Process for corrosion protection of iron containing materials

摘要

The present invention relates to a process for corrosion protection of an iron-containing substrate wherein a first zinc-nickel alloy layer, a second zinc-nickel alloy layer and a black passivate layer are deposited onto the substrate. The nickel concentration in the second zinc-nickel alloy layer is higher than the nickel concentration in the first zinc-nickel alloy layer. The substrate surface obtained is homogenously black with an appealing decorative appearance and both resistance against white rust and red rust are improved.

主权项

1. A process for corrosion protection of an iron-containing substrate comprising, in this order, the steps of
(i) providing a substrate made of an iron-containing material, (ii) electroplating onto said substrate a first zinc-nickel alloy layer having a nickel concentration in the range of 6 to 15 wt.-%, (iii) thereon, electroplating a second zinc-nickel alloy layer having a nickel concentration in the range of 12 to 30 wt.-% onto the first zinc-nickel alloy layer with the proviso that the concentration of nickel in the second zinc-nickel alloy layer is higher than the nickel concentration in the first zinc-nickel alloy layer, and (iv) depositing a black passivation layer onto the second zinc-nickel alloy layer,
wherein an acidic zinc-nickel electrolyte used for electroplating the first zinc-nickel alloy layer and an acidic zinc-nickel electrolyte used for electroplating the second zinc-nickel alloy layer are the same acidic zinc-nickel electrolyte andwherein the nickel concentrations in both zinc-nickel alloy layers are adjusted by changing pH value, temperature, or both the pH value and the temperature of one or both of the acidic zinc-nickel electrolyte used for electroplating the first zinc-nickel alloy layer and the acidic zinc-nickel electrolyte used for electroplating the second zinc-nickel alloy layer during the electroplating steps.