Abstract: A paint film structure formed on an aluminum member or aluminum alloy member has a first paint film layer formed on a surface of the aluminum member or aluminum alloy member and a second paint film layer formed on a surface of the first paint film layer, the first and second paint film layers being chiefly composed of a colloidal silica, an organoalkoxysilane part hydrolysis condensation product, and a polymer or copolymer of an unsaturated ethylenic monomer, polymeric content or copolymeric content of the unsaturated ethylenic monomer in the first paint film layer being less than polymeric content or copolymeric content of the unsaturated ethylenic monomer in the second paint film layer.

Abstract: A coating composition comprising a colloidal silica, a partial condensate of organoalkoxysilane hydrolyzate, a polymer or a copolymer of unsaturated ethylenic monomers, a surface active agent and glycol derivatives, which is coated on a wheel for vehicles shows excellent properties such as adhesive property, filiform corrosion resistance, stain resistance, weather-resistance and impact resistance. A wheel coated with the coating composition for vehicles also shows excellent properties such as filiform corrosion resistance, stain resistance, weather-resistance and impact resistance.