In my thesis, I presented welding of two copper alloys, Cu-HCP (CW0021A/C10300) and Cu-ETP (CW004A/C11000). I made a detailed chemical study of copper and outlined its physical properties. I briefly described alloying with other elements and the creation of alloys after the alloying process. I detailed the description of alloys, which were used in the welding process. I described and presented two welding processes, used in the research. These two processes were Friction Stir Welding (FSW) and the TIG welding process, both of which were described and schematically displayed. From welded joints, we made macro-sections and samples for a tensile test. Since two different welding processes were carried out, two different materials were used. At the TIG welding, we selected a material that contains phosphorus as it binds to oxygen. At FSW material does not melt, because the temperature is not high enough. We found out that the samples welded by the FSW endures lower tensile stresses than a TIG welded samples. It turned out that using a more suitable welding tool would increase the quality of the weld during a FSW. There are also differences in the microstructure of the welded pieces, because the temperature is higher during a fusion welding. Higher temperature effect on changes in the microstructure of the base material and the welded joint.