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Failure mechanisms in superplastic AA5083 materials

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Authors
Kulas, Mary-Anne
Green, W. Paul
Taleff, Eric M.
Krajewski, Paul E.
McNelley, Terry R.
Subjects
Advisors
Date of Issue
2006
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Abstract
The mechanisms of tensile failure in four 5083 aluminum sheet materials are evaluated under conditions of interest for superplastic and quick-plastic forming. Two mechanisms are shown to control failure of the AA5083 materials under uniaxial tension at elevated temperatures: cavitation and flow localization (i.e., necking). Conditions for which failure is controlled by cavitation correspond to those under which deformation is primarily by grain-boundary-sliding creep. Conditions for which failure is controlled by flow localization correspond to those under which deformation is primarily by solute- drag creep. A geometric parameter, Q, is used to determine whether final failure is controlled by cavitation or by flow localization. Differences in elongations to failure between the different AA5083 materials at high temperatures and slow strain rates are the result of differences in cavitation behaviors. The rate of cavitation growth with strain is nearly constant between the AA5083 materials for identical testing conditions, but materials with less tensile ductility evidence initial cavitation development at lower strain levels. The rate of cavitation growth with strain is shown to depend on the governing deformation mechanism; grain-boundary-sliding creep produces a faster cavitation growth rate than does solute-drag creep. A correlation is found between the early development of cavitation and the intermetallic particle-size population densities of the AA5083 materials. Fine filaments, oriented along the tensile axis, are observed on fracture surfaces and within surface cavities of specimens deformed primarily under grain-boundary-sliding creep. As deformation transitions to control by solute-drag creep, the density of these filaments dramatically decreases.
Type
Article
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Department
Mechanical Engineering
Organization
Naval Postgraduate School (U.S.)
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Sponsors
General Motors Corporation
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Format
11 p.
Citation
M.-A. Kulas, W.P. Green, E.M. Taleff, P.E. Krajewski, T.R. McNelley, "Failure mechanisms in superplastic AA5083 materials," Metallurgical and Materials Transactions A, v.37A, (March 2006), pp. 646- 655.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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