Simple process models are applied to predict microstructural changes due to
the thermal cycle imposed in friction stir welding. A softening model
developed for heat-treatable aluminium alloys of the 6000 series is applied
to the aerospace alloy 2014 in the peak-aged (T6) condition. It is found
that the model is not readily applicable to alloy 2024 in the naturally aged
(T3) temper, but the softening behaviour can still be described
semi-empirically. Both analytical and numerical (finite element) thermal
models are used to predict the thermal histories in trial welds. These are
coupled to the microstructural model to investigate: (a) the hardness
profile across the welded plate; (b) alloy softening ahead of the
approaching welding tool. By incorporating the softening model applied to
6082-T6 alloy, the hardness profile of friction stir welds in dissimilar
alloys is also predicted.