What is Hardcoat?
Hardcoat is a highly abrasion resistant, non-conductive aluminum oxide (Al2O3-xH2O) coating that makes an aluminum surface harder than tool steel due to greater thickness and weight than conventional anodic coatings. Anodic coatings form an excellent base for dry film lubricants, Teflon, paint, and adhesives.
Note: You cannot hardcoat over hardcoat, anodize over anodize, build up hardcoat over anodize, chromic over hardcoat, or just add another 0.0005″ to the surface.
Properties of Hardcoat
|Hardness||65 to 70 Rockwell C, 850 to 900 DPH, harder than hard chrome plate|
|Color||Dark Gray to Black|
|Coating Thickness||0.002″ average, 0.015″ for salvage purposes on selected alloys|
|Dielectric||Hardcoat is non-conductive and will withstand 800 volts per 0.001″ thickness.|
|Machining||Hardcoat can be ground, lapped, honed or polished.|
|Dyeing||Hardcoat may be dyed most colors but tends to come out dark.|
|Sealing||Hardcoat may be Dichromate, Ni-Acetate, hot water, or Teflon sealed.|
|Resistivity||between 106 to 1012 Ohm-cm|
Coating Thickness vs. Corner Radius
|Nominal Coating Thickness, inch||Radius on edge & inside corner|
|0.001||~ 1/32 inch|
|0.002||~ 1/16 inch|
|0.003||~ 3/32 inch|
|0.004||~ 1/8 inch|
Hardcoat and Thread Coating
Hardcoat thickness is typically 0.002″ (0.0508 mm). Half the coating thickness is build-up and half is penetration into the base metal. For the threaded rod seen in the figure below, the diameter increased by 0.002″ since half of the coating thickness (0.001″) built up the diameter on each side of the rod.
Hardcoat Blind Holes or Through Holes
Through holes (TH on drawing below) will hardcoat evenly up to twice the length of the diameter (X).
Blind holes (BH on drawing below) will only hardcoat to a depth equal to the diameter of the hole (X=Y).
Coating Thickness, Color and Alloys
See chart below. For example: Alloy 2024 may have a max. coating thickness of 0.005″ and will be gray in color.
Note: Coatings over 0.0035″ tend to chip and become milky in color and should only be used in the salvage of parts.