Introduction

Widely used by industry in general, and automotive manufacturers in particular, zinc nickel gives sacrificial protection to the underlying iron or steel, that is the zinc corrodes in preference to the substrate. This has the additional benefit that steel exposed at cut or abraded areas will not easily rust. This coating can be produced from acid or alkali solutions, the most popular now becoming the alkali as it is easier to control, is more ductile, gives a more consistent alloy and more even thickness than the acid solution.

Passivate Coating Salt Spray (hrs)
Cr6+ White Rust Red Rust
Black Chromate Free 240 720
Clear Trivalant Free 120 720
Heavy Trivalent Free 240 720
Blk Chromate + top Free 240 1200

Pre-treatment Process for Electro Nickel Plating

Proper pre- and post-treatment of the base product has a direct correlation to the quality and deposition rate of electro nickel plating. To help ensure uniform and quality adhesion, chemical or manual preparation includes the following three steps:

Pre-treatment surface cleaning : Surface cleaning entails eliminating contaminants through the use of solvents, abrasive materials, alkaline cleaners, acid etch, water, or a combination thereof.
Surface modification : Modifying the exterior of the base product improves adhesion through processes such as striking or metal hardening.
Post-treatment surface cleaning : Performing finishing operations, such as rinsing, end the electroplating process.

Once pre-treatment cleaning is complete, testing the level of cleanliness in the base material prior to beginning the electro nickel plating process is a good idea. To do this, the waterbreak test is recommended. In this test, the treated substrate is rinsed and held vertical. If contaminants such as oils are absent, then a thin sheet of water remains unbroken across the entire surface of the base material.

Zinc Plating

The zinc plating process offers several advantages to the metal. Zinc plated characteristics include an increase in corrosion resistance (comparable to cadmium) with an addition increase in resistance when chromates and sealers are used during the process. By zinc plating metal, it prolongs the life of the basis metal improves aesthetic value of the part and serves as a good paint base. Additionally, zinc plating increases the lubricity and can be used for identification purposes when combined with chromates and dyes.

Nickel Plating

Nickel is considered useful for electroplating metal because it provides superior ductility, corrosion resistance, and hardness. Electro nickel plating can also improve a product’s brightness and external appearance. Different nickel-plating chemicals incorporated into the process deliver anything from a semi-bright and fully bright cosmetic effect, to matte, pearl, or satin finishes

  1. Pretreatment : It is done whereby the surface of the substrate is cleaned to remove dusts, grease and rust if present to increase adherence of the coating. It can either be done mechanically by grinding or chemically by pickling in dilute hydrochloric or sulphuric acid .
  2. Fluxing : Fluxing is done to increase wetting of the substrate by the molten metal during dipping in molten aluminuim. This step also serves for further cleaning by immersing the substrate in a molten salt flux floating on top of the molten bath before immersion into the coating bath.
  3. Coating : The substrate is dipped in the molten bath for specific duration of time. The technique used will differ according to the shape and size of substrate that is to be coated.
  4. After-treatment : This refers to wiping, air-blasting or rolling of coated steel after withdrawal from coating bath. The objective is to reduce the amount of metal adhering to the sample.