The friction stir welding (FSW) process has been developed to obtain good joint mechanical and process properties. The development of FSW for lap joint manufacturing will expand the number of applications that can benefit from this technology. In this paper, experimental methods were performed on FSW lap joints, including interface morphology and mechanical properties. Microhardness measurements, lap shear testing, resulting material flow, and the effect of flow variation on the next mechanical properties of FSW butt lap joints in aluminum alloy 3003. The study also presents the effect of different parameters welding on the quality of lap joints. The hardness in the welded region gives importance to the influence of the studied parameters on the different zones of the weld. The fracture shows the characteristics of ductile-brittle mixed fracture.