The common surface treatment for aluminum parts is anodizing. In order to overcome the defects of surface hardness and wear resistance of aluminum alloys, to extend the application range and prolong the service life.
When the aluminum alloy is in the environment of the corresponding electrolyte and suitable temperature, the aluminum product has an anode, and an applied current will form an oxide film on the surface of the aluminum product. We call this process anodizing.
Anodization can be distinguished into 3 types. Chromic anodized, Sulfuric anodized, and hard anodized.
Sulfuric anodized is the most common anodized aluminum and is also called standard anodization. It has a moderate thickness of 1.8 μm to 25 μm (0.00007″ to 0.001″). Chromic anodized is the thinnest anodizing film (The thickness is about 0.0001”) and the surface is relatively smooth which is produced using chromic acid electrolytes. Hard anodized can be made between 13 and 150 μm (0.0005″ to 0.006″) thick. Both sulfuric anodized and hard anodized use sulfuric acid electrolytes, but involves low bath temperatures, and the sulfuric anodized film is thinner and doesn't share the roughened surface of hard anodized. In this article, let's talk about standard anodizing and hard oxidation.
Hard anodizing is also called hard coating anodizing. It is in a special cold electrolyte, usually using acid solution, which cools to the freezing point of water, and the electric current increases greatly. Through electrolysis, a thicker and denser alumina anodic coating is formed on the metal surface than the standard anodizing. Hard anodizing can be achieved by lowering the temperature or the concentration of sulfuric acid. Whether a high-quality hard oxide film can be formed on the surface of aluminum and aluminum alloy depends on the composition concentration, temperature, current density and raw material composition of the electrolyte.
The coatings of hard anodization are thicker and have a strong hardness, around 400 to 600 HV. In addition, hard anodized aluminum components have strong wear resistance comparable to hard chrome and high-speed steel.
Hard-coated anodized aluminum has a good heat resistance and can withstand high temperatures up to 2000°C. This is why hard oxidation is commonly used in cookware products.
Hard coat anodizing produces a thicker anodic coating, which improves its corrosion resistance. The thicker the coating, the better the oxidation resistance.
1) Thickness
The thickness of the hard coat anodizing film is thicker than standard anodizing. Hard coat anodizing film generally＞15 microns while standard anodizing is about 10-12 microns.
2) Transparent or not
The film of the standard anodizing is basically transparent, but hard coat anodizing is non-transparent due to the thick film.
The standard anodizing surface is very smooth.
hard anodizing has a rough surface but is more abrasion-resistant. Also, hard coat anodizing has a more uniform surface.
1) Sealing or not
Hard anodized no need sealing environment this is because the thicker surface is more durable and wear-proof and uneasy to color erosion in colored products. While standard anodizing needs to be sealed to close the pores produced in the process of conversion to aluminum oxide and prevents color erosion in colored products. This is why standard anodizing porosity is high.
2) Temperature
Hard anodized usually needs lower temperatures and higher current density. Generally is below 5℃. Standard oxidation is 18-22℃ or so, and it hightest can go to 30℃ if with additives.
Standard anodizing is generally can be done in a lower concentration environment like chromic acid or sulfuric acid electrolytes. while hard anodizing generally can be done in oxalic acid, amino sulfonic acid, or adding organic acid into sulfuric acid solution and sulfuric acid.
Hard Anodizing and Standard Anodizing use in different fields. Hard anodizing mainly utilize in fields that need wear-resistant surfaces like food cookware, pans, and other consumer products. Also, it can be found in hydraulics, pistons, and other industrial products.
Standard sulfuric anodized aluminum is suitable for decoration and not needed for wear-resistant surfaces including in architecture, aerospace, and automotive industries.
The above is all about hard oxidation and standard oxidation. Dronecarbon can supply both. If you need more wear-resistant CNC aluminum parts, hard anodizing would be an ideal choice.
The price of hard oxidation will be a little more expensive than standard oxidation. We do standard anodizing treatment for our CNC aluminum parts by default. If you need hard anodizing, please let us know in the quotation stage.