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

technical field [0001] The invention relates to an electroplating composition, especially an electroplating composition which can be used for electroplating zinc-nickel alloy. Specifically, the present invention relates to an electroplating composition containing electrolyte components and organic components, the electroplating composition is very suitable for electroplating zinc-nickel alloys in a relatively large current density range, and can obtain consistent and uniform nickel content. Background technique [0002] Electroplating of zinc or nickel is often required on substrates, especially metal and iron substrates, for the purpose of protecting and decorating them. For example, iron parts are often electroplated with zinc or nickel to improve the corrosion resistance of the iron substrate. With increasing demands on corrosion resistance, there is increasing interest in Zn-Ni alloys, especially Zn-Ni alloy coatings with enhanced corrosion protection properties relativ...

AI Technical Summary

Problems solved by technology

However, so far, the existing alkaline electrolytes and acidic electrolytes have many defects

[0004] A common problem encountered when using alkaline zinc-nickel alloy electrolytes is how to maintain effective levels of metal ions in the electrolyte

[0005] The disadvantage of using a chelating agent is that the chelating agent will cause metal ion complexation, so both the plating efficiency and the plating speed will be reduced

[0006] Acidic zinc-nickel alloy plating baths also present wastewater treatment issues, as the high ammonium ion content in acidic zinc-nickel alloy plating compositions makes metal ions more difficult to remove and therefore more expensive to dispose of

In addition, the discharge of solutions containing ammonium ions is subject to environmental discharge standards

[0007] In addition to wastewater disposal issues, deposits obtained by acid Zn-Ni plating have various inherent physical property defects: Zn-Ni coatings may lack ductility, be brittle and have high stress levels, which may cause Zn-Ni coatings to peel off from the substrate and detachment, especially in high current density regions

Another drawback of existing zinc-nickel alloy plating systems is that the alloy composition in the plating layer is not uniform

When the current density applied to the plated object is reduced, the nickel content in zinc-nickel alloys usually increases significantly, which may adversely affect the performance and aesthetics of the coating

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