Mechanical behavior analysis of the friction stir weld nugget of an aluminum alloy 2050 reveals a major role of the microstructure which varies with the distance to the weld surface. Three types of microstructure heterogeneities are considered namely grain size, precipitation state and textured bands. The grain size and the T1 precipitates density decrease with the distance from the weld surface. The density of T1 precipitates has a first order effect on micro-hardness variations and makes the Hall–Petch rule not valid in this case. Tensile tests combined with strain field identification done by digital image correlation measurements demonstrate the good correlation between textured bands and strain field heterogeneities. Crystal plasticity simulations by finite element method well account for the macroscopic mechanical behavior as well as strain field in textured bands.