Dynamic evolution of fine grained structure and superplasticity in an unrecrystallized 7075 aluminum alloy.

Yang, Xuyue; Sakai, Taku; Miura, Hiromi

doi:10.2464/jilm.49.383

Cited by 4 publications

(14 citation statements)

References 13 publications

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“…The authors [7][8][9][10][11][12] have studied superplasticity taking place in a cold-rolled 7075 aluminum alloy which was previously warm-deformed just before hot deformation. The results showed that the microstructures evolved under warmdeformation to over a critical strain can not be recrystallized for a long period of time (e.g.…”

Section: Introductionmentioning

confidence: 99%

Continuous Dynamic Recrystallization in a Superplastic 7075 Aluminum Alloy

2002

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New grain evolution taking place during superplasticity was studied by means of tensile tests as well as metallographic observation for a unrecrystallized coarse-grained 7075 aluminum alloy. Grain boundary sliding (GBS) frequently takes place even on the layered high angle boundaries (HABs) parallel to the tensile axis and brings about rotation of subgrains near the HABs and subsequently in grain interiors. The misorientations of (sub)grain boundaries evolved in the pancaked grains increase accompanied by a randomization of the initial texture, followed by development of new grains with HABs. This indicates that unrecrystallized and pancaked grain structure developed by cold rolling is an important prerequisite not only for the appearance of superplasticity, but also for the dynamic evolution of new fine grains. It is concluded that the mechanism of new grain evolution can be a deformation-induced continuous reaction, that is continuous dynamic recrystallization (CDRX). A model for CDRX is discussed in detail comparing with previous several models.

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Section: Introductionmentioning

confidence: 99%

Continuous Dynamic Recrystallization in a Superplastic 7075 Aluminum Alloy

2002

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“…It has also been reported that a GBS angle of 25 occurs with 50% deformation. 4,24,31) In the present study, we found that (1) the contribution ratio of intragranular deformation in the specimens after 50% deformation was 33.5% in the 473 K samples; (2) although had a very small value of 4.3 , GBS was likely; and (3) TEM observations showed the presence of subgrains with dislocations and the formation of equiaxial grains after fracture was confirmed in addition to elongated grains. From these findings, the contribution ratio of intragranular deformation is considered to be greater than the deformation mechanism of superplasticity reported.…”

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confidence: 65%

“…Crystal grains grew from 10 to 25 mm during deformation in the 673 K samples. As discussed in previous reports, 4,24) the deformation of 673 K samples is characterized by significant rotation of crystal grains and GBS, from which it is deduced that dynamic recrystallization and grain growth play a major role. In the 473 K samples, on the other hand, crystal grains were elongated in the tensile direction 0.8 mm in width (D LT ) and 1.7 mm in length (D L ).…”

Section: Appearance Of Superplastic Behaviormentioning

confidence: 96%

“…6 and 8 will not, in general, be formed. 4,24,30) The TEM microstructure of the specimens after deformation at 473 K and 2:8 Â 10 À3 s…”

Section: Formation Of Voidsmentioning

confidence: 99%

“…7 suggests that subgrains contribute in a minor way to sliding and rotation. According to Sakai et al, 4,24,31) the relationship between internal structure, rotation of crystal grains and GBS is explained by the occurrence of local GBS and rotation of subgrains, transforming low-angle grain boundaries changed to highangle grain boundaries and forming new fine grains in highstrain ranges; dynamic recrystallization is also reported to be a contributing factor. High-strain ranges in this case correspond to fewer than 150% deformation.…”

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Low Temperature Superplasticity and Its Deformation Mechanism in Grain Refinement of Al-Mg Alloy by Multi-Axial Alternative Forging

2003

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In practical application, an appearance of low temperature superplasticity (LSTP) is one of necessaries conditions. In this paper, to estimate an appearance and deformation mechanisms of this superplasticity, the role of grain boundary sliding (GBS), intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 mm using Multi-Axial Alternative Forging (MAF) technique. In these materials, it shows that the elongation and strain rate sensitivity (m-value) were 340% and 0.39, respectively, at 473 K under a strain rate of 2:8 Â 10 À3 s À1 . These results show that superplastic appearance is possible at 473 K. The void formed at 473 K elongated in parallel to the tensile direction, with a length of 15 mm and a width of 5 mm. The intragranular deformation contribution was estimated from the aspect ratio of the grains after deformation and its contribution ratio was about 33.5 %. Therefore, for the appearance of lower temperature superplasticity with large elongation and m-value, the role of intragranular deformation was the most important factor together with GBS under these conditions. As described above, the MAF technique is one of the most effective methods to produce ultrafine-grained material and appearance of lower temperature superplasticity.

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