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Gong X.,University of Alabama | Kang S.B.,Korea Institute of Materials Science | Cho J.H.,Korea Institute of Materials Science | Li S.,Central South University | Li S.,Key Laboratory of Nonferrous Metal Materials Science and Engineering
Materials Characterization | Year: 2014

In this study, ZK60 magnesium strips produced by twin-roll casting were subjected to differential speed rolling with velocity ratios of 1.2 and 1.5 and equal speed rolling. Annealing treatment was applied to the rolled strips to investigate its effect on microstructure, texture and mechanical properties. The results show that compared with the sheet processed by equal speed rolling, the sheets processed by differential speed rolling show more apparent shear bands in the rolled state and a higher fraction of fine grains after annealing. The sheets processed by differential speed rolling show a single-peak basal fiber with a decreased maximum pole intensity compared to a clear double-peak texture of the sheet processed by equal speed rolling, and both are weakened after annealing. The sheets processed by differential speed rolling present significantly higher ductility and slightly lower yield strength than the sheet processed by equal speed rolling. The annealing process contributes to decreases in the strengths and improvement in ductility, which can be attributed to the weakening of basal texture by recrystallization. These results suggest that the annealing is an effective way to enhance the formability of sheets produced by differential speed rolling. © 2014 Elsevier Inc. All rights reserved.

Ye L.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | Hu J.,Central South University | Tang C.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | Zhang X.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | And 3 more authors.
Materials Characterization | Year: 2013

The modification effect of gadolinium (Gd) on Mg2Si in the hypereutectic Mg-3 wt.% Si alloy has been investigated using optical microscope, scanning electron microscope, X-ray diffraction and hardness measurements. The results indicate that the morphology of the primary Mg2Si is changed from coarse dendrite into fine polygon with the increasing Gd content. The average size of the primary Mg2Si significantly decreases with increasing Gd content up to 1.0 wt.%, and then slowly increases. Interestingly, when the Gd content is increased to 4.0 and 8.0 wt.%, the primary and eutectic Mg2Si evidently decrease and even disappear. The modification and refinement of the primary Mg2Si is mainly attributed to the poisoning effect. The GdMg2 phase in the primary Mg2Si is obviously coarsened as the Gd content exceeds 2.0 wt.%. While the decrease and disappearance of the primary and eutectic Mg2Si are ascribed to the formation of vast GdSi compound. Therefore, it is reasonable to conclude that proper Gd (1.0 wt.%) addition can effectively modify and refine the primary Mg2Si. © 2013 Elsevier Inc.

Lei Q.,Central South University | Li Z.,Central South University | Li Z.,State Key Laboratory of Powder Metallurgy | Xiao T.,Central South University | And 4 more authors.
Intermetallics | Year: 2013

A new ultrahigh strength Cu-6.0 Ni-1.0 Si-0.5 Al-0.15 Mg-0.1 Cr alloy has been developed by alloying design and thermal mechanical treatment. Electrical conductivity, mechanical properties of the designed alloy such as hardness, tensile strength, yield strength, elongation and anti-stress relaxation resistance were tested. The mechanical properties and electrical properties of designed alloy were comparable to those of Cu-Be alloys, and its anti-stress relaxation resistance even was better than that of Cu-Be alloys at evaluated temperature. Microstructure observation revealed that β-Ni3Si phase precipitated in the initial stages ageing process, with further increasing the ageing time, β-Ni3Si, and δ-Ni2Si phase precipitates appeared and contributed to the ultrahigh strength by Orowan strengthening. The satellites spots around diffraction spots of Cu matrix symmetrically in [112]Cu zone crystal axis have been determined, resulting that satellites spots are from the electron diffraction of δ-Ni2Si precipitates. The crystal orientation relationship between matrix and precipitates is that: (111̄)cu//( 111̄)β//(02̄1)δ;[112]cu// [112]β//[012]δ. © 2013 Elsevier Ltd. All rights reserved.

Li H.-Z.,Central South University | Li H.-Z.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | Zeng M.,Central South University | Liang X.-P.,Central South University | And 2 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012

The flow stress features of PM Ti-47Al-2Cr-0.2Mo alloy were studied by isothermal compression in the temperature range from 1000 to 1150 °C with strain rates of 0.001-1 s -1 on Gleeble-1500 thermo-simulation machine. The results show that the deformation temperature and strain rate have obvious effects on the flow characteristic, and the flow stress increases with increasing strain rate and decreasing temperature. The processing maps under different deformation conditions were established. The processing maps of this alloy are sensitive to strains. The processing map at the strain of 0.5 exhibits two suitable deformation domains of 1000-1050 °C at 0.001-0.05 s -1 and 1050-1125 °C at 0.01-0.1 s -1. The optimum parameters for hot working of the alloy are deformation temperature of 1000 °C and strain rate of 0.001 s -1 according to the processing map and microstructure at true strain of 0.5. © 2012 The Nonferrous Metals Society of China.

Gao Z.,Central South University | Li H.,Central South University | Li H.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | Liu J.,Central South University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2014

The precipitation hardening and coarsening resistance of precipitates were studied in Al-Yb, Al-Zr and Al-Yb-Zr alloys during aging at 400 C. The aged Al-0.03Yb-0.06Zr alloy forms core-shell structured Al3(Yb,Zr) precipitates and the core and shell of precipitates are enriched in Yb and Zr respectively. Due to the dense and core-shell structured Al3(Yb,Zr) precipitates, the Al-0.03 at%Yb-0.06 at%Zr alloy obtains a maximum hardness of 485 MPa, which is greater than that of the Al-0.03 at%Yb and Al-0.06 at%Zr alloys. The Al3(Yb,Zr) precipitates in Al-0.03 at%Yb-0.06 at%Zr have remarkable coarsening resistance with a time exponent for the average radius of precipitates 1/n = 0.19 ± 0.02, which is smaller than that for Al-0.03Yb (0.34 ± 0.01). Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

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