ALUMINUM CONVERSION COATING
Alodine Coating Services
for Aluminum Parts
Specify chem film for corrosion protection, paint preparation or low-resistance contacts. Send the alloy, drawing and finishing requirements for review.
Alodine / chem film:
define the requirement before coating.
Chemical conversion coating reacts with the aluminum surface to form a protective film. It is different from anodizing and from depositing a metal plating. Select the chemistry and performance class for the job.
| Substrate | Aluminum and aluminum alloys. Supply the grade, temper and any prior surface treatment. Steel, copper and titanium require a different finishing review. |
|---|---|
| Appearance | Clear or gold options are listed for this service. Appearance depends on product, substrate and processing; specify the chemistry and acceptance criteria as well as the color. |
| Application | Immersion is the route described for this service. State any selective treatment, repair or touch-up requirement separately; method and chemical suitability need confirmation. |
| Specification | For controlled work, state MIL-DTL-5541 and its required revision, Type I or II, and Class 1A or 3. Supply customer specifications and approved-material restrictions with the RFQ. |
| Thickness & dimensions | No universal numeric thickness is promised here. Define final dimensions and any thickness or coating-mass requirement; suitability and the measurement method are reviewed for the selected system. |
| Contact performance | Where low electrical contact resistance matters, specify a Class 3 requirement and the test conditions. Do not use a color name as an electrical specification. |
| Order planning | Overall dimensions, weight, quantity, delivery date, masking, inspection and documentation are confirmed with the quotation. |
Alodine is a Henkel product-family name; chem film and chemical conversion coating describe the process more broadly. If a branded product is required, identify its exact designation and approved application method. See Henkel's BONDERITE M-CR 1200S AERO information; this reference does not identify the chemical used on your order.
CHEMISTRY & PERFORMANCE
Type selects the chemistry.
Class selects the functional priority.
These are two independent decisions in MIL-DTL-5541. Supply both on the drawing. Availability, compliance and required evidence must be confirmed with the quotation.
Type I
Contains hexavalent chromium
Specify it when required by the governing drawing or approved process. Do not substitute a different chemistry without the required engineering authorization.
Type II
Contains no hexavalent chromium
This does not necessarily mean chromium-free: a trivalent-chromium system may meet the definition. Request any required chemical or regulatory declaration for the actual system.
Class 1A
Corrosion-protection priority
The specification class for maximum corrosion protection, painted or unpainted. Agree the exposure, coating system and acceptance evidence.
Class 3
Low contact-resistance priority
For corrosion protection where low electrical resistance is required. Define contact surfaces and test conditions; it is not an unconditional guarantee for an assembled electrical joint.
Definitions: MIL-DTL-5541 official record and MIL-DTL-81706B, sections 1.2 and 6.1. These classifications describe specification requirements, not a certification claim by Prolean.
Do not specify chemistry by color alone.
A gold appearance is not proof of Type I, and a clear appearance is not proof of Type II or Class 3. Record the chemical designation, type and class rather than accepting appearance as compliance evidence.
5541 and 81706 serve different roles.
MIL-DTL-5541 addresses the coating on aluminum parts. MIL-DTL-81706 addresses conversion materials and qualification. A qualified chemical does not, by itself, establish conformity of a finished part or qualify a processing facility.
Where chem film fits
in a finished assembly.
Choose against the surface's job: resist corrosion, support a paint system, or maintain a specified electrical contact. Then agree the cosmetic expectation separately.
Electronic housings & chassis
Identify grounding faces, mating lands and any later paint coverage. Where electrical continuity matters, define the contact requirement in the assembly context.
Painted brackets & panels
Specify the primer / paint system, pretreatment route and adhesion acceptance. Conversion coating is a pretreatment option, not a replacement for validating the complete paint system.
Precision aluminum hardware
A low-build conversion route can be useful where a thicker finish would complicate fits. Still review cleaning, etching, existing coatings and the final tolerance.
