Alodine Finish Service

The Alodine coating is a chromate conversion coating that enhances the corrosion resistance and paint adhesion of aluminum and other metals. Our Alodine surface treatment service can provide long-lasting surface protection and complies with military and aerospace standards.

Chromate conversion coating
Enhanced corrosion resistance
MIL-DTL-5541 compliant finish

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Overview of Alodine Finishing

What Is Alodine: Alodine, also known as Chem Film, is a chromate conversion coating applied to aluminum and its alloys to enhance corrosion resistance and surface adhesion. This name originally came from a trademark of Henkel, referring to a chromium oxide coating technology for aluminum surfaces. Now, Henkel has actually changed the original “alodine” trademark to Bonderite®, but due to its long-term popularity, it has been used as a proper noun ever since. It forms a thin, protective layer without altering the metal’s strength or weight, and is widely used as a base for paint or primer in aerospace, military, and industrial applications.

How Does It Work: The Alodine coating process relies on an electrochemical reaction between the metal surface and a chromate solution that typically contains chromium compounds like chromic anhydride, sodium fluoride, and tetrafluoroborate. When a metal part—usually aluminum—is immersed, sprayed, or brushed with this solution, a chemical conversion occurs that forms a thin chromium oxide film, usually just tens to hundreds of nanometers thick. This layer, while thinner than anodizing, creates a gelatinous protective barrier that effectively isolates the substrate from corrosive elements such as moisture, air, and chemicals. The result is a surface with improved corrosion resistance, enhanced adhesion for subsequent coatings, and in some cases, increased surface hardness and wear resistance.

Other Surface Treatment

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

MIL-DTL-5541	Type I	Type II
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.
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.

Type I Chromating Process

Step 1: Clean the Metal Surface
Thoroughly clean the metal surface before applying the Alodine coating. Use a metal cleaner such as Alumiprep 33 to remove oils, grease, and other contaminants. After cleaning, rinse and dry the part to ensure optimal adhesion of the conversion coating.

Step 2: Mask and Etch
Mask off any areas that should remain uncoated, then etch the surface as needed to prepare it for coating. Etching ensures a uniform and effective chemical conversion layer. Rinse and dry the part after etching.

Step 3: Deoxidize
Remove oxides and other surface impurities by deoxidizing the metal. This step eliminates oxygen-based contaminants that could interfere with coating performance. Rinse the part thoroughly to remove any residual deoxidizing agents.

Step 4: Apply the Chem Film Coating
Immerse the part in an Alodine solution bath for a specified time based on the desired coating thickness and part geometry. Alternatively, you can apply the coating by spraying or brushing.

Step 5: Final Rinse and Dry
After coating, rinse the part with water to remove excess chemicals. For the best finish, perform a warm water rinse and allow the part to dry completely.

Type II Chromating Process

Step 1
Rinse the metal part at ambient (room) temperature to remove loose surface contaminants.

Step 2 (Cleaning Method)

Acid Cleaning: Clean the metal part using a diluted acid solution, which acts as an autocatalytic agent to open the pores on the metal surface, allowing better penetration of the chem film.
Alkaline Cleaning: Alternatively, treat the aluminum surface with a moderately alkaline solution to form a thin oxide layer that improves coating adhesion.

Step 3
Rinse the part thoroughly with water to remove any residual cleaning solution.

Step 4
Immerse the part—whether aluminum or another metal—in a trivalent chromium solution, following the time and conditions specified in the technical data sheet, to form the chemical conversion coating.

Step 5
Gently rinse the coated part with deionized water while the chem film continues to develop. Dry the surface using compressed air or allow it to air-dry naturally.

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.

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?webadmin2025-06-27T02:43:53+00:00

Is Alodine safe to use?

