High-Temperature Tensile Flow Behavior of Caliber-Rolled Mg-3Al-1Zn Alloy
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DUE to light weight, magnesium alloys are very popular in various sectors like aerospace, automobile, biomedical, architecture, and electronic industries.[1,2] However, these alloys have limited strength and elongation due to limited slip systems in hexagonal closepacked (HCP) crystal structure. Their mechanical processing is carried out at high temperature, at which there occur changes in microstructure and texture of the products.[3–9] In order to reduce the cost of manufacturing and for considerable freedom in designing the complex components, workability of material is very important. In general, workability of a given material is influenced by microstructure of the material, processing temperature, strain rate, and stress state in the deformation zone.[10] There are various methods of severe plastic deformation of metal used for grain refinement and improvement of mechanical properties.[11] Caliber rolling (CR) is one of these methods used for mass production that gives products of high precision and strength. This process is explained elsewhere.[12] When the deformation temperature is greater than 0.5Tm, Tm being absolute melting point of metal, there occurs high-temperature R.L. DOIPHODE, Lecturer, is with the Mechanical Engineering, Government Polytechnic, Kolhapur 416004, India, and also Ph.D. Research Scholar with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India. S.V.S. NARAYANA MURTY, Scientist, is with the Special Materials Division, Vikram Sarabhai Space Center, ISRO, Trivandrum 695022, Isndia. N. PRABHU and B.P. KASHYAP, Professors, are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay. Contact e-mail: [email protected] Manuscript submitted February 7, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
dynamic recrystallization. As the average grain size becomes smaller, the grain boundary area per unit volume increases. As a result, there appears a reduction in flow stress but improvement in elongation at elevated temperature.[13] However, also reported are some deviations on the effect of grain size on flow stress.[14–17] Partridge[18] showed that HCP metals deform plastically by simultaneous activation of twinning and slip. Munroe and Tan[19] studied the orientation dependencies of slip and twinning in HCP metals. Koike et al.[20] reported that twinning can provide additional slip systems during deformation, which can enhance the elongation. Barnett[21] explained that deformation obtained is not homogeneous in the wrought Mg-alloys. The inhomogeneity results from the variation in the ease of basal slip orientation among grains, micro-textures, shear banding, twinning, and grain boundary sliding. Wang et al.[22] reported a significant improvement in properties of Mg-alloy by controlling the texture without grain refinement. Twinning behavior depends on grain size as well as texture,[23,24] with the finer grained materials exhibiting lower volume fraction of twins;[25] the f
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