shield envelops both the arc and weld pool,
preventing oxidation from recurring while the metal
is molten.
Molten aluminum readily absorbs available
hydrogen. When the weld pool solidifies, most of
the hydrogen is released because it is practically
insoluble in solid aluminum. This released
hydrogen may become entrapped and cause porosity
in the weld, which may impair its strength and
weld metal from surface oils or from moisture on
the filler wire. To reduce weld porosity, the metal
surfaces must be carefully cleaned and care must be
taken to maintain the cleanliness of the filler wire
supplied by the manufacturer.
Figure 10-22.--Recommended joint designs for common
Cleaning the surfaces to be welded is of major
thickness of plate.
importance in all aluminum joining, regardless of
The joint design and root openings required for
the welding process. This cleaning should be done
GTA welding are determined by the thickness of the
j u s t before welding. Cleanliness cannot be
a l u m i n u m to be joined and the structural
overemphasized. Oxide, grease, or oil films
requirements of the weldment. Design varies from
remaining on the edges to be joined will cause
a square butt for one-eighth inch sheet to a
unsound welds. Unsoundness (porosity caused by
45-degree minimum included-angle vee joint for
gas, dross inclusions, ships, and so on) reduces the
one-half inch or thicker plate. For tubular sections
mechanical and electrical efficiency of the weld.
having a wall thickness greater than one-eighth inch,
Mildly alkaline solutions, and commercial degreasers
the edges should be beveled with a minimum
that do not produce toxic fumes during welding, are
60-degree included angle and have a zero to
used to remove surface contaminants before
one-sixteenth inch square butt lip. Recommended
welding. One common method of cleaning is for
joint designs for common thicknesses of plate and
the welder to wipe the edges of the joint with a
pipe are shown in figures 110-22 and 10-23. For
cloth that has been dipped in a solvent, such as
one-eighth inch thick and up, some root opening is
alcohol or acetone. All welding surfaces should be
recommended to ensure complete penetration.
dried after cleaning to prevent porosity in the weld
metal. Avoid use of carbon-chlorine solvents.
The joint design and root openings required for
GMA welding are determined by metal thickness
Oxide films should be removed from the surface
and structural requirements as in GTA welding.
of the aluminum by a suitable abrading process such
Aluminum sheet up to one-fourth inch thick can be
as brushing with a clean, stainless-steel wire brush
welded manually with complete penetration using a
immediately prior to welding. If you are ever in
square butt design. For manual welding, material
doubt whether to wire brush, DO IT. Black,
greater than one-fourth inch thick may have a
sooty-surfaced welds mean insufficient brushing.
Preparing Aluminum for Welding
The choice of joint design for welding aluminum
depends upon the thickness of the material and the
On relatively thin
process used for joining.
materials, one- to three-sixteenths inch thickness,
the square butt joint is usually satisfactory for both
processes. For thicker metal, either a single-vee
bevel or double-vee bevel may be necessary.
Figure 10-23.--Recommended joint design for pipe.
10-24
