Aqueous solution and method for the formation of a passivation layer

A method for the formation of a passivation layer on a zinc layer or zinc-alloy layer, the method comprising the steps:

• depositing a zinc or zinc-alloy layer on a substrate surface;
• treating the deposited zinc or zinc-alloy layer with an aqueous process solution according to claim 18.

Use of a compound according to the general formula

• wherein R is H, Li, Na, K, NH4, or a branched or unbranched alkyl group having 1 to 8 carbon atoms as additive in a composition for the deposition or passivation of metals on the surface of a substrate.

Passivation layer on a zinc layer or zinc-alloy layer, characterized in that the passivation layer has an average optical surface reflectance at a wavelength within the range of 360 nm to 710 nm of less than 8%, preferably less than 7%, wherein the fluctuation range of the reflectance is ≦2%, preferably ≦1%.

An aqueous process solution as set forth in any of claims 18 to 23 wherein said carboxylic acid comprises an α-hydroxy acid.

An aqueous process solution as set forth in any of claims 18 to 23 further comprising fluoride or bifluoride ions.