Metal Finishing

When it comes to the surface finishing of metal substrates, there are many different types of processes that can provide corrosion protection and wear resistance suitable for the needs of the part usage. It is important, meanwhile, to fully understand when one process should be used over another, and the benefits of those processes.

Many confuse the processes of electroplating, anodizing, conversion coatings and other various surface treatments. Each has its own benefit and specifications, and each are utilized for the same basic reason: to prevent the metal from deteriorating due to corrosion.


The electroplating process utilizes an electric current to dissolve cations that have a positively charged ion and deposit them onto an electrode as a thin coating. The plating processes uses an electrolytic bath that allows the electrical current to move ions to a metal surface to form the coating. There are several unique benefits of the electroplating process:

  • Corrosion Resistance: most substances that corrode can be coated with a layer of non-corrosive material such as zinc or nickel to form a protective layer.
  • Mechanical Durability: some malleable metals become more damage-resistant when coated with a second material, providing longer use time for the material.
  • Conduction: some metals have unique properties that allow them to transfer heat or even electricity, which can be used in electronics, aeronautics, automobiles and communications.
  • Heat Resistance: the aerospace and automotive industries utilize plated metals that have a high-heat tolerance and can withstand higher temperatures.
  • Cost-Effective: instead of using golf or silver, some parts can be made out of a less expensive metal and then coated with the more expensive metal.


The anodizing is different from electroplating in that, while plating is a thin coating of a metal on another metallic substance, anodizing actually changes the surface of a metal through an electrochemical process, but without changing the composition of the original metal. Parts being anodized use an electrolytic passivation process to increase the thickness of the natural oxide layer on the surface of metal parts, which results in a layer that is much higher in corrosion and abrasion resistance. While the plating process can often use toxic materials, anodizing is a safer process, while also being chemically stable and heat-resistant to the melting point of aluminum. As with electroplating, the anodizing process has numerous benefits:

  • Corrosion Resistance: the process has a longer life span, as it creates a layer of aluminum oxide that protects the aluminum underneath it.
  • Mechanical Durability: a complete bond and adhesion is created with the underlying aluminum, giving it greater durability and less maintenance to restore to its original appearance.
  • Stability: colors are more stable to ultraviolet rays, and do not chip or peel. The anodizing process allows coatings to be easily repeated.
  • Cost-Effective: the aluminum substrate has a relatively inexpensive cost and requires less maintenance costs.
  • Decorative or Ornamental Purposes: the finished coating has the ability to maintain its glossy, metallic finish and usually eliminates color variations, too. A clear coat can be added giving a lustrous quality to the product.

Conversion Coatings

For a number of metals, conversion coating is considered an alternative to anodizing. They are formed by immersing metallic parts into a chemical solution, which results in the growth of a coating layer from the substrate surface that is an integral part of the component surface, and not just deposited over the surface. Conversion coatings are applied to metals to either improve corrosion resistance, promote organic coating adhesion or do both. The coatings improve the paint adhesion capacity on zinc surfaces after preparation, and prevents the formation of “wet storage” staining and paint bonding to zinc-coated steel.