The development of new joint configurations suitable for dissimilar materials enables a wider range of applications and allows for an accelerated replacement of traditional structural construction materials by lightweight materials. The T-configuration is a joint configuration that has not been sufficiently studied for use with dissimilar materials, especially when created using the friction stir welding (FSW) process. In this study, a combined lap/butt design was introduced and implemented, seeking to create a T-joint between aluminium and steel. Characterization of the joints showed that FSW can be successfully used to join aluminium and steel in T-configuration. The formation of intermetallic bonds and kissing bonds was carefully analyzed, and their contribution to fracture behaviour during loading in the skin and stringer directions was studied. Finite element simulation was used to determine the stress state at the interface during loading. The characterization results showed that the intermetallic, as an indicator of metallurgical bonding, is formed when some special features are observed in the pattern of material flow. The fractography images showed that the stress state has a great impact on the fracture. The results of the present study can be effectively used to design and fabricate dissimilar joints according to the loading condition.
