Method of coating aluminum and aluminum alloy substrates and coated articles

摘要

A method of coating aluminum and aluminum alloy substrates not only imparts a corrosion resistance comparable or even superior to that afforded by chromate treatment but also improves the adhesion to the coating film, while the luster of aluminum is fully retained, notwithstanding the use of a chromium-free treating solution, resulting in an improved coated article with the coated surface having a metallic luster. The method comprises treating an aluminum or aluminum alloy substrate with an acidic solution containing sulfuric acid and 0.2 to 0.4 g/L of a ferric ion and having a pH value of 0.6 to 2.0, subjecting the same to chemical conversion treatment with an acidic coat-forming agent containing 0.01 to 0.125 g/L of a zirconium or titanium ion, 0.01 to 1.0 g/L of a phosphate ion, and 0.01 to 0.5 g/L of a fluoride ion and having a pH value of 1.5 to 4.0, followed by coating.