3-154. SOLDERING. Soldering of aluminum is limited in methods and application. Difficulty encountered in soldering is
due to the mutual attraction of aluminum for oxygen in which the atoms combine and instantaneously form an oxide
surface coating. Solder will not bond to the smooth oxide coating and therefore must be removed.
3-155. Another factor requiring consideration in reference to soldering aluminum is corrosion caused by electrogalvanic
action. Galvanic action occurs where two or more dissimilar metals are in contact in a solution that conducts electricity.
Aluminum solder contains at least two other metals, thus all the elements required to produce galvanic action in presence
of moisture. The moisture present in the atmosphere is sufficient to complete the electrogalvanic circuit.
Solder shall not be used on aerospace craft unless specifically authorized by approved
engineering data, etc. due to the above factor.
3-156. Soldering Procedure. The requirements for performing the soldering operation on aluminum are approximately
the same as with any other metal except as previously stated. Surfaces must be free from foreign matter. Surfaces can
be cleaned by the methods previously cited in para 3-108 thru 3-117.
3-157. Soldering aluminums require good control of heat application due to the inherent high conductivity. Generally a
torch is required because of higher heat output and the flame should be non-oxidizing.
3-158. The best soldering results are obtained in conjunction with high purity aluminum and the wrought alloys which
contain 1% or less manganese or magnesium.
3-159. Soldering alloys used for aluminum normally contain 50 to 75% tin and the remainder zinc. (See Specification
MIL-S-12204). Preferred alloy is 60% tin and 40% zinc which may be obtained in accordance with Specification MIL-S-
12204, Comp B.
3-160. Care should be taken to prevent overheating the solder and flux. This can be overcome to a certain degree by
applying the heat to the material being soldered and by letting the material heat the solder flux. When the flux begins to
fume or smoke apply the solder which will flow freely (Always use the correct flux and never overheat). The use of
temperature in excess of 750° F will break the flux down and contaminate the solder.
3-161. If difficulty is encountered because of poor adhesion, puddle the solder and while still molten rub through the
solder and abrade the underlying surface. This may be done with a sharp tool such as a stiff wire brush, hacksaw blade,
or other type of clean material with a high melting point.
3-162. RIVETING. Riveting is the most common method of assembling components fabricated from aluminum. Typical
advantages of this method of mechanical fastening are (1) simplicity of application, (2) consistent joint uniformity, (3)
easily inspected (X Ray and other type equipment not required.) (4) low cost, (5) in many cases lighter weight.
3-163. The rivets used in USAF Weapon System structures require that the alloys and shapes be closely controlled by
specification/standards, to assure structural integrity and uniformity. These rivets are presently classified as solid shank,
hi-shear, blind (structural-non-structural) explosive/chemical expanded. They are available in a variety of shapes, alloys,
sizes, lengths and types. The most common alloys utilized are aluminum because the structure alloys are normally
aluminum. In addition some of the aluminum rivet characteristics can be changed by heat treating which facilitates
application (see paragraph 3-37.
3-164. All of the aluminum alloys could be used to manufacture rivets; however, due to some alloys having superior
properties they have been selected as standard. See Table 3-17 for alloys head, identification, MS/AN standard cross
references, etc., for general rivets used on AF weapons systems.
3-165. Rivets in aluminum alloys 1100(A), 5056(B), 2117(AD) are used in the condition received. Alloys 2017(D) and
2024(DD) often referred to as "Ice Box Rivets" require heat treatment prior to use (see paragraph 3-43). Rivets in alloy
2017 and 2024 should be driven immediately after quenching with a maximum delay of 20 minutes or refrigerated to
delay aging. The customary procedure (unless only a few rivets are involved) is to place the rivets under refrigeration
immediately after heat treatment. The time the rivets may be used will depend on refrigeration equipment available.
Cooling to 32° F will retard natural aging to the extent that the rivets may be driven up to 24 hours. Cooling rivets +0-
10°F and below will retard natural aging to the extent that the rivets may be retained for use indefinitely.
3-166. Rivets utilized with extended driving time should be closely inspected after upsetting for cracks. If inspection
reveals that rivets are cracked, discontinue use, remove defective rivets and obtain reheat treated rivets prior to
continuing the assembly operation.
3-167. If for some reason it is necessary to determine if a rivet has been heat treated this may be done by Rockwell
Hardness testing. Test by supporting rivets in a vee block and hardness reading taken with a 1/16 inch ball 60 kilogram
load . A hardness of over 75 will indicate a heat treated rivet.