Anodizing & Coloring Rectifier

Working Principle

Anodizing is an electrochemical process where a metal part, typically aluminum, is immersed in an electrolytic bath and becomes the anode (positive electrode), causing oxygen ions to migrate to its surface and react to form a protective oxide layer, essentially creating a thicker layer of the metal's natural oxide on the surface, enhancing its corrosion resistance and wear resistance; this process often involves cleaning the metal surface before immersion, and the final step may include sealing the oxide layer to prevent further reactions with contaminants. Anodizing is a process that thickens the natural oxide layer on a metal part’s surface into an anodic oxide film. This extra thickness protects the part’s surface and improves aesthetics.

How does anodizing work?

The simplest way to understand how anodizing works is in the name. To anodize a part, you connect it to a positive terminal of an electrical circuit, also called an anode. You then submerge the part in an acidic electrolyte bath solution. This solution contains chemical compounds, such as sodium phosphate, which fill the bath with positive and negative ions.

Once the part is submerged and secured to a hanger so it doesn’t move around, you apply the negative end of the circuit, or cathode, to a metal electrode in the bath. When you send voltage through the circuit, the negative electrode attracts positive ions (cations) from the part, and the aluminum part attracts negative O2 ions (anions) from the solution.When positive aluminum ions leave the part’s surface, it becomes porous, reacting with the negative O2 ions to grow a layer of aluminum oxide.

Anodizing Finish Vs. Other Surface Finishes

Anodizing is similar to electroplating because they both use electrolysis. However, the key difference between both processes is that anodization forms a protective oxide layer in the alloy while electroplating deposits a secondary material on the workpiece/substrate.

The table below summarizes the anodizing vs powder coating;