A few of the characteristics of the zinc-cobalt plating process includes enhanced corrosion resistance for the base metal compared to traditional zinc plating of the same thickness. Additionally, bright luster is produced when the zinc cobalt alloy coating is applied. By electroplating zinc and cobalt to the particular metal, the end result is a uniform ductility that will withstand up to six times the corrosion resistance of conventional zinc plating. Zinc cobalt alloy plating is also becoming more popular because of its affordable operation costs compared to other zinc alloy coatings.
Introduction
- Zinc-Cobalt has greater corrosion resistance than traditional Zinc plating
- Increased corrosion resistance when combined with sealers and chromates
- Ductility characteristic of zinc-cobalt allows the part to be formed or shaped with minimal degradation to corrosion.
- Cobalt content and post treatment handling is extremely important
Electro Plating
Electroplating is the process of plating one metal onto another by hydrolysis, most commonly for decorative purposes or to prevent corrosion of a metal. There are also specific types of electroplating such as copper plating, silver plating, and chromium plating. Electroplating allows manufacturers to use inexpensive metals such as steel or zinc for the majority of the product and then apply different metals on the outside to account for appearance, protection, and other properties desired for the product. The surface can be a metal or even plastic.
Two coating weights are commonly used to meet the automobile industry’s requirements :
Grade A : coating weight > 24 g/m², average thickness 5 to 7 µm
Grade B : coating weight > 36 g/m², average thickness 8 to 10 µm
Greater coating weights may be applied to increase the duration of the corrosion protection
Types of Electroplating
There are different processes by which people can electroplate metals such as by mass plating (also barrel plating), rack plating, continuous plating, and line plating. Each process has its own set of procedures which allow for the ideal plating.
- Mass Plating–It’s not ideal for items that are detailed as it is not effective in preventing scratches and entanglement. However, this process plates a mass amount of objects efficiently.
- Rack Plating–More expensive than mass plating, but effective for either large or delicate parts. Often has parts submerged in solutions with “racks”.
- Continuous Plating–Parts such as wires and tubes are continuously passing anodes at a certain rate. This process is a bit cheaper.
- Line Plating–Cheaper, as fewer chemicals are used and a production line is used to plate parts.
ASTM Standards
B117 Practice for Operating Salt Spray (Fog) Apparatus
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B320 Practice for Preparation of Iron Castings for Electroplating
B322 Guide for Cleaning Metals Prior to Electroplating
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B499 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis Metals
B504 Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on Racks
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B602 Test Method for Attribute Sampling of Metallic and Inorganic Coatings
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Test Method of Variables Sampling of Metallic and Inorganic Coatings
B849 Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
B850 Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement
D3951 Practice for Commercial Packaging
Plating
Nickel Cobalt is an electroless nickel plating process, that deposits a true alloy of Nickel and Cobalt on metal surfaces. Because this process is electroless nickel cobalt, the plating is extremely uniform when used on complex geometries. This feature is not achievable with existing electroplating technology. The electroless nickel cobalt alloy deposit is highly corrosion resistant with the added benefit of exceptional wear and abrasion resistant properties.
Plating Electroless Nickel Cobalt is a precision plating process that can be used on close tolerance components for wear, corrosion, and anti-galling applications
Features/Benefits
- Exceptional Hardness
- Corrosion Resistance
- Good Lubricity
- Good Wear Properties
- Good Abrasion Resistance
Hardness
The hardness of electroless cobalt ranges from 120 to about 750 kg/mm-‘, dependihg on the phosphorus content and other factors. An increase in the hypophosphite concentration in the plating bath and an increase in the phosphorus content of the alloy increased hardness to the higher end of this A113range (35,80 Cobalt-nickel alloy deposits with a phosphorus content of 3.6 percent and a hardness of 450 to 480 kg/mm’ exhibited better resistance to wear than electroless nickel or cobalt coatings, when thickness was adjusted to 13 to 14 pm (82) However, both the nickel and cobalt coatings showed less wear than the alloy when thickness was in the range of 41 to 44pm