TT-C-490 Chemical Conversion Coatings And Pretreatments For Metallic Substrates Base For Organic CoatingsThis specification covers processes, pretreatments, and pre-primer surface preparations of metallic substrates for coating applicators. It covers metal surface preparation for delaying corrosion initiation and promoting primer adhesion. In addition, this specification covers the testing requirements for qualification of conversion coatings, the pretreatments and pre-primer coatings.

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TT-C-490F

risk. When specified, the painted specimens/coupons shall be scribed with two intersecting lines using the scribe tool described in ASTM D1654.

4.7.7.1  Ferrous surfaces. The specimens/coupons, prepared above (see 4.7.2), shall then be exposed to the 5 percent salt spray specified in ASTM B117. The primers shall be tested as specified in table II. When specified, the painted specimens/coupons shall be scribed with two intersecting lines using the scribe tool as described in ASTM D1654. Upon removal, rinse the specimens/coupons gently in warm running water until free from any visible salt deposits and examine for compliance as specified in 3.5.7 for CARC systems. When visual examination is indeterminate, the specimens/coupons shall be scraped with a 2 inch wide metal putty knife or strip primer and inspected for rust, pitting or corrosion not evident with paint present. Nonconformance shall constitute failure of test.

4.7.7.2  Zinc or zinc alloy coated surfaces. All pretreatments and primers used on zinc or zinc alloy coated surfaces shall be qualified for 40 cycles by the GMW 14872 accelerated cyclic corrosion test. The test protocol and calibration tests for mass loss shall be conducted as noted in the test specification. The test specimens/coupons shall be subjected to 40 cycles of testing. Upon removal from the cabinet, scrape them with a 2 inch wide metal putty knife. The specimens/coupons shall meet the acceptance criteria as specified in 3.5.7 for CARC systems.

4.7.7.3  Aluminum surfaces. Pretreatments shall be applied in accordance with manufacturer's instructions to clean aluminum surfaces. Unless specifically called for in the contract, a chromate containing primer shall not be used for qualification of a pretreatment. All pretreatments and primers shall be tested as specified in table II. Upon removal, rinse the specimens/coupons gently in warm running water until free from any visible salt deposits and examine for compliance as specified in 3.5.7 for CARC systems. When visual examination is indeterminate, the specimens/coupons shall be scraped with a 2 inch wide metal putty knife or strip primer and inspected for pitting or corrosion not evident with paint present. Evaluate for compliance as specified in 3.5.7 for CARC systems.

4.7.8  Hydrogen embrittlement relief test. Unless otherwise specified, the test for the effectiveness of the procedures used to control hydrogen embrittlement shall be performed using procedures outlined in ASTM F519 using type 1a.1, which is a standard size notched specimen/coupon at a frequency of every

120 days.

TABLE II.  CARC approved primers.

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