Microstructure, Thermal Stability during Creep and Fractography Study of Friction-Stir-Processed AA2024-T3 Aluminum Alloy

Friction stir processing (FSP) makes it possible to obtain a stir zone with very fine grain size with the aid of severe plastic deformation. Yet using FSP, it is impossible to obtain a uniform cross section as far as the microstructure and mechanical properties are concerned. To reduce the effect of this limitation, in the current study, the material was processed on both sides, thus yielding a wider, rectangular and more homogenous stir zone. In a recent publication, the authors focused on the mechanical properties, thermal stability and transmission electron microscopy (TEM) study of friction-stir-processed AA2024-T3, comparing this alloy to the parent material. While the previous study mentioned focused on the parent and on the as friction-stir-processed material, the current study focuses on post-creep specimens and hence completes the previous one with microstructural processes occurring during creep. The current paper completes the above precipitate analysis using electron-dispersive x-ray spectroscopy (EDS) mapping of the various precipitates reported after exposure to creep temperatures. The TEM study reported in the current paper revealed the formation of dislocation structures during creep, in parallel to the dynamic recrystallization (DRX) reported by the authors in the past. In addition, fractography study indicated premature cracking as the prevailing failure mechanism as well as in the case of friction stir welded creep specimens.