1. Material Selection and Suitability

Durability begins with material choice. Common materials include:

Polyethylene (PE): Flexible, low-temperature resistant (-40°C to 90°C), ideal for household storage (e.g., HDPE for clothing bins).
Polypropylene (PP): Semi-crystalline thermoplastic with high impact resistance and chemical stability (resistant to acids, alkalis, and organic solvents), widely used in industrial applications.
Other materials: Polystyrene (PS), polycarbonate (PC), etc., each requiring tailored testing.

2. Mechanical Performance Testing

(1) Impact Resistance

ASTM D3029: Falling weight method to test rigid plastic samples, measuring energy absorption.
ISO 180 Izod Impact Test: Pendulum impact method to break notched or unnotched specimens.
Drop Testing: Simulates real-world drops during transport. Silicone-treated containers show 50%+ lower breakage rates. Hazardous material packaging requires sub-zero testing (-40°C per GB/T 4857.5).

(2) Compression and Stacking Tests

GB/T 4857.3: Static load stacking test to evaluate deformation under long-term weight (e.g., 12.5 mm/min compression rate until failure).
DIN 55440-1: Tests maximum compression strength under controlled conditions (23°C, 50% RH).
Box Compression Test (BCT): Uses universal testing machines to measure load capacity before deformation.

3. Environmental Durability Testing

(1) Temperature and Humidity Cycling

ISO 4892: Simulates UV exposure and humidity to assess aging (e.g., brittleness, discoloration).
Standard Climates: 23°C±2°C, 50% RH±5% (non-tropical) or 27°C±2°C, 65% RH±5% (tropical) per ISO 2233.
HAST (Highly Accelerated Stress Testing): Accelerates aging under extreme conditions (e.g., 85°C, 85% RH) to evaluate sealing and structural integrity.

(2) Extreme Temperature Resistance

Low-Temperature Testing: Hazardous material containers undergo impact tests at -40°C.
High-Temperature Testing: Thermal aging tests in ovens to assess mechanical degradation.

4. Chemical Stability and Safety Testing

Chemical Corrosion Resistance: Expose containers to acids/alkalis; measure weight loss and deformation (silicone-treated surfaces perform better).
Food Contact Safety:
- GB 4806 Series: Tests heavy metal leaching (lead, cadmium) and residue limits.
- FDA Standards: Ensures non-toxicity and no chemical migration.
Airtightness Testing: GB/T 17344 requires zero leakage under specified pressures.

5. Specialized Application Tests

(1) Hazardous Material Packaging

GB 19270 Series: Covers stacking, drop, and airtightness tests aligned with UN Transportation of Dangerous Goods regulations.
Sub-Zero Drop Tests: Mandatory for non-PE containers at -40°C.

(2) Medical and Laboratory Use

Sterilization Compatibility: Validate structural integrity after autoclaving (e.g., 121°C steam).
Chemical Contamination Resistance: Assess surface durability against lab reagents.

6. Recycling and Sustainability Testing

Recyclability Verification: PP containers must retain performance after component removal.
ROHS & REACH Compliance: Ensure restricted substances (e.g., phthalates) meet EU limits.

Summary: Testing Workflow

Material Selection: Choose PE, PP, etc., based on application.
Prototype Testing: Mechanical tests (impact, compression, drop).
Environmental Simulation: Temperature/humidity cycling, UV aging.
Chemical & Safety Checks: Corrosion resistance, food safety, airtightness.
Specialized Testing: Sub-zero drops, sterilization, etc.
Certification: Compliance with ISO, ASTM, GB, etc.

Through this multi-dimensional approach, KingStar Mold’s wholesale custom design plastic storage boxes are rigorously validated for durability across household, industrial, and specialized uses.

How does Alodine differ from anodizing?webadmin2025-06-27T07:07:38+00:00

How does Alodine differ from anodizing?

While both Alodine and anodizing protect aluminum, they differ in thickness, durability, and electrical conductivity. Alodine applies a thin, conductive chemical film ideal for corrosion protection and paint adhesion, whereas anodizing builds a thicker oxide layer for superior wear resistance and color variety but reduces conductivity.

[Read more about Alodine vs. Anodizing here.]

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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