The article contains basic information associated with the impact of the FSW process parameters on the forming of a weld while friction welding of aluminium casting alloys. Research was conducted using specially made samples containing a rod of casting alloy mounted in the wrought alloy in the selected area of FSW tool acting. Research has thrown light on the process of joining materials of significantly dissimilar physical properties, such as casting alloys and wrought alloys. Metallographic testing of a weld area has revealed the big impact of welding conditions, especially tool rotational speed, on the degree of metal stirring, grain refinement and shape factor of a weld. As the result of research it has been stated that at the high tool rotational speed, the metals stirring in a weld is significantly greater than in case of welding at low rotational speeds, however this fails to influence the strength of a weld. Plastic strain occurring while welding causes very high refinement of particles in the tested area and changing of their shape towards particles being more equiaxial. In the properly selected welding conditions it is possible to obtain joints of correct and repeatable structure, however in the case of the accumulation of cavities in the casting alloy the FSW process not always eliminates them.