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.