SummaryIn this study, a joint between commercially pure titanium alloy and 7075 aluminium alloy was butt welded by using friction stir welding at a rotational speed of 1120 rpm and a traverse speed of 50 mmmin -1 . The evaluation of hardness and microstructure was performed by using scanning electron microscopy. The phases in the weld area were identified by applying the X-ray diffraction technique and the Energy Dispersive X-ray Spectroscopy (EDS) analysis was used for the evaluation of intermetallic compounds of the weld area. The weld zone is cone-shaped and consists of aluminium and titanium particles that play an important role in increasing hardness and tensile strength. The weld area has three zones, namely the titanium base metal zone, the aluminium base metal zone, and the titanium-aluminium intermetallic compound mixed zone. It was also observed that the joint area on the aluminium side includes the stirred area, the thermo-mechanically affected zone, and the heat-affected zone, while the titanium joint area contains the stirred zone and the heat-affected zone. The hardness value of the weld area was around 360 HV, which means that in this area, compared to the base metal of titanium and aluminium, hardness has increased by 6% and 20%, respectively. This can be attributed to severe plastic deformation and formation of intermetallic compounds of titanium and aluminium in this area.