A Quick Look at 6 Standard Mechanical Sheet Metal Finishes

May 20, 2016 | Sheet Metal Fabrication, Mechanical Engineering

Sheet metal forms can be processed and finished in a number of different ways.The process of applying a specialized finish to manufactured metal products is nothing new. Generations of manufacturers large and small have applied different finishing processes to metal products to enhance their corrosion resistance, impact/scratch resistance, and other properties.

However, as manufacturing science evolves, so too do the processes by which finishes are applied to metals. There are a number of different types of finishes that can be applied to sheet metal products.

Here are a few brief notes on some of the “standard” mechanical sheet finishes:

Passivated Finishes

By exposing some metal alloys to a citric and/or nitric chemical bath, iron and sulfuric contaminants on the surface of the metal can be stripped away. This process leaves a uniform layer of protective oxide film on the surface of stainless steels, improving their inherent corrosion resistance.

Passivation is often used as a first step to prepare stainless steel for coating with other materials.


This process is closely related to passivation, using a similar method and achieving similar results for improving the protective oxide layer in stainless steel materials.

Here, the workpiece is dipped in a chemical bath, just like with other passivation techniques. The primary difference is that the chemical bath is connected to a DC power supply. An electric current is run through the bath, dissolving the top layer of metal.

The end result is a microscopically smooth, clean surface that has an enhanced chromium/nickel content.

Electroplate Finishes

Technically, this could be categorized as a coating rather than a finish. Electroplating typically involves passing metal objects through a solution containing metal ions and using an electric charge to bond the metal ions to the surface of the metal object.

Electroplating can change the mechanical properties of the sheet metal being coated in different ways depending on the metals being used. In many cases, electroplating is used to enhance the corrosion resistance and useful life of the base material (chromium is often used for this purpose).

Electroless Plating Finishes

Similar to electroplating, electroless plating adds a thin layer of material to the surface of the workpiece. The main difference is that rather than using an electrical current to bond the two materials, a chemical reaction is used instead.

Case Hardening

Case hardening is a common process in manufacturing with steel, dating back hundreds of years. By heating a metal, shaping it, and then quickly cooling it, the surface hardness of a metal can be enhanced while leaving the core of the metal relatively pliable.

One issue with this technique is that some metal alloys react differently to rapid heating and cooling compared to others. It can change the magnetic properties of some metals, or even weaken some alloys. So, case hardening isn’t always a viable option.

Many of the above finishes/processes can produce different results in different metal alloys, so it’s important to review with an experienced mechanical engineer before settling on one process for your custom sheet metal forms.

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