An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process (SCRC),was explored.The mechanical properties and microstructures of the tensile samples...An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process (SCRC),was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%?13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1(Al) grains,which have the shape factor of 0.78?0.89 and the grain diameter of 35?45μm,can be prepared by the serpentine channel pouring process.The primary α2(Al) grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.展开更多
The effect of iron content on wear behavior of hypereutectic Al?17Si?2Cu?1Ni alloy produced by rheocasting process was investigated. The dry sliding wear tests were carried out with a pin-on-disk wear tester. The resu...The effect of iron content on wear behavior of hypereutectic Al?17Si?2Cu?1Ni alloy produced by rheocasting process was investigated. The dry sliding wear tests were carried out with a pin-on-disk wear tester. The results show that the wear rate of the rheocast alloy is lower than that of the alloy produced by conventional casting process under the same applied load. The fine particle-likeδ-Al4(Fe,Mn)Si2 and polygonalα-Al15(Fe,Mn)3Si2 phases help to improve the wear resistance of rheocast alloys. As the volume fraction of fine Fe-bearing compounds increases, the wear rate of the rheocast alloy decreases. Moreover, the wear rate of rheocast alloy increases with the increase of applied load from 50 to 200 N. For the rheocast alloy with 3% Fe, oxidation wear is the main mechanism at low applied load (50 N). At higher applied loads, a combination of delamination and oxidation wear is the dominant wear mechanism.展开更多
The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration (USV) process and then shaped by high press...The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration (USV) process and then shaped by high pressure diecasting (HPDC). The results show that fine and spherical a-Mg particles were obtained by USV at the nucleation stage, which was mainly attributed to the cavitation and acoustic streaming induced by the USV. Extending USV treatment time increased the solid volume fraction and average particle size, the shape factors were nearly the same, about 0.7. Excellent semisolid slurry of AZ91 magnesium alloy could be obtained within 6 rain by USV near its liquidus temperature. The rheo-HPDC samples treated by USV for 6 min had the maximum ultimate tensile strength and elongation, which were 248 MPa and 7.4%, respectively. It was also found that the ductile fracture mode prevailed in the rheocasting AZ91 magnesium alloy.展开更多
The microstructural distribution along thickness of asymmetric twin-roll cast AZ31 magnesium alloy slab was investigated. It was found that the microstructure along the thickness of the slab was significantly inhomoge...The microstructural distribution along thickness of asymmetric twin-roll cast AZ31 magnesium alloy slab was investigated. It was found that the microstructure along the thickness of the slab was significantly inhomogeneous. There were many deformed bands with flow form near the upper surface of twin-roll cast plate. Very few deformed bands could be seen in the central part of the plate where the dendrites were thick. Fine dendritic structures dominated near the lower surface of the twin-roll cast strip. It is concluded that the shear strain caused by linear velocity difference between surfaces of upper and lower rolls results in the deformed bands of the twin-roll cast slab. Aluminum, zinc and manganese segregate to the boundary of dendrites, while silicon distributes inside the α-Mg solid solution.展开更多
In order to improve the properties of ZA 27 and ZA4-3 zinc alloys and broaden their application ranges,SiC particlj1Ale composites, prepared by means of rheological casting technology, are investigated individually on...In order to improve the properties of ZA 27 and ZA4-3 zinc alloys and broaden their application ranges,SiC particlj1Ale composites, prepared by means of rheological casting technology, are investigated individually on their rT..t'llanical properties. The results of ne-cural strength, impact strensttl, compressive strength, hardness values and wear rate of the composites show that the addition of SiCp, leads to the increase of the compressive strength and hardness values at both room and higher temperature, and wear resistance of the materials, accompanying with the slight decrease of the fie-cural strength and sharp reduction of the impacttoughness. The factors affecting the mechanical properties of the composites are discussed in the paper.展开更多
The A356 aluminum alloy wheels were prepared by thixo-forging combined with a low superheat casting process. The as-cast microstructure, microstructure evolution during reheating and the mechanical properties of the t...The A356 aluminum alloy wheels were prepared by thixo-forging combined with a low superheat casting process. The as-cast microstructure, microstructure evolution during reheating and the mechanical properties of the thixo-forged A356 aluminum alloy wheels were investigated. The results show that the A356 aluminum alloy billet with fine, uniform and non-dendritic grains can be obtained when the melt is cast at 635 ℃. When the billet is reheated at 600 ℃ for 60 min, the non-dendritic grains are changed into spherical ones and the billet can be easily thixo-forged into wheels. The tensile strength and elongation of thixo-forged wheels with T6 heat treatment are 327.6 MPa and 7.8%, respectively, which are higher than those of a cast wheel. It is suggested that the thixo-forging combined with the low superheat casting process is an effective technique to produce aluminum alloy wheels with high mechanical properties.展开更多
