Chemical Conversion Coating

Specification

MIL-DTL-5541

Type I

Contains hexavalent chromium

Type II

No hexavalent chromium

Substrate

Aluminium and aluminium alloys

Process overview

Chemical conversion coating is a controlled chemical reaction that transforms the aluminium surface into a thin protective and adherent conversion layer.

What the process does

Improves corrosion resistance of aluminium and aluminium alloys.
Provides a suitable base for primer, paint and some adhesive systems.
Protects machined, fabricated and locally repaired aluminium surfaces.
Provides controlled electrical conductivity where Class 3 is specified.
Can be applied by immersion, spray, brush, wipe or qualified applicator device.

Type and class are separate requirements. Type II does not automatically mean Class 3, and Type I does not automatically mean Class 1A.

Type I

Type I uses conversion materials containing hexavalent chromium. Traditional chromate films provide strong corrosion protection and can retain mobile chromate species that contribute to active corrosion inhibition.

Hexavalent chromium is toxic and carcinogenic. Exposure, ventilation, waste treatment and regulatory controls require formal risk assessment.

Type II

Type II contains no hexavalent chromium. Systems may use trivalent chromium, zirconium, titanium, molybdate, silane or mixed proprietary technologies.

Type II should not be described universally as trivalent chromium because not every qualified Type II product uses the same chemistry.

Class 1A

Used where maximum corrosion protection is required, whether painted or unpainted. It is commonly specified beneath aerospace primers and paint systems.

Class 3

Used where corrosion protection and low electrical contact resistance are both required. Film formation must be controlled because heavier coatings can increase electrical resistance.

Chemistry and physical mechanism

MIL-DTL-5541 is a performance specification rather than a bath-formulation specification. Exact qualified product formulations are proprietary and must be processed to the chemical supplier’s technical data sheet, MIL-DTL-81706 qualification conditions and the approved process specification.

Important chemistry limitations

The chemicals listed below are representative constituents and reaction products found in conversion-coating technologies; they are not a production recipe.
A qualified product may contain only some of these substances, different salts of the same active element, proprietary accelerators, complexing agents, surfactants and corrosion inhibitors.
Do not add individual chemicals based on this information. Bath make-up, replenishment and adjustment must follow the approved supplier instructions.
Type II means that the conversion material contains no hexavalent chromium; it does not mean that every Type II product is a trivalent-chromium process.
The composition of the wet bath is different from the composition and oxidation state distribution within the final dried conversion film.

Type I — representative hexavalent-chromium bath chemistry

Type I materials use hexavalent chromium as a principal oxidising and corrosion-inhibiting component. In acidic aqueous solution, chromium(VI) exists as an equilibrium mixture whose distribution depends strongly on pH and concentration.

Representative chemical or species	Formula	Typical role or significance
Chromium trioxide	CrO₃	Hexavalent-chromium source; forms chromic-acid species in water.
Chromic acid	H₂CrO₄	Acidic oxidising chromate species; simplified representation of hydrated Cr(VI) chemistry.
Hydrogen chromate ion	HCrO₄⁻	Important Cr(VI) species in moderately acidic solutions.
Chromate ion	CrO₄²⁻	Cr(VI) oxyanion favoured as pH rises.
Dichromate ion	Cr₂O₇²⁻	Cr(VI) oxyanion favoured in more acidic or concentrated conditions.
Sodium dichromate dihydrate	Na₂Cr₂O₇·2H₂O	Possible soluble Cr(VI) source in traditional formulations.
Potassium dichromate	K₂Cr₂O₇	Possible soluble Cr(VI) source in traditional formulations.
Hydrofluoric acid	HF	Attacks the native aluminium oxide, activates the substrate and influences coating growth.
Sodium fluoride	NaF	Possible fluoride source and surface activator.
Ammonium bifluoride	NH₄HF₂	Possible fluoride-bearing activator in some proprietary chemistries.
Potassium tetrafluoroborate	KBF₄	Possible fluoride-bearing accelerator or formulation component.
Nitrate ions	NO₃⁻	May act as oxidising or accelerating species, depending on the formulation.
Ferricyanide ions	[Fe(CN)₆]³⁻	Historically used as an accelerator in some chromate formulations; not universal.
Surfactants / wetting agents	Proprietary	Improve wetting, drainage and access to complex geometry.

