Zinc-nickel alloy electroplating system

Abstract

The invention provides an aqueous zinc-nickel alloy electroplating composition particularly useful in an electroplating method for depositing a zinc-nickel alloy layer on a substrate, wherein the deposited layer exhibits uniform nickel concentration and good aesthetics across a broad range of current densities. The electroplating composition comprises an electrolyte composition and an organic composition. In one embodiment, the electrolyte composition comprises a zinc ion source, a nickel ion source, a pH buffering agent and at least one additional salt, and the organic composition comprises a Class I nickel brightener, a Class II nickel brightener, an aromatic carboxylic acid, an aldehyde or ketone compound, and a non-ionic or anionic surfactant. The electroplating composition is particularly free of chelators and free ammonium-producing agents.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 692,204, filed Jun. 20, 2005, which is incorporated herein in its entirety.FIELD OF THE INVENTION [0002] The present invention is directed to electroplating compositions, and more particularly to compositions useful for electroplating zinc-nickel alloys. The invention is specifically directed to an electroplating composition comprising an electrolyte composition and an organic composition, wherein the electroplating composition is particularly beneficial for depositing zinc-nickel alloys with a consistent nickel concentration across a broad range of current densities. BACKGROUND [0003] Electrodeposition of zinc and nickel metal onto a substrate, particularly a metal substrate, and very particularly a ferrous substrate, is a common practice for imparting protective and decorative properties to the substrate. For example, ferrous articles are often zinc or nickel e...

AI Technical Summary

Benefits of technology

[0011] The present invention provides an aqueous zinc-nickel alloy electroplating composition. The composition is particularly useful for depositing a layer of a zinc-nickel alloy on a substrate, wherein the zinc-nickel alloy layer has an average nickel concentration that is within a desired range when the zinc-nickel layer is applied using a broad range of current densities. In addition to a consistent average nickel concentration, the zinc-nickel alloy layer deposited according to certain embodiments of the invention is bright, lustrous, and ductile. Further, these properties, as well as other properties generally desirable in an electroplated coating, are achieved when the deposition is carried out using a broad range of current densities.

Problems solved by technology

When using an alkaline zinc-nickel alloy electroplating bath, a common problem encountered is maintaining a functional level of metal ions in the bath.

The use of chelators presents a disadvantage in that plating efficiency and plating rate can both be reduced as a result of the metal ion complexation caused by the chelator.

Furthermore, the presence of the metal ion complexes with the chelators makes the plating process environmentally unfavorable as the removal of the complexed metal ions from wastewater streams is difficult and costly.

Acidic zinc-nickel alloy electroplating baths also present wastewater treatment problems.

The high concentration of ammonium ions commonly found in acidic zinc-nickel alloy electroplating compositions tends to make metal ion removal more difficult, and accordingly more costly.

Apart from the waste treatment issues, the inherent physical properties of coatings applied by acidic zinc-nickel alloy electroplating have also been shown to be troublesome for various reasons.

The zinc-nickel alloy deposits can lack ductility, can be brittle, and can be highly stressed.

Each of these can cause the electroplated zinc-nickel alloy layer to flake and peel from the substrate, especially in regions of high current density.

Another limitation seen with previous zinc-nickel alloy electroplating systems is a lack of alloy composition uniformity in deposition layers applied with such systems.

This can lead to disadvantages related to coating performance, as well as coating aesthetics.