The effects of different cooling conditions on the mechanical properties and microstructures of a Sr-modified A356 (Al-7Si-0.3Mg) aluminum casting alloy were comparatively investigated using three moulding sands inc...The effects of different cooling conditions on the mechanical properties and microstructures of a Sr-modified A356 (Al-7Si-0.3Mg) aluminum casting alloy were comparatively investigated using three moulding sands including quartz, alumina and chromite into multi-step blocks. The results show that the mechanical properties and microstructures using chromite sand are the best. As the cooling speed increases, the dendrite arm spacing (DAS) decreases significantly and the mechanical properties are improved, and the elongation is more sensitive to the cooling speed as compared with the tensile strength. The increase of the properties is primarily attributed to the decrease of the DAS and the increase of the free strontium atoms in the matrix. In particular, the regression models for predicting both the tensile strength and the elongation for Sr-modified A356 aluminum casting alloy were established based on the experimental data.展开更多
Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dend...Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.展开更多
The as-cast ingot of equiatomic nickel-titanium shape memory alloy (NiTi SMA) was prepared by vacuum consumable arc melting. The tensile tests and the compressive tests with respect to as-cast NiTi SMA were performe...The as-cast ingot of equiatomic nickel-titanium shape memory alloy (NiTi SMA) was prepared by vacuum consumable arc melting. The tensile tests and the compressive tests with respect to as-cast NiTi SMA were performed to study its mechanical properties of fracture. The microanalysis of as-cast NiTi SMA as well as its fractured samples was performed so as to better understand microstructure evolution and fracture behavior of NiTi SMA. Under tensile loading, the as-cast NiTi SMA shows higher plasticity and is characterized by ductile fracture at 750℃, but it demonstrates poorer plasticity and is characterized by cleavage fracture as well as transcrystalline fracture at room temperature and -100 ℃. Under compressive loading at -100 ~C, the as-cast NiTi SMA is characterized by shear fracture where the normal to the shearing fracture surface inclines about 45° to the compressive axis, and belongs to cleavage fracture where the cracks exoand via transcrvstalline fracture.展开更多
Dry wear behavior of the rheo-casting Al-16Si-4Cu-0.5Mg alloy was investigated by micro-scratch and dry sliding weartests. Analyses of the microstructure, scratch grooves, wear tracks, worn surfaces and wear debris of...Dry wear behavior of the rheo-casting Al-16Si-4Cu-0.5Mg alloy was investigated by micro-scratch and dry sliding weartests. Analyses of the microstructure, scratch grooves, wear tracks, worn surfaces and wear debris of the alloy were carried out byoptical microscope and scanning electron microscope. The microstructural analysis showed that via rheo-processing, the primary Siwas refined and rounded, eutectics dispersed more homogenously, and even the skeleton AlFeMnSi phase was fragmented into facetshape. Micro-scratch test showed that the microstructural refinement resulted in better wear resistance. Dry sliding wear test revealedthat the rheo-processed sample exhibit obviously superior wear resistance because of the microstructure improvement. The dominantmechanism in mild wear condition is abrasion, but it turned to adhesion and oxidation in high applied load and fast sliding velocityconditions.展开更多
Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means ofoptical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-ca...Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means ofoptical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-casting (RC) andrheo-diecasting (RDC) ADC12 alloys are sheared off. The average size, as well as solid fraction of the primary Al increase withdescending pouring temperature. The mechanical properties of alloys are strengthened by rheo-processing. Ultimate tensile strengthsof RC samples increase with the decrease of the pouring temperature, and reach the maximum in the range from 580 to 600 °C. Atpouring temperature of 595 °C, the RDC sample obtains the best ultimate tensile strength and elongation. Great reductions onporosity and primary Al globularization are crucial to the mechanical properties. Relationships of the primary Al size and yield stressare depicted with Hall?Petch equation.展开更多
The miscibility and crystallization of solution casting biodegradable poly(3-hydroxybuty- rate)/poly(ethylene succinate) (PHB/PES) blends was investigated by differential scanning calorimetry, rheology, and opti...The miscibility and crystallization of solution casting biodegradable poly(3-hydroxybuty- rate)/poly(ethylene succinate) (PHB/PES) blends was investigated by differential scanning calorimetry, rheology, and optical microscopy. The blends showed two glass transition temperatures and a depression of melting temperature of PHB with compositions in phase diagram, which indicated that the blend was partially miscible. The morphology observation supported this result. It was found that the PHB and PES can crystallize simultaneously or upon stepwise depending on the crystallization temperatures and compositions. The spherulite growth rate of PHB increased with increasing of PES content. The influence of compositions on the spherulitic growth rate for the partially miscible polymer blends was discussed.展开更多
基金Project(2006AA03Z115) supported by the National High-tech Research and Development Program of ChinaProject(2011CB606302-1) supported by the National Basic Research Program of ChinaProject(50774007) supported by the National Natural Science Foundation of China
文摘An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process (SCRC),was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%?13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1(Al) grains,which have the shape factor of 0.78?0.89 and the grain diameter of 35?45μm,can be prepared by the serpentine channel pouring process.The primary α2(Al) grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.
