Friction stir welding (FSW) is a friction welding technology particularly useful for joining aluminium alloys which are difficult to weld or even unweldable by means of other methods. The study presents selected results of tests of butt welding of casting aluminium alloys and results of tests related to joining casting aluminium alloys and wrought alloys. According to the test results, casting alloys (and casting alloys with wrought alloys) can be joined by means of FSW obtaining relatively high quality of joints within a limited range of welding conditions. The quality of joints depends on applied welding process parameters, i.e. rotational speed of the tool, linear welding rate, forces and torques/moments. The structure of the weld is proper. It is possible to observe small micro-cracks in the weld, particularly in the area of intermetallic phases. The surfaces of the face and root of the weld are free from material discontinuities. During visual inspection, no imperfections such as “no joint” or porosity were detected.