A Modern View of the Thermodynamics and Kinetics of the Magnesium Silicide Presence in 6xxx Alloys
Roger N. Wright, Rensselaer Polytechnic Institute, Troy, NY (USA)
Metin Usta, Gebze Institute of Technology, Gebze/KOCAELI, TURKEY
Stephen Bartolucci, Rensselaer Polytechnic Institute, Troy, NY (USA)
Track: BILLET PROCESS AND EQUIPMENT - Homogenization
ABSTRACT --- The classical phase diagram is at variance with industrial practice
observations on 6xxx alloys. This is particularly the case regarding the persistence or
even coarsening of Mg2Si particles in some homogenization cycles. Recent work at
Rensselaer has established that Mg2Si coarsening can in fact occur in the classical
solid solution range, and that the solvus and solidus temperatures for the commercial
alloys studied are higher than indicated on the classical diagram. This paper reviews
the pertinent phase relations of the classical diagram and notes the discrepancies with
the observations on commercial alloys. Explanations for the discrepancies are
considered, and some engineering adjustments to the classical diagram are set forth.
The implications regarding industrial 6xxx processing are considered, including
tradeoffs in homogenization practice.
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