Type I solutions and wet residues can contain carcinogenic Cr(VI). Chemical handling, exposure control, ventilation, effluent treatment, waste segregation and emergency arrangements must be formally controlled.

Type I — simplified reaction chemistry

Aluminium oxidation at anodic sites:
Al → Al³⁺ + 3e⁻

Acid-assisted oxide dissolution:
Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O

Fluoride-assisted aluminium dissolution, simplified:
Al³⁺ + 6F⁻ ⇌ [AlF₆]³⁻

Dichromate reduction:
Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O

Chromate reduction:
CrO₄²⁻ + 8H⁺ + 3e⁻ → Cr³⁺ + 4H₂O

Precipitation as local pH rises:
Cr³⁺ + 3OH⁻ → Cr(OH)₃

These equations show principal electrochemical steps only. The real film develops through coupled dissolution, reduction, hydrolysis, precipitation and dehydration reactions on a chemically heterogeneous alloy surface.

Type I — typical film composition and structure

The final film is a thin, hydrated, amorphous-to-nanocrystalline mixed conversion layer. Reported constituents may include:

Hydrated chromium(III) oxide, often represented as Cr₂O₃·xH₂O.
Chromium(III) hydroxide, Cr(OH)₃.
Aluminium oxide and hydrated alumina, Al₂O₃ and Al₂O₃·xH₂O.
Aluminium hydroxide, Al(OH)₃.
Chromium–aluminium mixed oxides or hydroxides.
Retained soluble or sparingly soluble Cr(VI) species.
Fluoride, sulfate, nitrate or other residual ions depending on the qualified product.

The coating is not a uniform layer of one pure compound. Its chemistry and thickness vary over aluminium matrix areas and intermetallic particles.

Type I — active corrosion inhibition and self-healing behaviour

Traditional chromate films can retain mobile Cr(VI) species within a hydrated matrix. When moisture reaches a defect, scratch or locally active site, chromate can migrate through the hydrated film and participate in cathodic reduction and precipitation reactions.

A damaged or exposed aluminium area begins local electrochemical activity.
Moisture dissolves a small quantity of retained chromate species.
Chromate migrates toward the electrochemically active region.
Cr(VI) is reduced mainly to Cr(III), suppressing cathodic reaction kinetics.
Hydrated chromium(III) compounds precipitate and partially block the active site.

“Self-healing” is limited active inhibition, not restoration of the original coating thickness or appearance. Large scratches, severe abrasion or extensive corrosion still require approved repair.

Type II — representative hexavalent-chromium-free chemistry

Type II qualified materials use several different technology families. A product may be based on trivalent chromium, zirconium, titanium or a hybrid system. The following table shows representative species that may be encountered; it must not be interpreted as a universal formulation.

