Hot deformation behavior of extrusion preform of the spray-formed Al-9.0Mg-0.5Mn-0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300-450 ℃ and strain rate range of 0.01...Hot deformation behavior of extrusion preform of the spray-formed Al-9.0Mg-0.5Mn-0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300-450 ℃ and strain rate range of 0.01-10 s-1. On the basis of experiments and dynamic material model, 2D processing maps and 3D power dissipation maps were developed for identification of exact instability regions and optimization of hot processing parameters. The experimental results indicated that the efficiency factor of energy dissipate （η） lowered to the minimum value when the deformation conditions located at the strain of 0.4, temperature of 300 ° C and strain rate of 1 s-1. The softening mechanism was dynamic recovery, the grain shape was mainly flat, and the portion of high angle grain boundary （〉15°） was 34%. While increasing the deformation temperature to 400 ° C and decreasing the strain rate to 0.1 s-1, a maximum value of η was obtained. It can be found that the main softening mechanism was dynamic recrystallization, the structures were completely recrystallized, and the portion of high angle grain boundary accounted for 86.5%. According to 2D processing maps and 3D power dissipation maps, the optimum processing conditions for the extrusion preform of the spray-formed Al？9.0Mg？0.5Mn？0.1Ti alloy were in the deformation temperature range of 340-450 ° C and the strain rate range of 0.01-0.1 s-1 with the power dissipation efficiency range of 38%？43%.展开更多
Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is proce...Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.展开更多
Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening durin...Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening during hot compression. The flow behavior was successfully analyzed by the hyperbolic sine equation and the corresponding material constants A, n and αwere determined. The value of apparent activation energy was determined as 423 kJ/mol. The peak and steady state strains showed simple power-law dependence on the Zener-Hollomon parameter. The dynamic recrystallization kinetics was analyzed using Avrami equation and the corresponding exponent was determined to be about 2.7. This value, higher than 2 reported in the literatures, is associated with the mechanism of continuous dynamic recrystallization in the studied alloy. The flow curve up to the peak was modeled by the Cingara equation and the strain exponent, c, was determined about 0.85. The higher value of c compared with the value of 0.2 which has been reported for some stainless steels fortified the idea of extended dynamic recovery or continuous dynamic recrystallization in the studied alloy.展开更多
Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workab...Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workability of nanocomposite.Theactivation energy of285kJ/mol for the hot compression test is obtained by using hyperbolic sine function.By means of dynamicmaterial model(DMM)and the corresponding processing map,safe zone for the hot workability of AA6061/Al2O3is recognized attemperature of450°C and strain rate of0.0005s-1and at temperature of500°C and the strain rate range of0.0005-0.5s-1,with themaximum power dissipation efficiency of38%.Elongated and kinked grains are observed at400°C and strain rate of0.5s-1due tothe severe deformation.展开更多
In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. O...In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst. The crystal color changes from yellow to nearly colorless. The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive. The lowest synthesis conditions fell first and then rose with increasing aluminum. We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.展开更多
基金Project(51301065)supported by the National Natural Science Foundation of ChinaProject(15B063)supported by the Youth Research Foundation of Education Bureau of Hunan Province,China
文摘Hot deformation behavior of extrusion preform of the spray-formed Al-9.0Mg-0.5Mn-0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300-450 ℃ and strain rate range of 0.01-10 s-1. On the basis of experiments and dynamic material model, 2D processing maps and 3D power dissipation maps were developed for identification of exact instability regions and optimization of hot processing parameters. The experimental results indicated that the efficiency factor of energy dissipate （η） lowered to the minimum value when the deformation conditions located at the strain of 0.4, temperature of 300 ° C and strain rate of 1 s-1. The softening mechanism was dynamic recovery, the grain shape was mainly flat, and the portion of high angle grain boundary （〉15°） was 34%. While increasing the deformation temperature to 400 ° C and decreasing the strain rate to 0.1 s-1, a maximum value of η was obtained. It can be found that the main softening mechanism was dynamic recrystallization, the structures were completely recrystallized, and the portion of high angle grain boundary accounted for 86.5%. According to 2D processing maps and 3D power dissipation maps, the optimum processing conditions for the extrusion preform of the spray-formed Al？9.0Mg？0.5Mn？0.1Ti alloy were in the deformation temperature range of 340-450 ° C and the strain rate range of 0.01-0.1 s-1 with the power dissipation efficiency range of 38%？43%.
基金Project(50605015) supported by the National Natural Science Foundation of ChinaProject(HITQNJS.2008.012) supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology,China+1 种基金Projects(20090460884,20080440849) supported by China Postdoctoral Science FoundationProject(LBH-Q08104) supported by the Postdoctoral Foundation of Heilongjiang Province,China
文摘Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.
文摘Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 ℃ to 1200 ℃ and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening during hot compression. The flow behavior was successfully analyzed by the hyperbolic sine equation and the corresponding material constants A, n and αwere determined. The value of apparent activation energy was determined as 423 kJ/mol. The peak and steady state strains showed simple power-law dependence on the Zener-Hollomon parameter. The dynamic recrystallization kinetics was analyzed using Avrami equation and the corresponding exponent was determined to be about 2.7. This value, higher than 2 reported in the literatures, is associated with the mechanism of continuous dynamic recrystallization in the studied alloy. The flow curve up to the peak was modeled by the Cingara equation and the strain exponent, c, was determined about 0.85. The higher value of c compared with the value of 0.2 which has been reported for some stainless steels fortified the idea of extended dynamic recovery or continuous dynamic recrystallization in the studied alloy.
文摘Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workability of nanocomposite.Theactivation energy of285kJ/mol for the hot compression test is obtained by using hyperbolic sine function.By means of dynamicmaterial model(DMM)and the corresponding processing map,safe zone for the hot workability of AA6061/Al2O3is recognized attemperature of450°C and strain rate of0.0005s-1and at temperature of500°C and the strain rate range of0.0005-0.5s-1,with themaximum power dissipation efficiency of38%.Elongated and kinked grains are observed at400°C and strain rate of0.5s-1due tothe severe deformation.
基金supported by the New Century Excellent Talents in University and the National Natural Science Foundation of China (Grant Nos.50572032,50731006 and 50801030)
文摘In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst. The crystal color changes from yellow to nearly colorless. The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive. The lowest synthesis conditions fell first and then rose with increasing aluminum. We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.
