The solders used on aluminum alloys are generally
soldering difficult. In these cases, the soldering heat
may be provided by an oxyacetylene torch. Play the
tin-zinc or tin-cadmium alloys. They are usually called
flame of the torch on adjacent surfaces and then apply
aluminum solders. Most of these solders have higher
the solder cold, in bar or wire form, to an appropriate
melting points than the tin-lead solders used for
cross section of the area to be soldered. Flames should
ordinary soldering. Both corrosive and noncorrosive
not impinge directly on the fluxed surfaces. The heated
fluxes are used for soldering aluminum.
surfaces melt the solder, and the excess solder is
The first step in soldering aluminum is to clean the
removed by wiping the joint with a damp cloth before
surfaces completely and remove the layer of oxide. If a
complete solidification of the solder.
thick layer of oxide is present, remove the main part of
Soldered joints in low-pressure, low-temperature
it mechanically by filing, scraping, sanding, or wire
piping systems are sometimes made up by the torch
brushing. You can use a corrosive flux to remove a thin
soldering method. If you must solder a joint near a
layer of oxide. The flux, of course, must be completely
previously soldered joint, wrap the previously soldered
removed from the joint after the soldering is finished.
joint with a cool wet rag to keep the solder from melting.
After you clean and flux the surfaces, tin them with
SOLDERING BY SWEATING
aluminum solder. Apply flux to the work surfaces and
to the solder. You can tin the surfaces with a soldering
Sweating is commonly used to make electrical
iron or with a torch. If you use a torch, do not apply heat
connections. To make a sweated joint, clean and flux
directly to the work surfaces, to the solder, or to the flux.
each surface to be joined; then tin each surface. Hold
Instead, play the torch on a nearby part of the work and
the pieces firmly together and heat the joint with a
let the heat be conducted through the metal to the work
soldering copper or with a torch until the solder melts
area. Do not use any more heat than is necessary to melt
and begins to run out. Remove the source of heat and
hold the parts firmly in position until the solder has
the solder and tin the surfaces. Work the aluminum
solder well into the surfaces. After the surfaces have
been tinned, the parts may be sweated together.
SOLDERING ALUMINUM ALLOYS
Soldering aluminum alloys is more difficult than
soldering many other metals because aluminum alloys
The knowledge you have gained here will be
are always covered with a layer of oxide. The thickness
helpful to you. Silver brazing is a daily job for the Hull
of the layer depends on the type of alloy and the
Maintenance Technician. Braze welding, surfacing,
conditions to which it has been exposed.
powdered metal flame spraying, and soldering are not
Many aluminum alloys can be successfully
done as often as silver brazing, but they are done on a
soldered, if you use the proper techniques. Wrought
frequent basis. Review each of the processes and then
aluminum alloys are normally easier to solder than cast
practice them on scrap material. Knowledge is the first
aluminum alloys. Heat-treated aluminum alloys are
step in being efficient in your job. However, practice is
extremely difficult to solder, just as are aluminum alloys
containing more than 1 percent magnesium.