Technology family	Representative chemical or species	Formula	Typical role or significance
Trivalent chromium process (TCP)	Chromium(III) nitrate	Cr(NO₃)₃	Possible soluble Cr(III) source.
	Chromium(III) sulfate	Cr₂(SO₄)₃	Possible soluble Cr(III) source.
	Chromium(III) fluoride	CrF₃	Representative Cr(III)-fluoride chemistry; actual solution species are complexed and pH dependent.
	Chromium hydroxide	Cr(OH)₃	Principal precipitated Cr(III) compound within some TCP films.
	Chromium oxide	Cr₂O₃	May be present as hydrated or dehydrated Cr(III) oxide in the film.
Zirconium-based	Hexafluorozirconic acid	H₂ZrF₆	Common soluble zirconium-fluoride precursor.
	Hexafluorozirconate ion	ZrF₆²⁻	Zirconium complex present in acidic fluoride solution.
	Potassium hexafluorozirconate	K₂ZrF₆	Possible zirconium source.
	Zirconium hydroxide	Zr(OH)₄	Hydrolysed precipitate or film precursor.
	Zirconium dioxide	ZrO₂	Major inorganic barrier constituent after hydrolysis and dehydration.
Titanium-based	Hexafluorotitanic acid	H₂TiF₆	Common soluble titanium-fluoride precursor.
	Hexafluorotitanate ion	TiF₆²⁻	Titanium complex present in acidic fluoride solution.
	Potassium hexafluorotitanate	K₂TiF₆	Possible titanium source.
	Titanium hydroxide	Ti(OH)₄	Hydrolysed precipitate or film precursor.
	Titanium dioxide	TiO₂	Barrier-forming inorganic constituent.
Activators and hybrid constituents	Hydrofluoric acid	HF	Oxide removal, surface activation and control of deposition kinetics.
	Ammonium bifluoride	NH₄HF₂	Possible fluoride source.
	Sodium fluoride	NaF	Possible fluoride source.
	Molybdate ion	MoO₄²⁻	Possible corrosion-inhibiting or hybrid conversion species.
	Cerium(III) ions	Ce³⁺	Possible rare-earth corrosion-inhibiting species in alternative systems.
	Silane coupling agents	R–Si(OR′)₃	Form organic–inorganic networks and can promote adhesion.
	Organic polymers / complexing agents	Proprietary	Control solubility, film morphology, wetting, adhesion and corrosion performance.

Type II — trivalent chromium process mechanism

Many aerospace Type II systems are trivalent chromium processes containing Cr(III) together with zirconium-fluoride chemistry. The exact species are proprietary, but the general mechanism is:

Fluoride disrupts and dissolves the native aluminium oxide.
Aluminium dissolution and cathodic reactions occur at different microstructural sites.
Cathodic reactions consume H⁺ or generate OH⁻, increasing local interfacial pH.
Cr(III), zirconium and aluminium species hydrolyse and precipitate.
A very thin hydrated mixed oxide/hydroxide film forms and partially blocks the surface.

Representative precipitation:
Cr³⁺ + 3OH⁻ → Cr(OH)₃

Representative zirconium hydrolysis, simplified:
ZrF₆²⁻ + 4OH⁻ → ZrO₂·xH₂O + 6F⁻

Type II — zirconium and titanium deposition

Zirconium- and titanium-fluoride complexes are soluble in an acidic bath. When the local surface pH rises, the complexes hydrolyse and deposit as hydrated oxides or hydroxides.

Simplified zirconium route:
ZrF₆²⁻ + H₂O/OH⁻ → Zr(OH)₄ / ZrO₂·xH₂O + F⁻

Simplified titanium route:
TiF₆²⁻ + H₂O/OH⁻ → Ti(OH)₄ / TiO₂·xH₂O + F⁻

Deposition is often preferential at cathodically active intermetallic particles, so alloy microstructure has a strong effect on coating distribution, appearance and local thickness.

Type II — typical film composition and appearance

Depending on the qualified product, a Type II film may contain:

Chromium(III) hydroxide and hydrated chromium(III) oxide.
Zirconium dioxide or hydrated zirconia.
Titanium dioxide or hydrated titania.
Aluminium oxide, aluminium hydroxide and aluminium fluoride species.
Small quantities of sulfate, nitrate, fluoride, molybdate, silane or proprietary organic constituents.
Copper-, zinc-, magnesium- or silicon-containing species derived from alloy intermetallic particles.

A disadvantage of Type II conversion coatings is that they are usually clear, colourless or only faintly tinted. It can therefore be difficult to confirm visually that the coating is present or uniformly applied.

