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Aluminium Anodizing Services Process Flow

The general process of anodizing aluminum and aluminum alloys can be roughly divided into pre-treatment, anodizing, and post-treatment (non-decorative products can skip coloring).

Pre Anodized Aluminum Process

Mechanical pre-treatment usually serves two purposes: firstly, improving good surface conditions for subsequent anodizing; secondly, providing various surface decoration effects, such as glossy, matte, brushed, etc. Mechanical pre-treatment includes sandblasting, polishing, brushing, rolling, etc.

Aluminium Anodizing Degreasing

The purpose is to remove surface oil stains from previous processes such as stamping, CNC or polishing. If there are organic substances such as oil stains on the metal surface, it will affect the smoothness, bonding strength, corrosion resistance, etc. of the oxide layer. Moreover, it may lead to incomplete or loose deposition, even the peeling off of the oxide layer. Therefore, degreasing is very important before anodizing.

Aluminium Anodizing Alkaline Etching

Also known as alkaline stripping, the purpose is to remove the dense but uneven natural oxide film before anodizing aluminum and its alloys, leaving a pure aluminum substrate.

Aluminium Anodizing Ash Removal

The process of anodizing ash removal is also called neutralization or polishing treatment. As sulfuric acid or nitric acid is generally used for ash removal, it is also called acid washing. After alkaline etching, there may be a layer of gray-black ash on the surface of aluminum alloys, which is commonly referred to as "ash hanging." The reason is that aluminum alloys may have other insoluble adherents generated from iron, manganese, copper, silicon, etc. during alkaline etching, leaving it on the surface of workpieces. The purpose of ash removal is to remove the black ash layer on the surface of workpieces to obtain a brighter metal surface. At the same time, it can also neutralize the alkali remaining after alkaline etching to prevent polluting the electrolyte.

Aluminium Anodizing polishing

Here refers to chemical polishing, a method that selectively dissolves the concave and convex areas on the sample surface by the chemical etching effect of chemical reagents (acidic or alkaline) to eliminate scratches, immersion and planarize. It is used to eliminate mechanical defects on the workpiece surface, reduce surface roughness, and improve surface gloss.

Chemical polishing is divided into acidic and alkaline chemical polishing. Since aluminum can be dissolved in both strong acid and strong alkaline solutions, the chemical polishing of aluminum and its alloys is divided into acidic and alkaline chemical polishing. However, alkaline solution has a faster corrosion rate, larger weight loss, larger dimensional change, and difficult to achieve high brightness effect. It is not suitable for processing after mechanical polishing. But for workpieces after sandblasting, polishing has certain practical significance. Therefore, alkaline polishing is generally used for profiles or workpieces after rough processing. For workpieces requiring precision or glossiness, acidic polishing is generally selected.

Mechanical polishing cannot be directly used for anodizing, especially for bright anodizing. Although the aluminum alloy workpiece has obtained a bright surface after mechanical polishing, it is often difficult to maintain the polished gloss if the polished workpiece is directly anodized. Only a smooth surface can be obtained, but not a film layer with a higher reflection coefficient. This is mainly due to the uneven surface pressure during mechanical polishing, leading to the formation of a crystal deformation layer on the workpiece surface. Therefore, the workpiece after mechanical polishing must also undergo chemical polishing or electrochemical polishing to remove the crystal deformation layer formed during mechanical polishing and obtain a bright and delicate surface.

Ash removal after polishing: Since aluminum alloys generally contain copper, magnesium, silicon, and other elements, the workpiece surface is corroded and discolored after chemical polishing, thereby forming a uniform black floating ash. Therefore, ash removal treatment is required after polishing.

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