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Aluminum can be soldered using a wide variety of solders, fluxes and techniques. The solders for aluminum are usually alloys of zinc, tin, cadmium and lead, although small amounts of other elements have been added to many such solders. Before soldering aluminum, the oxide film on the surface must be removed, either mechanically while the surface is covered with molten solder, or with fluxes. Chloride-free organic fluxes can be used when soldering with low-temperature solders, but chloride-containing salt fluxes must be used when soldering with higher temperature solders.
All of the common soldering techniques can be used in soldering aluminum; and in addition, there are several techniques more applicable to aluminum than to other metals. These include rub soldering, ultrasonic soldering, and reaction-flux soldering. For some application, it may be desirable to plate the aluminum with copper, nickel or some other metal and then solder using procedures applicable to the plating metal.
The use of soldering as a method for joining aluminum depends largely upon the performance required of the resultant joints. Of the performance characteristics, resistance to corrosion is by far the most important, although in some cases other factors may be of consequence. The resistance to corrosion of soldered joints in aluminum varies greatly, depending upon solder composition, joint design, use of protective coatings, and the environment in which the soldered joints are exposed. Sound soldered joints that are adequately protected can be expected to give many years of satisfactory service in most environments.
Dowd, J. D.
Assistant Chief, Process Metallurgy Div. Alcoa Research Labs., Aluminum Company of America, New Kensington, Pa