Patent ID: 8496762

Claim:
A method of preparing an aluminum or aluminum alloy substrate to accept an adherent coating thereon, the method comprising the steps of: a) degreasing the substrate; b) deoxidizing the substrate; and c) providing a conversion coating on the degreased and deoxidized substrate, the conversion coating comprising: i) a source of fluoride ions; ii) a source of zirconium ions; iii) an acrylic resin; and iv) about 35 to about 100 ppm of an optical brightener selected from the group consisting of 4,4′-bis-(2-sulfostyryl)-biphenyl disodium salt, a bistriazinyl derivative of 4,4′-diaminostilbene-2,2′-disulfonic acid, sulfonated 2-(stilben-4-yl)naphthotriazoles, bis(azol-2-yl)stilbenes, bisstyrylbiphenyl sodium salt, a sufonated pyrazoline, and combinations of one or more of the foregoing, wherein a chromium-free conversion coating is formed on the aluminum substrate that can be observed by exposing the treated substrate to UV light.