Thermo-Mechanical Effects on the Presence of Magnesium-Silicide in 6xxx Alloys at Extrusion Temperatures
Roger N. Wright and Stephen Bartolucci, Rensselaer Polytechnic Institute
Track: EXTRUSION PROCESS - Metallurgy/Measurement
ABSTRACT --- Conventional views of the presence of Mg2Si during extrusion have
focused on temperature, as determined by billet preheat cycle, cooling en route to
actual extrusion, and on deformation and friction heating during extrusion. Recent
work at Rensselaer shows a strong role of hot deformation, per se, on Mg2Si presence.
Laboratory deformation processing simulations have been undertaken on 6063 and
6105 alloys. In general, heating to 450°C led to precipitation of Mg2Si, while further
heating to 515°C led to substantial dissolution. Hot deformation at 450°C led to
dissolution of Mg2Si, whereas hot deformation at 515°C led to precipitation of Mg2Si.
Workability, as implied by reduced flow stress and increased true strain at fracture,
actually increased in the face of the development of Mg2Si at 515°C. The implications
of this work regarding industrial 6xxx extrusion practice are considered.
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