HART-COAT® (Hard coating)

HART-COAT® (abbreviated to HC) is an electrolytic coating that has been specially developed for the functional finishing of aluminium materials. The process is also known by the generic terms anodising, hard coating and hard-anodic oxidation.

HART-COAT® layers are produced in a cold acid electrolyte. The aluminium workpiece to be coated is connected as an anode to a power source and immersed in a coating bath filled with electrolyte fluid. At the edge of the coating tank is a cathode. Under the influence of electric current a hard, ceramic-like aluminium oxide layer is formed on the workpiece surface, and is tightly bonded to the base material by atomic bonding forces. Therefore HART-COAT® layers have good adhesion to the base material. This aluminium oxide layer consists of regular hexagonal cells, which are perpendicular to the workpiece surface. Each cell has a pore which can be used for subsequent sealing of the layer. Finishing of an aluminium workpiece with the HART-COAT® process is carried out according to the ISO 100 74 standard.

HART-COAT® layers have remarkable properties, especially a good wear and corrosion resistance.

Hardness and morphology of the aluminium oxide will depend on the alloy of the base material. The achievable hardness of the HART-COAT® layer is dependent on composition and structure of the base material being between 400 and 500 HV0,025. Along with the hardness and morphology of the aluminium oxide produced there is also great wear resistance.

The thermal conductivity of the layer is about 1/10 to 1/30 of the thermal conductivity of the base material. Brief temperature peaks are not a problem for HART-COAT® layers, as long as they do not exceed 2,200 K.

At 20°C electrical resistivity is 4×1015 Ωcm. At higher temperatures it decreases slightly. The electric strength depends on the alloy of the base material. It increases with the layer's thickness but not proportionally. Measurements according to ISO 2376 establish an arithmetic mean electric strength of 914 V for a layer thickness of 30 µm HC on AlMgSi. For a layer thickness of 50 µm HC on AlMgSi1 the value rises to 1213 V.

Please note that all technical values listed here are subject to the test conditions specified. We therefore expressly point out that different conditions of use and the practical experience of the end users will determine the performance of the coating or the coating system.

Almost all wrought, cast and die-cast aluminium alloys which are of technical interest can be hard coated.

HART-COAT® coated materials are used in diverse industries: valve manufacturing, automobile manufacturing, mining, office and data technology, energy and reactor technology, household appliance industry, food industry, mechanical engineering, medical equipment manufacturing, measurement and control technology, pharmaceutical industry or defence technology.

Application examples include

  • Baffles
  • Bearing cups
  • Bearing rollers
  • Cam discs
  • Camera parts
  • Centrifuges
  • Clamping or holding devices
  • Compressor wheels
  • Coupling components
  • Cylinder heads
  • Cylinder tubes
  • Damping chambers
  • Gear wheels and gear rods
  • Guide cylinders
  • Guide rollers
  • Hot plates
  • Housings
  • Iron sole plates
  • Isolating bolts
  • Levers
  • Mounting plates
  • Nozzles
  • Pistons
  • Pneumatic and hydraulic cylinders
  • Rocker arms
  • Rollers
  • Spacers
  • Spools
  • Surgical instruments
  • Transport levers
  • Valves

HART-COAT® is a particularly versatile hard anodisation with different process variants and post-treatment options.

HART-COAT®-process variants from AHC Hangzhou

HC For wrought aluminium alloys as well as sandcast and permanent mould cast materials
HC-CU For aluminium alloys with a high copper content (2% - 6%)
HC-GD For die-cast aluminium alloys with high copper and / or silicon content
HC-GL For wrought, cast and die-cast aluminium alloys with a limited amount of copper, silicon and lead. This variant is suitable for components which must have especially smooth and wear-resistant surfaces.

Post-Treatments from AHC Hangzhou

HC-PLUS HC Sealing HC black
PTFE (polytetrafluoroethylene) is applied after the HART-COAT® layer. Anti-friction and corrosion behaviour as well as dry lubrication properties of the treated component are optimised. Surface cleaning is also easier due to the anti-adhesion properties of HC-PLUS. The sealing of a coated workpiece is carried out in the Hangzhou plant in deionised water with or without addition of sealing agents between 96 and 100 °C. Thereby the pores of the HC layer are closed, which further improves the corrosion behaviour. At the Hangzhou plant, the HC layer can be dyed black by immersion. This colouring produces a high resistance to light and weather.