Visual appearance alone is not reliable proof of Type II coating presence. Verification should rely on controlled processing, traceability, representative test panels and specified performance tests.

Type II — corrosion-protection mechanism

Type II protection is usually dominated by a thin, adherent barrier layer that slows transport of water, oxygen and aggressive ions and improves adhesion of subsequent primers or paints.

Hydrated oxide/hydroxide compounds partially block electrochemically active sites.
Zirconium-, titanium- and chromium-containing deposits reduce surface reactivity.
The film modifies cathodic and anodic reaction kinetics.
Paint or primer adhesion creates a combined conversion-coating/organic-coating protection system.
Some proprietary inhibitors may provide limited active inhibition, but this should not be assumed to equal traditional chromate self-healing.

How the film forms — physical and electrochemical sequence

Cleaning: Oil, coolant, fingerprints, polishing compound and temporary protectives are removed so the aqueous chemistry can wet the substrate.
Oxide removal: Deoxidising removes or modifies the naturally occurring aluminium oxide and exposes a chemically active surface.
Initial dissolution: The acidic conversion solution causes controlled aluminium dissolution and releases Al³⁺ into the interface.
Micro-galvanic activity: Aluminium matrix and alloy intermetallic particles behave differently, creating microscopic anodic and cathodic regions.
Local pH increase: Cathodic reactions consume hydrogen ions or generate hydroxide ions close to the surface.
Hydrolysis and precipitation: Chromium, zirconium, titanium and aluminium species become less soluble and deposit as hydrated oxides and hydroxides.
Barrier development: The growing film progressively reduces access of the bath to the aluminium and slows further reaction.
Rinsing: Soluble acids, fluoride, metal ions and unreacted product are removed before they can dry as corrosive residues.
Drying and ageing: Water is lost, the gel-like hydrated layer consolidates and the electrical and corrosion properties continue to stabilise.

Film thickness, coating weight and electrical behaviour

Conversion films are extremely thin compared with anodising, electroplating or paint.
Apparent thickness is difficult to define because the layer is hydrated, porous, compositionally graded and partly integrated with the substrate oxide.
Longer treatment does not necessarily improve performance; over-processing can produce loose, powdery or electrically resistive films.
Class 3 processing requires careful control because increased film development generally increases contact resistance.
Alloy, surface preparation, bath age, pH, temperature, fluoride activity and immersion time affect film mass and electrical properties.

Hydration, ageing and drying

Fresh conversion coatings are hydrated and mechanically delicate. Their structure and properties evolve after rinsing:

Initial water loss consolidates the film and improves handling resistance.
Continued ageing can alter corrosion resistance and electrical contact resistance.
Excessive heat may dehydrate, crack, embrittle or otherwise damage the conversion layer.
Handling while wet can wipe away or mark the film.
Testing should be performed after the conditioning period required by the applicable specification or approved process.

Type I and Type II chemistry comparison

Feature	Type I	Type II
Defining requirement	Conversion material contains hexavalent chromium.	Conversion material contains no hexavalent chromium.
Typical active chemistry	Chromate/dichromate Cr(VI), acids, fluoride activators and proprietary accelerators.	Trivalent chromium, zirconium, titanium or hybrid Cr(VI)-free chemistry.
Representative bath species	HCrO₄⁻, CrO₄²⁻, Cr₂O₇²⁻, HF and proprietary additives.	Cr³⁺ salts, ZrF₆²⁻, TiF₆²⁻, fluoride activators, complexants and proprietary inhibitors.
Typical film constituents	Hydrated Cr(III) oxides/hydroxides, aluminium compounds and retained Cr(VI).	Hydrated Cr(III), Zr, Ti and aluminium oxides/hydroxides, depending on technology.
Primary protection mechanism	Barrier protection plus active chromate inhibition.	Primarily barrier and surface-reaction suppression; system-dependent inhibitor effects.
Self-healing behaviour	Limited migration and reduction of retained chromate can inhibit small damaged areas.	Generally less active than Type I; should not be assumed to have equivalent chromate self-healing.
Typical appearance	Clear to yellow, gold, brown, olive or iridescent depending on product, alloy and film development.	Often clear, colourless or faintly blue, violet or iridescent.
Visual verification	Colour may assist inspection but does not prove performance or complete coverage.	Often difficult because the film may be almost invisible.
Electrical properties	Can meet Class 3 when the qualified product and process are controlled for low resistance.	Can meet Class 3; performance depends on qualified product, film development, ageing and test method.
Paint adhesion	Excellent when correctly cleaned, converted, rinsed, dried and painted within the approved window.	Excellent for qualified systems when the complete process is controlled.
Health and environmental concern	Cr(VI) is carcinogenic and requires stringent exposure and waste controls.	Eliminates intentionally added Cr(VI), although acids, fluoride and metal salts still require hazardous-chemical controls.

