Mechanical Properties of Mg-Gd and Mg-Y Solid Solutions
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DUE to favorable combination of strength and weight, magnesium alloys have been considered as attractive structural materials, especially in the transportation industry where the weight reduction of the vehicle becomes an important factor in environmental requirements for energy saving and decrease of the greenhouse gas emission. However, magnesium alloys exhibit limitations in their mechanical properties characterized by poor room-temperature ductility and relatively low strength.[1] Magnesium’s poor workability is generally attributed to its hexagonal closed-packed (hcp) crystal structure and the lack of sufficient number of slip systems, which can carry plastic deformation. It has been recognized that dilute binary and ternary Mg alloys containing rare-earth (RE) metals show an increased cold formability at room temperature.[2,3] The increased ductility of these alloys has been related to the strong influence of alloying elements on the deformation substructure and texture.[2–4] The addition of rare-earth elements has been considered as an effective way to improve the mechanical properties of
ANNA KULA, formerly Postdoctoral Fellow with McMaster University, 1280 Main Street West, Hamilton L8S4L8, Canada, is now Assistant Professor with AGH-University of Science and Technology, Av. Mickiewicza 30, 30-059 Cracow, Poland. Contact e-mail: [email protected] XIAOHUI JIA, formerly Graduate Student with McMaster University, is now Systems Specialist with Corrosion Service Company Limited, Markham, Canada. RAJ K. MISHRA, Technical Fellow, is with the Chemical and Materials Systems Lab, General Motors Research & Development Center, 30500 Mound Road, Warren, MI 48090. MAREK NIEWCZAS, Professor, is with McMaster University. Manuscript submitted September 17, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
magnesium alloys owing to the effect of solid solution strengthening[5,6] or precipitation strengthening.[1,7,8] Gadolinium (Gd) and Yttrium (Y) are considered to be the most effective RE elements to improve mechanical properties of magnesium alloys.[5,6,9] Their beneficial influence originates from strong solid solution strengthening, arising from (i) a large difference in the atomic radius between these elements and magnesium and (ii) the wide range of solubility limits.[10] Gd and Y are considered to be more effective strengthening elements than aluminum, zinc, or manganese.[5,6,11] The advantage of the influence of Gd and Y on alloy properties is also manifested by their effect on recrystallization texture.[4,12,13] Deformation of polycrystalline magnesium alloys leads typically to the development of sharp basal texture, which strongly suppresses basal slip. The addition of Gd or Y promotes weaker textures with broader distributions of the basal planes, favorably oriented for basal slip.[12,13] It is assumed that the texture weakening in RE-containing Mg alloys is inherited during recrystallization, however, the specific mechanisms are still not fully understood. It has been suggested that the weakened texture is obta
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