Friction Stir Welding (FSW) used for welding similar and dissimilar materials especially to join sheet Al alloys. In this study, commercial pure aluminum and copper sheets (Al/Cu) with a thickness of 3mm were joined. We first preheated on the Cu side by pinless welding tool. Three different tool rotational speeds of 700, 1000 and 1500 rpm were used while the axial load and transverse speed were kept constant at 7.5 KN and 30 mm/min, respectively. We measured different parameters to determine the best rotational speeds for welding. Such as Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Diffraction (XRD) analysis which showed that at 700 rpm there are three elements: Al, Cu and oxygen are present. While at 1500 rpm formation of different Intermetallic Compounds (IMCs). At 1000 rpm the interface has only Al and Cu in a uniform structure this result is due to the sufficient frictional heat generated at 1000 rpm and it considered perfect welds with acceptable mechanical properties.