Conversion coatings serve as corrosion protection for unpainted surfaces and help paint adhere to aluminum and aluminum alloys. Conversion coatings are the product of a reaction between the conversion chemicals and the surface material, altering the surface properties. The military and aerospace industries use conversion coatings most widely, but many industries could benefit from using chemical conversion coatings on their components and parts.
The MIL-DTL 5541 Standard
The MIL-DTL 5541 standard applies to conversion coatings on aluminum, aluminum alloys, and substrates that are not anodized. The Department of Defense approves this specification for use in all agencies and departments. This standard specifically applies to DoD applications, but commercial industries test to this standard as well.MIL-DTL 5541 covers two classes of conversion coatings:
- Class 1A: offers optimal protection against corrosion for painted and unpainted surfaces.
- Class 3: offers corrosion protection for materials requiring low contact resistance.
Class 3 coatings are thin, making them ideal for electrical applications. However, this also makes them less corrosion resistant. As a result, Class 3 coatings must undergo salt spray testing and electrical contact resistance testing to ensure compliance with the standard. MIL-DIL 5541 sets the contact resistance limit for Class 3 coatings at 5,000 microohms per in2 with electrode pressure at 200 psi. After 168 hrs of salt spray testing, the resistance must be below 10,000 microohms per in2.
Variables besides coating thickness may also contribute to contact resistance values. Samples with greater surface roughness show less contact resistance under contact electrode pressure because of coating fracture. Decreasing the contact area will raise the contact resistance. Electrodes with a given surface area that are not flat will make less contact, increasing the resistance compared to the expected value.
Contact Resistance Testing with ATS
Since 1967, Applied Technical Services has built a reliable reputation in several industries, including power transmission, metallurgy, aviation, railroads, solar, and automotive. We test to many recognized standards, such as MIL-DTL 5541. Our experienced specialists perform salt spray testing and contact resistance testing to verify that our clients’ conversion coating samples meet the applicable standards.
At ATS, we dedicate ourselves to providing an excellent customer experience. We deliver clear, accurate, and detailed results within a quick turnaround window. We complete all services in a professional manner, and our technicians are available for any questions regarding test results or data.
If you need contact resistance MIL-DTL 5541 testing, contact Applied Technical Services.
