Alodine Finish Service

Our Alodine coating (a chromate conversion finish) boosts aluminum/metal corrosion resistance and paint adhesion. It delivers long-lasting protection, meeting military & aerospace standards.

Chromate conversion coating for aluminum & other metals
Enhanced corrosion resistance
MIL-DTL-5541 compliant finish

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What Is Alodine? (aka Chem Film)

Alodine—commonly called Chem Film—is a specialized chromate conversion coating designed for aluminum and its alloys. Its primary role is to boost two critical metal properties: corrosion resistance and surface adhesion (key for paint or primer application).

Originally a trademark of Henkel for aluminum chromium oxide coating technology, the term “Alodine” has since become a generic industry reference—even though Henkel later rebranded the product as Bonderite®. A major advantage of Alodine coating is its thin, non-intrusive layer: it protects metal without altering its original strength or weight, making it ideal for high-stakes sectors like aerospace, military, and industrial manufacturing (where precision and durability matter most). Specifically, it works well for precision aluminum components that need to retain tight dimensions or parts requiring pre-treatment before painting, as its adhesion boost keeps coatings from chipping. But it’s not universal—Alodine only works on aluminum and its alloys (not steel, copper, or magnesium), can’t stand up to severe corrosion like saltwater, and isn’t durable enough for high-wear parts that rub against other components.

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Specifications for Alodine Finish Service

Parameter	Specification
Color	Golden, brown, transparent, or iridescent greenish-gold, depending on the Alodine type (e.g., Alodine 1000, 1001, 1200S, 5992)
Thickness	Typically 0.00001 to 0.00004 inches (0.25–1 μm)
Immersion Time	1 to 5 minutes, depending on the size of the part and desired coating thickness
pH Value	1.5 to 2.0
Temperature	70 to 100°F (21 to 38°C)
Standard Types	- MIL-DTL-5541 Type 1A: Minimum thickness 0.0001 inches (0.1 mil) - MIL-DTL-5541 Type 3: Maximum thickness 0.00001 inches (0.01 mil)
Special Types	- Alodine 1200S: Colorless or golden - Alodine 871: Hex-free, trivalent chromium-based - Alodine 5200, 5700, 5992: Other industrial applications
Minimum Part Size (mm)	2×2×2
Maximum Part Size (mm)	3000×2200×1100

Design Considerations

Selecting the Right Coating Class

Alodine finishings are available in different classes, including Class 3 and Class 1A. Class 3 is thinner and better suited for applications where maintaining conductivity is critical, such as electrical components. In contrast, Class 1A provides a thicker layer for superior corrosion resistance but may slightly reduce electrical conductivity.

Coating Thickness

Typical Alodine coating thickness ranges from 0.00001 to 0.00004 inches (0.25 to 1 micron). Despite being very thin, this layer offers effective corrosion protection. The appropriate thickness should be selected based on the specific requirements of the application.

pH and Temperature Control

Maintaining the correct pH and application temperature of the Alodine solution is essential. Deviations can result in poor adhesion or surface defects like spotting and streaking.

Toxicity and Safety

Certain Alodine solutions, especially those containing hexavalent chromium, are hazardous and require careful handling and proper waste disposal. Opting for hexavalent chromium-free Type 2 coatings can help mitigate these health and environmental risks.

MIL-DTL-5541 Standard and Process We Apply for Alodine Finish

At our facility, we don’t just follow the MIL-DTL-5541 standard—we tailor it to fit the unique needs of your industry and parts, ensuring compliance and performance that aligns with real-world use. Below is how we apply the standard, plus our specialized insights to match the right coating and process to your project.

