The first step in soldering aluminum is to clean the
surfaces and remove the layer of oxide. If a thick layer
of oxide is present, you should remove the main part of
it mechanically by filing, scraping, sanding, or wire
brushing. A thin layer of oxide can often be removed by
using a corrosive flux. Remember, remove any residual
flux from the joint after the soldering is finished.
After cleaning and fluxing the surfaces, you should
tin the surfaces with aluminum solder. Apply flux to the
work surfaces and to the solder. You can tin the surfaces
with a soldering copper or with a torch. If you use a
torch, do not apply heat directly to the work surfaces, to
the solder, or to the flux. Instead, play the torch on a
nearby part of the work and let the heat conduct through
the metal to the work area. Do not use more heat than is
necessary to melt the solder and tin the surfaces. Work
the aluminum solder well into the surfaces. After tinning
the surfaces, the parts may be sweated together.
Another procedure you can use for soldering alumi-
num alloys is to tin the surfaces with an aluminum solder
and then use a regular tin-lead solder to join the tinned
surfaces. This procedure can be used when the shape of
the parts prevents the use of the sweating method or
demands a large amount of solder. When using tin-lead
solder with aluminum solder, you do not have to use
After soldering is complete, you should clean the
joints with a wire brush, soap and water, or emery cloth.
Ensure that you remove all the flux from the joint since
any flux left will cause corrosion.
Brazing is the process of joining metal by heating
the base metal to a temperature above 800°F and adding
a nonferrous filler metal that melts below the base metal.
Brazing should not be confused with braze welding,
even though these two terms are often interchanged. In
brazing, the filler metal is drawn into the joint by capil-
lary action and in braze welding it is distributed by
tinning. Brazing is sometimes called hard soldering or
silver soldering because the filler metals are either hard
solders or silver-based alloys. Both processes require
distinct joint designs.
Brazing offers important advantages over other
metal-joining processes. It does not affect the heat treat-
ment of the original metal as much as welding does, nor
does it warp the metal as much. The primary advantage
of brazing is that it allows you to join dissimilar metals.
Brazing requires three basic items. You need a
source of heat, filler metals, and flux. In the following
paragraphs these items are discussed.
The source of heat depends on the type and amount
of brazing required. If you are doing production work
and the pieces are small enough, they can be put into a
furnace and brazed all at once. Individual torches can be
mounted in groups for assembly line work, or you can
use individual oxyacetylene or Mapp-oxygen torches to
braze individual items.
Filler metals used in brazing are nonferrous metals
or alloys that have a melting temperature below the
adjoining base metal, but above 800°F. Filler metals
must have the ability to wet and bond with the base
metal, have stability, and not be excessively volatile.
The most commonly used filler metals are the silver-
based alloys. Brazing filler metal is available in rod,
wire, preformed, and powder form.
Brazing filler metals include the following eight
Copper-zinc (brass) alloys
Brazing processes require the use of a flux. Flux is
the substance added to the metal surface to stop the
formation of any oxides or similar contaminants that are
formed during the brazing process. The flux increases
both the flow of the brazing filler metal and its ability to
stick to the base metal. It forms a strong joint by bringing
the brazing filler metal into immediate contact with the