The present investigation attempts to understand the friction welding characteristics of Aluminum alloy AlCu and steel AISI 4140. In spite, many trials were applied to achieve the sound weld zone of direct bonding between Aluminum and steel. The formation of intermetallic phase and crack in the near weld zone resulted in a lower tensile strength of joints relative to those of other welding technique. Therefore, to prevent intermetallic phase and crack formation at the interface, pure copper was used as insert powders for stress relief buffer layer. This study also envisages the influence of process parameters which include resident preform densities, friction pressure, upset pressure, and burn-off length on microstructure and mechanical properties of the welds. This work consolidates information on the aspects of diffusion joining of steel, copper and Aluminum component with wrought materials for practical execution. In the view point of tensile strength, the highest tensile strength between AlCu and AISI 4140 was acquired by using pure copper as insert powder.