Aluminum Anodizing Services: Type II & Type III Hardcoat
TYPE II AND TYPE III HARDCOAT ALUMINUM ANODIZING SERVICES
PFI Inc. provides aluminum anodizing services for OEMs and military suppliers in the aerospace, automotive, and industrial sectors. We perform Type II, Type IIB, and Type III hardcoat anodizing to MIL-PRF-8625.
Type II anodizing forms a dielectric aluminum oxide layer that protects parts from corrosion and electrically insulates the surface. The oxide layer can stay clear or take dye in black, blue, gold, olive drab, red, or green. Other colors beyond this standard range may also be available.
Hardcoat anodizing (Type III) builds a thicker oxide layer with hardness near 65 Rockwell C for parts exposed to abrasion and wear. The thicker layer adds more material to each surface and can affect close-tolerance dimensions. We offer masking for close-tolerance parts to keep selected features uncoated.
Buyers can submit a job for review through the quote form on our contact page or by calling 814-763-3707.
Type II Anodizing Services
We perform Type II anodizing in a sulfuric acid bath at about 68 to 70°F. The process grows a medium-thickness oxide layer on the surface and into the base metal. This layer reaches a hardness of about 40 to 50 Rockwell C and withstands about 800 volts per .001 in. of coating thickness. Type II also prevents the white, powdery corrosion that forms on bare aluminum exposed to the environment.
Electrical insulation makes Type II a common choice for electronic housings and aerospace components that must not conduct current. The porous oxide also serves as a base for dyes and paints. Type IIB uses a thinner sulfuric acid coating and serves as a non-chromate replacement for Type I chromic acid anodizing.
Type III Hardcoat Anodizing
Type III hardcoat anodizing is our most requested industrial coating. We run the sulfuric acid bath at about 34 to 36°F with a higher current density than Type II. This process produces an oxide layer with a dielectric strength of 800 to 2,000 volts per .001 in. Our Type III anodizing is certified to MIL-A-8625 [CONFIRM: MIL-PRF-8625 or MIL-A-8625]. PFI is also an ITAR-compliant anodizing company.
Type II vs. Type III Comparison Table
MIL-PRF-8625 defines both Type II and Type III anodizing for aluminum parts. Each type differs in the following areas:
| Type II Anodizing |
Type III Hardcoat Anodizing |
|
|
Finish options |
Clear or dyed in black, blue, gold, olive drab, red, or green. Other colors beyond this standard range may also be available. |
Clear or black most common, with gray and bronze tones possible |
|
Wear resistance |
A medium-thickness oxide layer that improves abrasion resistance for general-purpose parts |
A thicker and denser oxide layer with hardness near 65 Rockwell C for parts exposed to heavy abrasion and wear |
|
Dimensional considerations |
A thinner coating that grows about half into the base metal and half above the surface, which limits dimensional change |
A thicker coating that adds more material to each surface. A .002 in. hardcoat grows about .001 in. per surface. |
|
Typical applications |
Military and automotive parts; aerospace interior panels, housings, and brackets; electronic enclosures and cases; consumer products; architectural trim; and marine parts that do not require hardcoat |
Compressor fittings, automotive aluminum parts, military components, and parts used in high-heat, marine, or heavy-wear service |
Masking and Close-Tolerance Anodizing
Anodizing converts part of the aluminum surface into oxide. About half of the coating grows into the base metal and half builds above the original surface. This growth pattern changes part dimensions less than plating at the same thickness. A part hardcoated to .002 in. still grows about .001 in. per surface or .002 in. in overall dimension.
Part designers account for this growth on close-tolerance features before anodizing. Masked features stay uncoated and keep their original dimensions. Our team has experience holding tight tolerances and maintains final part dimensions through the anodizing process.
Aluminum Anodizing FAQs
WHICH METALS AND ALLOYS CAN YOU ANODIZE?
We anodize aluminum and aluminum alloys only. Other metals such as steel and brass would be damaged by the sulfuric acid bath and do not form a protective oxide layer in the same way. Coating thickness, hardness, and dye color all vary by aluminum alloy. For non-aluminum parts, we offer other coating services.
DIFFERENCES BETWEEN TYPE II VS. TYPE III
The difference between Type II and Type III anodizing comes from bath temperature and current density in the same sulfuric acid process. Running Type III colder at higher current builds a thicker and harder oxide layer for abrasion resistance and heavy wear. Type II forms a thinner corrosion-resistant coating with clear or dyed finish options for general-purpose and decorative parts.
DO ANODIZED PARTS NEED SEALING?
Type III hardcoat is usually left unsealed. Dyed coatings should be sealed to limit dye fading. Available sealing methods include precipitation and hydrothermal sealing.
WHAT COLORS ARE AVAILABLE?
Type II anodizing offers the widest color range. We can also formulate custom Type II shades on request. Type III hardcoat has a limited dye range and is most commonly supplied clear or black. Anodizing cannot produce a white finish.
WHAT SHOULD I INCLUDE WITH A QUOTE REQUEST?
Send a part drawing and tell us the aluminum alloy, the anodize type, the coating thickness, and the color. Mark any features that need masking on the drawing so they stay uncoated and keep their original dimensions. We price the job and set a lead time from the part quantity, the part size, whether the parts need sealing, and whether you require a certificate of conformance.