Hard Anodizing

Basics

Hard anodizing is a coating developed especially for the functional improvement of aluminum materials.

Coating takes place in a cooled acid electrolyte. In this case the workpiece is connected in series as an anode and oxidized in the course of the treatment. As a result of the oxidation the surface of the treated workpiece changes into a ceramic-like layer. This aluminium oxide layer is composed mainly of amorphous y-aluminium oxide, it takes the shape of regular cells vertical to the workpiece surface, encases the workpiece and protects the workpiece against wear and corrosion.
Hard Anodizing
Hard anodizing surface treatment plant.
 

Properties

The properties of the hard anodizing layer can be adapted to the type of material being treated by means of variable process parameters according to the specific requirements.

Wear resistance and hardness

The great wear resistance is due to the hardness and morphology of the aluminum oxide, which is alloy-dependent. The hardness layer depends on the composition and structure of the base material and it varies between 400 and 500 HV 0.025.

Heat conductivity

The heat conductivity amounts to about 1/10 to 1/30 of the heat conductivity of the base material.

Temperature resistance

The layers can resist for short spans of time to temperature peaks of up to 2,200°K.

Electrical resistivity

The electrical resistivity amounts to 4.10 to the power of 15 Ωcm at 20°C, 0.8×1015 Ω cm at 100°C and 0.11×1015 Ω cm at 200°C.

Electric strength

The electric strength is alloy-dependent and it increases with the layer's thickness but not proportionally. The arithmetical mean value of 10 single measurements according to ISO 2376 amounts to 914 V with 30 µm of HC on AlMgSi1 and 1213 V with 50 µm of HC on AlMgSi1.

Color

The colors range is depended by alloy and thickness. From grey-brown to black, greenish grey to dark grey or golden yellow to greyish yellow.

All technical values published here are subject to the test conditions specified. We therefore empasise that the applications and operating conditions, along with the end user’s practical experience, will ultimately determine the level of performance achieved by the coating and/or coating system.

Hard Anodizing
 

Materials

Hard anodizing is an especially versatile coating. By means of various process variants it makes it possible to coat almost any aluminum wrought, cast and die-cast alloys.
Hard Anodizing
Gears for automotive sector with Hard Anodizing.
Hard Anodizing
Carbon mold coated with a 50µm HC/PTFE layer for mold releasing.
Hard Anodizing
Machinery part with a 50µm thick layer.
 

Applications

Hard Anodizing gives aluminium materials a wide array of functional properties. Thus the hard anodizing coating allows the use of products made with these materials in the most diverse sectors.
  • Mechanical engineering
  • Metal fittings sector
  • Automotive sector
  • Mining
  • Office and data technology
  • Energy and reactor technology
  • Household appliance industry
  • Food processing industry
  • Medical technology
  • Measuring and control technology
  • Pharmaceutical industry
  • Defence sector
Hard Anodizing
G5 Chuck plate for TFT industry is protected against wear and ESD by 50µm HC/PTFE layer.
 

Post-treatment

Special post-treatment enable anodizing layers to fulfill particularly demanding specifications with respect to, for example, increased wear and corrosion resistance or improved anti-friction properties.

PTFE

HC/PTFE consists in impregnating an hard anodizing layer with PTFE (polytetrafluoroethylene). It improves the anti-friction and corrosion properties of the treated workpiece. Moreover, the PTFE particles in the layer allow optimal dry lubrication without any additional layer build-up. In the case of abrasive wear the anti-friction properties of the coating remain unaltered.

 

Hot water sealing

The anodizing layer consists of aluminum oxide in the form of regular cells and each cell has a pore. The sealing of a coated workpiece is usually carried out in deionized water, generally without the addition of condensers, within a temperature range of 96 and 100 °C. This way the pores in the anodizing layer are sealed and the already good corrosion resistance is further increased.