Characteristics of Hard Anodic Oxidation Coating

The main purpose of Hard Anodic Oxidation Coating is to improve the properties of aluminum and aluminum alloys. Including corrosion resistance, wear resistance, weather fastness, insulation, and adsorption. It is suitable for extruding aluminum alloy and casting aluminum alloy parts.

This article introduces the series:

• Characteristics of Hard Anodic Oxidation Coating
• Working Principle of Hard Anodic Oxidation
• Difference Between Hard Anodic Oxidation and White Anodizing
• Several Classifications for Hard Anodic Oxidation Treatment of Aluminium Profiles
• Precautions for Hard Anodic Oxidation Staining of Aluminium Profiles

Industrial aluminium profile’s hard anodic oxidation coating compared with ordinary oxide film has the following characteristics: thicker oxide film (average thickness is not less than 25 um), more hardness (more than 350 hv), good wear resistance, low porosity, high breakdown voltage, resistance and surface smoothness may appear less.

There is no essential difference in the principle, equipment, process and detection of hard anodic oxidation and general oxidation. Hard oxidation can reduce the dissolution of the oxide film. The main features are:

1. The bath has a low temperature (about 20 degrees or less), and the oxide film with low temperature is generally high;
2. Low concentration of tank (20% of normal sulfuric acid concentration and less than 15%). Low concentration of concentration is low in membrane solubility;
3. Organic acid is added in the tank, and oxalic acid or tartaric acid in sulfuric acid;
4. Extra voltage and current high (ordinary current 1.5a/dm2, voltage 18V, hard current 2~ 5A/dm2, voltage 25V above.Up to 100V).

Foundry industry industrial aluminum profiles usually need to hard anode oxidation to improve its performance. Aluminum casting industry commonly used industrial aluminum-silicon alloy and industrial aluminum/copper alloy. Industrial aluminum silicon has good casting properties and wears resistance and dosage the biggest, widely used in the structure and components. Sometimes adding copper and magnesium to improve mechanical properties and heat resistance.

The industrial aluminum profile copper series is also commonly used as casting alloy, which is mainly used to withstand large static load and uncomplicated sand type castings. Aluminum casting industry because contain nonmetallic elements such as need of electrolyte and power waveform was improved, the electrolyte can generally add some metal salt or organic acid in sulfuric acid, sulfuric acid, oxalic acid, tartaric acid solution, acid – dry oil solution; In general, the power supply is changed to dc superposition, asymmetric current, pulse current, etc., and the pulse effect is better. Before the oxidation of the electric casting, the rhomb guide garden and the removal of the burrs should be used to prevent the concentration of the current.