The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure ca...The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.展开更多
Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was con...Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was conducted in two consecutive cycles on the AZ91 magnesium alloy,and microstructural evolution,mechanical properties and corrosion behavior were investigated.The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods.Its ability in improving strength and ductility simultaneously was also shown.The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen,respectively.Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%.The potentials derived from the polarization curves were high and the currents were much low for the processed samples.Also,the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples.The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC.HCEC is a unique SPD method,which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.展开更多
A new severe plastic deformation(SPD)technique for improvement of the metallurgical properties of the magnesium alloys is presented.In this process,a cyclic extrusion compression angular pressing(CECAP)process is foll...A new severe plastic deformation(SPD)technique for improvement of the metallurgical properties of the magnesium alloys is presented.In this process,a cyclic extrusion compression angular pressing(CECAP)process is followed by an extrusion step in the outlet playing the role of additional back pressure.Therefore,more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing(ECAP).In order to evaluate the effectiveness and capabilities of this new method,an AM60 magnesium alloy was processed.Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method.In addition,~110%increase in compressive stress was observed in new method compared to the conventional ECAP.Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refinedβ-phase along the boundaries.It may be concluded that the new process is very promising for future magnesium alloy products.展开更多
The cyclic extrusion compression （CEC） was applied to severely deform the as-extruded GW102K （Mg- 10.0Gd-2.0Y-0.5Zr, wt%） alloy at 350, 400, and 450 ℃, respectively. The microstructure, texture, and grain boundar...The cyclic extrusion compression （CEC） was applied to severely deform the as-extruded GW102K （Mg- 10.0Gd-2.0Y-0.5Zr, wt%） alloy at 350, 400, and 450 ℃, respectively. The microstructure, texture, and grain boundary character distribution of the CECed alloy were investigated in the present work. The mechan- ical properties were measured by uniaxial tension at room temperature. The crack initiation on the longitudinal section near the tensile fracture-surface was investigated by high-resolution scanning elec- tron microscopy （SEM）. The result shows that the microstructure was dramatically refined by dynamic recrystallization （DRX）. The initial fiber texture was disintegrated and obviously weakened. The 8-passes/ 350 ℃ CECed alloy exhibited yield strength of 318 MPa with an elongation-to-fracture of 16.8%, increased by 41.3% and 162.5%, respectively. Moreover, the elongation-to-fracture of the 8-passes/450 ℃ CECed alloy significantly increased more than 3 times than that of the received alloy. The cracks were mainly initi- ated at twin boundaries and second phase/matrix interfaces during tensile deformation. The microstructure refinement was considered to result in the dramatically enhanced of the strength and ductility. In ad- dition, the texture randomization during CEC is beneficial for enhancing ductility. The standard positive Hall-Petch relationships have been obtained for the CECed GW102K alloy.展开更多
The effects of CEC passes, isothermal holding time and reheating temperature on the microstructure evolution and grain coarsening behaviour of AZ61 magnesium alloy produced by the recrystallisation and partialmelting ...The effects of CEC passes, isothermal holding time and reheating temperature on the microstructure evolution and grain coarsening behaviour of AZ61 magnesium alloy produced by the recrystallisation and partialmelting （RAP） process were investigated. Before partial remelting, as-cast AZ61 alloy was deformed by cyclic extrusion compression （CEC） with one pass and two pass at 330 ℃. After CEC, the microstructure consisted of unrecrystallized grains and deformed eutectic compounds. Increasing isothermal holding time resulted in the formation of spheroidal grains surrounded by liquid films. With increasing the isothermal holding time, the solid grain size increased and the degree of spheroidization was improved. With increasing the reheating temperature, namely increasing liquid fraction, the solid grain size obviously decreased during the period from 560 ℃ to 570 ℃ and then slightly increased after 570 ℃, while the shape factor increased monotonously. During partial remelting, increasing reheating temperature can properly short the isothermal holding time to obtain fine structure. Moreover, increasing the numbers of CEC passes could produce finer semi-solid microstructure. The coarsening behavior of solid grains in the semi-solid state obeys Ostwald ripening and grain coalescence mechanisms. The coarsening rate constant, K, 595 ℃. After CEC plus partial remelting, the ideal and fine was suitable for thixoforming. was 80μm^3.s^-1 for samples partially remelted at semi-solid state structure can be obtained, which展开更多
Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition a...Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition and die geometry on the distribution of total equivalent plastic strain were investigated. The results show that the strain distributions in the workpieces are inhomogeneous after CEC deformation. The strains of the both ends of the workpieces are lower than that of the center region. The process parameters have significant effects on the strain distribution. The friction between die and workpiece is detrimental to strain homogeneity, thus the friction should be decreased. In order to improve the strain homogeneity, a large corner radius and a low extrusion angle should be used.展开更多
The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression(CEC) up to 8 passes at 503 K were investigated.The local crystallographic text...The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression(CEC) up to 8 passes at 503 K were investigated.The local crystallographic texture,grain size and distribution,and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction(EBSD).The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number.The fraction of low angle grain boundaries(LAGBs) decreases after CEC deformation,and a high fraction of high angle grain boundaries(HAGBs) is revealed after 8 passes of CEC.Moreover,the initial fiber texture becomes random during CEC processing and develops a new texture.展开更多
Grain refinement of AZ31 Mg alloy during cyclic extrusion compression （CEC） at 225-400 ℃ was investigated quantitatively by electron backscattering diffraction （EBSD）. Results show that an ultrafine grained micro...Grain refinement of AZ31 Mg alloy during cyclic extrusion compression （CEC） at 225-400 ℃ was investigated quantitatively by electron backscattering diffraction （EBSD）. Results show that an ultrafine grained microstructure of AZ31 alloy is obtained only after 3 passes of CEC at 225 ℃. The mean misorientation and the fraction of high angle grain boundaries （HAGBs） increase gradually by lowering extrusion temperature. Only a small fraction of {101^-2} twinning is observed by EBSD in AZ31 Mg alloys after 3 passes of CEC. Schmid factors calculation shows that the most active slip system is pyramidal slip {101^-1}〈1120〉and basal slip {0001}〈1120〉 at 225-350 ℃ and 400 ℃, respectively. Direct evidences at subgrain boundaries support the occurrence of continuous dynamic recrystallization （CDRX） mechanism in grain refinement of AZ31 Mg alloy processed by CEC.展开更多
In this study,the effect of severe plastic deformation on the Mg grain refinement and recovery mechanism was investigated.Technical pure magnesium was deformed at room temperature by cycling extrusion-compression(CEC)...In this study,the effect of severe plastic deformation on the Mg grain refinement and recovery mechanism was investigated.Technical pure magnesium was deformed at room temperature by cycling extrusion-compression(CEC)process up to large deformation.Several steps of deformation have been used by applying 1,2 and 4 passes of CEC giving a total effective plastic strain ofε=3.1.Mechanical and structural properties of Mg in initial state and the states after successive steps of deformation were investigated.The mechanical properties were determined by microhardness and compression tests at room temperature.The structural investigations involved light microscope observations,electron back scattered diffraction and texture measurements by X-ray diffraction.It was found that the CEC process refines the grain size down to 6.4μm and reduces strong rolling texture components.However,only the first two passes had a strong effect on mechanical properties while a larger number of CEC cycles(above 4)led to failure of the samples with a small effect on hardness.This observation correlates with texture evolution indicating a more random orientation distribution that slows down the typical for hep metals rapid work hardening.It was found that the CEC process activated twin dynamic recrystallization in deformed Mg.This process led to the formation of new randomly oriented grains inside the twinned areas and as a consequence it reduced the strong rolling texture components.展开更多
The biomagnesium alloys have been considered to be one of the most potential biodegradable metal materials due to its good mechanical compatibility, biological compatibility, biological security and biodegradable char...The biomagnesium alloys have been considered to be one of the most potential biodegradable metal materials due to its good mechanical compatibility, biological compatibility, biological security and biodegradable characteristics. However, the two major problems of high degradation rates in physiological environment and low mechanical properties prevent the development of biomagnesium alloys. In the present work, the samples of Mg-Zn-Y-Nd alloy were prepared by cyclic extrusion compression （CEC） and equal channel angular pressing （ECAP）. The microstructures, mechanical properties of alloy and its corrosion behavior in simulated body fluid （SBF） were evaluated. The results reveal that Mg-Zn-Y-Nd alloy consists of equiaxial fine grain structure with the homogeneous distribution of micrometer size and nano-sized second phase, which was caused by the dynamic recrystallization during the ECAP and CEC. The corrosion resistance of alloy was improved. The tensile and corrosion resistance were improved, especially the processed alloy exhibit uniform corrosion performances and decreased corrosion rate. This will provide theoretical ground for Mg-Zn-Y-Nd alloy as vascular stent application.展开更多
基金Projects(ZD20081901,QC2010110,QC2012C006)supported by the Natural Science Foundation of Heilongjiang Province,ChinaProject(2012RFQXS113)supported by Special Fund Project for Scientific and Technological Innovation Talents of Harbin,ChinaProject(201210214008)supported by Training Programs of Innovation and Entrepreneurship for Undergraduates,China
文摘The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.