The standard’s Type I (hexavalent chromium) and Type II (hexavalent-free) classes each have strengths—but we help you pick the one that balances protection, conductivity, and compliance for your specific application:

MIL-DTL-5541	Type I	Type II	KingStar's Application Guidance
Class 1A	A thicker chromate coating, with a darker color, offers stronger corrosion protection and provides greater adhesion for the paint finish; Contains hexavalent chromium	A thicker chromate coating, with a darker color, offers stronger corrosion protection and provides greater adhesion for the paint finish; Hexavalent chromium has been replaced by safer alternatives such as trivalent chromium, titanium, or zirconium.	Ideal for aerospace structural parts (e.g., wing skins, landing gear) or automotive engine brackets—we recommend Type I for U.S. military/defense clients (who prioritize legacy compatibility) and Type II for EU/global clients (to meet REACH hexavalent chromium restrictions). For example, a recent aerospace customer’s fuselage panels used Type I Class 1A, passing 72-hour salt spray tests with zero corrosion.
Class 3	A thinner chromate coating, lighter in weight, offers slightly weaker corrosion protection and reduces interference with conductivity; Contains hexavalent chromium	A thinner chromate coating, lighter in weight, offers slightly weaker corrosion protection and reduces interference with conductivity; Hexavalent chromium has been replaced by safer alternatives such as trivalent chromium, titanium, or zirconium.	Perfect for electronic enclosures, heat sinks, or grounding components (e.g., telecom hardware). We often use Type II Class 3 for medical device chassis—since it keeps electrical conductivity high (critical for device performance) while avoiding toxic chemicals that could risk contamination.

We’ve refined the standard processes to address common pain points (e.g., uneven coating on complex parts, residue that harms adhesion) and match the material/use case of your components.

Why This Matters for Your Project?

For example, a client making aluminum radar housings for marine use needed corrosion resistance and compliance with global environment protection rules—we recommended Type II Class 1A, and the parts passed 500-hour salt spray testing (well beyond their 300-hour requirement). For a defense client’s electrical enclosures, we chose Type I Class 3 to keep conductivity high (critical for signal integrity) while meeting their military standard needs.

By tailoring MIL-DTL-5541 to your parts and industry, we ensure you get a coating that doesn’t just “meet the standard”—it works for your product’s lifecycle.

Type I Chromating Process

We use this process when durability is non-negotiable—like for parts in harsh environments (e.g., military vehicles, offshore aluminum hardware). Our tweaks ensure consistency, even on intricate parts:

Clean the Metal Surface: We skip one-step cleaning—instead, we use a two-stage process (pre-clean with a mild degreaser, then Alumiprep 33) for parts with heavy oil or machining residue (e.g., engine blocks). This removes hidden contaminants that cause coating failure later. After cleaning, we air-dry parts at 80°F (27°C) to prevent water spots.
Mask and Etch: For parts with threaded holes or electrical contacts (e.g., sensor housings), we use high-temperature-resistant tape (not just standard masking) to keep uncoated areas protected during etching. Our etching solution is adjusted by part material—for cast aluminum (porous surface), we use a milder etch to avoid surface pitting; for forged aluminum (smooth surface), a slightly stronger etch to ensure coating adhesion.
Deoxidize: We use a pH-balanced deoxidizer (not harsh acids) to remove oxides without weakening thin aluminum parts (e.g., aerospace sheet metal). We also rinse with deionized water here—tap water minerals can leave residues that break down the coating over time.
Apply the Chem Film Coating: Immersion is our go-to, but for large parts (e.g., 3000mm-wide industrial frames), we use a low-pressure spray system to ensure even coverage on vertical surfaces. We adjust bath time by thickness needs—for Class 1A, we hold parts 4–5 minutes; for Class 3, 1–2 minutes—to avoid over-coating (which harms conductivity).
Final Rinse and Dry: We finish with a warm (90°F/32°C) deionized water rinse (not cold) to speed up drying and reduce streaks. For critical parts (e.g., military communication gear), we use compressed air (filtered to remove oil) to dry hard-to-reach areas—preventing moisture buildup that causes corrosion.