Chemistry variables that strongly influence coating formation

Variable	Effect on chemistry or film	Typical risk when uncontrolled
Alloy and temper	Changes intermetallic population, micro-galvanic behaviour and dissolution rate.	Mottling, poor coverage, pitting or variable electrical resistance.
Cleaning effectiveness	Determines whether solution can wet and react uniformly.	Bare areas, fingerprints, adhesion failure and local corrosion.
Deoxidising / desmutting	Controls native oxide removal and removal of copper-, silicon- or iron-rich residues.	Nonuniform nucleation, dark smut, pitting and poor coating performance.
Bath pH	Controls metal-complex stability, hydrolysis and precipitation rate.	No coating, slow coating, excessive attack or powdery film.
Fluoride activity	Controls oxide dissolution, activation and metal-complex chemistry.	Insufficient activation, over-etching, pitting or unstable coating growth.
Temperature	Changes reaction kinetics, dissolution and precipitation.	Under-developed or over-developed film and shortened bath life.
Treatment time	Controls film development until the reaction becomes self-limiting.	Bare areas if too short; heavy, powdery or resistive film if too long.
Dissolved aluminium	Builds up through normal substrate dissolution and changes bath equilibrium.	Sludge, reduced activity, altered coating morphology and inconsistent results.
Metal contamination	Copper, iron, zinc and other contaminants can alter deposition and corrosion behaviour.	Discolouration, pitting, poor corrosion resistance and bath instability.
Agitation and solution movement	Controls mass transfer, gas-bubble release and replenishment at the surface.	Patchy coating, trapped-air bare spots and nonuniform reaction.
Rinse quality	Removes soluble acid, fluoride, metal ions and unreacted chemistry.	Staining, salt deposits and delayed corrosion.
Drying conditions	Controls dehydration, consolidation and ageing of the hydrated film.	Water marks, soft film, cracking or heat damage.

Typical process sequence

The precise process must follow the approved chemical supplier instructions, customer requirements and qualified processing method.

1. ReviewConfirm alloy, temper, type, class, drawing, masking and subsequent processing.

2. Mask and rackProtect prohibited areas and use clean, compatible tooling.

3. Pre-cleanRemove oil, grease, coolant, fingerprints and temporary protectives.

4. Non-etch Alkaline cleanClean - Avoid caustic etching unless material removal is required or contract requires it.

5. Rinse (1 minute min.)Stop alkaline attack and prevent contamination of the deoxidiser.

6. DeoxidiseRemove oxide and smut and activate the aluminium surface.

7. Rinse (1 minute min.)Remove acid, dissolved metals, fluoride and residual smut.

8. ConvertApply the qualified Type I or Type II material under controlled conditions.

9. Final rinse (1 minute min.)Remove soluble residues without damaging the soft new film.

10. Post-treatUse only approved seal or final rinse treatments.

11. DryDrain and dry using clean air or controlled low-temperature heat.

12. InspectCheck coverage, defects, masking, records, testing and packaging.

Cleaning controls

Concentration and alkalinity.
Temperature and immersion time.
Oil loading and dissolved aluminium.
Water-break-free inspection.
Prevention of over-etching and dimensional change.

