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Analysis of Peripheral Coarse Grain Recrystallization in 6xxx Aluminum Alloy

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Analysis of Peripheral Coarse Grain Recrystallization in 6xxx Aluminum Alloy Extrusion

William H. Van Geertruyden, Wojciech Z. Misiolek, Institute for Metal Forming, Lehigh University, and
Paul T. Wang, Alcoa Technical Center, Alcoa, Inc.

Track: EXTRUSION PROCESS - Peripheral Coarse Grain

ABSTRACT --- The fundamentals of peripheral coarse grain (PCG) structure formation
in extrusion of 6xxx aluminum alloys is not yet completely understood. The objective of
this paper is to understand the origins and mechanisms of the formation of surface
imperfections for peripheral coarse grain structure as the first step to understand
surface behavior of extruded aluminum alloys. Small-scale indirect extrusion tests are
performed in which deformation parameters of strain, strain rate, and temperature are
closely controlled. The deformed material is characterized via traditional metallography
and Orientation Imaging Microscopy, in order to understand the influence of processing
conditions and alloy chemistry on surface defect formation. It was found that
decreasing recrystallization-inhibiting elements such as chromium as well as increasing
the starting extrusion temperature, extrusion ratio, and ram speed all increased the
depth of the PCG. Additionally, a mechanism for favorable coarse grain formation at
the surface of the extrudate is proposed based on microstructure development during

© 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.