What Are Metal Finishing Coatings and Why?

Purpose of Metal Finish

The purpose of metal finishing is to provide a sacrificial and barrier coating over a metal substrate for the purpose of either corrosion protection or cosmetics.  

Chem-Plate Industries focuses primarily on sacrificial corrosion protective coatings over ferrous metal parts, though many coatings also provide a decorative quality.

2 Types of Corrosion Protection

There are two types of corrosion protection coating mechanisms in general use in the industry.

1 - Protective Barrier Coating

The first type is a protective barrier coating that covers the steel, including some kinds of paint and oils. The barrier coatings can be applied by spraying or dipping.

Once a barrier coating is damaged, the base metal will immediately begin to corrode.

2 - Sacrificial Coating

The second type of corrosion protective coating is known as a sacrificial coating.

In essence, when a steel part is coated with a sacrificial coating the coating material itself begins to corrode before the underlying steel and the steel will not corrode until the coating is completely gone.

Examples of sacrificial coatings are:

• Zinc and Zinc alloy electroplating

• Mechanical Zinc alloy plating

• Thermal Diffusion Zinc/Iron (ArmorGalvR)

The corrosion resistance of these coatings can be augmented with the further application of passivates and topcoats.  Other properties can be enhanced, such as color, wear resistance, and coefficient of friction, as well as aesthetics.

When the barrier coating is damaged or compromised, the exposed steel begins to corrode immediately.

When the sacrificial coating is damaged or compromised, the exposed steel does not begin to corrode until all of the sacrificial coatings are corroded away.

SACRIFICIAL COATINGS

• Zinc

• Zinc/Iron Thermal Diffusion

• Zinc/Nickel

• Cadmium

• Aluminum

• Magnesium

BARRIER COATINGS 

• Paint

• Nickel

• Copper

• Brass

• Tin

• Silver

• Gold

A sacrificial coating may be further protected with an additional barrier coating to further enhance corrosion resistance; or, add mechanical properties such as lubricity, scratch resistance, and decorative colors. See the Spec Approvals page for process packages that contain both a sacrificial coating and barrier coating, such as GMW 4205.

As a quality-conscious, service-oriented, commercial heat-treating and plating company for the fastener industry, our products are regularly used by companies all over the world, including, but not limited to:

• Chrysler

• Ford

• GM

• Daimler

• Toyota

• Nissan

• Honda

• Tesla

• John Deere

• U.S. Air Force

• U.S. Navy

• Continental Teves

• U.S. Army

• GE

• Siemens

• Akebono