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Hard anodizing

Hard anodizing

Functional refinement of aluminium parts as anode in special electrolytes.

What is so special about these layers?

What is so special about these layers?

These layers involve so-called conversion layers. Particles of the base material become incorporated into the layer, which results in the enormous adhesive strength of the anodic layers.


CompCote® is an aluminium oxide polymer composite coating with pioneering properties. CompCote® coatings are formed by anodic oxidation of the base material and simultaneous molecular bonding of the aluminium oxide layer to polymers. The layers grow into and out of the base material, resulting in an optimal bond with the base material. Due to the molecular polymer content, CompCote® offers chemical bond bridges with a coordinated choice of top coats, so that a very good bond strength is achieved here as well.

The process is patented in Europe, the US and other countries, and classified as safe for contact with food by the US Food and Drug Administration (FDA).

  • Properties

    Based on the very hard aluminium oxide, CompCote® has a high hardness. It is alloy and process dependent. The coating demonstrates excellent wear resistance in the Taber Abraser test, which can be better than conventional anodisation coatings. CompCote® is corrosion resistant and outperforms normal anodising layers through the presence of molecular polymers. CompCote® produces a fibrous fracture pattern in the notched-bar impact test. In contrast, conventional oxide layers break like brittle glass.

    CompCote® roughens the surface comparatively little and has an optimised microstructure. In various friction pairings and friction tests, the composite coatings show very good anti-seizing properties. Sometimes the friction values even decrease with repeated trials (self-smoothing effect). Stick-slip effects are reduced.

    CompCote® is excellent for colouring. Standard colours are black, titanium grey, blue, red, gold and green. The coloured surfaces are more lightfast than coloured standard anodised coatings.

    In addition to the CompCote® process, there is also CompCote®-H, which is characterised by higher hardness as well as better wear and corrosion properties.

  • base material

    CompCote® is suitable for almost all aluminium alloys.

  • Application

    Low density aluminium combined with CompCote® opens new avenues in technical and decorative applications with increased quality requirements.

    CompCote® has no influence on the bending fatigue strength of the base material. This property makes the coating interesting for aerospace applications.

    Examples of other areas of application in which CompCote® is successfully used are: architecture, automotive industry, electrical engineering, photographic and video technology, household appliances, hydraulics, information technology, hunting weapons, food industry, mechanical engineering, medical technology, pneumatics, sporting goods, packaging machines, defence technology.


As early as the early 1960s, AHC laid the foundation for hard-anodising in Germany with the introduction of the HART-COAT® process. HART-COAT® (or HC) is a specially developed coating for the functional finishing of aluminium materials (also called hard coating). With the help of electric current, the workpiece surface transforms into a hard, ceramic-like aluminium oxide layer. This aluminium oxide layer builds up in the form of regular hexagonal cells, which stand like honeycombs perpendicular to the workpiece surface. The workpiece is thus primarily protected against wear and corrosion.

Hard coating is a particularly versatile hard-anodising coating with different process variants and post-treatment options. Every year, more than half a billion components are hard-coated by AHC to ISO 100 74 standards.

  • Properties

    HART-COAT® layers are very wear resistant and hard as a consequence of the morphology of the aluminium oxide. During hard coating, half of the oxide grows into the base material and half outwards. As a result, the bond between the layer and the base material is exceptionally high. The ceramic-like HART-COAT® layer is a good electrical insulator and has a low thermal conductivity and high dielectric strength. As a protective layer on engine piston bases, it can withstand extremely high temperatures in the short term.

    Special post-treatments make it possible to adapt HART-COAT® coatings to special requirement profiles such as increased wear and corrosion resistance or improved anti-friction properties.

  • base material

    Almost all technically interesting aluminium alloys, be they wrought alloys, cast alloys or die-cast alloys, can be finished with HART-COAT ®.

    With components that are being delivered for coating, please note the following:

    • no material, machining or surface defects
    • as free from oil and residue as possible
    • part-specific protective packaging where possible
    • the pre-coating operation should be machining
    • no foreign bodies in the workpiece surface
    • edges and corners well deburred and as rounded as possible
    • tolerances must be taken into account
    • vent holes may be necessary
  • Application

    Due to its good wear resistance, a hard-coated aluminium material can replace expensive wear-resistant steel. The same applies to the replacement of expensive corrosion-resistant materials. Potential applications are where contact corrosion should be prevented, anti-friction properties improved, electrical or heat insulation increased.

    The density of aluminium alloys is about one third of the value of conventional ferrous and non-ferrous metals. By switching from steel or brass to aluminium materials, inertia forces of high-speed machine parts can be substantially reduced. This results in new constructional options and savings in energy costs. The required surface durability is achieved by using HART-COAT®.

    Examples of HART-COAT® hard-anodised components are: spacers, iron soleplates, surgical instruments, damping chambers, nozzles, guide cylinders, housings, fixings, levers, heating plates, insulating bolts, camera parts, rocker arms, clamps, pistons, clutch parts, bearing rollers, bearing shells , baffles, guide rollers, mounting plates, cam discs, pneumatic and hydraulic cylinders, rollers, spools, transport levers, valves, compressor wheels, gears wheels and racks, centrifuges, cylinder heads, cylinder tubes.

    The industrial sectors using HART-COAT®-finished components include, amongst others: gauge construction, automotive, mining, office technology, data technology, energy technology, household appliance industry, food industry, mechanical engineering, medical device construction, measurement technology, pharmaceutical industry, reactor technology, control technology, defence technology.

Product enquiry

If you would like to tell us something about the product presented here, you are welcome to do so. Your enquiry, your comment, your wishes will be forwarded directly to your personal contact person.

More Surface Treatments

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