• 21 April 2024

Anodized aluminum helps prevent oxidation of aluminum in the open air and protect it from possible mechanical damage. The anodized coating makes an aluminum product, such as aluminum sheet or aluminum profile, paintable.

What is aluminum anodizing?

Aluminum anodizing or anodic oxidation is the process of forming an oxide layer on the surface of the metal. In general, the technical operation goes as follows: the aluminum product is immersed in a container of acidic electrolyte, usually a solution (250-300 g/l) of 20% sulfuric acid, and connected to the positive pole of a current source with a density of 10-50 mA/cm 2 at a source voltage of up to 100 V.

Anodizing is a chemical process that results in the formation of a protective layer on the surface of the workpiece. Unlike most metalworking processes such as annealing, tempering, normalizing, galvanizing, etc., anodizing does not require heating the workpiece and therefore does not change its properties. Anodizing aluminum is usually carried out by electrolysis, in which oxides from the electrolyte are deposited on the aluminum workpiece. Oxide ions from the electrolyte are deposited on the aluminum workpiece, forming an anodic layer that protects it from corrosion and enhances its aesthetic qualities. The process of anodizing aluminum can be divided into five different stages: cleaning, etching, anodizing, painting and sealing. Typically, an overhead crane is used to move large items from one stage to the next, while small items are handled by hand.

The temperature range during this process can vary from -20 o C to +20 o C. The chosen temperature directly affects the density and shade of the future oxide layer: when it is positive, the layer is loose and thin, easy to paint with any dye. At minus temperatures - the layer is thick and has a natural color (yellow tones).

Anodizing methods

The anodizing process itself can be done in three ways:

- Heat anodization of aluminum - this technology is relatively simple. One electrolyte (sulfuric acid) is used. The process is carried out at room temperature using organic dyes. Among other things, this method makes it possible to obtain the desired color coating. It is even possible to obtain several shades of color on a single surface. The aluminum product, previously degreased, is hung and carefully fixed, anodized to a milky color, and then washed in cold water. Dyeing is carried out in a hot solution.

- Cold anodizing - is carried out at temperatures from -10 o C to +10 o C. One electrolyte (sulfuric acid) is used. The use of organic dyes is impossible, and coloring occurs naturally. The final color depends on the composition of the aluminum alloy and can range from green to black. In this case, the aluminum product is degreased, hung and carefully fixed, anodized to a thick layer, washed with hot or cold water and fixed by boiling in distilled water. Important: to obtain a hard and wear-resistant coating, the product must be thoroughly cooled.

- The process of hard anodizing is the technology with the greatest application in industry. A characteristic feature of this method is the use of several electrolytes (sulfuric acid, boric acid, acetic acid or oxalic acid). The density of the electric current gradually increases and entails a change in structure, leading to the formation of a film with increased strength.

Advantages of anodized aluminum

Aluminum has excellent technical properties: high thermal and electrical conductivity, corrosion resistance, ease of processing. Despite these properties, corrosion of aluminum is still possible. Anodizing makes it possible to increase the metal's resistance to corrosion so that it can be used in aggressive environments. In addition to increasing the durability of the anodized coating, the process has a number of other advantages:

- Increased resistance to wear and corrosion.

- High thermal insulation properties.

- Increased resistance to weathering.

- Delayed corrosion of aluminum and resistance to cracking.

- Resistance to increased loads.

- Decorative appearance.

- Ease of processing.

It is worth noting that anodized aluminum is an environmentally friendly material that does not emit harmful gases even when exposed to UV rays. In turn, the durability of the anodized coating allows it to be used more widely.

Application of anodized aluminum

Resistance to increased loads and light weight make anodized aluminum an excellent alternative to heavy metals. And because of its resistance, anodized aluminum is in demand in the shipbuilding industry - ship window profiles are made exclusively of anodized aluminum. In addition, parts made of aluminum that have been anodized find applications when it comes to:

- Lighting equipment.

- Design and architecture.

- Construction: glazing of facades, roofs, etc.

- Production of household appliances, acoustic systems.

- Manufacturing of mobile devices.

- Production of furniture.

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