Texture Modification in a Magnesium-Aluminum-Calcium Alloy During Uniaxial Compression
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MAGNESIUM alloys comprise the lowest density class of structural metals, and there has been significant interest in implementing them for applications where light weight is critical. While cast magnesium product has seen some adoption, wrought magnesium has lagged behind.[1] This is largely a result of the limited room temperature ductility and formability, due, at least in part, to the rapid development of a strong crystallographic texture during deformation processing. The basal texture (c-axes normal to the sheet surface) developed during rolling is particularly problematic for magnesium sheet products due to a lack of mechanisms that can accommodate the deformation required for forming operations. Weakened texture development during thermomechanical processing would aid in achieving sufficient levels of ductility necessary for widespread implementation of wrought magnesium alloys.[2,3] Substantial research has been devoted to texture modification in magnesium alloys, particularly via alloying additions of rare earth (RE) or alkaline earth elements. RE additions have been observed to significantly weaken deformation textures and, upon recrystallization, result in the formation of a new texture component which, in rolled sheet, has the basal poles tilted 45 deg from the sheet normal direction. Ball and Prangnell suggested that the texture modification was the result of particle stimulated nucleation (PSN) during dynamic recrystallization.[4] However, it has recently VICTORIA M. MILLER, Graduate Student Researcher, and TRESA M. POLLOCK, ALCOA Professor and Chair, are with the Materials Department, University of California Santa Barbara, Santa Barbara. Contact e-mail: [email protected] Manuscript submitted June 12, 2014. Article published online January 28, 2016 1854—VOLUME 47A, APRIL 2016
been demonstrated that single-phase solid solution RE-containing alloys also undergo the same evolution in texture, indicating that intermetallic particles are not required.[2,5,6] While it is likely that the solute additions are responsible for texture modification, the precise mechanism is not yet fully defined. It has been suggested that the new texture component is the result of special RE-influenced shear bands, and that solute effects (including segregation to grain boundaries) are responsible for the weakened shear band and texture intensity (e.g., References 2, 3, 7 through 10). While texture modification via solute effects in single-phase Mg-RE alloys has been widely discussed, many RE elements have very low solubility in magnesium and tend to form intermetallic particles, even at low levels of alloy content. Relatively little work has been conducted to explicitly consider the dependence of texture on both intermetallic particles and solid solution content during deformation, recovery, and recrystallization, particularly for coarse intermetallic particles. Basu et al.[11] observed less texture modification in a particle-containing Mg-Ce alloy compared to a single-phase Mg-Gd alloy and suggested it may simply be due to
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