Hot compression tests were conducted on a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy at 450 ℃ and a strain rate of 2 s-1. Dynamic recrystallization （DRX） mechanisms were investigated by optical microscope （OM）, scanni...Hot compression tests were conducted on a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy at 450 ℃ and a strain rate of 2 s-1. Dynamic recrystallization （DRX） mechanisms were investigated by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM） systematically. The crystallographic orientation information is obtained through electron back-scattering diffraction （EBSD）. The result shows that the flow stress firstly reaches a peak rapidly followed by declining to a valley, and then increases gradually again when the alloy is compressed to a strain of-1.88. DRX related to {10]2} tensile twins is extensively observed at small strains, resulting in an evident grain refinement. DRX grains first nucleate along the edges of twin boundaries with about 30~ （0001） off the twin parents. While at large strains, conventional continuous DRX （CDRX） is frequently identified by the formation of small DRX grains along the original grain boundaries and the continuously increasing misorientation from the centre of large original grains to the grain boundaries. Evidence of particle-stimulated nucleation （PSN） is also observed in the present alloy.展开更多
The effects of the addition of 0.6%Ca（mass fraction） on the as-cast microstructure and mechanical properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc magnesium alloys were investigated and compared by optical...The effects of the addition of 0.6%Ca（mass fraction） on the as-cast microstructure and mechanical properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc magnesium alloys were investigated and compared by optical microscopy and scanning electron microscopy,differential scanning calorimetry analysis,and tensile and creep tests.The results indicate that the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can refine the grains of the two alloys.At the same time,the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can effectively improve the tensile properties of the two alloys.In addition,the addition of 0.6%Ca can also improve the creep properties of the Mg-3Ce-1.2Mn-0.9Sc alloy but is not beneficial to the creep properties of the Mg-4Y-1.2Mn-0.9Sc alloy.The different effects of minor Ca on the creep properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys are possibly related to the difference in the solid solubilities of Ce and Y in Mg.展开更多
The microstructures and mechanical properties of Mg-4.2Zn-1.5RE-0.7Zr alloy were investigated under different heat treatment conditions. The as-cast alloy consisted ofα-Mg phase, T-phase and Mg51Zn20 phase. After agi...The microstructures and mechanical properties of Mg-4.2Zn-1.5RE-0.7Zr alloy were investigated under different heat treatment conditions. The as-cast alloy consisted ofα-Mg phase, T-phase and Mg51Zn20 phase. After aging treatment （single-step （325 °C, 10 h） and two-step （325 °C, 4 h）＋（175 °C, 14 h））, neither T-phase nor Mg51Zn20 phase dissolved into the matrix and the coarsening ofα-Mg phase was not significant. When peak-aged at 325 °C for 10 h, dense short rod-likeβ′1 phase precipitated in the matrix. Further ageing at 325 °C led to coarsening ofβ′1 phase and a decrease in number density. Alloy aged at 325 °C for 10 h achieved the highest yield strength （YS） and ultimate tensile strength （UTS） of 153.9 MPa and 247.0 MPa, which were increased by 48 MPa and 23 MPa from as-cast condition, respectively. While the elongation slightly decreased to 15.6%. Comparatively, the YS and UTS of alloy two-step aged by （325 °C, 4 h）＋（175 °C, 14 h） showed little difference from those of single-step aged alloy, but with a lower elongation of 13.4%. In addition, the fracture surfaces of Mg-4.2Zn-1.5RE-0.7Zr alloy under different thermal conditions were mainly characterized by quasi-cleavage feature, but with differences in the details.展开更多
Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were ...Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.展开更多
文摘Hot compression tests were conducted on a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy at 450 ℃ and a strain rate of 2 s-1. Dynamic recrystallization （DRX） mechanisms were investigated by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM） systematically. The crystallographic orientation information is obtained through electron back-scattering diffraction （EBSD）. The result shows that the flow stress firstly reaches a peak rapidly followed by declining to a valley, and then increases gradually again when the alloy is compressed to a strain of-1.88. DRX related to {10]2} tensile twins is extensively observed at small strains, resulting in an evident grain refinement. DRX grains first nucleate along the edges of twin boundaries with about 30~ （0001） off the twin parents. While at large strains, conventional continuous DRX （CDRX） is frequently identified by the formation of small DRX grains along the original grain boundaries and the continuously increasing misorientation from the centre of large original grains to the grain boundaries. Evidence of particle-stimulated nucleation （PSN） is also observed in the present alloy.
基金Projects (CSTC2013jcyjC60001) supported by the Chongqing Science and Technology Commission of ChinaProject (KJ120834) supported by the Chongqing Education Commission of ChinaProject (CQUT1205) supported by the Open Funds from Key Laboratory of Manufacture and Test Techniques for Automobile Parts(Chongqing University of Technology),Ministry of Education,China
文摘The effects of the addition of 0.6%Ca（mass fraction） on the as-cast microstructure and mechanical properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc magnesium alloys were investigated and compared by optical microscopy and scanning electron microscopy,differential scanning calorimetry analysis,and tensile and creep tests.The results indicate that the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can refine the grains of the two alloys.At the same time,the addition of 0.6%Ca to the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys can effectively improve the tensile properties of the two alloys.In addition,the addition of 0.6%Ca can also improve the creep properties of the Mg-3Ce-1.2Mn-0.9Sc alloy but is not beneficial to the creep properties of the Mg-4Y-1.2Mn-0.9Sc alloy.The different effects of minor Ca on the creep properties of the Mg-3Ce-1.2Mn-0.9Sc and Mg-4Y-1.2Mn-0.9Sc alloys are possibly related to the difference in the solid solubilities of Ce and Y in Mg.
基金Project (51275295) supported by the National Natural Science Foundation of ChinaProject (USCAST2012-15) supported by the Funded Projects of SAST-SJTU Joint Research Centre of Advanced Aerospace Technology,ChinaProject (20120073120011) supported by the Research Fund for the Doctoral Program of Higher Education of China
文摘The microstructures and mechanical properties of Mg-4.2Zn-1.5RE-0.7Zr alloy were investigated under different heat treatment conditions. The as-cast alloy consisted ofα-Mg phase, T-phase and Mg51Zn20 phase. After aging treatment （single-step （325 °C, 10 h） and two-step （325 °C, 4 h）＋（175 °C, 14 h））, neither T-phase nor Mg51Zn20 phase dissolved into the matrix and the coarsening ofα-Mg phase was not significant. When peak-aged at 325 °C for 10 h, dense short rod-likeβ′1 phase precipitated in the matrix. Further ageing at 325 °C led to coarsening ofβ′1 phase and a decrease in number density. Alloy aged at 325 °C for 10 h achieved the highest yield strength （YS） and ultimate tensile strength （UTS） of 153.9 MPa and 247.0 MPa, which were increased by 48 MPa and 23 MPa from as-cast condition, respectively. While the elongation slightly decreased to 15.6%. Comparatively, the YS and UTS of alloy two-step aged by （325 °C, 4 h）＋（175 °C, 14 h） showed little difference from those of single-step aged alloy, but with a lower elongation of 13.4%. In addition, the fracture surfaces of Mg-4.2Zn-1.5RE-0.7Zr alloy under different thermal conditions were mainly characterized by quasi-cleavage feature, but with differences in the details.
基金the Czech Science Foundation (P108/12/G043)the Academy of Sciences of the Czech Republic(KAN300100801)for the financial support
文摘Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.
