In semi-solid forming process, preparing the slurry with rosette or globular microstructure is very important. A new approach named the damper cooling tube method （DCT）, to produce the semi-solid metal slurry, has b...In semi-solid forming process, preparing the slurry with rosette or globular microstructure is very important. A new approach named the damper cooling tube method （DCT）, to produce the semi-solid metal slurry, has been introduced. To optimize the technical parameters in designing the apparatus, the finite volume method was adopted to simulate the flow process. The temperature effects on the rheological properties of the slurries were also considered. The effects of the technical parameters on the slurry properties were studied in detail.展开更多
To produce a high quality semisolid slurry that consists of fine primary particles uniformly suspended in the liquid matrix for rheoforming, chemical refining and electromagnetic or mechanical stirring are the two met...To produce a high quality semisolid slurry that consists of fine primary particles uniformly suspended in the liquid matrix for rheoforming, chemical refining and electromagnetic or mechanical stirring are the two methods commonly used. But these two methods either contaminate the melt or incur high cost. In this study, the damper cooling tube （DCT） method was designed to prepare semisolid slurry of A356 aluminum alloy, and was compared with the low superheat casting （LSC） method - a conventional process used to produce casting slab with equiaxed dendrite microstructure for thixoforming route. A series of comparative experiments were performed at the pouring temperatures of 650 ＆#176;C, 638 ＆#176;C and 622 ＆#176;C. Metal ographic observations of the casting samples were carried out using an optical electron microscope with image analysis software. Results show that the microstructure of semisolid slurry produced by the DCT process consists of spherical primary α-Al grains, while equiaxed grains microstructure is found in the LSC process. The lower the pouring temperature, the smal er the grain size and the rounder the grain morphology in both methods. The copious nucleation, which could be generated in the DCT, owing to the cooling and stirring effect, is the key to producing high quality semisolid slurry. DCT method could produce rounder and smal er α-Al grains, which are suitable for semisolid processing; and the equivalent grain size is no more than 60 μm when the pouring temperature is 622 ＆#176;C.展开更多
A novel cambered surface steel tube damper(CSTD)with a cambered surface steel tube and two concave connecting plates is proposed herein.The steel tube is the main energy dissipation component and comprises a weakened ...A novel cambered surface steel tube damper(CSTD)with a cambered surface steel tube and two concave connecting plates is proposed herein.The steel tube is the main energy dissipation component and comprises a weakened segment in the middle,a transition segment,and an embedded segment.It is believed that during an earthquake,the middle weakened segment of the CSTD will be damaged,whereas the reliability of the end connection is ensured.Theoretical and experimental studies are conducted to verify the effectiveness of the proposed CSTD.Formulas for the initial stiffness and yield force of the CSTD are proposed.Subsequently,two CSTD specimens with different steel tube thicknesses are fabricated and tested under cyclic quasi-static loads.The result shows that the CSTD yields a stable hysteretic response and affords excellent energy dissipation.A parametric study is conducted to investigate the effects of the steel tube height,diameter,and thickness on the seismic performance of the CSTD.Compared with equalstiffness design steel tube dampers,the CSTD exhibits better energy dissipation performance,more stable hysteretic response,and better uniformity in plastic deformation distributions.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (No.50374014).
文摘In semi-solid forming process, preparing the slurry with rosette or globular microstructure is very important. A new approach named the damper cooling tube method （DCT）, to produce the semi-solid metal slurry, has been introduced. To optimize the technical parameters in designing the apparatus, the finite volume method was adopted to simulate the flow process. The temperature effects on the rheological properties of the slurries were also considered. The effects of the technical parameters on the slurry properties were studied in detail.
基金supported by the National Science Foundation of Jiangsu province,China (No.BK20131193)
文摘To produce a high quality semisolid slurry that consists of fine primary particles uniformly suspended in the liquid matrix for rheoforming, chemical refining and electromagnetic or mechanical stirring are the two methods commonly used. But these two methods either contaminate the melt or incur high cost. In this study, the damper cooling tube （DCT） method was designed to prepare semisolid slurry of A356 aluminum alloy, and was compared with the low superheat casting （LSC） method - a conventional process used to produce casting slab with equiaxed dendrite microstructure for thixoforming route. A series of comparative experiments were performed at the pouring temperatures of 650 ＆#176;C, 638 ＆#176;C and 622 ＆#176;C. Metal ographic observations of the casting samples were carried out using an optical electron microscope with image analysis software. Results show that the microstructure of semisolid slurry produced by the DCT process consists of spherical primary α-Al grains, while equiaxed grains microstructure is found in the LSC process. The lower the pouring temperature, the smal er the grain size and the rounder the grain morphology in both methods. The copious nucleation, which could be generated in the DCT, owing to the cooling and stirring effect, is the key to producing high quality semisolid slurry. DCT method could produce rounder and smal er α-Al grains, which are suitable for semisolid processing; and the equivalent grain size is no more than 60 μm when the pouring temperature is 622 ＆#176;C.
基金This study was funded by the National Key R&D Program of China(No.2017YFC0703600).
文摘A novel cambered surface steel tube damper(CSTD)with a cambered surface steel tube and two concave connecting plates is proposed herein.The steel tube is the main energy dissipation component and comprises a weakened segment in the middle,a transition segment,and an embedded segment.It is believed that during an earthquake,the middle weakened segment of the CSTD will be damaged,whereas the reliability of the end connection is ensured.Theoretical and experimental studies are conducted to verify the effectiveness of the proposed CSTD.Formulas for the initial stiffness and yield force of the CSTD are proposed.Subsequently,two CSTD specimens with different steel tube thicknesses are fabricated and tested under cyclic quasi-static loads.The result shows that the CSTD yields a stable hysteretic response and affords excellent energy dissipation.A parametric study is conducted to investigate the effects of the steel tube height,diameter,and thickness on the seismic performance of the CSTD.Compared with equalstiffness design steel tube dampers,the CSTD exhibits better energy dissipation performance,more stable hysteretic response,and better uniformity in plastic deformation distributions.
