ELECTRODEPOSITION COMPOSITION PROCESS FOR PROVIDING A ZN/SI/P COATING ON METAL SUBSTRATES AND ARTICLES SO COATED

摘要

The present invention relates to an aqueous composition for electrodepositing at a pH of about 1 to 3.5, a ductile, highly adhesive, adsorptive and absorptive zinc coating on a metal article. The article with the electrodeposited zinc coating can be subjected to further treatment, such as, a second functional or decorative coating or painting and forming. The ductile zinc coating is resistant to cracking during forming and metal articles treated in accordance to the present invention, including the formed areas, are highly resistant to corrosion, stress corrosion cracking, wear and galling. In the preparation of solution, metallic zinc and silicon are contacted with phosphoric acid and alkali metal hydroxide. The reaction is allowed to proceed until gas evolution ceases, residual metal is removed and the pH is adjusted to at least 2.5.