AND, IN PROPER CONCENTRATION, MAY CAUSE AN EXPLOSION. WATER IN CONTACT
WITH MOLTEN MAGNESIUM PRESENTS A STEAM EXPLOSION HAZARD. EXTINGUISH
FIRES OF MAGNESIUM WITH ABSOLUTELY DRY TALC, CALCIUM CARBONATE, SAND,
OR GRAPHITE BY APPLYING THE POWDER TO A DEPTH OF 1/2 INCH OR MORE OVER
THE BURNING METAL. DO NOT USE FOAM, WATER, CARBON TETRACHLORIDE, OR
CARBON DIOXIDE.
B. Corrosion Removal -Mechanical
(1)Positively identify the metal as magnesium.
(2)Protect adjacent area to prevent additional corrosion damage from corro-sion products removed during mechanical removal.
(3)If grease or soil is present, clean the rework area per par. 5.
(4)Strip paint per par. 6, if applicable.
(5)Determine extent of damage per par. 3.
(6)Remove loose corrosion products with aluminum wool.
(7)Remove corrosion by one of the following:
Volume 1
20-40-00
Page 12
OCT 01/01
CAUTION: DO NOT USE CARBON STEEL BRUSH OR STEEL WOOL ON MAGNESIUM SURFACES.
TINY METAL PRATICALS WILL BECOME IMBEDDED IN THE MAGNESIUM CAUSING
FURTHER CORROSION AND SUBSEQUENT DAMAGE TO PART.
DO NOT USE SILICONE CARBIDE ABRASIVES ON MAGNESIUM SURFACES.
(a)
Light corrosion shall be removed by light hand sanding, selecting
abrasive paper indicated in Fig. 3 or:
(b)
Light corrosion and stains may be removed with pumice paste. Prepare
pumice paste by mixing pumice powder with water to form a slurry
paste. Apply to stain, using a clean, soft cloth and rub gently. When
paste has dried to a white powder, wipe off with a clean, dry, soft
cloth. If corrosion products still exist, use No. 600 grit wet or dry
abrasive paper and water to remove the remaining corrosion.
(c)
Remove heavy corrosion products by hand scraping with any of the
following items:
1) Carbide-tipped scraper
2) Fine fluted rotary file
3) 400 grit alumina abrasive paper
4) Stainless steel brush (bristles of the brush not to exceed 0.10
inch in diameter)
After use of the stainless steel brush or file, surface shall be
polished with 400 grit alumina abrasive paper, then with 600 grit
alumina abrasive paper.
CAUTION: VIGOROUS, HEAVY, CONTINUOUS RUBBING (SUCH AS WITH POWER
DRIVEN WIRE BRUSHES) CAN GENERATE ENOUGH HEAT TO CAUSE MET-ALLURGICAL CHANGE.
(d) Mechanically remove moderate or severe corrosion by stainless steel
wire brush or abrasive blasting. Refer to par. 7.E., for procedures.
Select appropriate abrasives from Fig. 3.
NOTE: Bristles of stainless steel wire brush should not exceed 0.010
inch in diameter.
(e) Dry abrasive blasting is an approved method for corrosion removal
from magnesium alloys. Refer to par. 7.E. Air pressures of 10 to 35
psi shall be used on magnesium alloy surfaces.
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