These are engineering selection examples. If your program requires an approved source, named chemistry or special-process approval, include that requirement before quoting.
| Decision | Chem film | Anodizing |
|---|---|---|
| Primary mechanism | Thin chemical conversion film; no anodizing current. | Electrochemically formed aluminum oxide. |
| Electrical contacts | Class 3 is the relevant specified route for low resistance. | Oxide is insulating; contact surfaces may need masking. |
| Wear & appearance | Not a hard wear layer or a broad decorative dye palette. | Decorative and hardcoat routes have different performance requirements. |
| Dimensions | Low build-up, but pretreatment and final tolerance still matter. | Coating growth must be included in fits. |
Still choosing between conductivity and wear performance?
Include the surface function with your drawing.
DESIGN & PROCESS CONTROL
A thin film still needs
a complete finishing plan.
Cleaning, solution access, handling and process order affect the result. Treat functional faces as explicit requirements rather than assuming every surface should be treated identically.
Conceptual illustration. Coating state and permitted masking are agreed per drawing.
Contact lands & masking
A Class 3 coated contact is different from a bare masked contact. Specify which condition is required, along with later paint masking and assembly requirements.
Fits, threads & surface texture
Low build-up is not a zero-change guarantee. Pretreatment can remove material; stripping and reprocessing may change precision features. State finished dimensions and final Ra where functional.
Cavities, cleaning & handling
Identify blind holes, trapped liquid paths and enclosed features. Agree cleaning, rinsing, drainage, drying and handling so contamination or retained solution does not compromise the part.
Agree the route before production.
Machine / form → deburr → clean and prepare → conversion coat → rinse / dry as specified → inspect and protect.
Welding, painting, anodizing, repair and dissimilar-metal assembly can change the required sequence. Selective chem film and anodizing on different areas need an approved route and defined boundaries; do not assume one layer simply goes over another.
Drawing note template for controlled work
Use approved values and the required revision. Confirm the selected type, class, material and application method before production.
CHEMICAL CONVERSION COAT PER MIL-DTL-5541 [REVISION]. TYPE [I / II]; CLASS [1A / 3]. APPROVED MATERIAL / CUSTOMER PROCESS: [ ]. COATED, MASKED AND CONTACT SURFACES: [DRAWING VIEWS]. FINAL DIMENSIONS / ROUGHNESS APPLY AT: [ ]. PAINT / ASSEMBLY SEQUENCE: [ ]. INSPECTION, SAMPLING AND REQUIRED RECORDS: [ ].
Replace every bracketed field with approved project values before use.
Technical indicators and inspection:
separate reference tests from order acceptance.
A specification name, test method and acceptance criterion are different things. Request the test conditions, specimens, sampling and records needed for your application. Testing and documentation are confirmed in the quotation.
