DEFORMATION MECHANISMS OF LOW-TEMPERATURE SUPERPLASTICITY IN 8090 Al-Li ALLOYS

Research output: Chapters, Conference Papers, Creative and Literary Works (RGC: 12, 32, 41, 45)32_Refereed conference paper (with ISBN/ISSN)peer-review

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Author(s)

Detail(s)

Original languageEnglish
Title of host publicationSUPERPLASTICITY AND SUPERPLASTIC FORMING 1995
EditorsAmit K. Ghosh, Thomas R. Bieler
PublisherThe Minerals, Metals & Materials Society (TMS)
Pages33-40
ISBN (Print)0-87339-300-7
Publication statusPublished - Feb 1995
Externally publishedYes

Conference

TitleConference on Superplasticity and Superplastic Forming
PlaceUnited States
CityLas Vegas
Period13 - 15 February 1995

Abstract

The 8090 Al-Li alloys, after special thermomechanical processes, exhibited low-temperature superplasticity (LTSP) from 350 to 450 °C, behaving differently from the conventional high-temperature superplasticity (HTSP). The LTSP sheets after ~700% elongation at 350 °C and 8×10-4 s-1 still possessed fine (sub)grains 3.7 μm in size and narrow surface Li-depletion zones 11 μm in width. It results in a post-SP T6 strength of ~500 MPa, which is higher than that of the conventional superplastic 8090 alloys tested at 525 °C or above. The tensile behavior and deformation mechanisms of the LTSP and HTSP sheets were investigated over the strain-rate range 10-5-10-2s-1 and strain range 0.5-1.0. At ε=0.5, the strain rate sensitivity (m-value) for the LTSP and HTSP materials was found to be ~0.33 and 0.50, respectively. The activation energy was extracted to be 92 kJ/mole for the LTSP sheets and to be 141 kJ/mole for the HTSP sheets. As straining to ε=1.0, the m-value of the LTSP materials increased to 0.37 and the activation energy decreased slightly to 82 kJ/mole. By SEM examinations, the movement of surface grains in LTSP samples confirmed the role of grain boundary sliding (GBS). TEM observations revealed that the deformation mechanism consists of a large amount of dislocation motion resulting in the subgrain formation and rotation; and TEM observations from the transverse section might explain the anisotropic deformation behavior during the initial superplastic strain. The primary and rate-controlling deformation mechanisms for the HTSP and LTSP sheets are considered to be GBS and dislocation creep, respectively.

Citation Format(s)

DEFORMATION MECHANISMS OF LOW-TEMPERATURE SUPERPLASTICITY IN 8090 Al-Li ALLOYS. / Pu, H.-P.; Huang, J. C.

SUPERPLASTICITY AND SUPERPLASTIC FORMING 1995. ed. / Amit K. Ghosh; Thomas R. Bieler. The Minerals, Metals & Materials Society (TMS), 1995. p. 33-40.

Research output: Chapters, Conference Papers, Creative and Literary Works (RGC: 12, 32, 41, 45)32_Refereed conference paper (with ISBN/ISSN)peer-review