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The Effect of Scandium and Zirconium Additions on Aluminum Extrusion

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The Effect of Scandium and Zirconium Additions on Aluminum Extrusion and Post-Braze Grain Structure

Frank F. Kraft, Ohio University, Athens, USA
Cory Williams, Ohio University, Athens, USA

Track: BILLET PROCESS and EQUIPMENT - Metallurgy

ABSTRACT --- The control of grain structure in wrought aluminum parts is
paramount in improving properties for any alloy, and much work has been done
to assess thermo-mechanical histories with respect to structure and properties of
standard alloys. The contribution of alloy composition to aid grain structure
control has been thoroughly investigated in tandem with processing, and research
in both areas continues. Small additions of scandium in aluminum alloys are
known to increase strength, control grain structure, and retard
annealing/recrystallization. This can be of particular importance in extruded
parts that are used in furnace-brazed assemblies. Extruded parts such as microchannel
tube for automotive climate control systems are sized and straightened
prior to assembly into a heat exchanger. This small amount of plastic strain
(cold-work) is the driving force for recrystallization and large grain growth
during the brazing process, which takes place at approximately 600°C. This
generally coincides with a significant decrease in part strength. The primary
objective of this work is to prevent recrystallization and grain growth, and retain
the pre-braze strength in extruded and cold-worked aluminum extrusions. This
paper presents the evaluation of a 1xxx alloy with additions of 0.2 percent
Scandium (Sc), and 0.05 percent Zirconium (Zr). The behavior of extruded
micro-channel tube is evaluated with respect to the brazing thermal cycle, and a
typical amount of cold-work imposed during straightening/sizing. The effect on
extrusion is considered, and a comparison is made to a conventional alloy for this
application.

© 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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