3-113. Mechanical removal of oxides shall be confined to the immediate weld area, application to other surfaces of the
metal shall be avoided.
3-114. Do not over apply the mechanical cleaning, application should be controlled and only applied until the surface is
clean of oxide.
3-115. Flux Removal from Aluminum Alloy. After each welding operation (complete) where flux has been used, the
parts or material will be thoroughly cleaned to remove the flux. Most of all flux acts as a deoxiding agent and if allowed
to remain on the surface, corrosion attack of the area applied and adjacent area will occur.
3-116. Flux is removed by washing parts with water (preferably warm 140° F 180° F) or with steam (et) if available. If
there is any possibility that all flux was not removed by washing with water, the part should be immersed in one of the
following acid cleaning solutions:
Acid solution shall not be used if assembly has any dissimilar metal or areas where acid
solution may be entrapped and cannot be readily rinsed. On these type parts repeat washing
of parts with water, agitate flux area with a non-metallic bristle brush.
NITRIC-HYDROFLUORIC ACID CLEANING The solution shall consist of:
1 gallon technical citric acid (58-62% HNO3) 39.5°
½ pint technical hydrofluoric acid (48° HF) (1.15 Sp)
9 gallons of water.
Parts shall be immersed for 3 to 5 minutes in cold acid.
SULPHURIC ACID CLEANING The solution shall be mixed as follows:
1 gallon technical sulphuric acid (93% H2So4) (66° Be)
19 gallons of water.
Parts shall be immersed for 10 to 15minutes in cold acid or 4 to 6 minutes in acid held at 150°F.
NITRIC ACID CLEANING The solution shall be mixed as follows:
1 gallon technical nitric acid (58-62%HNO3) (39.5° Be)
14 Ounces Sodium dichromate (Na2Cr207)
1 gallon of water.
Immerse parts 5 to 10 minutes in hot acid.
3-117. After removing from acid, the parts shall be washed in fresh hot or cold running water for a sufficient length of
time to thoroughly remove the acid. Dilute solutions of chromic acid or of sodium or potassium dichromate may be
added to the rinse water as a corrosion inhibitor. The time for treatment with the above solution depends on the
freshness of the solution and the amount of flux remaining on the part after washing. The rinsing time depends upon the
size and design of the part and the amount of water circulated. One half hour or less should be sufficient. Parts shall
then be completely dried by clean air blast or other approved method.
3-118. INERT-GAS SHIELDED TUNGSTEN ARC WELDING (AC). Inert atmosphere arc welding processes can be
used to make clean and sound welds in aluminum without the use of corrosive fluxes. Two types of inert gas can be
used to provide the shield for this type welding, which are argon and helium. Argon has certain advantages over helium
for this use. Argon is a heavier gas and provides more protection and better arc characteristics than helium.
3-119. The power source for this type welding is electricity which may be ordinary 60 cycle alternating current. The
alternating current provides the required combination of arc stability and oxide removal. Reverse polarity direct current
provides adequate oxide removal but the arc is unstable and difficult to control.
3-120. Filler metal will present a problem in this type welding if the end of the rod is maintained at a position near the
puddle, the rod will soften and melt outside the envelope of inert gas. This will produce oxidation of the rod surface and
slow up welding as the operator must remove the oxide. Also, it may introduce oxide into the weld.' To avoid this, apply
the end of the rod intermittently to the molten pool, but do not withdraw from the protective envelope of gas as this will
3-121. Composition of filler rods for tungsten arc welding is same as used for gas welding. Mechanical properties of
weld deposits for 1100 rod are about 17,500 psi tensile and 25% elongation in 2 inches; and for 4043 rod about 22,000
psi tensile and 8% elongation in 2 inches.