In welding aluminum more than 0.188 of an inch
thick, bevel the edges and notch them, as shown in view
C of figure 5-10. The included angle of bevel maybe
from 90 to 120 degrees.
After you have prepared the edges of the pieces
properly, you should then clean the surfaces to be
welded. If heavy oxide is present on the metal surface,
you may have to use a stainless-steel wire brush to
remove it. Dirt, grease, or oil can be removed by wiping
the weld area with a solvent-soaked rag.
Aluminum plate 1/4 of an inch thick or greater
should be preheated to a temperature ranging between
500°F to 700°F. This aids in avoiding heat stresses.
Preheating also reduces fuel and oxygen requirements
for the actual welding. It is important that the preheating
temperature does exceed 700°F. If the temperature does
go above 700°F, the alloy maybe severely weakened.
High temperatures also could cause large aluminum
parts to collapse under their own weight. Thin material
should be warmed with the torch before welding. This
slight preheat helps to prevent cracks.
WELDING TECHNIQUES. After preparing
and fluxing the pieces for welding, you should pass the
flame, in small circles, over the starting point until the
flux melts. Keep the inner cone of the flame off the flux
to avoid burning it. If the inner cone of the flame should
burn the flux, it will be necessary to clean the joint and
apply new flux. Next, scrape the rod over the surface at
about 3- or 4-second intervals, permitting the rod to
come clear of the flame each time. If you leave the rod
in the flame too long, it melts before the parent metal
does. The scraping action indicates when you can start
welding without overheating the metal. Maintain this
cycle throughout the course of welding except for allow-
ing the rod to remain under the flame long enough to
melt the amount of metal needed. With practice, the
movement of the rod can be easily mastered.
Forehand welding is usually preferred for welding
aluminum alloys because the flame points away from
the completed weld, and this preheats the edges to be
welded that prevents too rapid melting. Hold the torch
at a low angle when you are welding thin material. For
thicknesses 0.188 of an inch and above, you should
increase the angle of the torch to a near vertical position.
Changing the angle of the torch according to the thick-
ness of the metal minimizes the possibility of burning
through the sheet during welding.
When welding aluminum alloys up to 0.188 of an
inch thick, you have little need to impart any motion to
the torch other than moving it forward. On flanged
material, care must be taken to break the oxide film as
the flange melts down. This may be done by stirring the
melted flange with a puddling rod. A puddling rod is
essentially a paddle flattened and shaped from a 1/4-
inch stainless steel welding rod.
With aluminum alloys above 0.188 of an inch in
thickness, you should give the torch a more uniform
lateral motion to distribute the weld metal over the entire
width of the weld. A slight back-and-forth motion assists
the flux in its removal of oxides. Dip the filler rod in the
weld puddle with a forward motion.
The angle of the torch is directly related to the
welding speed. Instead of lifting the flame from time to
time to avoid melting holes in the metal, you will find it
advantageous to hold the torch at a flatter angle to the
work The welding speed should be increased as the
edge of the sheet is approached. The inner cone of the
flame should never be permitted to come in contact with
the molten metal, but should beheld about 1/8 of an inch
away from the metal.
In the vertical position, the torch is given an up-and-
down motion, rather than a rotating one. In the overhead
position, alight back-and-forth motion is used the same
as in flat welding.
Heat-treatable alloys should be held in a jig for
welding, whenever possible. This helps to eliminate the
possibility of cracking. The likelihood of cracking can
also be reduced by the use of a 4043 filler rod. This rod
has a lower melting range than the alloy being joined
which permits the base metal to solidify before the weld
puddle freezes. As the weld is the last area to solidify,
all of the contraction strains are in the weld bead, rather
than throughout the base metal. You may reduce weld
cracking by tack welding the parts while they are in the
jig and then loosening the clamps before completing the
As soon as the weld is completed and the work has
had time to cool, you should thoroughly wash the weld.
This can be done by vigorously scrubbing it with a stiff
brush while hot water runs over it until all traces of the
flux are removed. This is important, because if any flux
is left on the weld, it can corrode the metal. If hot water
is not available, you may use a diluted solution of 10
percent sulfuric acid. The acid solution should then be
washed off with cold, fresh water after using.