by | May 6, 2024

Among the myriad of standards that guide the aerospace and defense industries, MIL-DTL-81706 governs the application of chemical conversion coatings on aluminum and aluminum alloys. As technologies evolve and the demand for more robust and reliable materials increases, understanding and adhering to MIL-DTL-81706 standards has never been more important. 

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What Is MIL-DTL-81706?

MIL-DTL-81706 is a specification issued by the United States Department of Defense that defines the requirements for chemical conversion materials used on aluminum and aluminum alloys. These materials are intended to provide a surface coating that improves corrosion resistance and provides a base for the application of paint and other coatings. The specification covers both the composition and performance requirements of these chemical conversion coatings.


What Is The Purpose Of MIL-DTL-81706?

Its primary purpose is to detail the types of conversion coatings approved for military use, testing methods for verifying the coating’s effectiveness, and guidelines for application and quality assurance. 

It covers various types of conversion coatings, including both chromate and non-chromate coatings, to address environmental and health concerns associated with chromium compounds. By establishing a uniform standard, MIL-DTL-81706 ensures that components across the aerospace and defense industries meet a consistent level of quality and performance.


How Are Chemical Conversion Coatings Classified Under MIL-DTL-81706?

Under MIL-DTL-81706, chemical conversion coatings are classified based on the type of coating material used and its intended application or performance characteristics. The classifications include:


Type of Coating

  • Type I: Contains hexavalent chromium. These coatings are known for their excellent corrosion protection but have raised environmental and health concerns due to the toxic nature of hexavalent chromium. Type I coatings are being phased out or restricted in many applications due to these concerns.
  • Type II: Contains no hexavalent chromium. Developed as an environmentally friendly alternative to Type I coatings, Type II coatings are based on trivalent chromium or other non-hexavalent substances. They offer good corrosion protection while minimizing environmental and health risks.


Class of Coating

Each Type can be further classified into classes which define the application or performance requirement of the coating:

  • Class 1A: Offers maximum protection against corrosion, for unpainted items or items that will be painted. Class 1A coatings are typically thicker and can significantly improve paint adhesion. They are suitable for a wide range of applications where durability and long-term protection are critical.
  • Class 3: Provides protection against corrosion where low electrical resistance is required. Class 3 coatings are thinner than Class 1A and are used in applications where maintaining the electrical conductivity of aluminum parts is important, such as in electrical connectors.


What Are The Benefits Of Chemical Conversion Coatings?

Enhanced Corrosion Resistance

The primary benefit of chemical conversion coatings is their ability to significantly improve the corrosion resistance of metal parts. This protection is crucial in harsh environments where moisture, salt, and other corrosive elements are prevalent. 


Improved Adhesion

These coatings also enhance the adhesion of paint and other finishes, which is essential for the aesthetic and protective properties of aerospace and defense components. Better adhesion means longer-lasting finishes and less frequent maintenance requirements.


Electrical Conductivity

For certain applications, maintaining electrical conductivity is essential. Class 3 coatings, in particular, are designed to provide corrosion resistance without compromising the electrical performance of the aluminum alloy surface.


Electrical Conductivity


In What Ways Are Chemical Coatings Used In Aerospace And Defense Equipment?

Chemical conversion coatings are applied to a wide range of parts, including:

  • Structural Components: Airframe structures benefit from corrosion-resistant coatings to ensure longevity and structural integrity.
  • Electrical Systems: Components within electrical systems, where conductivity is crucial, are treated with specific types of coatings to maintain performance while preventing corrosion.
  • Exterior Surfaces: For parts exposed to the elements, such as the outer surfaces of aircraft, these coatings provide a crucial first line of defense against environmental damage.


How Do You Comply With MIL-DTL-81706 Requirements?

