Although Friction Stir Welding is a new joining technique for metal, it is gaining impressive interest in manufacturing. This is because of its ability to dissipate heat in a precise location without dras-tically affecting the internal properties of a material and the environmental aspects. It is growing to be an alternative joining technique for aluminium alloys because of its lower melting point, formation of aluminium oxide, hot cracking and porosity during melting and solidification when joined by conventional methods. However, the joint properties depend upon the process param-eters such as rotating speed, axial load, tilt angle, traverse speed, tool material, etc. A new combi-nation of joining technique, butt joint of aluminium bars inside aluminium block was explored in this study and the microstructural and mechanical properties of weld are studied. Individual welds were done on each side of the block with bars inserted. The rotational speed of the Friction Stir Welding robot was chosen as a varying process parameter, and three joints have been prepared accordingly at 1000, 1200, and 1400 RPM. Microstructure of the overall cross-section and various parts of the weld were taken, and the hardness of different sections was measured. The joints were defect-free with proper material flow, irrespective of the kissing bonds, hooking and cold lap remnants, which are the typical microstructural characteristics of friction stir welding. Non-destructive testing showed that the welds were free from external defects, and a normal joint was prepared. The microstructure at the Stir zone has an equiaxial microstructure, which further changes into distorted in the thermo-mechanical affected zone and elongated and unidirectional at the base material. The grains at the double stir zone were finer than those at the single stir zone because of double stirring and recrystallisation. S-line and swirling flow patterns were observed in the stir zone because of the stirring of materials, and unidirectional flow along the tool's rotating and moving direction was observed outside the stir zone. The FSW process was monitored using temperature, axial force and tool RPM, and it shows that the welds were normal, and there was an increase in temperature within the weld during higher RPM. The hardness results showed a nar-rower range of hardness at the stir zone and base material, which also predicts the reliability of the joining technique. The hardness at the double stir zone has increased slightly compared to other zones because of the double stirring of the material. Additionally, it is improved at higher tool rotational speeds. Furthermore, 3 joints were welded in a single block which were further ma-chined and tensile tested using tensile testing equipment. Joints with 1400 RPM were prepared because the defects (mainly kissing bond) were improved at this RPM, with comparatively higher hardness than at other RPMs. The joint's ultimate tensile strength and elongation were 60-63 MPA and 14-19 %, respectively. The joint started to elongate from the retreating side of the joint, and the necking occurred without breakage into two distinct parts. This is because of the absence of root defect within the stir zone and the ductile behaviour of aluminium. The fractured parts had numerous torn edges and dimples. Although the Friction Stir Welding of bars were feasible, some optimization in the process parameters is required. The possibility of two-pass welding for the tensile testing can also be explored. Therefore, the Friction Stir Welding was successful, showing improved properties and further optimisation in the process parameters, and further welding con-figurations such as multiple-pass or AS-AS welding can be explored.