Microstructure evolution during friction stir welding of commercial aluminum alloys.

The aim of this work was to investigate the microstructure evolution during friction stir welding (FSW) of two different wrought aluminum alloys : a work hardened commercially pure At (1050-H14) and an Al-Mg-Sc alloy. Thanks to optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the recrystallization together with precipitates distribution have been analyzed and linked to microhardness profiles measured across the welds. In both alloys, the weld is softer than the initial material. In this paper, we discuss this loss of hardness in the light of the different hardening mechanisms contributing to the base material properties. The material flow during the FSW process was also investigated in the thermomechanically affected zone (TMAZ) of the Al-Mg-Sc alloy. Optical microscopy pictures clearly point out wavy features which strongly suggest shearing as the deformation mode in the vicinity of the advancing pin.