FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 2. Testing of Metals | 4-23. Aluminum Testing
AC 43.13-1B
9/8/98
4-22. MAGNETIC TESTING. Magnetic
testing consists of determining whether the
specimen is attracted by a magnet. Usually, a
metal attracted by a magnet is iron, steel, or an
iron-base alloy containing nickel, cobalt, or
chromium. However, there are exceptions to
this rule since some nickel and cobalt alloys
may be either magnetic or nonmagnetic.
Never use this test as a final basis for identifi
cation. The strongly attracted metals could be
pure iron, pure nickel, cobalt, or iron-nickel
cobalt alloys. The lightly attracted metals
could be cold-worked stainless steel, or monel.
The nonmagnetic metals could be aluminum,
magnesium, silver, or copper-base alloy, or an
annealed 300-type stainless steel.
4-23. ALUMINUM TESTING. Hardness
tests are useful for testing aluminum alloy
chiefly as a means of distinguishing between
annealed, cold-worked, heat-treated, and heat-
treated and aged material. It is of little value
in indicating the strength or quality of heat
treatment. Typical hardness values for alumi
num alloys are shown in table 4-5.
a. Clad aluminum alloys have surface
layers of pure aluminum or corrosion-resistant
aluminum alloy bonded to the core material to
inhibit corrosion. Presence of such a coating
may be determined under a magnifying glass
by examination of the edge surface which will
show three distinct layers. In aluminum alloys,
the properties of any specific alloy can be al
tered by work hardening (often called strain-
hardening), heat treatment, or by a combina
tion of these processes.
b. Test for distinguishing heat-treatable
and nonheat-treatable aluminum alloys. If
for any reason the identification mark of the
alloy is not on the material, it is possible to
distinguish between some heat-treatable alloys
and some nonheat-treatable alloys by immers
ing a sample of the material in a 10 percent
solution of caustic soda (sodium hydroxide).
Those heat-treated alloys containing several
percent of copper (2014, 2017, and 2024) will
turn black due to the copper content. High-
copper alloys when clad will not turn black on
the surface, but the edges will turn black at the
center of the sheet where the core is exposed.
If the alloy does not turn black in the caustic
soda solution it is not evidence that the alloy is
nonheat-treatable, as various high-strength
heat-treatable alloys are not based primarily on
the use of copper as an alloying agent. These
include among others 6053, 6061, and
7075 alloys. The composition and heat-
treating ability of alloys which do not turn
black in a caustic soda solution can be estab
lished only by chemical or spectro-analysis.
TABLE 4-5. Hardness values for aluminum alloys. (Ref
erence MIL-H-6088G.)
Material
Commercial
Designation
1100
3003
2014
2017
2024
2025
6151
5052
6061
7075
7079
195
220
C355
A356
Hardness
Temper
0
H18
0
H16
0
T6
0
T6
0
T4
T6
T6
0
H36
0
T4
T6
T6
T6
T6
T4
T6
T6
Brinell number
500 kg. load
10 mm. ball
23
44
28
47
45
135
45
105
47
120
110
100
47
73
30
65
95
135
135
75
75
80
70
4-24.4-35. [RESERVED.]
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Par 4-22