Solder aluminum

The joining of metals is one of the typical processing forms. Of course you can also add aluminum. One method is soft soldering. Everything you need to know about soldering aluminum has been summarized in this guide.

Aluminum is a special metal

Aluminum is one of the special metals that are significantly different from steels, ferrous and other metals. For example, the magnetization of aluminum works quite differently than that of, for example, ferrous metals. But aluminum welding, which ultimately also includes soldering, has special features.

Joining process for aluminum

There are a variety of techniques available for joining aluminum:

  • Glue aluminum
  • Screw aluminum
  • Weld aluminum
  • Braze aluminum
  • Solder aluminum

Gluing, welding and brazing aluminum

The brazing of aluminum is hardly used anymore. If anything, aluminum is preferably welded if it is to be a very strong compound. However, the thermal conductivity of the light metal is very high, which is why the bonding of aluminum is becoming increasingly important.

The soldering of aluminum

In many areas, however, it is sufficient to add aluminum by means of soft soldering. For example, when connecting aluminum pipes or aluminum profiles, in many electrical and electronic applications. Nevertheless, important properties of the light metal must also be considered when soldering aluminum.

The oxide layer on the aluminum surface

One crucial aspect is above all the oxide layer that forms on the surface of aluminum or an aluminum alloy. As soon as the aluminum comes into contact with the air or with oxygen, the oxidation already starts. When you cut or grind aluminum, this oxide layer forms within a few minutes.

This oxide layer certainly has advantages. Since aluminum can not rust under ordinary circumstances, this oxide layer also protects against unusual requirements that can lead to aluminum corrosion (pitting). However, a look at the properties of the oxide layer reveals the problem with soft soldering: the melting temperature of the oxide layer is around 2,070 degrees Celsius.

The aluminum itself has a melting point between 580 and 680 degrees Celsius (the melting point of pure aluminum is 660.30 degrees Celsius, but most of the aluminum materials are alloys with a different melting point). When soldering is then anyway still to the fact that the working temperature is below 450 degrees.

What happens when soldering aluminum?

Now it is important to know what happens during soldering. Imagine a sponge cooled to less than 0 degrees, which is your aluminum workpiece. Water is the lot. You need to heat the sponge and the water now. Now the water can penetrate into the pores of the sponge in the area that has been heated.

The principle of soldering

This is also the difference to welding: during welding, solder or welding wire and aluminum workpiece are heated to such an extent that they melt and mix. During soldering, the solder penetrates only into the pores. Imagine now the oxide layer like an aluminum foil wrapped around the sponge.

With the temperature that liquefies water and heats the sponge far enough, the film can not be penetrated. So this layer has to be removed first. This is done either mechanically (grinding from aluminum) or chemically (pickling from aluminum). When removing mechanically, there is a great danger that the oxide layer will reform quickly.

The oxide layer must be removed during soldering

So, in soft soldering, the chemical removal of the oxide layer is preferred. For this purpose, a specially prepared for the brazing of aluminum flux is used. So, when soldering aluminum, be sure to choose the right flux. The specialized trade offers here different products. Then you can solder with the right soldering aluminum professional and well connected.

Tips & Tricks

When soldering and welding aluminum, you need expertise as well as expertise. While other metals change their color when heated and form the so-called tempering color (blue), the aluminum does not change optically. So if you're not paying attention, you could quickly get past the maximum temperature of 450 degrees for soft soldering, and even over the melting point of aluminum.

Video Board: How to solder aluminum.