A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating ...A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating with the evolution of mechanical properties is systematically characterized during the subsequent aging treatment at 200°C.The extruded alloy presents an outstanding strength with tensile yield strength of 466 MPa and ultimate tensile strength of 500 MPa at peak aging condition,while the elongation drops from 9.2%in extrusion state to 3.1%.It is found there obviously exist a rapidly decreasing range of ductility at the early stage of aging.Just during this time,the nano precipitates form preferentially at lamellar dislocation boundaries(LDBs)within the elongated grains,but there is no dense and uniform precipitation in the matrix.The results suggest that the low elongation in the aged Mg^(-1)5Gd alloy is mainly attributed to the nano precipitates prior formed at the LDBs with a high density in the elongated grains.The related mechanism has been clarified.展开更多
Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experiment...Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experimentally first.Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results.Typical transient flame shape was studied and then simulated numerically by using temperature.The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results.The predicted results were validated by comparing with experimental data,which demonstrated that an IFW can be simulated by Computational Fluid Dynamics.Numerical results for flame surface,temperature,and flame length agreed well with the experimental results.The IFW flame region and intermittent region were longer than those for an ordinary pool fire.The modified empirical formula for centerline temperature was derived.Variations of vertical and tangential velocity in axial and radial directions were also shown.The vortex core radius was found to be determined by the fuel bed size.Velocity field was not measured extensively due to resources limitation.Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate,air flow and pressure gradient.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.52171121,51971151,52201131,52201132,52171055 and 52071220)Liao Ning Xingliao Program(XLYC1907083)+1 种基金Natural Science Foundation of Liaoning Province of China(2022-NLTS-18-01)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education(HEU10202205).
文摘A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating with the evolution of mechanical properties is systematically characterized during the subsequent aging treatment at 200°C.The extruded alloy presents an outstanding strength with tensile yield strength of 466 MPa and ultimate tensile strength of 500 MPa at peak aging condition,while the elongation drops from 9.2%in extrusion state to 3.1%.It is found there obviously exist a rapidly decreasing range of ductility at the early stage of aging.Just during this time,the nano precipitates form preferentially at lamellar dislocation boundaries(LDBs)within the elongated grains,but there is no dense and uniform precipitation in the matrix.The results suggest that the low elongation in the aged Mg^(-1)5Gd alloy is mainly attributed to the nano precipitates prior formed at the LDBs with a high density in the elongated grains.The related mechanism has been clarified.
基金sponsored by the National Natural Science Foundation of China(No.11402061)The work described in this paper was also partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region,China,for the project“A study on electric and magnetic effects associated with an internal fire whirl in a vertical shaft”(Project No.PolyU 15206215)with account number B-Q47D.
文摘Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experimentally first.Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results.Typical transient flame shape was studied and then simulated numerically by using temperature.The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results.The predicted results were validated by comparing with experimental data,which demonstrated that an IFW can be simulated by Computational Fluid Dynamics.Numerical results for flame surface,temperature,and flame length agreed well with the experimental results.The IFW flame region and intermittent region were longer than those for an ordinary pool fire.The modified empirical formula for centerline temperature was derived.Variations of vertical and tangential velocity in axial and radial directions were also shown.The vortex core radius was found to be determined by the fuel bed size.Velocity field was not measured extensively due to resources limitation.Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate,air flow and pressure gradient.
