PSI - Issue 60

B.P. Kashyap et al. / Procedia Structural Integrity 60 (2024) 494–509 B.P. Kashyap et al. / Structural Integrity Procedia 00 (2023) 000 – 000 9

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 From the work of Fan et al. (Fan and Chaturvedi, 2000; Fan et al., 2003), shown in Fig. 5(a-c) are (a) stress strain curve (T = 803 K, ̇ =1×10 −3 s -1 ) of AA8090 Al-Li alloy with arrows at which microstructure and texture evolutions were examined (b), along with the variation in fraction of low angle boundary as a function of strain (c). It is noted that there occur simultaneous grain growth and reduction in the grain aspect ratio, causing a change from elongated to equiaxed grains. With increasing deformation, the texture is also noted to be getting randomized. The multiple changes in microstructure cause flow hardening, which suggests the dominant hardening effect of grain growth over the softening effect of grain morphology and texture randomization. In another study, Kashyap and Chaturvedi (2003) reported occurrences of dynamic recrystallization, Fig. 5(d), and cavitation, Fig. 5(e), during deformation in a prior annealed AA8090 Al-Li alloy. Interestingly, the microstructure under the superplastic condition of larger elongation ( e f = 402%, at T = 803 K, ̇ =2×10 −4 s -1 , Fig. 5(e)) shows coarse grain size and large size cavities whereas the sample deformed under non-superplastic condition (at T = 803 K, ̇ =2×10 −2 s -1 , Fig. 5(d)) underwent necking with a lower elongation ( e f = 199%) but exhibited dynamic recrystallization. The examination of stress-strain curves from this work suggests that the grain size and cavity size both increase concurrently with deformation, but the flow hardening effect of grain growth is dominant initially whereas the softening effect of cavity becomes dominant at larger strain.