How can aluminum be welded

Welding aluminum

Welding process for welding aluminum

Again and again we hear that welding aluminum requires special welding equipment, that aluminum cannot be welded at all or that only special welding processes can be used. This is absolutely not the case. The following welding processes can all be used when welding aluminum:

  • Oxy-fuel welding
  • MIG welding
  • TIG welding
  • CMT welding
  • Electrode welding

Autogenous welding of aluminum

Oxy-fuel welding is particularly interesting because aluminum has a high thermal conductivity. This is four times that of steel. This means that - even when soldering aluminum - two differently sized workpieces made of aluminum that are to be welded together also heat up differently.

The melting temperature of aluminum alloys

It is therefore customary to preheat the light metal accordingly when welding aluminum with oxy-fuel. On the one hand, it is advantageous here that the melting point of aluminum is relatively low.

With pure aluminum it is almost exactly 660 degrees Celsius. However, the melting point can deviate from this and be between 580 and 680 degrees, since most aluminum components are alloys. Depending on the alloy, the melting point is then different.

Difficulty heating up - no temper color

There is also a major disadvantage when welding aluminum, which already shows effects when soldering: As you may know, steel discolors when you heat it - it reaches what is known as the tempering color. Based on the tempering color, the optimal temperature for welding can be determined very well.

Unfortunately, aluminum does not discolour when heated. This also means that there is no annealing color, which makes it much more difficult to identify the optimum welding temperature. Experience with aluminum welding is extremely important here, especially when it comes to oxy-fuel welding of aluminum or when you have to preheat aluminum.

MIG welding of aluminum

MIG welding is a very widespread welding technique. It is often referred to as MIG / MAG welding. This has to do with the protective gas and how it reacts. MIG welding is an inert shielding gas. Without delving too deeply into the material: with arc welding without gas, the melt would be directly exposed to the air.

However, this immediately causes oxidation and the properties of the slag also change. This process is prevented by the arc at the welding point being surrounded by shielding gas. This means that there can be no reaction with the ambient air. Colloquially, this form of welding is therefore also known as inert gas welding. The current-carrying electrode burns off during MIG welding.

TIG welding of aluminum

TIG welding is also an inert shielding gas that is used. Tungsten plays a role here. In general, one of the most obvious differences between TIG welding and MIG welding is that it consumes less electricity. This means that even thin sheets can be welded much better. This means that the sheet metal burns through are much less often the case here.

Because when MIG welding very thin sheets in particular, it becomes exhausting even for professionals to weld without burning through the sheet, if possible. This is why the TIG welding process is often used on car bodies. The butt electrode does not burn off during TIG welding, the welding filler is also added manually or automatically (depending on the welding machine).

The CMT welding of aluminum

This is a welding process that is rarely found among do-it-yourselfers. The welding wire runs backwards until it drips, then forwards again in the pushing direction. At the same time, the welding current is repeatedly reduced in this cycle. Since it is not used by do-it-yourselfers, we do not want to go into more detail.

Electrode welding of aluminum

Electrode welding is probably the simplest form of electric welding. A distinction is made between the most diverse versions of the devices, from inverter welding devices to direct current welding devices. The electrode burns down here and also carries current. Compared to the gas-shielded welding process mentioned, electrode welding works without gas from the nozzle and therefore without a gas bottle.

However, since welding in air has disadvantages, this problem is solved differently with electrode welding. Here are the corresponding welding consumables and flux in the electrode. Either the electrodes are coated or filled. In all welding processes for aluminum, as well as for welding other metals, attention must be paid to the composition of the electrodes.

The electrodes for welding aluminum

Depending on the aluminum alloy to be welded, the appropriate alloy is also selected for the electrode. In the case of electrodes for aluminum welding, the correct composition with alloys (silicates, magnesium, copper, etc.) must be ensured.

The oxide layer

If it is also a welding process that does not contain a suitable flux to dissolve the oxide layer, you will have to resort to other options. You can grind the aluminum, but the oxidation layer will reappear immediately. There are also electrolyte solutions for marking aluminum in order to remove the oxide layer.

The significantly higher melting point of the oxide layer

The oxide layer must be removed because the melting point of the aluminum alloy will be between 580 and 680 degrees, but the melting point of the oxide layer will be around 2,050 degrees. This means that you cannot conventionally melt the oxide layer. This prevents the perfect joining of the materials and the structure is inferior. The oxide layer must therefore be removed. Incidentally, this also applies to soldering aluminum.

In the in-house journal you will find numerous topics from the field of "aluminum processing". Here we will also show you how surface refinements such as chrome plating of aluminum are carried out.