Thixocasting requires manufacturing of billets with non-dendritic microstructure.Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer.Subsequent heat treat...Thixocasting requires manufacturing of billets with non-dendritic microstructure.Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer.Subsequent heat treatment was used to produce a transition from rosette to globular microstructure.The current and the duration of stirring were explored as control parameters.Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles.The effect of processing parameters on the dendrite fragmentation was discussed.Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process.A non-isothermal alloy solidification model was used for simulations.The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one.Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale.The results were interpreted in the light of existing theories of microstructure refinement and globularisation.展开更多
The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dend...The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure.The microstructure depended on several process parameters such as stirring intensity,stirring frequency,cooling rate,and melt initial superheat.Through a series of computational studies and controlled experiments,a set of process parameters were identified to produce the best microstructures.Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components.The reheating process was characterized for various reheating cycles using a vertical-type reheating machine.The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet,and the heating was continued until the liquid fraction reached about 50%.These parameters were determined with the help of a computational fluid dynamics(CFD) model of die filling and solidification of the semisolid alloy.The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine.The results show that the castings are near net shape,free from porosity,good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.展开更多
Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an incli...Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an inclined surface which is cooled from underneath.The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry.However,the final microstructure of the ingot depends on several process parameters such as cooling rate,incline angle of the cooling slope,length of the slope and initial melt superheat.In this work,a CFD model using volume of fluid(VOF) method for simulating flow along the cooling slope was presented.Equations for conservation of mass,momentum,energy and species were solved to predict hydrodynamic and thermal behavior,in addition to predicting solid fraction distribution and macrosegregation.Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases.The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains.The alloy chosen for the study was aluminum alloy A356,for which adequate experimental data were available in the literature.The effects of two key process parameters,namely the slope angle and the pouring temperature,on temperature distribution,velocity distribution and macrosegregation were also studied.展开更多
文摘Thixocasting requires manufacturing of billets with non-dendritic microstructure.Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer.Subsequent heat treatment was used to produce a transition from rosette to globular microstructure.The current and the duration of stirring were explored as control parameters.Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles.The effect of processing parameters on the dendrite fragmentation was discussed.Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process.A non-isothermal alloy solidification model was used for simulations.The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one.Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale.The results were interpreted in the light of existing theories of microstructure refinement and globularisation.
基金The financial support from Ministry of Mines,TIFAC,Department of Science and Technology and Defense Research and Development Organization
文摘The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure.The microstructure depended on several process parameters such as stirring intensity,stirring frequency,cooling rate,and melt initial superheat.Through a series of computational studies and controlled experiments,a set of process parameters were identified to produce the best microstructures.Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components.The reheating process was characterized for various reheating cycles using a vertical-type reheating machine.The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet,and the heating was continued until the liquid fraction reached about 50%.These parameters were determined with the help of a computational fluid dynamics(CFD) model of die filling and solidification of the semisolid alloy.The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine.The results show that the castings are near net shape,free from porosity,good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.
文摘Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an inclined surface which is cooled from underneath.The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry.However,the final microstructure of the ingot depends on several process parameters such as cooling rate,incline angle of the cooling slope,length of the slope and initial melt superheat.In this work,a CFD model using volume of fluid(VOF) method for simulating flow along the cooling slope was presented.Equations for conservation of mass,momentum,energy and species were solved to predict hydrodynamic and thermal behavior,in addition to predicting solid fraction distribution and macrosegregation.Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases.The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains.The alloy chosen for the study was aluminum alloy A356,for which adequate experimental data were available in the literature.The effects of two key process parameters,namely the slope angle and the pouring temperature,on temperature distribution,velocity distribution and macrosegregation were also studied.
