3. Trivalent chromium treatments

3.1 Treatment trends

The first trivalent chromium-based passivates were developed commercially in the 1970s. The aim was to obtain a bluish-colored passivation film, mainly for decorative purposes. The relatively high cost of trivalent chromium salts meant that very small quantities of trivalent chromium were used in the passivation electrolyte (< 1 g · L ^–1 ), and the anti-corrosion performance of these coatings was consequently very limited (around 24 hours in the salt spray test before white rusting according to ASTM B 117-03).

These electrolytes are based on a combination of trivalent chromium salts and an oxidizing agent that replaces the chromate present in chromating with Cr ^VI...