基金Project(2015M572135)supported by the China Postdoctoral Science FoundationProject(2012CB619600)supported by the National Basic Research Program of China
文摘The effect of iron content on wear behavior of hypereutectic Al?17Si?2Cu?1Ni alloy produced by rheocasting process was investigated. The dry sliding wear tests were carried out with a pin-on-disk wear tester. The results show that the wear rate of the rheocast alloy is lower than that of the alloy produced by conventional casting process under the same applied load. The fine particle-likeδ-Al4(Fe,Mn)Si2 and polygonalα-Al15(Fe,Mn)3Si2 phases help to improve the wear resistance of rheocast alloys. As the volume fraction of fine Fe-bearing compounds increases, the wear rate of the rheocast alloy decreases. Moreover, the wear rate of rheocast alloy increases with the increase of applied load from 50 to 200 N. For the rheocast alloy with 3% Fe, oxidation wear is the main mechanism at low applied load (50 N). At higher applied loads, a combination of delamination and oxidation wear is the dominant wear mechanism.
文摘The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration (USV) process and then shaped by high pressure diecasting (HPDC). The results show that fine and spherical a-Mg particles were obtained by USV at the nucleation stage, which was mainly attributed to the cavitation and acoustic streaming induced by the USV. Extending USV treatment time increased the solid volume fraction and average particle size, the shape factors were nearly the same, about 0.7. Excellent semisolid slurry of AZ91 magnesium alloy could be obtained within 6 rain by USV near its liquidus temperature. The rheo-HPDC samples treated by USV for 6 min had the maximum ultimate tensile strength and elongation, which were 248 MPa and 7.4%, respectively. It was also found that the ductile fracture mode prevailed in the rheocasting AZ91 magnesium alloy.
基金Project (2006BAE04B02) supported by the National Key Technology R&D Program during the 11th Five-Year Plan of China
文摘The microstructural distribution along thickness of asymmetric twin-roll cast AZ31 magnesium alloy slab was investigated. It was found that the microstructure along the thickness of the slab was significantly inhomogeneous. There were many deformed bands with flow form near the upper surface of twin-roll cast plate. Very few deformed bands could be seen in the central part of the plate where the dendrites were thick. Fine dendritic structures dominated near the lower surface of the twin-roll cast strip. It is concluded that the shear strain caused by linear velocity difference between surfaces of upper and lower rolls results in the deformed bands of the twin-roll cast slab. Aluminum, zinc and manganese segregate to the boundary of dendrites, while silicon distributes inside the α-Mg solid solution.
文摘In order to improve the properties of ZA 27 and ZA4-3 zinc alloys and broaden their application ranges,SiC particlj1Ale composites, prepared by means of rheological casting technology, are investigated individually on their rT..t'llanical properties. The results of ne-cural strength, impact strensttl, compressive strength, hardness values and wear rate of the composites show that the addition of SiCp, leads to the increase of the compressive strength and hardness values at both room and higher temperature, and wear resistance of the materials, accompanying with the slight decrease of the fie-cural strength and sharp reduction of the impacttoughness. The factors affecting the mechanical properties of the composites are discussed in the paper.
基金Project(2012B090600051)supported by the Guangdong Provincial Department of Science and Technology,ChinaProject(2013EG115006)supported by the Special Program for Technology Development from the Ministry of Science and Technology of China
文摘The A356 aluminum alloy wheels were prepared by thixo-forging combined with a low superheat casting process. The as-cast microstructure, microstructure evolution during reheating and the mechanical properties of the thixo-forged A356 aluminum alloy wheels were investigated. The results show that the A356 aluminum alloy billet with fine, uniform and non-dendritic grains can be obtained when the melt is cast at 635 ℃. When the billet is reheated at 600 ℃ for 60 min, the non-dendritic grains are changed into spherical ones and the billet can be easily thixo-forged into wheels. The tensile strength and elongation of thixo-forged wheels with T6 heat treatment are 327.6 MPa and 7.8%, respectively, which are higher than those of a cast wheel. It is suggested that the thixo-forging combined with the low superheat casting process is an effective technique to produce aluminum alloy wheels with high mechanical properties.
