3-105. Gas welding is normally but not specifically confined to material 0.032 to 0.087 inch thickness. The thickness of
the material will also determine the method of edge preparation. The edges are prepared in the same manner as steel of
the same thickness, with the exception to the thinner natural 0.040 inch and thinner which are formed to a 90° flange
about the same height as the thickness of material or higher. The flange will help prevent warpage and buckling and
serve as filler metal. The flange should be straight and square and if desired it may be used on material up to 1/8 inch in
thickness provided the finished part will meet specification requirements.
3-106. WELDING ROD. Two types of welding rods will generally permit the gas welding of the various aluminum alloys.
Commercially pure aluminum (1100) Federal Specification QQ-R-566 and 95% aluminum (4043) Federal Specification
QQ-R-566 are the two standard filler rods most commonly used for welding. The 1100 rod is used when maximum
resistance to corrosion and ductility are of prime importance. To minimize the tendency to crack and where greater
strength is required, 4043 alloy is used. Other types of rods are used to provide resistance to specific chemicals and to
meet special strength and specification requirements.
3-107. The diameter of filler rod for gas welding should be selected according to thickness of material to be welded. For
material 0.064 inch thick use 3/32 inch diameter rod; 0.065 to 0.155 inch thick use 1/8 inch rod; 0.166 to 0.249 inch thick
use 5/32 inch diameter rod; 0.250 to 0.374 inch thick use 3/16 inch diameter rod and 0.375 inch thick and up 3/16 inch or
¼ inch diameter rod.
For additional information on welding see JAN-STD-19 Welding Symbols; MILSTD-22A,
Welded Joint Designs; MILSTD-20, Welding Terms and Definitions; MIL-STD-272, Welding and
Allied Processed; MIL-W-22248, Weldments, Aluminum and Aluminum Alloys and MIL-W8604
Welding of Aluminum Alloys.
3-108. CLEANING. Proper cleaning is often an important factor that controls the final results of a welding operation.
This is especially true when welding with oxy-acetylene, oxy-hydrogen or other types of gas and spot welding (resistance
3-109. Heavily soiled parts can be pre-cleaned by vapor degreasing with trichloroethylene, Specification O-T-620, or
immersing in dry cleaning solvent, I Specification P-D-680 Type II. The degreasing operation will remove the oil/grease
and dirt but it has no effect on the oxide film. To remove the oxide film, the vapor degreasing should be followed by
alkaline cleaning in a solution of 6 ounce Federal Specification P-S-751 to one gallon of water, heated to 180° - 200° F.
Parts should be immersed for 20 minutes or until surface shows no water break and then rinse with tap water. The oxide
can then be removed chemically by immersion for 4 - 6 minutes at room temperature in a solution of 9 oz/gal sulfuric
acid; 1.0 - 2.0 oz/gal sodium dichromate and 0.02 oz/gal (by weight) hydrofluoric acid mixed with water. After removal of
the parts from the solution rinse with tap water and air dry.
3-110. Welding should be accomplished immediately after deoxiding and no later than 48 hours (preferably within 24
hours) after the deoxidize operation.
3-111. The chemical cleaning operation should be precisely timed, since over or under application time will increase the
contact resistance and any chemical that will remove the oxide will also attack the aluminum.
Trichloroethylene Solvent, Specification O-T-620, produces dangerous and toxic fumes. Do
not breathe fumes for prolonged periods. Use with adequate ventilation. When using
solvents, alkaline solution and acids wear approved clothing, acid/solvent resisting gloves,
aprons/coveralls, face shields and respirators. If solutions are splashed into eyes, flush
thoroughly with water immediately, and then report to dispensary. For specific instructions
contact local safety office.
3-112. Mechanical Oxide Removal. Stainless brushes (hand or rotary), stainless steel wool and some abrasives can be
used to mechanically remove oxides from unclad aluminum. The strand diameter of the wire brush utilized shall not be
over 0.005 inch. Abrasives shall not be any coarser than 300 grit. Abrasive mats Specification MIL-A-9962, Type 1,
Grade AAA1 (very fine) can also be used.