Solder aluminum

The typical machining techniques of aluminum include joining. This includes soldering aluminum. Compared with other metals, aluminum has some special features in soldering. Therefore, below we have created a guide for soldering aluminum for you.

The joining of aluminum

Aluminum can be processed in many ways. In addition to conventional work such as the painting of aluminum, this includes different joining techniques:

  • the gluing of aluminum
  • the soldering of aluminum
  • the brazing of aluminum
  • the welding of aluminum

What is soldering anyway?

To better understand the specificities of soldering aluminum, it is important to understand what soldering actually means and where the differences lie with welding.

For this we imagine a sponge that embodies the metal. Water is our "replacement" for the solder, so the solder wire as solder. Now we also assume that we have temperatures that are responsible for the fact that the usual state of aggregation of water is frozen.

The process of soldering

During soldering, the solder is heated and liquefied. It can now penetrate into the sponge like the liquid water. If you put two sponges together and bring them under freezing, they "stick together" with each other through the freezing water. Since the water has penetrated into the sponge at the same time, the connection is relatively strong, but not strong enough load.

The process of welding

In welding, on the other hand, we would melt the two plastic sponges on the surface and add molten plastic between two molten sponge edges so that enough plastic is present so that both sponges can be connected together.

Differences between the two methods

During soldering, the workpiece (s) are heated to such an extent that the pores open well and the solder that has also melted during this process can penetrate into these pores and solidify again. This creates a relatively strong connection, but can be solved again. Either by renewed heating or by strong mechanical force.

When welding, on the other hand, the work piece (s) are also liquefied - like the welding wire. Then both materials are mixed together; The result is a fusion of all components (one or two workpieces and welding wire with each other).

This compound can be separated only by cutting (flame cutting, cutting, etc.) or by extremely massive mechanical force. However, the material tears and can not really be separated as before.

The soldering of aluminum

When soldering aluminum such as an aluminum pipe with another aluminum pipe, nothing else is done. However, to understand the specifics of soldering (and also aluminum welding, by the way), it is necessary to know the properties of aluminum.

The problem: the oxide layer on the aluminum

Like other metals, aluminum corrodes and oxidizes under certain conditions. If aluminum comes in direct contact with oxygen, an oxidation or oxide layer forms directly on the light metal. In contrast to ferrous metals, however, no corrosion sets in, which could eat through the metal. Rather, an oxide layer forms on the surface, which can be equated with a seal.

Not always bothers the oxide

Under certain conditions, this oxide layer is even useful and valuable. Therefore, aluminum is often oxidized or anodized. Anodizing is a special oxidation process. But when welding and soldering interfere with the properties of the oxide layer.

Melting points of aluminum and oxide

The melting point of aluminum is around 580 to 680 degrees Celsius. The exact melting point (which may also differ from the stated temperature range in corresponding individual cases) depends on the specific aluminum alloy that is present.

The oxidation layer can also be melted. However, this temperature range is considerably higher. Again, depending on the different alloys, the melting point of the oxide layer on aluminum can be between 1,600 and 2,100 degrees Celsius.

The oxidation layer has to be removed elsewhere...

This means that even with significantly hotter welding, the oxide layer can be broken up and melted, and certainly not when soldering aluminum. The oxide layer must first be removed. So you can grind this oxidation layer or stain the aluminum.

... without the oxide being able to form again

This still does not completely solve the problem. As we mentioned earlier, aluminum oxidizes immediately within a few minutes. The risk that you would then solder at least on a partial oxide layer into which the solder can not penetrate is very high.

Therefore, you must use a special flux that is suitable for aluminum brazing. In principle, the same happens as with the pickling of aluminum, except that the flux closes the now freed from the oxide surface in addition to oxygen. This can then no longer form an oxide layer during the soldering of aluminum.

Solder aluminum: brazing and soldering

Now you have to differentiate between brazing and soldering. Soft soldering is when the temperature during soldering is below 450 degrees Celsius, above that it is brazing. However, it should be noted that the brazing of aluminum hardly finds application, since the cost is similar to the welding of aluminum. However, welded aluminum forms a much firmer structure. The really important thing is the soldering of aluminum.

Solder aluminum

The important thing when soldering aluminum is the right temperature. However, unlike other metals, aluminum does not form a tempering color on heating, at which point the soldering temperature could be read. So there is a lot of feeling and experience for soldering aluminum.

Tips & Tricks

A similar complex and demanding aluminum machining represents the polishing of aluminum. Follow the link, you will receive a detailed polishing instructions for aluminum.

Video Board: How to solder aluminum.