文摘Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was conducted in two consecutive cycles on the AZ91 magnesium alloy,and microstructural evolution,mechanical properties and corrosion behavior were investigated.The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods.Its ability in improving strength and ductility simultaneously was also shown.The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen,respectively.Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%.The potentials derived from the polarization curves were high and the currents were much low for the processed samples.Also,the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples.The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC.HCEC is a unique SPD method,which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.
文摘A new severe plastic deformation(SPD)technique for improvement of the metallurgical properties of the magnesium alloys is presented.In this process,a cyclic extrusion compression angular pressing(CECAP)process is followed by an extrusion step in the outlet playing the role of additional back pressure.Therefore,more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing(ECAP).In order to evaluate the effectiveness and capabilities of this new method,an AM60 magnesium alloy was processed.Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method.In addition,~110%increase in compressive stress was observed in new method compared to the conventional ECAP.Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refinedβ-phase along the boundaries.It may be concluded that the new process is very promising for future magnesium alloy products.
基金supported by the National Natural Science Foundation of China (No. 51204117)Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxithe Natural Science Foundation of Shanxi province (No. 2015021017)
文摘The cyclic extrusion compression （CEC） was applied to severely deform the as-extruded GW102K （Mg- 10.0Gd-2.0Y-0.5Zr, wt%） alloy at 350, 400, and 450 ℃, respectively. The microstructure, texture, and grain boundary character distribution of the CECed alloy were investigated in the present work. The mechan- ical properties were measured by uniaxial tension at room temperature. The crack initiation on the longitudinal section near the tensile fracture-surface was investigated by high-resolution scanning elec- tron microscopy （SEM）. The result shows that the microstructure was dramatically refined by dynamic recrystallization （DRX）. The initial fiber texture was disintegrated and obviously weakened. The 8-passes/ 350 ℃ CECed alloy exhibited yield strength of 318 MPa with an elongation-to-fracture of 16.8%, increased by 41.3% and 162.5%, respectively. Moreover, the elongation-to-fracture of the 8-passes/450 ℃ CECed alloy significantly increased more than 3 times than that of the received alloy. The cracks were mainly initi- ated at twin boundaries and second phase/matrix interfaces during tensile deformation. The microstructure refinement was considered to result in the dramatically enhanced of the strength and ductility. In ad- dition, the texture randomization during CEC is beneficial for enhancing ductility. The standard positive Hall-Petch relationships have been obtained for the CECed GW102K alloy.
文摘The effects of CEC passes, isothermal holding time and reheating temperature on the microstructure evolution and grain coarsening behaviour of AZ61 magnesium alloy produced by the recrystallisation and partialmelting （RAP） process were investigated. Before partial remelting, as-cast AZ61 alloy was deformed by cyclic extrusion compression （CEC） with one pass and two pass at 330 ℃. After CEC, the microstructure consisted of unrecrystallized grains and deformed eutectic compounds. Increasing isothermal holding time resulted in the formation of spheroidal grains surrounded by liquid films. With increasing the isothermal holding time, the solid grain size increased and the degree of spheroidization was improved. With increasing the reheating temperature, namely increasing liquid fraction, the solid grain size obviously decreased during the period from 560 ℃ to 570 ℃ and then slightly increased after 570 ℃, while the shape factor increased monotonously. During partial remelting, increasing reheating temperature can properly short the isothermal holding time to obtain fine structure. Moreover, increasing the numbers of CEC passes could produce finer semi-solid microstructure. The coarsening behavior of solid grains in the semi-solid state obeys Ostwald ripening and grain coalescence mechanisms. The coarsening rate constant, K, 595 ℃. After CEC plus partial remelting, the ideal and fine was suitable for thixoforming. was 80μm^3.s^-1 for samples partially remelted at semi-solid state structure can be obtained, which
基金Projects (51074106, 50674067) supported by the National Natural Science Foundation of ChinaProject (09JC1408200) supported by the Science and Technology Commission of Shanghai Municipality, China+1 种基金Project (2011-079) supported by the Shaanxi Scholarship Council,ChinaProject (20102015) supported by the Doctoral Startup Fund of TUST, China
文摘Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition and die geometry on the distribution of total equivalent plastic strain were investigated. The results show that the strain distributions in the workpieces are inhomogeneous after CEC deformation. The strains of the both ends of the workpieces are lower than that of the center region. The process parameters have significant effects on the strain distribution. The friction between die and workpiece is detrimental to strain homogeneity, thus the friction should be decreased. In order to improve the strain homogeneity, a large corner radius and a low extrusion angle should be used.
