(12)
Brush alodize (Alodine 1200S) areas of clad and nonclad aluminum, which are to be painted.
(13)
Brush alodize (Alodine 1000) areas of clad aluminum, which are not to be painted.
NOTE: After corrosion removal, all nonclad areas must be refinished using Alodine 1200S plus either two coats primer or one coat primer followed by one coat enamel to match surrounding surface.
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B. Light Skin Corrosion (aluminum)
NOTE: Optional to par. A.
(1)
Preferably remove corrosion mechanically with an approved aircraft polish.
(2)
After polishing, remove residues from surface, recesses and corrosion pits by means of solvent, or by use of a solvent alkaline or emulsion cleaner followed by a thorough water rinse (Ref Chapter 12, Cleaning and Washing).
(3)
Apply phosphoric acid corrosion remover, suitably diluted with water.
(4)
Rinse as in step A.(11).
4. Magnesium Corrosion Removal
A. Remove most of the corrosion with aluminum wool and a stiff-fiber brush, or if necessary use aluminum oxide abrasive, 220 grit or finer. Do not use silicon carbide abrasive.
B. Mask off other materials and parts, especially bearings and cast or pressed-in inserts, against contact with the treating solution or its fumes.
C. Dissolve corrosion from pits with Dow 1 solution as follows:
(1)
Brush on generous quantities of a freshly prepared Dow 1 solution containing 1-1/2 pounds of sodium dichromate and 1-1/2 pints of concentrated nitric acid per gallon.
(2)
Wipe dry, rinse with clean water, and again wipe dry.
D. Treat with Dow 19 solution as follows:
(1)
Prepare solution in clean glass or plastic container by adding in order given: 1-1/3 ounces Chromic Acid (CrO3), 1 ounce powered Calcium Sulfate (CaS04, 2H20), and 1 gallon of water. Stir for at least 15 minutes then allow to settle. Prior to use, the clear solution is poured off and must be free of suspended material when applied.
(2)
Apply solution by swabbing until the surface becomes dull golden to dark brown in color. Use caution in applying the solution, as severe rubbing of the wet surface will damage the coating.
(3)
Rinse with clean water.
(4)
Dry with circulating air, 180°F max temp or by a mild blast of filtered compressed air.
E. Apply following protective finish as soon as possible to avoid soiling, scuffing or initiation of new corrosion:
(1)
Apply two coats primer.
(2)
Apply one coat enamel if part is located on airplane exterior.
5. Steel Corrosion Removal (Steel Parts Heat-Treated to 180 ksi or less)
NOTE: When heat-treat of a specific part is unknown or doubtful, treat as though over 180 ksi per par. 6 and do not treat with acidic materials.
A. Remove loose rust with steel wool and a wire brush.
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B. Dissolve the remainder of the rust with Kelite Process K, Greater Mountain Chemical 801, Oakite 31 or Turco Prepaint, diluted one part to three parts of water.
CAUTION: CONFINE THE SOLUTION TO THE VICINITY OF THE RUSTED AREA AND ALLOW TO REMAIN SEVERAL MINUTES OR UNTIL A GRAY COATING IS OBSERVED.
C. Rinse with clean water.
D. Wipe with a damp cloth, and allow to dry. Force dry if possible.
E. Apply protective finish without unnecessary delay as follows:
(1)
Apply one coat of primer.
(2)
Apply one coat of enamel.
6. Steel Corrosion Removal (Mandatory for Parts Heat-Treated over 180 ksi, Optional for Parts Less than 180 ksi)
A. Remove corrosion by abrading with 220 or finer abrasive paper or dry abrasive blast.
B. Solvent clean.
C. Apply protective finish as follows:
NOTE: Metal is quite reactive after blasting. Primer coats must be applied within 1 hour after sanding or blasting.
(1)
Apply one coat of primer.
(2)
Apply one coat of enamel.
7. Corrosion Removal from Corrosion Resisting Steels (all types), Nickel-Base Alloys, and Titanium
A. Remove corrosion by abrading with stainless steel wool, stainless steel wire brush, fine abrasive paper or abrasive blasting.
NOTE: Abrade slightly beyond the point of removal of visible corrosion to ensure that no corrosion products remain.
B. Polish with 400 grit aluminum oxide paper to remove scratches.
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