Type II Chromating Process

This is our top choice for clients focused on sustainability (e.g., medical devices, EU-exported parts) or worker safety. We’ve optimized it to match Type I’s performance without the hazards:

Ambient Rinse: We start with a gentle ambient rinse, but for parts with light rust (e.g., stored aluminum components), we add a small amount of non-abrasive cleaner to lift debris—no harsh scrubbing that damages the part.
Cleaning Method (Acid vs. Alkaline): We don’t just pick one—we match the cleaner to your aluminum alloy:
- Acid Cleaning: Used for cast aluminum parts (e.g., automotive battery housings) to open tiny pores in the metal, so the chem film penetrates deeper for better protection.
- Alkaline Cleaning: Better for forged or extruded aluminum (e.g., medical device frames) to form a thin oxide layer that boosts adhesion—without etching the smooth surface.
Post-Clean Rinse: We do a double rinse here—first with tap water to remove most cleaner, then deionized water to eliminate mineral residues. This step is non-negotiable for clients making food-contact or medical parts (to avoid contamination).
Trivalent Chromium Bath: We use a temperature-stabilized bath (kept at 85°F/29°C) to ensure consistent coating thickness—even for small, intricate parts (e.g., electronic connectors). We follow the technical data sheet but add a 30-second “soak check” halfway through to confirm the film is forming evenly.
Final Rinse & Dry: We rinse with deionized water while the film is still developing (a tweak that enhances its uniformity) and let parts air-dry in a low-humidity room—ideal for parts where compressed air might force water into small gaps (e.g., sensor ports).

Pros of Alodine Coating

Straightforward Process: Applying chromate conversion coatings is simple, fast, and cost-effective, without the need for expensive furnaces required for finishing processes on iron substrates.
Corrosion Resistance: Alodine coatings protect aluminum alloys by forming a thin, protective layer—often just hundreds of nanometers thick—that seals microscopic cracks and pores, preventing water penetration and reducing corrosion risks.
Paint Adhesion: The chem film layer enhances paint adhesion and supports vibrant color application, making Alodine finishes ideal for aerospace components and other painted surfaces.
Electrical Conductivity: Unlike some surface treatments, Alodine coatings maintain excellent electrical conductivity while offering corrosion protection, as the thin film does not significantly alter the metal’s conductive properties.

Cons of Alodine Coating

Thin Coating: The Alodine layer is too thin to provide substantial resistance to abrasion, friction, or heavy wear, and is not ideal as a decorative finish. It is recommended as a pre-coating preparing for more surface treatment to come.
Toxicity: Some Alodine solutions contain carcinogenic chemicals, making them hazardous to handle and difficult to dispose of safely due to environmental regulations.
Lower Durability: Alodine coatings are generally less durable than other finishes like anodizing or powder coating and may fade over time.
Limited Color Options: Alodine finishes are usually limited to a few translucent or transparent shades, lacking the wide color variety available with anodizing or paint coatings.

What’s the Difference between Alodine Coating & Anodizing?

