Microstructure, Thermal Stability during Creep and Fractography Study of Friction-Stir-Processed AA2024-T3 Aluminum Allo
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JMEPEG https://doi.org/10.1007/s11665-020-04696-y
Microstructure, Thermal Stability during Creep and Fractography Study of Friction-Stir-Processed AA2024-T3 Aluminum Alloy Michael Regev and Stefano Spigarelli (Submitted September 19, 2019; in revised form February 18, 2020) 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. Keywords
AA2024-T3, aluminum, creep, friction stir processing
1. Introduction In 2000, FSP was derived from friction stir welding (FSW) with the aim of using severe plastic deformation to obtain a stir zone with very fine grain size (Ref 1, 2). FSP is identical to FSW except that in FSP the rotating tool does not weld the parts to one another. Thus, its operation may be referred to as a ‘‘bead on plate’’ process. Very few publications deal with FSP of the 2024 aluminum alloy (Ref 2-10). Nadammal et al. (Ref 2) applied a bottom-up approach for optimizing the process parameters; their results included mechanical properties and residual stress analysis together with grain size and precipitate studies conducted using scanning electron microscopy (SEM). Charit and Mishra (Ref 3) studied the superplastic behavior of friction-stir-processed AA2024-T4. Based on qualitative transmission electron microscope (TEM) examination, they claimed that the grain size obtained at the stir zone was 3.9 lm. Suri This article is an invited submission to JMEP selected from presentations at the Symposium ‘‘Joining and Related Technologies,’’ belonging to the topic ‘‘Processing’’ at the European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2019), held September 1-5, 2019, in Stockholm, Sweden, and has been
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