Two precipitation hardened aluminium alloys developed for aerospace applications have been studied after friction stir welding: 6056-T78 and 7349-T6. General properties of friction stir welds made of precipitation hardened aluminium alloys are highlighted and discussed. The heat affected zone (HAZ) is characterised by a coarsening/transformation of initial hardening precipitates. The dissolution is favoured in the thermomechanically affected zone (TMAZ) and the central weld nugget, the latter being characterised by a full dissolution of initial hardening precipitates. The cooling part of the thermal cycles encountered during welding can favour locally the heterogeneous precipitation : on dispersoids in the TMAZ of the 6056-T78 alloy and at grain boundaries in the weld nugget of the 7349-T6 alloy. In both cases, the minimum of hardness corresponds to a coarse and extensive precipitation. The tensile behaviour of the weld is strongly influenced by those microstructural variations : yielding will occur first in the weak zone, then in the TMAZ and the weld nugget. The partitioning of the plastic deformation between those zones leads to a satisfactory elongation to rupture of the whole weld.