The undergraduate thesis consists of two parts, theoretical and experimental. In the theoretical part of the the thesis, the properties and characteristics of aluminium alloys in general are listed and the aluminium alloy 5083 (EN AW-5083 H111) is described in more detail. The most common welding defects that occur when welding aluminium alloys were explained. After that, the MIG welding process is described. The advantages, disadvantages and the equipment used for the said process are listed. Types of metal transfer used in MIG welding were described. The AC MIG welding process is explained in more detail and the parameters that affect welding are listed. The properties of shielding gases argon and helium and their influence on the properties and appearance of the weld were described. In the experimental, the welding of the corner joint between the plates made of aluminium alloy 5083 (EN AW-5083 H111) with a thickness of 8 mm was carried out using the AC MIG welding process. As a shielding gas in welding process, pure argon and a mixture of argon and helium were used. After welding, a macroanalysis of the samples was carried out, where the shape and macrostructure of the samples were compared when different gases and different welding speeds were used. Based on the results of the analysis, it was concluded that the use of argon and helium mixture improves penetration into the base material, reduces the occurrence of porosity and increases the weld surface area compared to using pure argon. When comparing different welding speeds, the results showed that as the welding speed increases, the penetration into the base material reduces and the weld surface area decreases.