The Friction Stir Welding (FSW) process generally induces a gradient of properties and a softer behaviour along the welded joint. To design aeronautical structures welded by FSW in fatigue, it is necessary to study the impact of this localized soft behaviour on the overall structure. In this study, the 2198-T8 hardening structural aluminium alloy is considered. Monotonic and cyclic mechanical tests are performed by combining conventional extensometric measurements with digital image correlation (DIC) to measure the local displacement fields around the welded zone. Based on these experimental data, constitutive equations are proposed and identified, zone by zone, across the welded joint. In parallel, a quantification of T1 (Al 2 CuLi) strengthening precipitates is performed in different regions of the joint with a transmission electron microscope in order to identify a relationship between the microstructure and the mechanical parameters. Finally, once all the material parameters are identified, the model is validated by a 3D finite element analysis representative of FSW samples.