| Characteristic | Technical reference | What your RFQ should define |
|---|---|---|
| Corrosion evidence | MIL-DTL-5541F sections 3.6.1 and 4.4.1 specify 168 h in 5% salt spray for corrosion testing under the specified conditions. MIL-DTL-81706B Table I uses 168 h for the listed Class 1A / Class 3 material-conformance exposures. It also lists 336 h for certain Class 1A qualification tests, with an exception for the specified touch-up form / method. | Specify the applicable coating / material standard, alloy, exposure, specimen and acceptance criteria. These standard material-test values are not a Prolean salt-spray guarantee or proof of finished-part conformity. |
| Electrical contact | Class 3 material testing under MIL-DTL-81706B section 3.7 uses a specified electrode pressure of 200 psi (about 1.38 MPa). | MIL-DTL-5541F section 3.7 requires the acquisition documents to specify the part resistance test method, frequency and required values. State the contact geometry, load and pre-/post-exposure condition. Do not compare measurements taken with a different fixture or load as equivalent. |
| Film thickness / mass | Define any requirement against the chosen chemistry and specification. There is no universal coating thickness assigned to all Alodine systems here. | Agree a suitable method. ASTM B244's eddy-current method explicitly excludes conversion coatings as too thin for that method; do not reuse an anodizing inspection plan unchanged. |
| Paint adhesion | Use the complete coating specification and its specified paint / test procedure. ASTM D3359 is a tape-adhesion test method, not a stand-alone finishing approval. | Name the paint system, cure / conditioning, test method, specimen and required rating. Confirm whether panels and testing are included. |
| Coverage & workmanship | Visual inspection against the applicable process and agreed significant surfaces. | Define coverage, permitted contact / masking areas, handling marks and appearance reference. Appearance alone cannot prove chemistry or electrical performance. |
| Conformity & traceability | Records must identify the agreed coating requirements and applicable lot or order. | Request chemical / process identification, certificate of conformity, traceability and any specified reports before ordering. Availability is not implied by listing a standard. |
References: MIL-DTL-5541F, sections 3.6.1, 3.7 and 4.4.1; MIL-DTL-81706B with Amendment 1, Table I and section 3.7; ASTM B244 scope; ASTM B117. Salt-spray exposure does not directly predict outdoor service life. Use the revision required by your contract.
For procurement and supplier qualification
Include approved-source restrictions, chemistry requirements, inspection scope, quantity and required date. Ask the quotation to identify what is included, what needs additional testing and any unresolved technical conditions.
For repeat orders and enterprise programs
Reference the drawing revision, process approval, visual sample and traceability requirements. Agree first-article review and approval of changes to material, chemistry, method or acceptance conditions where required by your program.
Alodine coating service FAQ
Is Alodine the same as chem film?
Alodine is a product-family name commonly associated with aluminum conversion coating. Chem film describes the broader process. If a specific branded chemistry is required, name the product rather than relying on the generic finish description.
What is the difference between Class 1A and Class 3?
Class 1A prioritizes maximum corrosion protection, painted or unpainted. Class 3 is for corrosion protection where low electrical resistance is required. State the required class and acceptance conditions on your RFQ.
Does Type II mean completely chromium-free?
No. Type II means the composition contains no hexavalent chromium. Some Type II systems use trivalent chromium. Request the exact chemical designation and any required declaration for your program.
Will chem film change precision dimensions?
The film has low build-up, but cleaning, etching, stripping or reprocessing can affect dimensions. Identify tight fits and final tolerances for review rather than assuming zero change.
Can it replace anodizing on a wear surface?
Do not treat a thin conversion film as a hard wear layer. Compare anodizing or another engineered surface where abrasion or wear is the primary requirement.
Can chem film and anodizing be used on one part?
Different surfaces can require different treatments. Send the coated, anodized, masked and contact-area boundaries for an approved process-sequence review.
What do you need to quote customer-supplied parts?
Provide the alloy and temper, quantity, overall size, existing finish, prior processing, condition and required specification. Confirm suitability and handling before shipping parts.
Are salt-spray testing and certificates included?
Request them with your RFQ. The test method, specimens, acceptance criteria, schedule, reports and costs must be explicitly agreed. A reference to a standard on this page does not mean every order includes every test.
YOUR NEXT STEP
Request an Alodine
coating quote.
Send the drawing and tell us what the finished surface must do. Review the machining, conversion coating, contact areas and inspection scope together.
Your files are treated as confidential.
Optional NDA ↗
Include with your inquiry
- 2D / 3D files, alloy and temper
- Quantity, overall size and required date
- Specification revision, type and class
- Required chemistry or approved-source restrictions
- Coated, masked, contact and cosmetic surfaces
- Final dimensions and paint / assembly sequence
- Testing, reports and traceability requirements
Compare the finishing routes.
Technical sources and specification scope
Public references checked on 16 October 2026. These explain coating selection and test scope; they do not certify a facility, chemical or individual order. Verify full requirements against the specified revision.