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Anodizing Type II

Anodizing & conversion coatings · Electrolytic bath

Type II sulfuric anodizing converts aluminum into a porous aluminum-oxide coating that can be clear or dyed.

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Anodizing Type II on a machined part

What is Type II anodize?

It is the standard decorative and moderate-corrosion anodize specified on machined, formed, cast, and additively manufactured aluminum parts.

How it works

The aluminum workpiece is the anode in a sulfuric-acid electrolyte, commonly near room temperature at roughly 12–20 V. Oxygen generated at the surface converts aluminum into porous aluminum oxide. Dye can enter those pores for Class 2 color, after which hot-water, nickel-acetate, or other sealing closes them. MIL-A-8625 Type II commonly runs 5–25 µm, with Class 2 color work often 8–15 µm; approximately half of the oxide projects above the original surface and half penetrates it.

Why specify it

  • Provides a hard 200–400 HV oxide
  • Supports clear and many dyed colors
  • Sealed coatings meet a 336-hour ASTM B117 requirement under MIL-A-8625
  • Adds only about half the coating thickness to each surface

Where it falls short

  • Electrically insulating at contact surfaces
  • Color varies on 2000 series, 7000 series, cast, and AM alloys
  • Sharp edges and deep recesses coat nonuniformly
  • Strong alkaline cleaners attack the oxide

Type II anodize at a glance

Type II anodize is strongest on corrosion protection (71 of 100) and cosmetic quality (88 of 100), at a standard cost.

Corrosion protectionVery good71 / 100
Surface hardnessFair54 / 100
Cosmetic qualityExcellent88 / 100
LubricityLow18 / 100
Relative costStandard24 / 100
CorrosionHardnessCosmeticLubricityEconomy

Each score is 0–100 against every finish in this catalog. Corrosion comes from salt-spray life (ASTM B117, log scale) and hardness from the finish layer's Vickers or pencil hardness; cosmetic, lubricity and cost are FabDigit's engineering assessment. Economy on the radar is the inverse of cost.

Type II anodize key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among anodizing & conversion coatings finishes.

Thickness5–25 µm0.2–0.98 mil
Hardness200–400 HV
Salt spray336 h
Max service temp.80 °C176 °F
Thickness
5–25 µm (0.0002–0.0010 in) for MIL-A-8625 Type II; Class 2 color work is commonly 8–15 µm.
Hardness
200–400 HV — Typical sulfuric-anodize microhardness; alloy, thickness, and sealing affect the result.
Corrosion (salt spray)
336 h per ASTM B117, sealed, per MIL-A-8625 — The specification evaluates corrosion spots on standard test specimens after 336 hours.
Electrical
Insulating
Colours
  • clear
  • black
  • red
  • blue
  • gold
  • custom dye
Appearance
Clear satin to matte or dyed color; gloss and color depth follow alloy and pre-treatment.

Where Type II anodize sits among all finishes

Surface hardness (Vickers, log scale) against corrosion protection (salt-spray hours, log scale) for every coating FabDigit offers, one cloud per finish group. Type II anodize is highlighted; hover a dot for its name or open the full map.

02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finisheshard, low corrosion protectionhard and protectiveprotective, softsoft, little protectionBSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERPowder coatZinc plateZinc-nickelHard chromeDLCTiN PVDTin plateCadmium plateE-coatCerakoteWet paintHot-dip zincNitridingHVOF coatingType II anodize — corrosion 71, hardness 54Type II anodize
02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finishesBSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERPowder coatZinc plateType II anodize — corrosion 71, hardness 54Type II anodize
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for Type II anodize

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard, and US Government documents are free to download there.

StandardType / ClassThicknessRequirement / testStatus
MIL-A-8625
Anodic Coatings for Aluminum and Aluminum Alloys · DoD
Type II Class 12–25 µmConventional sulfuric-acid anodize, non-dyed. · At least 1000 mg/ft² unsealed (0.1076 g/dm²). · Coating weight; sealed corrosion test, ASTM B117, 336 h.Supersedednow MIL-PRF-8625
Type II Class 22–25 µmConventional sulfuric-acid anodize, dyed. · At least 1000 mg/ft² unsealed (0.1076 g/dm²). · Coating weight; sealed corrosion test, ASTM B117, 336 h; light fastness when specified.
AMS 2471
Anodic Treatment of Aluminum Alloys, Sulfuric Acid Process, Undyed Coating · SAE · alternative
———Active
AMS 2472
Anodic Treatment of Aluminum Alloys, Sulfuric Acid Process, Dyed Coatings · SAE · alternative
Class 1—Dyed coating principally for identification or marking. · Minimum 600 mg/ft² unsealed. · Coating weight, color, appearance, and 336 h salt spray.Active
Class 2—Heavier dyed coating for decorative service. · Minimum 2500 mg/ft² unsealed. · Coating weight, color, appearance, and 336 h salt spray.
ISO 7599
Anodizing of Aluminium and Its Alloys — Method for Specifying Decorative and Protective Anodic Oxidation Coatings on Aluminium · ISO · alternative
AA5≥ 5 µmNominal 5 µm thickness class · Average and local coating thicknessActive
AA10≥ 10 µmNominal 10 µm thickness class · Average and local coating thickness
AA15≥ 15 µmNominal 15 µm thickness class · Average and local coating thickness
AA20≥ 20 µmNominal 20 µm thickness class · Average and local coating thickness
AA25≥ 25 µmNominal 25 µm thickness class · Average and local coating thickness

Test and related methods: ASTM B117 (Standard Practice for Operating Salt Spray (Fog) Apparatus).

