Passivation composition and method for depositing a chromium-comprising passivation layer on a zinc or zinc-nickel coated substrate

An aqueous passivation composition for depositing a chromium-comprising passivation layer on a zinc or zinc-nickel coated substrate, the aqueous passivation composition comprising:

• (i) trivalent chromium ions, present in a total concentration from 0.5 g/L to 10 g/L, based on the total volume of the aqueous passivation composition;
• (ii) at least one complexing agent for the trivalent chromium ions selected from the group consisting of monocarboxylic acids, dicarboxylic acids, salts thereof, and mixtures thereof, and
• (iii) at least one corrosion-inhibiting agent, which is different from the at least one complexing agent for the trivalent chromium ions and comprises
• (A) one or more than one substituted azole compound and/or salts thereof, together in a total concentration below 10 mg/L, comprising at least 3-mercapto-1,2,4-triazole in a range from 3.0 mg/L to 9.4 mg/L, based on the total volume of the aqueous passivation composition,
• (B) one or more than one unsubstituted or substituted aliphatic organic acid with at least one mercapto-group and/or salts thereof, together in a total concentration in a range from 0.001 mg/L to 100 mg/L, comprising at least 3-mercapto-propionic acid and/or salts thereof in a range from 2 mg/L to 35 mg/L, based on the total volume of the aqueous passivation composition,
• or both (A) and (B), and
• wherein the aqueous passivation composition has a pH in a range from 1.0 to 4.0.