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Plasma Electrolytic Oxidation

Anodizing & conversion coatings · Electrolytic bath

Plasma electrolytic oxidation, also called micro-arc oxidation, creates a thick ceramic oxide on aluminum or magnesium using high-voltage micro-discharges.

CNC machiningSheet metal3D printingCastingHigh cost $$$$Insulating
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Reference page — PEO is not in the instant-quote configurator. Upload the part, name the finish in the notes, and an engineer quotes it with the part.

Plasma Electrolytic Oxidation on a machined part

What is PEO?

It is selected for wear, dielectric, thermal, and corrosion performance beyond conventional anodizing, usually under a processor-specific specification.

How it works

The light-alloy part is immersed in an alkaline electrolyte and driven at high pulsed voltage. Once dielectric breakdown begins, many short-lived micro-discharges locally transform the growing oxide into hard crystalline ceramic phases. Commercial coatings commonly span 10–150 µm and include a dense inner barrier plus a porous outer layer that may be polished or sealed. Aluminum systems can form alumina-rich phases; magnesium systems form magnesium-oxide and electrolyte-derived compounds. Waveform, electrolyte, alloy, and post-seal dominate final properties.

Why specify it

  • Commercial systems span roughly 10–150 µm
  • Local ceramic phases can measure about 700–2,000 HV
  • Treats both aluminum and magnesium alloys
  • Can combine wear, dielectric, and thermal functions

Where it falls short

  • No single universal PEO specification or chemistry
  • Rough porous outer layer often needs sealing or finishing
  • Edge effects and microdischarge intensity affect uniformity
  • Higher cost and fewer suppliers than conventional anodizing

PEO at a glance

PEO is strongest on corrosion protection (70 of 100) and surface hardness (74 of 100), at a high cost.

Corrosion protectionVery good70 / 100
Surface hardnessVery good74 / 100
Cosmetic qualityFair35 / 100
LubricityLow20 / 100
Relative costHigh78 / 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.

PEO key numbers

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

Thickness10–150 µm0.39–5.9 mil
Hardness700–1,500 HV
Thickness
Commercial aluminum and magnesium systems commonly use 10–150 µm; supplier-specific ranges are much narrower.
Hardness
700–1,500 HV — Reported local ceramic-phase microhardness; effective coating hardness is lower because of porosity. 2000 HV values are literature extremes, not a drawing acceptance range.
Electrical
Insulating
Colours
  • white
  • gray
  • dark gray
Appearance
Matte ceramic white, gray, or dark gray with a microtextured surface.

Where PEO 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. PEO 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 protectionType II anodize — corrosion 71, hardness 54BSA 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 73Sherardizing — 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 & POWDERHard anodizeType II anodizePowder coatZinc plateZinc-nickelHard chromeDLCTiN PVDTin plateCadmium plateE-coatCerakoteWet paintHot-dip zincNitridingHVOF coatingPEO — corrosion 70, hardness 74PEO
02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finishesType II anodize — corrosion 71, hardness 54BSA 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 73Sherardizing — 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 platePEO — corrosion 70, hardness 74PEO
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for PEO

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard.

Drawing call-out

PLASMA ELECTROLYTIC OXIDATION PER APPROVED PROCESS SPECIFICATION FD-PEO-001, 50 ± 10 µm, SEALED, FINAL HARDNESS 900 HV0.05 MIN; MASK THREADS

Which materials take PEO?

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

Material familyVerdictNotes
Aluminum
YesMany wrought, cast, and AM aluminum alloys can be processed after qualification.
  • Alloy strongly affects phase formation and porosity
Magnesium Alloy
YesA principal PEO substrate; sealing is usually important for corrosion.
  • Use an alloy-specific qualified system
DMLS / SLM
With careAluminum or magnesium AM parts only, after porosity and powder review.
Titanium
LimitedPEO is technically possible but outside this aluminum/magnesium record's core offering.
Zinc Alloy
LimitedSome zinc PEO systems exist but are outside this aluminum/magnesium core offering.
Brass
NoBrass is not a PEO substrate.
Copper Alloy
NoCopper alloys are not PEO substrates.
FDM
NoFused-filament polymers are incompatible with this process.
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 a standard PEO substrate in this offering.
Steel
NoThis PEO record covers valve metals (Al/Mg/Ti), not steel.

How PEO is applied, and what it does to the part

  1. 1Clean
  2. 2Mask and rack
  3. 3Immerse in alkaline electrolyte
  4. 4Apply pulsed high voltage
  5. 5Rinse
  6. 6Seal or polish if specified
  7. 7Inspect
DimensionsDo not assume 50% outward growth; obtain the selected supplier's growth ratio and machine allowances for the specified 10–150 µm system.
Build-up per side5–100 µm — Growth ratio is process-dependent and cannot use the conventional anodize 50% rule universally.
MaskingUsually needed. Mask precision fits, threads, electrical contacts, and edges where high-voltage concentration is unacceptable.
ElectricalInsulating
AppearanceMatte ceramic white, gray, or dark gray with a microtextured surface.
Added lead time7–15 working days on top of the bare part

Design rules for PEO

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

  1. Qualify one supplier system before releasing dimensions.Growth ratio and porosity differ materially by chemistry and waveform.
  2. Specify post-seal or final grind.The as-processed outer layer is porous and rough.
  3. Round edges and provide robust rack contacts.High voltage concentrates at edges and contact quality controls arcing.
  4. State a test method with each property.Local HV values do not alone predict effective wear or dielectric life.

PEO versus the alternatives

Finishes engineers weigh against PEO, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
PEO
this page
707435$$$$10–150 µm—
Hard Anodizing Type III
PEO vs Hard Anodizing Type III →
716150$$$25–75 µmwhen a standardized aluminum wear coating is adequate
CorrosionHardnessCosmeticLubricityEconomy
PEOHard Anodizing Type III

The radar overlays PEO with Hard Anodizing Type III, its most common alternative — chosen when a standardized aluminum wear coating is adequate. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Plasma Electrolytic Oxidation is a high-cost finish ($$$$): more expensive than about 84 % of the finishes FabDigit quotes.

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

Lead time and compliance

Added lead time7–15 working days
RoHSConditional
NotesMany alkaline PEO systems avoid hexavalent chromium, but proprietary electrolyte and seal chemistry must be declared.

What PEO is used for

  • Light-alloy pump components
  • Magnesium electronic housings
  • Wear sleeves
  • Dielectric heat-management components

PEO — frequently asked

What is plasma electrolytic oxidation?

PEO uses high-voltage micro-discharges in an electrolyte to turn aluminum or magnesium surfaces into ceramic oxide. Commercial coatings commonly range from 10 to 150 µm.

Is PEO the same as micro-arc oxidation?

Yes, micro-arc oxidation and MAO are common names for the same process family. Individual supplier chemistries and waveforms are not interchangeable.

PEO vs hard anodize: which is harder?

PEO ceramic phases are often reported around 700–2,000 HV, while Type III anodize is commonly 400–600 HV. Porosity and test method mean those numbers do not directly predict component wear life.

Can magnesium be plasma electrolytic oxidized?

Yes, magnesium is a major PEO substrate. The resulting oxide normally needs a qualified seal when corrosion protection is critical.

How thick is micro-arc oxidation?

Commercial systems broadly span about 10–150 µm, but one qualified process uses a much narrower band. The drawing should state thickness, seal, and supplier specification.