Drawing call-out

ANODIZE PER MIL-A-8625 TYPE II CLASS 2, BLACK, 0.0005 IN THICK; MASK ALL THREADS AND ELECTRICAL CONTACTS

Pattern: ANODIZE PER MIL-A-8625 TYPE <I|IB|IC|II|IIB|III>, CLASS <1|2>, [COLOR], [THICKNESS FOR TYPE III], [SEAL], [MASKING]

Which materials take Type II anodize?

Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library.

Material familyVerdictNotes
Aluminum
YesWrought and cast aluminum are the intended substrates.
  • 5000 and 6000 series generally anodize uniformly
  • 2000 and 7000 series can be darker
  • High-silicon cast and AM alloys often appear gray and mottled
DMLS / SLM
With careOnly aluminum DMLS/SLM parts can be processed; steel and titanium builds cannot.
Brass
NoBrass is not anodized by this aluminum process.
Copper Alloy
NoCopper alloys are not anodized by this aluminum process.
FDM
NoFused-filament polymers are incompatible with this process.
Magnesium Alloy
NoMagnesium requires magnesium-specific anodizing or conversion coating.
MJF
NoPolymer powder-bed prints are incompatible with this process.
Polymer
NoOrganic polymers cannot take this inorganic metal-finishing process.
SLA
NoPhotopolymer prints are incompatible with this process.
SLS
NoPolymer powder-bed prints are incompatible with this process.
Stainless Steel
NoStainless steel is not anodized by MIL-A-8625 processes.
Steel
NoThis is an aluminum anodic process; steel does not form this oxide.
Titanium
NoTitanium uses a different anodizing process.
Zinc Alloy
NoZinc alloys are not anodized by this aluminum process.

How Type II anodize is applied, and what it does to the part

  1. 1Clean / degrease
  2. 2Etch
  3. 3Desmut
  4. 4Anodize in sulfuric acid
  5. 5Dye if Class 2
  6. 6Seal
  7. 7Dry
DimensionsAllow roughly 2.5–12.5 µm outward growth per treated surface for a 5–25 µm coating.
Build-up per side3–13 µm — About 50% grows outward and 50% consumes the aluminum.
MaskingUsually needed. Mask threads, electrical contacts, bearing fits, and precision bores unless tolerance already includes buildup.
ElectricalInsulating
Temperature limit80 °C (176 °F) continuous
AppearanceClear satin to matte or dyed color; gloss and color depth follow alloy and pre-treatment.
Added lead time3–5 working days on top of the bare part

Design rules for Type II anodize

What to decide on the drawing before the part goes to the finisher.

  1. Allow about 50% of coating thickness as outward growth.A 12 µm coating typically adds about 6 µm per surface.
  2. Round exposed edges to at least 0.25 mm where practical.Current concentrates at sharp edges and can burn or craze the oxide.
  3. Add a rack contact area that may remain unfinished.Electrical contact is required during anodizing.
  4. Specify alloy and color together on cosmetic assemblies.Different alloys do not dye to an exact visual match.

Type II anodize versus the alternatives

Finishes engineers weigh against Type II anodize, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
Type II anodize
this page
715488$$5–25 µm—
Chemical Conversion Coating
Type II anodize vs Chemical Conversion Coating →
60—35$0.1–1.5 µmwhen electrical conductivity is required
Hard Anodizing Type III
Type II anodize vs Hard Anodizing Type III →
716150$$$25–75 µmwhen severe wear resistance is required
CorrosionHardnessCosmeticLubricityEconomy
Type II anodizeChemical Conversion Coating

The radar overlays Type II anodize with Chemical Conversion Coating, its most common alternative — chosen when electrical conductivity is required. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Anodizing Type II is a standard-cost finish ($$): cheaper than about 74 % of the finishes FabDigit quotes.

Finishing is priced per part with a lot minimum, from FabDigit's own China-side rates cross-checked against US job-shop pricing. The exact figure appears on the instant quote once the part is uploaded.

Lead time and compliance

Added lead time3–5 working days
RoHSCompliant
NotesSulfuric anodizing and common non-hexavalent sealing systems can meet RoHS; verify dye and seal chemistry.

What Type II anodize is used for

  • Consumer electronic housings
  • Decorative aluminum trim
  • Aerospace interior brackets
  • Marine-grade enclosures

Type II anodize — frequently asked

Does anodizing add thickness?

Yes. About half of a Type II coating grows outward, so a 12 µm coating adds roughly 6 µm per treated surface and about 12 µm across a coated diameter.

What is Type II vs Type III anodizing?

Type II is typically 5–25 µm and 200–400 HV for corrosion and color. Type III is commonly 25–75 µm, around 350–550 HV, and chosen for wear.

Can you anodize 7075 aluminum?

Yes, 7075 is routinely anodized. Its copper and zinc content can produce a darker gray or yellow cast, so exact color matching to 6061 should not be assumed.

Is anodized aluminum electrically conductive?

The aluminum core conducts, but the aluminum-oxide surface is electrically insulating. Mask bonding areas or specify Class 3 chem film where a reliable electrical contact is needed.

How corrosion resistant is Type II anodize?

Properly sealed MIL-A-8625 Type II specimens are tested for 336 hours in ASTM B117 salt spray. Field life still depends on alloy, seal quality, scratches, and environment.