Anodizing of aluminium and its alloys

In principle, the discovery of the anodic oxidation of aluminum and its alloys closely follows that of the metal itself.

As early as 1857, Buff discovered that aluminum formed an oxide when placed as an anode in an electrolytic cell. In 1911, De Saint-Martin proposed the basic principles of sulfuric anodizing. In 1923, Bengough and Stuart developed chromic anodizing.

Subsequently, numerous refinements to anodic treatment processes were introduced, taking advantage of the great diversity available in this field. By modifying electrolytes, operating conditions and treated alloys, a wide variety of surface properties can be achieved.

While aluminum and its alloys are widely used for their intrinsic properties (lightness, good corrosion resistance, thermal or electrical conductivity, etc.), it should be stressed that anodizing treatments can be used to add very specific properties, depending on the application:

• significantly improved corrosion resistance ;

• improved hardness and abrasion resistance ;

• reduced coefficient of friction ;

• thermal insulation ;

• electrical insulation ;

• possibility of coloring ;

• bonding base before organic coating or galvanic deposition, etc.

This is why anodizing processes are so widely used in industry today, for a wide variety of applications ranging from transport and construction to leisure, decoration, electronics, mechanical parts and cookware...

This article presents the various anodizing processes, their basic aspects and, for the most common ones, their industrial applications. The anodizing range must be considered in its entirety, which is why preliminary and subsequent treatments to anodic oxidation are also covered.

A glossary of terms is provided at the end of the article.