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
AC 43.13-1B
9/8/98
6-151. IN-PLACE TREATMENT OF
MAGNESIUM CASTINGS. Magnesium
castings, in general, are more porous and more
prone to penetrating attack than wrought mag
nesium skin. However, treatment in the field
is, for all practical purposes, the same for all
magnesium. Bellcranks, fittings, and numer
ous covers, plates, and handles may also be
magnesium castings. When attack occurs on a
casting, the earliest practical treatment is re
quired to prevent dangerous corrosive penetra
tion. Engine cases in salt water can develop
moth holes and complete penetration over
night.
a. If at all practical, faying surfaces in
volved shall be separated to treat the existing
attack effectively and prevent its further prog
ress. The same general treatment sequence as
detailed for magnesium skin should be fol
lowed. Where engine cases are concerned,
baked enamel overcoats are usually involved
rather than other top coat finishes. A good air
drying enamel can be used to restore protec
tion.
b. If extensive removal of corrosion
products from a structural casting is involved,
a decision from the aircraft manufacturer or a
DER may be necessary to evaluate the ade
quacy of structural strength remaining. Refer
to the aircraft manufacturer if any questions of
safety are involved.
6-152. EXAMPLE OF REMOVING
CORROSION FROM MAGNESIUM. If
possible, corroded magnesium parts shall be
removed from aircraft. When impossible to
remove the part, the following procedure will
be used.
a. Positively identify metal as magnesium.
b. Clean area to be reworked.
c. Strip paint if required.
d. Determine the extent of corrosion
damage.
e. Remove light to moderate corrosion by
one of the following means.
(1) Non-Powered Corrosion Removal.
(a) Non-powered removal can be ac
complished using abrasive mats, cloth, and pa
per with aluminum oxide grit (do not use sili
con carbide abrasive). Metallic wools and
hand brushes compatible with magnesium such
as stainless steel and aluminum, may be used.
(b) When a brush is used the bristles
should not exceed 0.010 inch in diameter.
After using a brush, the surface should be pol
ished with 400 grit aluminum oxide abrasive
paper, then with 600 grit aluminum oxide
abrasive paper.
(c) Pumice powder may be used to
remove stains or to remove corrosion on thin
metal surfaces where minimum metal removal
is allowed.
(2) Chemical Corrosion Removal.
(a) Chemical corrosion removal on
magnesium alloys is usually done with a
chromic acid pickle solution. Chemical corro
sion removal methods are not considered ade
quate for areas that have:
1 Deep pitting,
2 Heavy corrosion and corrosion
by products,
3 Previously had corrosion re
moved by mechanical means, or
4 Previously been sand blasted.
Page 6-30
Par 6-151