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Influence of Geometric Dynamic Recrystallization in the Dead Metal Zone

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Influence of Geometric Dynamic Recrystallization in the Dead Metal Zone on Peripheral Coarse Grain Defect Formation in Indirect Extrusion

Alexander Bandar, Scientific Forming Technologies Corp., Columbus, USA
William Van Geertruyden, EMV Technologies LLC, Bethlehem, USA
Wojciech Z. Misiolek, Institute for Metal Forming, Lehigh University, Bethlehem, USA

Track: EXTRUSION/DIE, THEORETICAL - Microstructure

ABSTRACT --- Careful metallurgical analysis of partially indirectly extruded
AA6061 billets has revealed a region of very fine, equiaxed, high-angle boundary
(HAB) grains in the dead metal zone (DMZ), “leaking” into the region of the
extrudate, which subsequently develops into the peripheral coarse grain (PCG)
defect. The fact that the DMZ may not be completely dead, and that a
microstructural evolutionary phenomenon is creating very fine HAB grains in
this region, which then develops into the PCG defect, has inspired a more
thorough experimental investigation and microstructural analysis of the indirect
extrusion process, and of microstructure evolution of the defect-forming region.
Finite Element Modeling (FEM) analyses indicate that indeed the DMZ does
undergo significant deformation during indirect extrusion, rather than remaining
completely static at the die face, thereby suggesting that there is sufficient
deformation in this region for Geometric Dynamic Recrystallization (GDRX) to
occur. As existing quantitative models for GDRX tend to underpredict the
fraction of HABs present, a more detailed mesoscale model of the GDRX
phenomenon is presented, with particular attention to the 3-D geometry of grains,
their ratio of low-angle boundaries to high-angle boundaries, the effect of grain
shape change (GSC) during deformation, and other phenomena. Experimental
results, FEM simulations, and EBSD analyses are presented.

© Extrusion Technology for Aluminum Profiles Foundation (ET Foundation). All rights reserved. No part of The Proceedings may be reproduced in any form without the express written permission of the ET Foundation.