Easy Glide in a Coarse-Grained Mg-2Zn-2Nd Alloy
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lide in single crystals is referred to as the first stage of work hardening[1,2] and corresponds to the condition where only single slip is taking place. In this case, the work hardening rate is only about 104 l, where l is the shear modulus.[3,4] This stage comes to an end when multiple slip systems are activated. By contrast, in polycrystalline materials, multiple slip generally takes place from the initiation of straining. In the present study of the deformation of a coarse-grained Mg-2Zn-2Nd alloy, steady-state flow was observed to take place from about 0.03 true strain onwards at 0.001/ s, accompanied by a very low rate of work hardening. This is attributed to a type of easy glide. The composition of the present Mg-2Zn-2Nd alloy is given in Table I. Cylindrical compression samples were cut from one side of a billet produced by continuous casting. They had heights of 9 mm and diameters of 6 mm and their axes were aligned with the casting direction. In this material, the temperature gradients established during cooling were inclined at about 45 deg to the casting direction; see in Figure 1.[5] Thus, the grains grew along these directions and their c-axes were also inclined at about 45 deg to the specimen axes. Prior to testing, the samples were homogenized at 723 K (450 °C) for 2 hours. In order to reduce friction during
TONG WANG, Ph.D. Student, and JOHN J. JONAS and STEPHEN YUE, Professors, are with the Department of Mining and Materials Engineering, McGill University, Montreal, QC, H3A 2B2, Canada. Contact e-mail: [email protected] Manuscript submitted May 2, 2016. Article published online August 1, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
testing, boron nitride powder and mica sheets were placed between the sample and the compression anvils. The samples were heated to the test temperature of 673 K (400 °C) and held for 10 minutes before testing. They were then compressed at the strain rates of 0.001, 0.01, and 0.1/s to the true strains of 0.05, 0.1, 0.2, and 0.3. The samples were quenched in water within 2 seconds of deformation. Longitudinal sections of the undeformed and deformed samples were prepared for microstructural and X-ray observations. These were first ground using SiC papers of grit size 600, 800, and 1200, then mechanically polished with 3- and 1-lm diamond paste. Colloidal silica was employed for final polishing. The initial macrotexture was measured by x-ray diffraction over a 4 mm 9 4 mm area of a typical sample on a Bruker D8 co-source diffractometer. For investigations by optical and scanning electron microscopy (SEM), the samples were etched in a picric acid solution.[6] For the electron backscattered diffraction (EBSD) analysis, the samples were electropolished in a 10 pct Nital solution at 253 K (20 °C) for 2 seconds. The EBSD measurements were carried out on an SU3500 scanning electron microscope equipped with an HKL system and Channel 5 software. For the EBSD measurements, the samples were scanned with the compression direction aligned along the horizontal direction. The init
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