Alodine / Iridite / Chem-Film

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Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

You'll love this book. Finishing.com has sold a thousand copies without a return request  🙂

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Aluminum is often 'chromate conversion coated', usually in compliance with military specification MIL-DTL-5541 [⇦ this spec on DLA], as a corrosion resistant final finish or as a pretreatment for painting or powder coating.

'Alodine' and 'Iridite' are trade names of two of the largest suppliers pf proprietary products for these processes. The slang term 'Chem film' is widely used in the USA.

Traditionally these processes were based on toxic, carcinogenic, hexavalent chromium. But these days, due to environmental pressures, trivalent chromium processes (TCP) are usually used instead.