Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary ...Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary current distribution.Nernst-Planck equations are solved in the bulk of slag,and faradaic reactions are regarded at the metal-slag interface.Aiming at exploring electrochemical effects on the behavior of the ESR process,the calculated field structures are compared with those obtained using the classical ohmic approach,namely,primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored.Also,the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered.The impact of the polarity of electrode,whether positive,also known as direct current reverse polarity(DCRP),or negative,as known as direct current straight polarity(DCSP),on the transport of oxygen to the ingot of ESR is investigated.The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process.展开更多
The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is propo...The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is proposed to simulate the cooling channel process of A356 Aluminum alloy.The three phases are liquid,solid and air respectively and treated as separated and interacting continua,sharing a single pressure field.The mass,momentum,enthalpy transport equations for each phase are solved.The developed model can predict the evolution of liquid,solid and air fraction as well as the distribution of grain density and grain size.The effect of pouring temperature on the grain density,grain size and solid fraction is analyzed in detail.展开更多
A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of f...A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.展开更多
文摘Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary current distribution.Nernst-Planck equations are solved in the bulk of slag,and faradaic reactions are regarded at the metal-slag interface.Aiming at exploring electrochemical effects on the behavior of the ESR process,the calculated field structures are compared with those obtained using the classical ohmic approach,namely,primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored.Also,the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered.The impact of the polarity of electrode,whether positive,also known as direct current reverse polarity(DCRP),or negative,as known as direct current straight polarity(DCSP),on the transport of oxygen to the ingot of ESR is investigated.The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process.
文摘The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process.A three-phase model based on volume averaging approach is proposed to simulate the cooling channel process of A356 Aluminum alloy.The three phases are liquid,solid and air respectively and treated as separated and interacting continua,sharing a single pressure field.The mass,momentum,enthalpy transport equations for each phase are solved.The developed model can predict the evolution of liquid,solid and air fraction as well as the distribution of grain density and grain size.The effect of pouring temperature on the grain density,grain size and solid fraction is analyzed in detail.
基金supported by the Austrian Research Promotion Agency(FFG)through the project of Bridge Early Stage(No.842441)technically supported by the industrial partner Primetals(former Siemens VAI)
文摘A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.
