Unraveling Recrystallization Mechanisms Governing Texture Development from Rare-Earth Element Additions to Magnesium
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THE propensity for magnesium (Mg) to develop sharp textures during thermomechanical processing (TMP) has plagued its future as an ideal lightweight material in the automotive, aerospace, and defense applications. In a similar manner to single crystals, sharp textures respond to mechanical loads with strong
AIDIN IMANDOUST is with the Department of Mechanical Engineering, Auburn University, Auburn, AL. CHRISTOPHER D. BARRETT and HAITHAM EL KADIRI are with the Department of Mechanical Engineering, Mississippi State University, Mississippi, MS, 39762; and also with Center for Advanced Vehicular Systems, Mississippi State University, Mississippi, MS, 39762; Contact e-mail: [email protected] TALAL AL-SAMMAN is with the Institute of Physical Metallurgy and Metal Physics, RWTH Aachen University, Aachen, Germany. MARK A. TSCHOPP is with the Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, MD, 21005. ELHACHMI ESSADIQI is with the Aerospace Engineering School, Rabat, Universite´ Internationale de Rabat, UIR, Technopolis Shore Bypass, Rabat-Sale´, Morocco. NORBERT HORT is with the Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, 21502, Geesthacht, Germany. Manuscript submitted October 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
anisotropy and asymmetry.[1,2] This can be problematic in application. For example, a typical rolled sheet cannot withstand large strains along arbitrary directions prior to fracture, a severe problem for forming of Mg alloys. Moreover, a thin-walled hollow tubes made from Mg alloys are observed to shatter into pieces prior to absorbing impact under crash conditions.[3-10] The ease of basal slip and the dislocation recovery mechanisms operating in Mg alloys have been long understood to promote sharp textures. Basal slip causes the basal poles to align themselves with the loading direction,[1,2] whereas dynamic recovery confines these planes to rotate, only around the hci-axis within sub-grains formed by prismatic dislocations, and the prismatic axes within sub-grains constructed by basal and pyramidal dislocations.[11,12] Those types of rotations occur because [0001] is the Taylor axis for prismatic slip, while h1010i is the common one to both basal and pyramidal hc + ai slips.[11,13-15] Weak textures could have well developed if rotations could have been effected around an axis that deviates the hci-axis from the main loading direction. However, there is no active slip mode with such a desirable Taylor axis.
Dynamic recrystallization (DRX) has been observed to occur either continuously (CDRX) or discontinuously (DDRX) depending on the temperature, strain, and strain rate. These external factors directly affect dislocation generation and multiplication at mantle regions, while microstructure and defects such as grain boundaries (GBs), solutes, and particles could either promote or limit the driving force underscored in dislocation recovery.[16-22] Regardless of the predominant DRX mechanism in the processing condition, the sharp deformati
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