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Big Twin
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Posts: 1,030
Join Date: Jun 2001
Location: West Sussex
Mood: Ugly girls (749) are more dirty.....
Felix,
I was wrong...Alodine 1200 is not listed in my source manual for magnesium alloy. The process still involves chromic acid conversion but appears to be slightly different
Here is how to do it:
All magnesium alloy surfaces that have been reworked must be cleaned and treated with a
conversion coating.
Materials Required:
(1) Chromic Acid
(2) Calcium Sulfate
(3) Cheesecloth
(4) Solvent - General Cleaning of Metal (Series 88)
(5) Sodium Hydroxide
(6) Sulfuric Acid
Prepare the Solution
NOTE: The solution must be prepared and stored in polyethylene or glass container.
(1) Fill a clean polyethylene or glass container to the 9/10 level with distilled water.
(2) Slowly add 1-1/3 fluid ounce (39.5 milliliters) of chromic acid per gallon of final solution.
(3) Add 1 fluid ounce (29.6 milliliters) of calcium sulfate per gallon of final solution.
(4) Fill to final solution level with distilled water.
(5) Stir vigorously for 15 minutes to ensure that the solution is saturated with calcium sulfate.
(6) Let solution stand for 15 minutes to allow undissolved calcium sulfate to settle to the
bottom of the container.
(7) Decant to another polyethylene or glass container without transferring undissolved calcium
sulfate.
(8) Adjust pH with additions of Sodium Hydroxide or Sulfuric Acid to bring within a range of 1.2 to 1.6.
Prepare the surface for conversion coating.
(1) Mask all surfaces likely to be affected by running, dripping, or splashing of the solution.
(2) Seal or plug all holes, gaps, and inlets to assemblies containing honeycomb or foam
plastic with suitable sealing or caulking material or rubber plugs to prevent entry of any
solution.
(3) Wipe treatment area with dry clean cheesecloth to remove loose particles and residue.
(4) Wipe with cheesecloth dampened (not saturated) with solvent, Series 88. Repeat using clean cheesecloth until no visible residue transfers to the cheescloth.
(5) Allow to dry to a minimum of 15 minutes.
Apply the conversion coating
CAUTION: SEVERE RUBBING OF WET SURFACE CAN CAUSE COATING DAMAGE.
(1) Apply solution by swabbing with brush, swab, swatches, cellulose sponge, or white blotting
paper. Maintain a continuous wet film until metal surface becomes dull golden or dark
brown in color. Discard used solution.
(2) Rinse with cold clean water.
CAUTION: DO NOT DIRECT HIGH PRESSURE AIR TO SURFACE WHILE DRYING
AS COATING IS STILL SOFT.
(3) Allow to dry at ambient temperature. If possible, use low pressure air to dry the surface.
(4) Restore the original finish as soon as possible after drying. Handle parts with clean gloves
and keep parts clean and dry to avoid surface contamination.