Patterns of Recrystallization in Warm- and Hot-Deformed AA6022
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RODUCTION
THE
deformation[1–12] and recrystallization[10–35] behavior of fcc aluminum is a subject of intense academic and applied interest. Research over the past few decades has contributed to a better understanding, but there are still questions that need to be addressed before a comprehensive picture can emerge. It is now accepted[11–14] that the origin of all recrystallized grains exists in the deformed state; for aluminum recrystallization, as in the case of the present study, the typical recrystallization sources are the deformed grains and bands[11–16,21–27] and the deformation zones around second-phase particles.[28–35] The deformed bands generalize, especially at higher strains, typical pancaked grains of different orientations. The so-called cube f001gh100i band, a potent source of recrystallized grains,[11,12,14,21–26] was often thought[5,36] to be a transition band; today, however, it is generally accepted[11,12,14,23–26,37] as being the fragmented pieces of original (i.e., present in the undeformed state) cube grains. Coarse second-phase particles (e.g., constituent particles present in an aluminum alloy) can trap[38,39] dislocations and form deformation zones, which are the source of the so-called particle-stimulated nucleation
S. RAVEENDRA, Research Scholar, S. MISHRA, Assistant Professor, and I. SAMAJDAR, Professor, are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra, India 400076. Contact e-mail: [email protected] K.V. MANI KRISHNA, Scientific Officer-C, is with the Materials Science Division, Bhabha Atomic Research Centre, Mumbai, India 400085. H. WEILAND is with the Alcoa Technical Center, Alcoa Center, PA. Manuscript submitted January 31, 2008. Article published online August 8, 2008 2760—VOLUME 39A, NOVEMBER 2008
(PSN).[11,12,14,28–35] Typically, competitions between the sources determine the formation of the recrystallized microstructure.[11,12,14,32,33,40] Competitions between different sources, e.g., deformed bands and PSN, and between different orientations of the same source, e.g., deformed bands of different orientations, are decided by the nucleation and growth advantage or disadvantage.[12,14,24,26,40,41] This is also a subject of a decades-old debate: the oriented nucleation[11–14,20–27,41] and oriented growth.[11–20,41] It should be pointed out that, unlike the classic phase transformation, recrystallization does not involve the creation of new nuclei.[11,12,14] Typical recrystallized nuclei are ‘‘strain-free’’ regions or subgrains of the deformed matrix, which have grown beyond a ‘‘certain’’ size.[12,14,24,26] To achieve this size, both nucleation and limited or local growth may be involved.[12,24] This necessitates the use of a different approach, i.e., looking at the recrystallized microstructure in terms of the frequency or size advantage of recrystallized grains from different sources or orientations.[12,14,24,26,40,41] At a given strain, warm and hot working may involve differing temperatures and s
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