance properties on the surface of the aluminum alloy. The method includes steps of surface adjusting the surface of the aluminum alloy by a surface adjustor containing a predetermined volume of zinc phosphate particles, copolymer containing carboxylic acid group, and natural hectorite and / or synthetic hectorite respectively, and chemical conversion treating the surface of the resultant aluminum alloy by a zinc phosphate treating agent containing a predetermined volume of chelating agent that can chelate bond with iron ion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from Japanese Patent application No. 2004-347244 filed on Nov. 30, 2004, the contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a method for surface treatment of aluminum alloy. More particularly, it relates to a method for surface treatment of aluminum alloy that can form a zinc phosphate coating that is uniform, dense and excellent in corrosion resistance. [0004] 2. Related Art [0005] In the field of vehicle bodies and automobile parts, building materials, and furniture, etc., metallic materials such as steel plates, galvanized steel plates and aluminum alloys have been used. These metallic materials are, after molding, painted to be final products. Paint is applied to improve the appearance of these metallic materials, and has its principal object, to prevent corro...

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Benefits of technology

[0012] In order to solve the aforementioned problems, the present invention offers an improvement in both a surface adjustor and a chemical conversion treatment agent. It is an object of the present invention to provide a method for surface treatment of an aluminum alloy that can form a uniform and highly dense zinc phosphate coating with excellent corrosion resistance properties on the surface of the aluminum alloy.

[0016] According to the present invention, a method for surface treatment of aluminum alloy can be provided that can form a uniform and highly dense zinc phosphate coating with excellent corrosion resistance properties on the surface of the aluminum alloy.

Problems solved by technology

In these members wherein aluminum is a base metal, there may be a case wherein aluminum is excessively dissolved in the chemical conversion treatment agent to disturb a proper formation of the chemical conversion coating.

Use of insulating materials, however, disturbs current flow of the aluminum alloy during the next electro-deposition coating step, leading to failure of a proper coating.

A larger content of copper in aluminum alloy reduces its corrosion resistance property, in particular, filiform rust resistance and water adherence resistance properties.

Degradation of these properties is caused by a large potential difference existing between the aluminum and copper that lead to a considerable amount of dissolution of aluminum under the corrosive environment.

In order to assure excellent corrosion resistance property, contents of copper in the aluminum alloy need to be reduced; however, this solution poses a problem as it leads to a cost increase.

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