Compliance with MIL-DTL-81706 involves several key steps, beginning with a thorough understanding of the standard’s requirements. Manufacturers and treatment facilities must:

  • Select the Appropriate Coating Type and Class: Based on the intended application, environmental considerations, and performance requirements, the correct type and class of coating must be chosen to ensure optimal protection and compliance.
  • Implement Strict Process Controls: The application of chemical conversion coatings requires precise control over process parameters, including solution concentration, temperature, and immersion time. Adhering to specified conditions is crucial for achieving consistent and compliant coatings.
  • Conduct Rigorous Testing: To verify compliance, coated components undergo a series of tests, including adhesion tests, corrosion resistance evaluations, and, where applicable, electrical conductivity measurements. These tests ensure that the coatings meet or exceed the standards set forth in MIL-DTL-81706.


Why Is Valence The Industry Leader For MIL-DTL-81706 Coatings?

Expertise and Experience

Our knowledge of the processes, materials, and quality control measures required to meet or exceed these stringent standards is critical for success.


Comprehensive Services

Our ability to provide various classes of coatings (Class 1A for maximum corrosion protection and Class 3 for applications requiring low electrical resistance) further demonstrates our capability to serve partners in the aerospace and military industry.


Quality and Certification

Adherence to MIL-DTL-81706 requires strict quality control measures to ensure that the coatings meet all specified performance criteria. 


Certification and Accreditation

We hold various certifications and accreditations that attest to our quality management systems and compliance with industry standards, including ISO 9001, AS9100 for aerospace, and Nadcap (National Aerospace and Defense Contractors Accreditation Program) for special processes.


Customization and Technical Support

We offer customized solutions and strong technical support for projects requiring specific performance criteria or facing unique challenges. The ability to tailor coatings to specific needs and receive expert guidance throughout the process can result in better outcomes and more efficient problem-solving.


Innovation and Environmental Compliance

With increasing environmental regulations, especially concerning the use of hexavalent chromium, we’re at the forefront of developing and implementing innovative, environmentally friendly coating solutions that meet the Type II classification under MIL-DTL-81706, offering similar performance without environmental and health risks.


Customer Focus and Support

Beyond technical capabilities, our leadership in the industry also means providing excellent customer service, technical support, and tailored solutions to meet the specific needs of clients, ensuring that all application and performance requirements are fully met. 

Explore how Valence can elevate your project’s success with our expert chemical processing services today.


Why Is Valence The Industry Leader For MIL-DTL-81706 Coatings?


Frequently Asked Questions

How does MIL-DTL-81706 relate to MIL-DTL-5541?

MIL-DTL-81706 specifies the chemicals used in the conversion coating process, while MIL-DTL-5541 outlines the performance requirements for the coatings themselves.


Can MIL-DTL-81706 coatings be used as a standalone finish?

Yes, these coatings can provide corrosion protection on their own but are often used as a base for additional coatings or paints.


What methods are approved for applying coatings under MIL-DTL-81706?

The specification includes various application methods, such as immersion, spray, brush-on, and wipe-on techniques.


What are the environmental considerations with MIL-DTL-81706 coatings?

The specification includes considerations for environmentally friendly alternatives to hexavalent chromium, promoting safer chemical conversion coatings.


How is compliance with MIL-DTL-81706 verified?

Compliance is typically verified through specific tests that check for coating thickness, adhesion, and corrosion resistance among other properties.


Are there any recent updates to MIL-DTL-81706?

The specification is periodically reviewed and updated to incorporate new technologies and environmental regulations.


What industries commonly use MIL-DTL-81706 coatings?

These coatings are widely used in the aerospace, automotive, and defense industries for protecting metal surfaces.


Can MIL-DTL-81706 coatings be used on non-aluminum metals?

While primarily designed for aluminum and its alloys, some formulations may be suitable for other metals, but specific compatibility must be verified.


What are the visual appearance options for MIL-DTL-81706 coatings?

Coatings can vary in appearance from colorless to various shades of gold or iridescent, depending on the specific type and class.


How does surface preparation affect the performance of MIL-DTL-81706 coatings?

Proper surface preparation is crucial for ensuring the coating adheres well and provides the intended level of protection.

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