基金Project (50971087) supported by the National Natural Science Foundation of ChinaProject (11JDG070) supported by the Senior Talent Research Foundation of Jiangsu University, China
文摘The effects of different cooling conditions on the mechanical properties and microstructures of a Sr-modified A356 (Al-7Si-0.3Mg) aluminum casting alloy were comparatively investigated using three moulding sands including quartz, alumina and chromite into multi-step blocks. The results show that the mechanical properties and microstructures using chromite sand are the best. As the cooling speed increases, the dendrite arm spacing (DAS) decreases significantly and the mechanical properties are improved, and the elongation is more sensitive to the cooling speed as compared with the tensile strength. The increase of the properties is primarily attributed to the decrease of the DAS and the increase of the free strontium atoms in the matrix. In particular, the regression models for predicting both the tensile strength and the elongation for Sr-modified A356 aluminum casting alloy were established based on the experimental data.
文摘Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.
基金Project (51071056) supported by the National Natural Science Foundation of ChinaProject (HEUCFR1132) supported by the Fundamental Research Funds for the Central Universities of China
文摘The as-cast ingot of equiatomic nickel-titanium shape memory alloy (NiTi SMA) was prepared by vacuum consumable arc melting. The tensile tests and the compressive tests with respect to as-cast NiTi SMA were performed to study its mechanical properties of fracture. The microanalysis of as-cast NiTi SMA as well as its fractured samples was performed so as to better understand microstructure evolution and fracture behavior of NiTi SMA. Under tensile loading, the as-cast NiTi SMA shows higher plasticity and is characterized by ductile fracture at 750℃, but it demonstrates poorer plasticity and is characterized by cleavage fracture as well as transcrystalline fracture at room temperature and -100 ℃. Under compressive loading at -100 ~C, the as-cast NiTi SMA is characterized by shear fracture where the normal to the shearing fracture surface inclines about 45° to the compressive axis, and belongs to cleavage fracture where the cracks exoand via transcrvstalline fracture.
基金Project(51404153)supported by the National Natural Science Foundation of ChinaProject supported by the Joint Ph D Program of the China Scholarship Council(CSC)
文摘Dry wear behavior of the rheo-casting Al-16Si-4Cu-0.5Mg alloy was investigated by micro-scratch and dry sliding weartests. Analyses of the microstructure, scratch grooves, wear tracks, worn surfaces and wear debris of the alloy were carried out byoptical microscope and scanning electron microscope. The microstructural analysis showed that via rheo-processing, the primary Siwas refined and rounded, eutectics dispersed more homogenously, and even the skeleton AlFeMnSi phase was fragmented into facetshape. Micro-scratch test showed that the microstructural refinement resulted in better wear resistance. Dry sliding wear test revealedthat the rheo-processed sample exhibit obviously superior wear resistance because of the microstructure improvement. The dominantmechanism in mild wear condition is abrasion, but it turned to adhesion and oxidation in high applied load and fast sliding velocityconditions.
基金Project(51404153)supported by the National Natural Science Foundation of China
文摘Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means ofoptical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-casting (RC) andrheo-diecasting (RDC) ADC12 alloys are sheared off. The average size, as well as solid fraction of the primary Al increase withdescending pouring temperature. The mechanical properties of alloys are strengthened by rheo-processing. Ultimate tensile strengthsof RC samples increase with the decrease of the pouring temperature, and reach the maximum in the range from 580 to 600 °C. Atpouring temperature of 595 °C, the RDC sample obtains the best ultimate tensile strength and elongation. Great reductions onporosity and primary Al globularization are crucial to the mechanical properties. Relationships of the primary Al size and yield stressare depicted with Hall?Petch equation.
基金ACKNOWLEDGMENT This work was supported by the Key Science Foundation of Education Ministry of China and the Anhui Science Foundation.
文摘The miscibility and crystallization of solution casting biodegradable poly(3-hydroxybuty- rate)/poly(ethylene succinate) (PHB/PES) blends was investigated by differential scanning calorimetry, rheology, and optical microscopy. The blends showed two glass transition temperatures and a depression of melting temperature of PHB with compositions in phase diagram, which indicated that the blend was partially miscible. The morphology observation supported this result. It was found that the PHB and PES can crystallize simultaneously or upon stepwise depending on the crystallization temperatures and compositions. The spherulite growth rate of PHB increased with increasing of PES content. The influence of compositions on the spherulitic growth rate for the partially miscible polymer blends was discussed.