基金Projects(50674067,51074106) supported by the National Natural Science Foundation of ChinaProject(09JC1408200) supported by the Science and Technology Commission of Shanghai Municipality,China
文摘The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression(CEC) up to 8 passes at 503 K were investigated.The local crystallographic texture,grain size and distribution,and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction(EBSD).The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number.The fraction of low angle grain boundaries(LAGBs) decreases after CEC deformation,and a high fraction of high angle grain boundaries(HAGBs) is revealed after 8 passes of CEC.Moreover,the initial fiber texture becomes random during CEC processing and develops a new texture.
基金Projects(50674067,51074106,51374145)supported by the National Natural Science Foundation of ChinaProject(09JC1408200)supported by the Science and Technology Commission of Shanghai Municipality,China+1 种基金Project(2011BAE22B01-5)supported by the National Key Technology R&D Program of ChinaProjects(182000/S10,192450/I30)supported by the Research Council of Norway
文摘Grain refinement of AZ31 Mg alloy during cyclic extrusion compression （CEC） at 225-400 ℃ was investigated quantitatively by electron backscattering diffraction （EBSD）. Results show that an ultrafine grained microstructure of AZ31 alloy is obtained only after 3 passes of CEC at 225 ℃. The mean misorientation and the fraction of high angle grain boundaries （HAGBs） increase gradually by lowering extrusion temperature. Only a small fraction of {101^-2} twinning is observed by EBSD in AZ31 Mg alloys after 3 passes of CEC. Schmid factors calculation shows that the most active slip system is pyramidal slip {101^-1}〈1120〉and basal slip {0001}〈1120〉 at 225-350 ℃ and 400 ℃, respectively. Direct evidences at subgrain boundaries support the occurrence of continuous dynamic recrystallization （CDRX） mechanism in grain refinement of AZ31 Mg alloy processed by CEC.
基金The project was performed within the activity(11.11.180.653)of the Department of Materials Science and Non-Ferrous Metals Engineering at AGH-UST Krakow,Poland.
文摘In this study,the effect of severe plastic deformation on the Mg grain refinement and recovery mechanism was investigated.Technical pure magnesium was deformed at room temperature by cycling extrusion-compression(CEC)process up to large deformation.Several steps of deformation have been used by applying 1,2 and 4 passes of CEC giving a total effective plastic strain ofε=3.1.Mechanical and structural properties of Mg in initial state and the states after successive steps of deformation were investigated.The mechanical properties were determined by microhardness and compression tests at room temperature.The structural investigations involved light microscope observations,electron back scattered diffraction and texture measurements by X-ray diffraction.It was found that the CEC process refines the grain size down to 6.4μm and reduces strong rolling texture components.However,only the first two passes had a strong effect on mechanical properties while a larger number of CEC cycles(above 4)led to failure of the samples with a small effect on hardness.This observation correlates with texture evolution indicating a more random orientation distribution that slows down the typical for hep metals rapid work hardening.It was found that the CEC process activated twin dynamic recrystallization in deformed Mg.This process led to the formation of new randomly oriented grains inside the twinned areas and as a consequence it reduced the strong rolling texture components.
基金Acknowledgements The authors are grateful for the support by National Key Technology R＆D Program of China （Grant No. 2012BAI18B01） and the National Natural Science Foundation of China （Grant No. 51171174）.
文摘The biomagnesium alloys have been considered to be one of the most potential biodegradable metal materials due to its good mechanical compatibility, biological compatibility, biological security and biodegradable characteristics. However, the two major problems of high degradation rates in physiological environment and low mechanical properties prevent the development of biomagnesium alloys. In the present work, the samples of Mg-Zn-Y-Nd alloy were prepared by cyclic extrusion compression （CEC） and equal channel angular pressing （ECAP）. The microstructures, mechanical properties of alloy and its corrosion behavior in simulated body fluid （SBF） were evaluated. The results reveal that Mg-Zn-Y-Nd alloy consists of equiaxial fine grain structure with the homogeneous distribution of micrometer size and nano-sized second phase, which was caused by the dynamic recrystallization during the ECAP and CEC. The corrosion resistance of alloy was improved. The tensile and corrosion resistance were improved, especially the processed alloy exhibit uniform corrosion performances and decreased corrosion rate. This will provide theoretical ground for Mg-Zn-Y-Nd alloy as vascular stent application.
