What is Anodizing? – Requirements, Process, Advantages & Applications

The process of deposition of an oxide film on a metal surface is known as anodizing. The anodizing is an electrolytic passivation process, mainly used to increase the thickness of the natural oxide layer on the surface of the metal.

This process is called anodizing because the metal part to be treated forms the anode electrode of the electric circuit of the process. The anodizing increases the corrosion resistance and wear resistance and provides better adhesion for paint primers and glues as compared to the bare metal.

Requirements of Anodizing

The anodizing of metals is used for the following requirements −

• To provide the protective coating on the metallic surface.

• For the attractive appearance and the shining of the surface.

• To obtain the various desired color effects of the base metal.

Process of Anodizing

The process of anodizing involves four steps that are described below −

Step 1 – Pre-Treatment of Metal

The first step of anodizing involves the pre-treatment of the metal through degreasing and pickling and providing a visible finish on the metal surface.

Step 2 – Anodic Oxide

In this step, the material being treated is submerged in an acid electrolyte bath while an electric current passes through it. The metal to be treated acts as an anode, so that the oxygen ions are released and combine with the metal atoms at the surface.

Step 3 – Color Anodizing

This step involves immersing the anodized metal in an inorganic metal salt bath. An electric current is passed through this bath so that the metal salts oxidize in the pores of the metal. The metal color will vary depending upon the chemical conditions of the bath and the length of time of immerge.

Step 4 – Sealing

The final step of anodizing is known as sealing. Sealing is the process that prevent the corrosion and water leakage of the metal. Sealing also prevents any scratching or straining of the metal surface.

Advantages of Anodizing

The anodizing of the metal has several advantages which are described below.

• Durability – The anodized products have an extremely long life and provides economic advantages through operating and maintenance savings.

• Color Stability – The exterior anodic coating provides good stability to UV rays and does not peel.

• The anodic coatings are easily repeatable.

• The anodic coatings provide ease of maintenance, i.e., a mild soap and water cleaning will restore an anodized surface to its original appearance.

• Anodizing offers a large number of gloss and color alternatives and minimizes the color variations.

• Anodizing provides low initial finishing cost along with low maintenance cost.

• Anodizing is a safe process which is not harmful to human health and it is also chemically stable.

Applications of Anodizing

The anodizing process is commonly used for anodized finishing of −

• Structures and architectural categories of all types.

• Appliances and furniture

• Jewellery and artworks

• Motor vehicle components

• Commercial and residential building products

• Food preparation equipment

• Sporting goods and boats, etc.