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Flow of Billet Surface Material during Extrusion of Al Alloys

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Flow of Billet Surface Material during Extrusion of Al Alloys; Effect of
Billet Quality and Process Conditions

Oddvin Reiso, Martin Lefstad*, Jostein Røyset and Ulf Tundal
Hydro Aluminium Research and Technology Development (RTD), Sunndalsøra, Norway
*SINTEF, Trondheim, Norway

Track: EXTRUSION/DIE PRACTICAL - Tooling and Performance

ABSTRACT – The paper describes the flow of the billet surface material during successive
extrusion of billets prepared with contrast material as an artificial surface segregation layer. The
results show that even with thin surface segregation layers in the billet, these layers will
accumulate on the container wall during successive extrusion of billets and may eventually flow
into the profile, causing surface defects in the same way as if the surface segregation layer in the
billet was thicker. It is shown that the severity of these inflow problems will largely be controlled
by the clearance between the dummy block and the container wall. Examples are given of how
this clearance is affected by equipment and process conditions at the press. The paper also
describes the importance of having a billet quality that has a narrow inverse segregation zone
(ISZ), as well as a low enrichment of alloying elements in the zone, in order to avoid/minimize
the damage from a possible inflow of the ISZ during extrusion.

© 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.