In the aviation industry, there is a constant need for the parts made with a combination of various materials. This follows from the requirement of reducing production costs, reducing the mass of aircraft and using different mechanical properties in each segment of the airplane. Friction stir welding process has proven to be an effective substitute for riveted joints. The construction parts produced by this process, when selecting the appropriate welding parameters, achieves improved mechanical properties than with rivets, and the construction of the joint is simple. However, one of the main problems of such joints is a heterogeneous microstructure with many phases, tensile residual stresses, increased roughness and fluctuation of hardness in the welding joint. In the thesis we analyzed the effects of friction stir welded joints made from dissimilar high-strength aluminum alloys 2017A-T451 and 7075-T651. In the first phase we evaluated longitudinal residual stresses along the length of the welded joint, then measured the microhardness and analyzed roughness and waviness. In the last part, we have also performed stereological analysis in various microstructural areas. The results confirmed the general trend of increasing the tensile residual stresses towards the center of the joint and the increased roughness and waviness at the transition of the base material/joint. In the middle of the welding joint, we confirmed a decrease in the micro-hardness with an extremely isotropic and fine-grained structure in the range of ~ 4 μm due to the effect of dynamic recrystallization.