Aluminium welding techniques: the MIG method

The processing of aluminium offers many opportunities in various sectors due to its unique characteristics such as lightness, corrosion resistance and thermal and electrical conductivity. However, welding aluminium can be particularly complicated, mainly due to its low melting temperature and the formation of surface oxides. Of the various welding techniques available, the MIG (Metal Inert Gas) process stands out due to its effectiveness and speed in achieving quality joints. In this article, we will take a closer look at the MIG process and its applications in aluminium welding.

The MIG process in aluminium welding

The MIG process, also known as GMAW (Gas Metal Arc Welding), is an arc welding method that uses a continuous wire as a filler metal and an inert or semi- inert gas to protect the welding area from oxidation and atmospheric contamination. When welding aluminium, argon is typically used as a shielding gas, as it ensures good arc stability and prevents the formation of porosity in the weld bead.

Advantages of the MIG process for aluminium welding

The main advantages of the MIG process in aluminium welding are:

•  Welding speed: the MIG process allows joints to be obtained quickly and with high productivity, due to its continuous and automatable nature.
•  Good joint quality: the use of inert gas and the stability of the arc make it possible to limit the formation of oxides and porosity in the weld seam, thus ensuring good mechanical strength of the joint.
•  Wide range of weldable thicknesses: the MIG method can be used to weld aluminium of different thicknesses, from a few tenths of a millimetre up to several hundred millimetres.

MIG welding techniques for aluminium

In order to achieve optimal results when welding aluminium using the MIG method, it is essential to follow certain operational guidelines and adopt the most suitable techniques. Below we list some basic aspects to consider during the MIG welding process on aluminium.

Surface cleaning and preparation

It is essential to clean aluminium surfaces thoroughly before welding, removing any traces of dirt, grease, paint or surface oxides. This step is crucial to ensure good adhesion of the weld bead and prevent the formation of porosity or defects in the joint. Surfaces can be cleaned by brushing, degreasing with solvents or specific chemical treatments.

Choice of filler material

The choice of filler material is another critical factor in achieving satisfactory results in aluminium MIG welding. In general, it is advisable to use silicon (e.g. 4043) or magnesium (e.g. 5356) alloyed aluminium wires, depending on the chemical composition of the base material and the mechanical properties required for the final application.

Adjustment of welding parameters

To achieve effective welding on aluminium using the MIG method, special attention must be paid to the adjustment of welding parameters such as voltage, current, filler wire speed and shielding gas flow rate. Some practical tips for adjusting the parameters are:

•  Use a higher voltage than when welding ferrous materials, in order to compensate for the higher electrical resistance of aluminium and to facilitate penetration of the weld bead.
•  Set an adequate current for the wire feed to avoid arc instability and ensure good fusion of the filler material.
•  Adjust the speed of the filler wire according to the thickness of the base material and the characteristics of the filler material itself, to prevent feeding problems or burns in the weld bead.
•  Maintain a constant flow of shielding gas throughout welding to ensure good protection from oxidation and atmospheric contamination.

Alternatives to the MIG process: TIG welding and brazing

In addition to the MIG method, there are other welding techniques suitable for aluminium, including TIG (Tungsten Inert Gas) welding and brazing. TIG welding is particularly suitable for precision work on thin materials and for applications that require a high aesthetic quality of the joints. Brazing, on the other hand, is a low-temperature process used to join aluminium parts without melting the base material, exploiting the ability of aluminium surface oxides to adhere to specific brazing alloys. Each of these techniques has different advantages and disadvantages compared to the MIG process, and it is advisable to evaluate which is the most suitable according to the specific needs of each application.