Control of Grain Structure in Al-Mg-Si Extrusions
Nick Parson, Simon Barker, Ann Shalanski, and Chris Jowett, Alcan International Limited
Track: EXTRUSION PROCESS
ABSTRACT --- The grain structure of an Al-Mg-Si extrusion is an important feature of
the product in a wide range of applications. It can impact on strength, formability,
machinability, anodized appearance, toughness, and crash energy absorption. The
grain structure can be unrecrystallized fibrous, fully recrystallized, or a mixture of the
two. In the recrystallized condition, a wide range of grain sizes can be encountered for
a given alloy. The interaction of extrusion process variables with grain structure is
poorly understood, and the industry guideline is “keep the exit temperature low.” Using
results obtained on Alcan’s experimental press, this paper describes the effect of the
main process variables, extrusion ratio, billet temperature, ram speed, and exit
temperature on grain structure for alloys AA6061, AA6082, AA6005A, and AA6063.
The trends are explained in terms of the underlying metallurgy. Practical guidelines for
grain structure control are developed.
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