Tensile and fatigue crack growth tests of the 6056 T651 and T6 aluminium alloys were carried out. The fatigue crack propagation tests were performed on compact tension 4mm thick (CT) specimens, under cyclic loading with R ratios 0.1 and 0.5. The resulting data was used to predict the fatigue behaviour of stiffened panels subjected to fatigue loading under similar R ratios. The AA6056-T651 panels were fabricated using High Speed Machining (HSM) starting with 30mm thick plates. AA6056-T651 CT specimens were cut from the panels mentioned above, whereas AA6056-T6 CT specimens were machined from 5mm thick material. It was found that the AA6056-T651 (HSM material) specimens, machined from a 30mm thick plate presented higher rupture and yield stress than the AA6056-T6 material extracted from a 5mm thick plate. When tested at the same R value the AA6056-T6 specimens present higher crack growth rate than the AA6056-T651 specimens.