Rinsing controls

Immediate transfer between stages.
Complete wetting and vigorous solution movement.
Controlled conductivity, hardness and chloride.
No drying between active process stages.
Attention to recesses, blind holes and casting porosity.

Poor rinsing (not following the 1 minute rule etc) can leave invisible soluble salts that later rehydrate and cause staining, corrosion, blistering or adhesion failure.

Drying controls

Prevent water pooling and rack drips.
Use clean, oil-free air.
Avoid excessive drying temperature.
Do not handle the coating while wet or soft.
Ensure complete drying before painting or packaging.

Touch-up and local repair

Use only a qualified and approved material of the correct type, class, form and method. Remove corrosion products, clean the area and comply with drawing or contractual limitations.

Compatible aluminium materials

MIL-DTL-5541 is intended for aluminium and aluminium alloys. Alloy chemistry and condition strongly affect preparation, colour and performance.

Alloy family	Typical characteristics	Special considerations
1xxx	Commercially pure aluminium; often forms relatively uniform films.	Usually straightforward to clean. Appearance may be pale or nearly colourless.
2xxx	Aluminium-copper alloys such as 2024.	Copper-rich particles increase corrosion sensitivity. Deoxidising and desmutting are critical; excessive etching can expose copper-rich residues.
3xxx	Aluminium-manganese alloys.	Generally processable by conventional pretreatment. Rolled-in contamination and lubricant must be removed.
5xxx	Aluminium-magnesium alloys.	High-magnesium grades may be sensitive to aggressive alkaline cleaning and excessive etching.
6xxx	Aluminium-magnesium-silicon alloys such as 6061 and 6082.	Widely processed. Extrusion die lines and embedded soils may remain visible after coating.
7xxx	High-strength aluminium-zinc-magnesium-copper alloys such as 7075.	Corrosion-sensitive. Copper- and zinc-rich particles may cause colour variation. Cleaning and deoxidising need tight control.
Cast aluminium	May contain silicon-rich phases, porosity and entrapped contamination.	Risk of dark smut, retained process solution, staining, variable colour and difficult rinsing. Use a process suitable for the casting alloy.

Equipment and facilities

Equipment must be compatible with the selected chemistry and designed to control contamination, worker exposure and environmental discharge.

Production equipment

Chemical-resistant cleaner, deoxidiser, conversion and rinse tanks.
Spray cabinet or spray tunnel where applicable.
Solution circulation, agitation and filtration.
Temperature control and calibrated timers.
Racks, baskets, jigs and compatible masking materials.
Forced-air or low-temperature drying facilities.
Bunds, drip trays and controlled chemical storage.

Laboratory and control equipment

Calibrated pH meter and buffers.
Titration equipment, burettes and pipettes.
Analytical balance and temperature probes.
Conductivity, hardness and chloride test equipment.
Fluoride ion-selective electrode where required.
Salt-spray cabinet and test-panel preparation equipment.
Paint adhesion and electrical resistance test equipment.

Safety and environmental controls

Local exhaust ventilation and suitable air monitoring.
Chemical-resistant gloves, eye protection, face protection and clothing.
Emergency shower and eyewash facilities.
Spill-response arrangements and segregated waste containers.
Effluent treatment suitable for chromium, fluoride, metals, acids and alkalis.
Respiratory protective equipment where risk assessment requires it.

Process controls

Control limits must be taken from the qualified chemical supplier instructions, approved process specification and customer requirements.

