ASTM B449-93 pdf free.Standard Specification for Chromates on Aluminum.
Colorless，light yellow, or lightgreen iridescent chromate layers of low mass per unit areaincrease the electrical resistance between an electrical contactand the aluminum to a very small extent. When measured at9-V and a 2-A current the resistance should be less than 0.1.Highly colored brown，yellow,or green coatings show amarked increase in electrical contact resistance with increasingmass per unit area of the chromate layer and may reachresistances of 10 000 Q or more.The coatings shall be adherent and non-powdery.There are no practical tests for measuring theadhesion of a chromate conversion coating on aluminum.However, a practical evaluation of the adhesion can be madeby measuring the adhesion of a secondary organic film appliedto the chromated aluminum. When specified,the chromateconversion coating shall pass the organic coating adhesion testin Test Methods D 3359 or the equivalent Iso 2409.
Class 4 coatings intended for use under MIL-C-5541shall have their adhesion evaluated by Method 6301 of Fed.Std. No.141.Additional treatments applied under MIL-C-5541 canbe found in Practices D 1730,Methods 5,6, and 7. Corrosion Resistance-When subjected to the neutralsalt spray test specified in Practice B 117 or in the equivalentIso 3768, three separate test specimens of the coating shallwithstand exposure for the hours shown in Table 2 withoutgiving evidence, to the unaided eye, of more than a total of 8isolated spots or pits. None shall be larger than 1 mm indiameter. Each individual test specimen shall not have morethan 5 isolated spots or pits, none larger than 1 mm in diameteron their respective surfaces. Spots within 10 mm of the edgesof the panels are not counted. Coating Mass Per Unit Area-The mass of the coatingper unit area of coated surface shall conform to the valuesgiven in Table 1.Use the procedure in ISO 3892 as referencedin Guide B 767.Colorless，Yellow,or Brown Coatings —The determi-nation of chromium in the coating will identify the layer as achromate conversion coating. Use the test in Appendix X1.It is necessary to determine thepresence of phosphate and the absence of zinc in order todistinguish chromate-phosphate coatings from anodized coat-ings or zinc phosphate coatings. Use the test in Appendix X1.ASTM B449 pdf download.