Energy dissipation efficiency in aluminum dependent on monotonic flow curves and dynamic recovery
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I.
INTRODUCTION
D E F O R M A T I O N mechanism and fracture mechanism maps were introduced more than a decade ago, and have proven extremely useful in conceptualization of the stress-temperature domains for certain mechanisms. [1,2~ In one article on processing maps for A1, [2] a region of dynamic recrystallization (DRX) was specified as a result of misinterpretations of limited evidence.[3-6[ While the illusion of DRX would be dispelled by a thorough review of the literature, it has been referred to by some as an absolute confirmation. In the discussion of this article, the preceding misconceptions will be clarified to show that there is no foundation for occurrence of DRX in super or commercially pure AI~ Extensive review of A1 deformation at high temperatures shows that restoration depends only on dynamic recovery (DRV). ~7-2q Reviews of DRX have consistently excluded AI. [7-10,12.15,17,19,21-26]
Dynamic materials modeling analyzes the energy dissipation efficiency (EDE = ~7 = 2 m/[1 + m]), relating it to the value of the strain rate sensitivity. ]27,28] EDE maps are used to predict avoidance of unstable shear banding in forging as an extension of the use of m as a prediction of potential for superplastic elongation. The high values of efficiency exhibited in certain strain domains by A1 have been ascribed to DRX on the basis of inadequate microstructural analysis misguided by the process mechanism maps discussed previously) 2.27.28[Such conclusions will be refuted by presenting flow curves and constitutive analyses that match the mechanical data in the EDE analysis, and for which the microstructural observations provide unanimous support for DRV being the sole restoration mechanism. A review of the extensive evidence for DRV leads to an exploration of why
H.J. McQUEEN, Professor, is with the Department of Mechanical Engineering, Concordia University, Montreal, PQ, Canada H3G IM8. E. EVANGELISTA, Professor, is with the Department of Mechanics, University of Ancona, 60131 Ancona, Italy. N. JIN, Research Associate, formerly with Concordia University, is with the Mining and Metallurgy Department, McGill University, Montreal, PQ, Canada H3A 2A7. M.E. KASSNER, Professor, is with the Department of Mechanical Engineering, Oregon State University, Corvallis, OR 97331. Manuscript submitted April 25, 1994. METALLURGICALAND MATERIALSTRANSACTIONSA
DRX does not occur in A1 alloys except in a few special cases. Finally, it will be argued that high EDE is not dependent on DRX. It was deemed important to clarify this matter, since the claims based on EDE by Ravichandran and Prasad (R and p)[27[ w e r e being accepted as definitive despite extensive evidence to the contrary. ]3-5.7-21]
II.
RESULTS
The flow curves for 99.7A1 reported by Hockett [29[ and McQueen and Hockett [3~ are produced in Figure 1 with the flow curves of R and p[27]for both 99.5A1 and 99.94A1. Because of the latter's copious and high quality data, [27] it was possible to conduct a numerical analysis of the data and thus interpolate the flow curves (d
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