FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 9. Magnesium and Magnesium Alloys | 6-152. Example of Removing Corrosion From Magnesium
9/8/98
AC 43.13-1B
(b) Do not use this method for parts
containing copper and steel-based inserts (un
less the inserts are masked off) and where it
might come into contact with adhesive bonded
skins or parts.
(3) The following solution may be used
to remove surface oxidation and light corro
sion products from magnesium surfaces.
(a) Solution Composition and Op
eration:
1 Chromium Trioxide. 24 oz.
2 (O-C-303, Type II). Water to
Make 1 gal. Reaction Time 1 to 15 min.
3 Operation Temperature. (Solu
tion can be operated at room temperature for a
longer reaction time if desired.) 190 to 202 °F.
4 Container Construction. Lead-
lined steel, stainless steel, or 1100 aluminum.
(b) Mask off nearby operating
mechanisms, cracks and plated steel to keep
the solution from attacking them.
f. Remove moderate to heavy corrosion by
one of the following means.
(1) Powered Corrosion Removal.
(a) Powered corrosion removal can
be accomplished using pneumatic drill motor
with either an aluminum-oxide-impregnated
abrasive wheel, flap brush, or rubber grinding
wheel with an abrasive value to approximately
120 grain size.
(b) Also a rotary file with fine flutes
can be used for severe or heavy corrosion
product buildup on metals thicker than
0.0625 inch. If a flap brush or rotary file is
used, it should only be used on one type of
metal. Do not use either a hand or rotary car
bon steel brush on magnesium.
(c) Pneumatic sanders are acceptable
if used with disk or paper of aluminum oxide.
When using sanders, use extra care to avoid
over heating aircraft skins thinner than
0.0625 inch.
(d) Do not use rotary wire brushes on
magnesium.
(c) Apply chromic acid solution care
fully to the corroded area with an acid-resistant
brush.
(d) Allow the solution to remain on
the surface for approximately 15 minutes.
Agitation may be required.
(e) Thoroughly rinse the solution
from the surface with plenty of clean water.
(f) Repeat the preceding sequence as
necessary until all corrosion products have
been removed and the metal is a bright metal
lic color.
WARNING: Cuttings and small
shavings from magnesium can ignite
easily and are an extreme fire hazard.
Fires of this metal must be extin-
guished with absolutely dry talc, cal-
cium carbonate, sand, or graphite by
applying the powder to a depth of
1/2 inch over the metal.
(2) Blasting. Abrasive blasting is an
approved method of corrosion removal on
magnesium alloys of a thickness greater than
0.0625 inch. Remove heavy corrosion prod
ucts by hand brushing with a stainless steel or
fiber brush followed by vacuum abrasive
Par 6-152
Page 6-31