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Metallurgical Analysis of Surface Streaking Defect in AA6060 Extrudate

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Metallurgical Analysis of Surface Streaking Defect in AA6060
Extrudate

Andrew J. Thome 1, Joshua E. Walker 2, Timotius Pasang 2, Wojciech Z. Misiolek 1
1 Institute for Metal Forming, Lehigh University, Bethlehem, Pennsylvania, U.S.A.;
2 Department of Mechanical Engineering, AUT University, Auckland, New Zealand

Track: VALUE-ADDED PROCESSES - Metallurgical Factors

ABSTRACT—An industrial profile extruded from Superflow® AA6060 alloy was examined to
determine the cause of longitudinal streaks visible on the specimen surface. Streaking is an
imperfection that appears on the surface of an extruded product and is seen by differences in
reflectance from the bulk of the extrudate, particularly after anodizing. These streaks manifest
above certain geometrical features of the extrudate, such as screw ports and other distinctive
parts, which deviate from the nominal profile and are sources for inhomogeneous deformation.
To understand the origin of these metal flow inhomogeneities, several metallurgical techniques
were employed. Light optical microscopy and scanning electron microscopy were used to
examine the microstructure texture. The micro-hardness was recorded across the streaking defect
in order to establish the presence of any microstructure/hardness property gradient, which would
affect the physical appearance of the extrudate surface. The electron backscatter diffraction
(EBSD) technique was used to identify trends in crystallographic alignment that are responsible
for changing the reflectance of the specimen. The understanding of these defects allows for the
possibility of modifications to the manufacturing process in order to eliminate these undesired
features.

© 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.

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