Stage	Typical controls	Potential reaction plan
Cleaner	Concentration, alkalinity, temperature, time, oil loading, dissolved aluminium, water-break test.	Adjust chemistry, remove oil, renew solution, investigate loading or contamination.
Rinse	Conductivity, overflow, agitation, chloride, hardness, visual cleanliness.	Increase flow, renew water, investigate carry-over, improve drainage and orientation.
Deoxidiser	Acidity, concentration, fluoride, dissolved metals, temperature, time, smut removal.	Analyse, adjust, replace or investigate incorrect alloy/process selection.
Conversion bath	Product identity, type, class, concentration, pH, temperature, time, free fluoride, dissolved aluminium, contamination.	Stop processing where required, quarantine work, adjust bath, process test panels and requalify.
Drying	Temperature, time, air cleanliness, drainage, complete dryness.	Correct temperature, clean air system and prevent part contact or pooling.
Records	Lot traceability, bath analysis, operator, date, time, test panels, inspection, concessions and rework.	Hold product where required and reconstruct traceability before release.

Inspection and testing

Visual inspection identifies gross defects but does not replace required performance testing.

Visual acceptance

Continuous and visibly discernible coating where applicable.
No bare areas, loose powder, pits, scratches or staining.
No fingerprints, excessive contact marks or masking errors.
Recognise that Type II films may be nearly colourless.

Corrosion resistance

Salt-spray exposure is typically used for process-control and conformance testing. Panel alloy, preparation, edge condition, test solution and exposure conditions must comply with the applicable requirement.

Paint adhesion

Where required, apply the specified primer or paint system and perform the required wet-tape or other adhesion test. Failure may indicate poor cleaning, powdery film, contamination, poor rinsing (quick dips rather than 1 minute immersion) or an excessive delay before painting.

Electrical contact resistance

Control electrode material, geometry, contact area, applied load, measurement current, panel alloy, coating age and surface cleanliness. Electrical results are not meaningful without a defined test method.

Failure modes and troubleshooting

Select a symptom below to review likely causes, consequences and corrective actions.

Observed problem

Drawing and purchase-order information

Clear technical flow-down is essential because type, class, method, alloy and subsequent processing all affect the required result.

Recommended drawing information

MIL-DTL-5541 revision.
Type I or Type II.
Class 1A or Class 3.
Areas to coat and areas to mask.
Application restrictions.
Paint, primer, bonding or electrical requirements.
Touch-up permission or prohibition.
Any customer-specific process specification.

Recommended purchase-order information

Part and drawing revision.
Alloy and temper.
Specification, revision, type and class.
Approved processor or qualified material requirements.
Certification, test report and traceability requirements.
Packaging and subsequent processing requirements.
Notification requirements for process or chemistry changes.

Example callout

CHEMICAL CONVERSION COAT TO MIL-DTL-5541, TYPE II, CLASS 1A. USE MATERIAL QUALIFIED FOR THE SPECIFIED TYPE, CLASS AND APPLICATION METHOD. MASK IDENTIFIED BONDING AND ELECTRICAL CONTACT SURFACES.

This example is guidance only. The design authority must define the contractual requirement and applicable revision.

Further information and web links

Always verify the current revision, qualification status and contractual applicability before use.

Reference	Use	Link
MIL-DTL-5541	Requirements for chemical conversion coatings on aluminium and aluminium alloys.	DLA Quick Search
MIL-DTL-81706	Requirements for qualified chemical conversion materials, forms and application methods.	DLA Quick Search
QPL / QPD information	Qualified products and qualification status for conversion materials.	DLA Qualified Products Database
NASA PRC-5005	Process guidance for chemical conversion coating of aluminium alloys.	NASA PDF
SAE AMS2473	General-purpose chemical film treatment of aluminium alloys.	SAE Standards
SAE AMS2474	Low electrical resistance chemical treatment of aluminium alloys.	SAE Standards
OSHA Chromium (VI)	Worker exposure and health information for hexavalent chromium.	OSHA
US EPA Chromium	Environmental and health information.	US EPA

External links are provided for further research. Access, revision status and availability may change.