Microstructural Gradients Near the Surface of Large 6xxx Aluminum Extrudates Due to Localized Deformation
P. T. Wang, Process Technology Division, Alcoa Technical Center, Alcoa Center
W. H. Van Geertruyden and W. Z. Misiolek, Institute for Metal Forming, Lehigh University
Track: EXTRUSION PROCESS - Peripheral Coarse Grain
ABSTRACT --- Surface coarse grain formation has become one of the critical issues in the
control of microstructure uniformity in extrusion products. A lab-scale indirect extrusion is
conducted to observe the surface behavior of Al-Mg-Si alloy. The influence of various
thermomechanical histories under extremely large strains, strain rates, and elevated
temperatures is investigated. Lab-deformed samples are characterized by traditional
metallography and electron backscatter diffraction (EBSD) techniques to understand key
mechanisms. We propose an energetic approach through Gibbs free energy and an internal
state variable theory to represent a recrystallization front criterion. This criterion is sensitive to
the drag force imposed by dispersoid, and thermal and deformation histories. Mechanisms of grain evolution under extreme deformation conditions are discussed, and applications of this approach to extrusion processes and die design are proposed.
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