Various methods and treatments have been suggested in order to form a black oxide layer on the surface of aluminum alloy. These methods require anodizing or dipping the aluminum alloy into anodizing bath. However, this method is expensive because of the large surface area involved. Moreover, anodizing does not change the surface hardness of the aluminum alloy. Therefore, the present invention provides a solution that enables the manufacturing of aluminum alloys with a black oxide coating without the use of anodizing.
The invention describes a method of forming a black oxide coating on the surface of aluminum alloys using a novel treatment solution. The solution is produced by one of two novel combinations of catalysts. The first catalyst combination is based on sodium molybdate dihydrate and sodium benzoate. This solution has been successfully used to treat various aluminum alloys.
The second catalyst combination is based on sodium phosphate dibasic and sodium benzoate. This solution has also been successfully used to produce a black oxide coating on the surface of various aluminum alloys. The solutions produced by these methods are not only economical, but are also more efficient and practical for mass production.
The process described in the present invention is particularly suited for the manufacturing of heat exchangers in the automotive industry. However, it is equally applicable to various other applications. The invention is a more economical method that does not require anodizing or dipping the alloy in anodizing bath.