When you are demanding more thick and durable CNC aluminum parts, hard anodizing is an ideal choice, its production process differs from standard anodizing. Here we'll present what is hard anodizing, some properties of hard anodized aluminum and the difference between hard anodized and anodized. 

What is Hard Anodizing and How Hard Anodizing Process is Done?

Hard anodizing is a functional refinement term, also known as hard coat anodizing, refers to the process of anodizing aluminum parts in a special cold electrolytes, which is the acid solution that cooled to the freezing point of water and the amount of electric current increased substantially, for creating a non-metallic conversion coating thicker than standard anodizing. Hard anodizing can be realized by reducing the temperature or the sulfuric acid concentration. Whether a high-quality hard oxide film can be formed on the surface of aluminum and aluminum alloy depends on the composition concentration of electrolyte, temperature, current density and the composition of raw materials. The advantages or benefits of hard anodizing including low cost, light weight, enhanced performance, and appearance. 

How Thick is Hard Anodized?

Generally, the thickness of the hard anodizing coating is required to be 25-150um, most of which are 50-80um. The hard anodized aluminum parts with thickness less than 25um are used for tooth key, spiral and other occasions The thickness of anodizing parts for wear-resistant or insulation is about 50um. Under some special process conditions, it is required to produce a hard anodizing film with a thickness of more than 125um. However, the thicker the anodized coating is, the higher the surface roughness of the film is.

The Hardness of Hard Anodized Aluminum

Hard anodizing generating a coating of aluminum oxide on the surface of machining aluminum parts and components, increases the hardness and makes the aluminum alloy is more wear-resistant, abrasion-resistant and corrosion-resistant. When the hard anodize at its optimal thickness (measured up to Rockwell 70C), the hardness of the aluminum oxide equivalent to the surface of case-hardened steel.

The Difference Between Hard Anodized and Anodized

1. Thickness and appearance. The notable difference between anodized and hard anodized is the thickness. Hard anodized aluminum is thicker than standard anodized, which gives the surface of hard anodized aluminum part higher abrasion resistance. It also has a more uniform surface than regular anodized aluminum.

2. Production condition. When the thickness greater than 25 microns, the hard anodizing coating is produced in lower temperatures and higher current density.

3. Electrolytes. Standard anodizing can be done in chromic acid or sulfuric acid electrolytes, while hard anodizing generally uses the sulfuric acid solution and sulfuric acid added with an organic acid, such as oxalic acid, aminosulfonic acid, etc.

4. Sealing. Standard anodized aluminum needs to be sealed to close the pores produced in the process of conversion to aluminum oxide. While hard anodized aluminum does not need because its thicker oxide layer is more durable and wear-resistant. 

5. Application. Hard anodized aluminum products are suitable for applications and environments that require a heavy-duty, wear-resistant surface, such as hydraulics, pistons, some food cookware, pans, and exterior of buildings. Hard anodizing can be found more in industrial or commercial applications than in consumer products. Standard sulfuric anodized aluminum is applicable for architecture, aerospace and automotive industries.