Comparison Dimension	Alodine Coating (Chem Film)	Anodizing
Core Type & Formation	Chemical conversion film: Forms via a chemical reaction between aluminum and chromate solution (no electricity required).	Electrochemical oxide layer: Grows via electrolysis (aluminum acts as anode in acid bath), thickening the metal’s natural oxide layer.
Typical Thickness	Ultra-thin: 0.25–1 μm (0.00001–0.00004 inches); minimal impact on part dimensions.	Thicker: 5–25 μm (0.0002–0.001 inches) for standard use; up to 100 μm for high-wear applications. Adds measurable thickness to parts.
Corrosion Resistance	Moderate: Protects against mild moisture/pollutants (e.g., indoor use). Unpainted Alodine fails in harsh environments (saltwater); works best as a pre-coat for paint.	Superior: Dense oxide layer resists saltwater, UV, and chemicals. Ideal for outdoor/harsh conditions (e.g., marine parts, outdoor furniture) without additional topcoats.
Abrasion & Wear Resistance	Poor: Thin film offers little protection against friction or impacts; easily worn off. Not suitable for high-wear parts.	Excellent: Hard oxide layer (up to 60+ Rockwell hardness) withstands scratches, rubbing, and mechanical stress. Used for parts like tool handles or bicycle frames.
Electrical Conductivity	High: Thin film preserves aluminum’s conductivity (critical for electrical components). Class 3 Alodine is optimized for minimal conductivity interference.	Low/Insulating: Thick oxide layer is non-conductive; disrupts electrical bonding. Not recommended for grounding parts or electronic enclosures.
Paint Adhesion	Excellent: Rough, porous surface creates a strong bond with paint/primer. Class 1A Alodine is industry-standard for aerospace/automotive pre-painting.	Poor (without treatment): Smooth oxide layer repels paint. Requires etching or priming to improve adhesion—adds extra process steps.
Color Options	Limited: Translucent, golden, brown, or iridescent greenish-gold (depends on Alodine type, e.g., 1200S is colorless). No vibrant or custom colors.	Wide: Can be dyed to nearly any color (red, blue, black, etc.) or left natural (clear/silver). Electrolytic coloring creates durable, fade-resistant hues.
Process Complexity & Cost	Simple & Low-Cost: No electricity needed; uses immersion/spraying. Fast (1–5 minutes per part). Lower equipment/maintenance costs.	Complex & Higher-Cost: Requires electrolytic tanks, power supplies, and precise acid bath control. Longer process (30–60 minutes per part). Higher upfront/operational costs.
Environmental Impact	Riskier (Type I): Contains hexavalent chromium (carcinogenic); requires hazardous waste disposal. Type II (hex-free) is safer but still needs chemical management.	Moderate: Uses sulfuric/nitric acids; generates acidic wastewater (must be treated). No heavy metals (e.g., chromium) in standard processes.
Ideal Applications	- Aerospace/defense: Pre-paint base for fuselage parts, electrical bonding components. - Electronics: Enclosures, heat sinks, grounding parts. - Automotive: Engine brackets (pre-painted).	- Decorative: Outdoor furniture, consumer goods (e.g., smartphone cases). - High-wear: Tooling, marine hardware, bicycle components. - Corrosion-prone: Coastal infrastructure, outdoor lighting.
Compliance Standards	MIL-DTL-5541 (military/aerospace), AMS 2471 (aerospace).	MIL-A-8625 (military), ISO 7599 (aluminum anodizing), ASTM B580.

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Frequently Asked Questions

How long does an Alodine coating last?webadmin2025-06-27T03:00:16+00:00

How long does an Alodine coating last?

The lifespan of an Alodine coating varies by environment and whether it’s used alone or under paint.

Indoor environments (mild conditions): Unpainted Alodine coatings can last 5–10 years with minimal corrosion.
Outdoor environments (moderate exposure): Expect 2–5 years of protection if unpainted, though performance depends on pollutants, moisture, and UV exposure.
Marine or highly corrosive environments: Unpainted Alodine alone is insufficient; a topcoat is essential. With proper paint systems over Alodine, protection can exceed 10–20 years in many cases.
Aerospace applications: When used as a primer base layer under paint, Alodine coatings help achieve corrosion protection goals of 20+ years, depending on aircraft maintenance cycles.

Regular inspections and maintenance are crucial for maximizing coating life, especially in critical applications.

What industries commonly use Alodine finishing?webadmin2025-06-27T02:57:54+00:00

What industries commonly use Alodine finishing?

Alodine finishing is widely used across multiple industries because it offers corrosion protection, good paint adhesion, and electrical conductivity without significantly altering the dimensions of metal parts.

Aerospace: Used for aircraft fuselage panels, wing skins, landing gear components, and internal structural parts to protect lightweight aluminum alloys from corrosion while maintaining electrical bonding properties critical for lightning strike protection.
Electronics: Applied to enclosures, chassis, and heat sinks where good electrical conductivity and corrosion resistance are necessary for reliable performance.
Automotive: Found in parts like engine brackets, heat shields, and battery housings, where a thin protective coating prevents corrosion while allowing for subsequent painting or assembly processes.
Defense and Military: Used for equipment housings, communication devices, and vehicle armor panels, ensuring corrosion resistance and proper paint adhesion under harsh conditions.
Marine: Applied to aluminum boat parts, radar housings, and marine hardware exposed to saltwater environments where corrosion protection is essential.
Medical Devices: Used on aluminum frames, housings, and components for medical equipment that require both corrosion resistance and biocompatibility in non-implantable applications.

Overall, Alodine is valued wherever lightweight metals like aluminum need durable protection, conductivity, and readiness for further finishing processes such as painting or sealing.

