Skip to content


Hard anodizing for marine engines: an effective treatment for corrosion protection

Hard anodizing for marine motors-blue

Our Opera (Milan) production plant, specialised in technical anodizing and hard anodizing, was recently contacted by one of the leading international manufacturers of marine engines. After verifying the superior corrosion resistance of its sterndrives compared to those of competitors, the company requested our support to further improve the corrosion resistance of its products.

It is important to remember that the marine environment is damaging for most materials and aluminium alloys used for marine engines are no exception. Specific anodizing treatments are required to prevent corrosion and extend the life of engines. This involves controlled oxidization, creating a protective layer of aluminium oxide on the surface of the metal.

For sterndrives, a process called “hard anodizing” or “hard coating” has been chosen, which is particularly effective in cases requiring maximum resistance to wear and corrosion of moving parts in very aggressive environments. This is achieved by creating a thicker and more resistant layer of aluminium oxide compared to other forms of anodizing.

Hard anodizing involves the creation of a hard oxide layer on the aluminium surface by passing electrical current through tanks at sub-zero temperatures.

This process greatly increases surface hardness and reduces roughness, with a consequent increase in corrosion resistance, improved insulation, thermal stability and anti-friction properties.

The layer of aluminium oxide created by hard anodizing can be vary in thickness from 20 to 50 microns (compared to 5–20 microns with standard anodizing), but in specific cases a thickness of up to 100 microns can be achieved.

Once the component has been anodized, it can be painted. The aluminium oxide created by hard anodizing offers an ideal surface for painting, because its porous nature enables better adhesion of the paint. Painting not only improves engine aesthetics but also creates an additional layer of corrosion protection.

However, due to the structure of a sterndrive, there are certain areas of the surfaces to be treated that require greater attention during the anodizing process. These small areas, such as those covered by caps, are not easily accessible with standard anodizing processes and therefore require an additional and more accurate treatment to guarantee full protection of the surface.

Adopting these specific measures, using the best technology and advanced systems and careful controls on the finished product, mean that hard anodizing is definitely the best surface treatment for marine engines, because it can help to extend product life and aesthetics, even in the most challenging environments.