The standard “MIL-DTL-81706B Chemical conversion materials for coating of aluminum and aluminum alloys” developed by the United States Department of Defense describes the requirements for chemical conversion materials used in the formation of coatings by reaction of the material with the surfaces of aluminum and aluminum alloys.
Chemical conversion materials and application methods are of the following types, classes, material forms and methods:
The method of creating part or identification numbers (PINs) to be used for chemical conversion materials to coat aluminum and aluminum alloys obtained according to this standard is also explained in the standard.
Chemical conversion materials provided under this specification must be products authorized by the qualifying activity to be listed on the applicable qualified products list before the contract is awarded.
All components used in chemical conversion materials shall meet the requirements of this specification. Type I materials shall be formulated from hexavalent chromium compounds, other inorganic salts such as phosphates or fluorides, catalysts, activators and accelerators. Type II materials shall be formulated from salts, catalysts, activators and accelerators that do not contain hexavalent chromium. The materials shall form a non-electrolytic conversion coating in an aqueous solution.
The material shall be a material selected for the processing of metal prepared by spray, brush, dip or applicator application in accordance with the supplier's instructions after proper mixing. Class 1A material supplied premixed in liquid forms III and IV shall be in the concentration required for the process and shall not require further dilution. The conversion coating shall not be exposed to a surface temperature greater than 60 degrees during drying or curing. After application, the coating shall be continuous and substantially free from dust and loose areas. The coating shall also be free from chips, scratches, defects or other defects which would reduce serviceability or impair appearance, protective value or paint bonding properties. The material shall deposit a conversion coating which is visibly noticeable in daylight.
Material and processing baths or solutions should not have an adverse effect on personnel health when used as intended in accordance with local process characteristics.
After proper testing for the applicable salt spray exposure times specified in the table, samples shall show no signs of corrosion when compared to unexposed control panels to the naked eye. Areas within 6,35 mm of the panel edges, identification marks, and panel holding points during processing or salt spray exposure are not evaluated. Differences in color between test panels and control panels are not grounds for rejection.
In terms of paint adhesion (wet tape), when tested after application of epoxy polyamide primer in accordance with this specification, no intercoat separation shall occur between the paint system, the conversion coat or the base metal.
After panel repair and immersion in test fluid for paint adhesion (wet tape) after repair, scratched panels should not show peeling and should be rated at least 3359A per ASTM-D4. There should be no bubbling in the unscratched coated area.
When tested in accordance with this specification, type I coating weight shall not be less than 40 milligrams per square meter (430 milligrams per square meter) of surface area. Class 1A, type I, form VI, method D coating weight shall not be less than 10 milligrams per square meter (107,5 milligrams per square meter) of surface area. Class 1A, type II coating weight shall not be less than 10 milligrams per square meter (107,5 milligrams per square meter) of surface area.
The storage life of materials complying with this specification shall not be less than 12 months. Products for which storage stability is to be determined shall be supplied in containers specified by the qualification activity.
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