Colour anodizing: what it is and how it is done
Various surface treatments can be used to improve the properties of metals. Among these, anodizing (or anodic oxidation) is undoubtedly the most useful and, above all, the most popular in industry. What does it involve? This special treatment protects metal surfaces from corrosion. In particular, it can be used to improve the properties of certain objects, generally those made of aluminium, but also others. Anodizing is a non-spontaneous electrochemical process that leads to the formation of a protective layer on the surface. With thicknesses ranging from 5 to 20 microns, it does not affect the size of the object, but makes the material much more durable and resistant.
Three phases in the process: preliminary treatment, electro-oxidation and colouring
There are three main steps involved in the industrial anodizing process. The first concerns preliminary treatments, starting with mechanical brushing and degreasing or etching, through to neutralization and pickling. Once this specific treatment has been completed, we move on to the actual anodizing process, in which an oxide film forms on the metal, making it porous. This porosity is precisely the ideal condition for the third step in the process: colouring. There are many areas in which colour anodizing can be used, from architecture to aeronautics, not to mention applications in electronics, transport and the industrial and private sectors.
Tones and aesthetic finishes: how the pigment bonds to the object
Colour anodizing can be done in a multitude of shades, covering practically the entire colour scale. More traditional colours can be chosen, as well as unique colours at your specific request. This step can also be preceded by aesthetic finishes, for example chemical etching or brushing, as well as micro shot blasting and chemical brightening.
We have mentioned that anodizing is mainly performed on aluminium alloys. Thanks to this particular process, the pigment will remain forever because it is trapped in the very surface of the treated part. Aluminium is anodized to increase resistance to corrosion, wear and abrasion.
There are many colours of anodized aluminium, including black, silver, blue, gold and, of course, red. Aluminium alloys are extremely ductile and light and are regularly used in a multitude of sectors, in everyday life as well as in industrial contexts. Colour anodizing is generally used for certain articles marketed to make a strong impact (designer objects and furniture design, for example).
How colour anodizing is carried out, step by step
The part is coloured simply by immersing it in specific colouring solutions. Parts can be coloured during the anodizing process to achieve a decorative effect. The colouring solutions enter the pores of the material, forming different chemical bonds. But what determines the choice of colour? It depends on the application, so certain colours are better than others, for example, if the object is to be used outdoors.
The anodizing layer must be about 15 microns thick to allow the colour to hold correctly, and the tone is influenced by the composition of the aluminium alloy. The colour ends up becoming an integral part of the object itself, not just a layer added on top of the layer of oxidation.
Colour anodizing of certain products enables certain decorative effects to be achieved, improving the appearance. Quality and durability as well as corrosion resistance are not affected or reduced in any way. The effect of the workmanship is not compromised. Instead, the object is given something extra, becoming more attractive and high-performing on the outside.
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