Effects of Solute and Second-Phase Particles on the Texture of Nd-Containing Mg Alloys
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IT has been discovered that if Mg is alloyed with rare earth (RE) elements, the resulting alloy can develop weaker textures during deformation processing[1] or subsequent annealing.[2,3] After first discovering this texture weakening effect in an extruded Mg alloy, denoted WE54, Ball and Prangnell hypothesized this phenomenon to be the result of particle-stimulated nucleation (PSN) during dynamic recrystallization (DRX).[1] However, it has been observed that PSN is not a necessary requirement for Mg-RE alloys to undergo texture weakening, as solid solution Mg-RE alloys have been shown to exhibit similar effects.[2–6] Other mechanisms have been proposed, and a part of this study is devoted to the exploration of Zener drag as a contributing mechanism. In order to approach the question of whether Zener drag is active, two aspects of the sample microstructure were investigated: the grain size of the matrix and the size and volume fraction of the second-phase particles. These values were then compared to predictions of classical Zener pinning theory. Recently, work on hot-rolled binary Mg alloys with Y, Ce, and Nd revealed that more dilute compositions exhibited textures typical of pure Mg, while the more JASON P. HADORN, Postdoctoral Researcher, and SEAN R. AGNEW, Heinz and Doris Wilsdorf Distinguished Research Associate Professor of Materials Science and Engineering, are with the Materials Science and Engineering Department, University of Virginia, Charlottesville, VA 22904-4745. Contact e-mail: [email protected] KERSTIN HANTZSCHE, Graduate Research Assistant, SANGBONG YI and JAN BOHLEN, Scientists, and DIETMAR LETZIG, Head of Department, are with the Magnesium Innovation Center (MagIC), Helmholtz Centre Geesthacht, 21502 Geesthacht, Germany. Manuscript submitted March 14, 2010. Article published online February 3, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
concentrated alloys exhibited weaker textures.[4] Additionally, for a given solute, the texture weakening effect occurred dramatically with increasing alloy content (Figure 1). The relationships between composition, grain size, and texture shown in this prior work form the basis of the present study. After 20 minutes of subsequent static annealing at the rolling temperature (673 K (400 C)), the strongly textured alloys showed an increase in texture strength while the texturing weakening alloys actually showed a decrease (compare Figures 1(a) and (b)). This is attributed to two facts: (1) the material was not fully recrystallized in the as-rolled state and (2) the completion of recrystallization imparted a significant randomization to the texture of the concentrated alloys. Intragranular misorientation axis (IGMA) analysis is a valuable tool, because it allows dislocation information to be extracted from a statistically significant region of a sample using electron backscatter diffraction (EBSD) via scanning electron microscopy. IGMA distributions can elucidate the geometrically necessary dislocation (GND) content in deformed grains. Consider a case of singl
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