Soldering aluminum does not have to be a complicated process. In fact, most jobs can be accomplished at home with very simple tools. This is good news for folks who have been wary of investing in the equipment necessary for aluminum welding. In many applications including pot metal repair, custom vehicle work, and more, aluminum soldering (as opposed to welding) with nothing more that a propane torch can produce strong and durable results.
First a note about materials: The only things required for this job are a basic torch, some flux, and soldering rod. Be advised that not all rods are created equal. Many will do the job better and stronger than others. A little experimenting should quickly indicate which is which. A few recommended products include BernzOmatic Aluminum Soldering Rod, Model AL-3, Turner Brazing/Welding Rods, Rod #3, Cat A5040, and Master Marketing Products, ALUMIWELD.
The advantage of soldering or brazing aluminum over welding is that is requires less equipment: just a torch instead of an electric arc welder plus accessories. If done correctly, soldering can offer a strong and durable connection much more easily. Here are a few pointers as you get started.
As with any joining job, the first step is to clean all surfaces that will be soldered. The most common way to do this is to use rubbing alcohol and a wire brush. Cleaning your surfaces will allow proper bonding to occur. You want the surface to be shiny and smooth, and you will want to avoid contaminating the area with fingerprints.
When setting up the pieces to be joined, it is always a good idea to secure them using some kind of jig unless gravity is already doing the job for you. This is because pieces will tend to shift as heat expands the metal.
While using flux is not essentially necessary, it often helps to produce better results. This compound, applied to the joint before adding heat, helps to clean the area while evening out temperatures. Using this material can often help you to avoid problems with uneven solder flow.
When all is ready, you can use your propane torch to heat up the metal. If one piece is bigger and heavier than the other is, direct most of the heat there. The idea is to bring both pieces up to the right temperature at the same time.
The secret to successful aluminum soldering, as opposed to cast iron welding is breaking through the oxidization layer that naturally forms as the metal is heated. The way to do this is to use the soldering rod itself to scratch through this layer. The technique is to rub the rod into the joint until adhesion is achieved. Usually this will require heating up the metal and applying the rod alternatively until you achieve the correct conditions.
If many cases, the oxide layer will remain in a few areas, and will prevent complete adhesion. This can be frustrating to first timers as they try to fix the problem by adding more solder. This usually just results in a buildup of material where you don’t want it. Your best bet in this situation is to scratch through the oxide layer with a stainless ‘solder aid’ tool, and then use heat to draw the existing solder into the gaps.
As with any joining technique, the best way to get a feel for it is to practice. Using aluminum cans is a great way to get a feel for the heat required and to develop good technique. With a little practice, anyone can solder aluminum, and the best part is, it doesn’t require any expensive tools or materials.