The paper presents the results of research and analysis of the effect of joining by the RFSSW method of alclad sheets made of Al2024 with an anodic oxide coating, with the using the tool with modified geometry of the front surface of inner sleeve. The different effects of the modifications made on the phenomenon of plasticization and stirring of materials in the process of creating a weld, microstructure of welds and mechanical strength of lap joints were shown. The tests were carried out on 1.27 mm thick sheets, with the use of an unmodified tool and modified tools with three variants of the geometry. The welds and the joints samples were subjected to metallographic and strength tests. It has been shown that the use of a properly selected modified geometry has a beneficial effect on the transport of materials to be joined in the joint zone (flow pattern of plasticized layers and the stirring effect) during the welding, which translates into the strength of the joints and the nature of the weld failure.