by the oxygas process if necessary; however, thinner
material is usually spot or seam welded.
MELTING CHARACTERISTICS. Before at-
tempting to weld aluminum alloy for the first time, you
should become familiar with how the metal reacts when
under the welding flame.
A good example of how aluminum reacts when
heated can be seen if you place a small piece of sheet
aluminum on a welding table and heat it with a neutral
flame. Hold the flame perpendicular to the surface of
the sheet and bring the tip of the inner cone almost in
contact with the metal. Observe that almost without
warning the metal suddenly melts and runs away, leav-
ing a hole in the sheet. Now repeat the operation with
the torch held at an angle of about 30 degrees to the plane
of the surface. With a little practice, you will be able to
melt the surface metal without forming a hole. Now try
moving the flame slowly along the surface of the sheet,
melting a small puddle. Observe how quickly the puddle
solidifies when the flame is removed. Continue this
practice until you are able to control the melting. When
you have mastered this, proceed by practicing actual
welding. Start with simple flanged and notched butt
joints that do not require a welding rod. Next, you should
try using a welding rod with thin sheet and then with
WELDING RODS. Two types of welding rods
available for gas welding aluminum alloys are the 1100
and 4043 rods. The 1100 rod is used when maximum
resistance to corrosion and high ductility are of primary
importance. The 1100 rod is used for welding 1100 and
3003 type aluminum alloys only. The 4043 rod is used
for greater strength and minimizes the tendency for
cracking. It also is used for all other wrought aluminum
alloys and castings.
WELDING FLUXES. The use of the proper flux
in welding aluminum is extremely important. Alumi-
num welding flux is designed to remove the aluminum
oxide by chemically combining with it. In gas welding,
the oxide forms rapidly in the molten metal. It must be
removed or a defective weld will result. To ensure
proper distribution, you should paint flux on the welding
rod and the surface to be welded.
Aluminum flux is usually in powder form and is
prepared for use by mixing with water to form a paste.
The paste should be kept in an aluminum, glass, or
earthenware container because steel or copper contain-
ers tend to contaminate the mixture.
It is essential that plenty of flux be applied to the
edges of flanged joints because no filler rod is used in
Figure 5-10.Edge preparation for gas-welding aluminum.
these joints. In all cases, the flux should be applied to
both the bottom and top sides of the sheet in the area of
the weld. After you finish welding, it is important that
you remove all traces of flux. You can do this by using
a brush and hot water. If aluminum flux is left on the
weld, it will corrode the metal.
WELDING PREPARATION. The thickness of
the aluminum determines the method of edge prepara-
tion. On material up to 0.062 of an inch, the edges should
be formed to a 90-degree flange. The height of the flange
should be about the same height, or a little higher, as the
thickness of the material (fig. 5-10, view A). The only
requirement for the flanges is that their edges be straight
and square. If desired, material up to 0.125 of an inch
can be welded with a flange joint. No filler rod is
necessary if you flange the edges.
Unbeveled butt welds can be made on thicknesses
from 0.062 of an inch to 0.188 of an inch; but in these
applications, it is necessary to notch the edges with a
saw or cold chisel in a manner similar to that shown in
view B of figure 5-10. Edge notching is recommended
in aluminum welding because it aids in getting full
penetration and prevents local distortion. All butt welds
made in material over 0.125 of an inch thick are usually
notched in some manner.