Characterisation of the microstructural evolution during friction stir welding of aluminium alloys: a comparative study of 5251 and 2024 alloys

摘要

High temperatures and large deformation involved during FSW induce complex interactions between deformation, recrystallisation and precipitation. In order to understand interactions between plasticity and precipitation and to separate both effects on weld characteristics, two alloys have been studied: a work hardened class Al-Mg alloy (5251-O), which enables the characterisation of the deformation and grain structure evolutions, and a precipitation hardened Al-Cu-Mg alloy (2024-T351) in which the precipitation takes place in addition to the previous phenomena. The HAZ and TMAZ microstructures are very different in the two alloys. The 5251 TMAZ presents a dynamic recrystallisation grain structure. In comparison, the precipitation in the 2024 delays the recrystallisation and the base material grain structure is retained. Moreover, the presence of dislocations in the 2024 HAZ is shown to accelerate the precipitation kinetics.