APPLICATION OF HOT WORKABILITY STUDIES TO EXTRUSION PROCESSING .2. MICROSTRUCTURAL DEVELOPMENT AND EXTRUSION OF AL, AL-MG, AND AL-MG-MN ALLOYS

In uniform hot working tests, the flow curves strain harden to a stead y slate plateau that depends on temperature and strain rate. The under lying mechanism is dynamic recovery which rises with strain to balance the work hardening, resulting in subgrains that are larger and more p erfect as T rises and epsilon falls. Subgrains are observed in the ext rudate following the pattern established in hot workability tests. Mor eover, their formation in the upset biller and throughout the deformat ion zone has been examined as a means to delineate its thermal and mec hanical development. Substructure in the extrudate substantially impro ves its mechanical properties. With increasing Mg solute, substructure recovery is reduced so that the strength and the tendency for recryst allization are increased. Moreover, in alloys above 5% Mg, most notabl y containing large Mn-rich constituent particles, dynamic recrystalliz ation nuclei form in the most intensely strained regions of the deform ation zone and also speed up state recrystallization in the extrudate. Copyright (C) 1996 Published by Elsevier Science Ltd.