Can Alodine parts be painted afterward?webadmin2025-06-27T02:56:12+00:00

Can Alodine parts be painted afterward?

Yes. One of Alodine’s key benefits is improving paint adhesion, making it an excellent base layer for subsequent painting or powder coating. But compared to Class 3, Class 1A provides better adhesion for the paint.

Is Alodine safe to use?webadmin2025-09-02T02:07:36+00:00

Is Alodine safe to use?

Whether Alodine is safe to use mostly comes down to the type of chromium it contains and how you handle it. Type I Alodine, which has hexavalent chromium, carries some potential risks—if you’re exposed to its mist for a long time or touch it regularly, it can irritate your skin or airways, and there are more serious health concerns too. So when using this type, you must take precautions: wear chemical-resistant gloves and safety goggles, use a respirator if you’re in a closed space, and make sure the area is well-ventilated.

Type II Alodine, on the other hand, is way safer because it doesn’t have hexavalent chromium—instead, it uses gentler alternatives. You just need to avoid letting it sit on your skin for too long, and it won’t cause big issues. No matter which type you use, anyone handling it should know basic safety steps: if it splashes on your skin or eyes, rinse with water for at least 15 minutes right away, and clean up any spills in the workspace quickly. Also, don’t just pour used Alodine solution or rinse water down the drain—especially Type I, which is considered hazardous waste. You need to have a licensed company dispose of it to follow environmental rules.

Overall, Type II is much easier to use safely for daily needs. If you’re unsure how to use Alodine properly, just check the Safety Data Sheet (SDS) from your supplier—it’ll have all the specific details you need.

Does Alodine coating work on all aluminum alloys?webadmin2025-09-02T02:53:23+00:00

Does Alodine coating work on all aluminum alloys?

No, Alodine coating isn’t universal for all aluminum alloys—it works best on most common aluminum grades but may require extra preparation (or isn’t ideal) for certain types, depending on their alloy composition.

Most heat-treatable aluminum alloys (e.g., 6061, 7075, 2024) are perfect for Alodine: their composition (with moderate amounts of magnesium, silicon, or copper) reacts consistently with chromate solutions, forming a uniform, durable coating—this is why they’re widely used in aerospace and automotive parts treated with Alodine.

However, high-silicon aluminum alloys (e.g., 3003, 3105, or die-cast aluminum like A380) need extra steps: the silicon in these alloys can create a “barrier” that stops the chromate reaction, leading to patchy or thin coatings. For these, we typically add a pre-etch step with a specialized acid to remove excess surface silicon before applying Alodine, ensuring the coating adheres evenly.

Pure aluminum (1000 series, e.g., 1100) also works with Alodine, but the coating may be slightly lighter in color and offer marginally less corrosion resistance compared to heat-treatable alloys—this makes it suitable for low-stress parts (e.g., decorative trim) but less ideal for harsh environments.

If you’re unsure about your alloy, we recommend sharing the aluminum grade (e.g., 6061-T6) with your coating provider—they can test or adjust the process to match your material.

Is Alodine coating electrically conductive?webadmin2025-06-27T02:31:17+00:00

Is Alodine coating electrically conductive?

Yes—Alodine coatings are generally electrically conductive, but the level of conductivity depends on the coating class and type.

Class 1A coatings (under MIL-DTL-5541 Type 1 or Type 2) are thicker and designed for maximum corrosion protection. While they still conduct electricity, they slightly reduce electrical conductivity due to the thicker protective layer. These are often used where corrosion resistance is the priority, such as in aerospace and defense applications.
Class 3 coatings are thinner and specifically intended for applications requiring good electrical conductivity, like electronic enclosures and grounding components. They provide some corrosion protection but focus on maintaining low electrical resistance.
Type 1 coatings use traditional hexavalent chromium chemistry, offering reliable conductivity but involving higher toxicity concerns.
Type 2 coatings use trivalent chromium or other safer chemistries. They also provide electrical conductivity similar to Type 1, with the added benefit of being less hazardous and more environmentally friendly.

Overall, Alodine coatings are an excellent choice when you need both corrosion protection and electrical conductivity, especially for aluminum parts in electrical or electronic applications.

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