Presence Of Electromagnetic Stirring Research Articles

Numerical Modeling of Macrosegregation in Binary Alloys Solidifying in the Presence of Electromagnetic Stirring

A model for predicting solidification and solute segregation of binary alloys undergoing electromagnetic stirring has been developed. A dual-zone formulation was employed to describe the velocity fields in the mushy region. The key feature of this model lies in its accounting for flow damping in the suspended particle region via turbulent interactions the crystallite surfaces. The damping force is given in terms of the turbulent kinetic energy, fraction solid, and the crystallite sphericity. The computed macrosegregation results for Al-4.5 pctCu alloy were validated against, and were found to agree with, experimental measurements. The effect of final grain size and frequency on segregation was also determined. This validated model represents a rigorous mathematical framework for describing the flow behavior and solute segregation in electromagnetically stirred melts.

Studies on Transport Phenomena during Continuous Casting of an Al-Alloy in Presence of Electromagnetic Stirring

In the present work, a numerical study is performed to predict the transport phenomena during continuous casting of an aluminum alloy (A356) in presence of weak stirring. A set of volume averaged single phase conservation equations (mass, momentum, energy and species) is used to represent the casting process. The electromagnetic forces are incorporated in the momentum equations. The governing equations are solved based on the pressure-based finite volume method according to the SIMPLER algorithm using TDMA solver along with an enthalpy update scheme. The simulation predicts the temperature, solid fraction and species in the computational domain. A parametric study is also performed.

Effect of process parameters on transport phenomena during solidification in the presence of electromagnetic stirring

In the present work, a numerical study is performed to predict the effect of process parameters on transport phenomena during solidification of aluminium alloy A356 in the presence of electromagnetic stirring. A set of single-phase governing equations of mass, momentum, energy and species conservation is used to represent the solidification process and the associated fluid flow, heat and mass transfer. In the model, the electromagnetic forces are incorporated using an analytical solution of Maxwell equation in the momentum conservation equations and the slurry rheology during solidification is represented using an experimentally determined variable viscosity function. Finally, the set of governing equations is solved for various process conditions using a pressure based finite volume technique, along with an enthalpy based phase change algorithm. In present work, the effect of stirring intensity and cooling rate are considered. It is found that increasing stirring intensity results in increase of slurry velocity and corresponding increase in the fraction of solid in the slurry. In addition, the increasing stirring intensity results uniform distribution of species and fraction of solid in the slurry. It is also found from the simulation that the distribution of solid fraction and species is dependent on cooling rate conditions. At low cooling rate, the fragmentation of dendrites from the solid/liquid interface is more.

Achieving Low Temperature Superplasticity from Ca‐Containing Magnesium Alloy Sheets

The application of hot extrusion and high-speed-ratio differential speed rolling (HRDSR) to a Ca-containing Mg-3Al-1Zn magnesium alloy, processed by electromagnetic casting in the presence of electromagnetic stirring, produced a novel microstructure, composed of an ultrafine grain size of less than 1 μm and very fine (Al,Mg) 2 Ca particles that were uniformly and densely distributed over the matrix. The HRDSR processed alloy exhibited excellent superplasticity at relatively low temperatures (below 523 K).

Forging of Mg–3Al–1Zn–1Ca alloy prepared by high-frequency electromagnetic casting

The 1 wt.%Ca–AZ31 alloy produced by electromagnetic casting (EMC) in presence of electromagnetic stirring (EMS) was extruded and then subjected to the closed-die forging to make a pulley for automobile application. Effective dynamic recrystallization (DRX) took place during the forging process, leading to formation of fully recrystallized grains with the average size of 3–4 μm. High-forging ability and high degree of grain refinement achieved during the forging were attributed to the novel microstructure of the cast composed of small and equiaxed grains with the average size of ∼50 μm and thin layer (Al, Mg) 2 Ca phase at grain boundaries, which would provide more nucleation sites and a faster rate of recrystallization during deformation by forging as compared to that of the conventionally processed cast composed of large size grains and thick layer (Al, Mg) 2 Ca phase. The forged pulley exhibited the ultimate tensile strength of 273–286 MPa with tensile elongations of ∼30%. The present result demonstrates a possibility that EMC + EMS techniques can be used in producing magnesium feed stocks with high-forging ability.

A scaling analysis of alloy solidification in presence of electromagnetic stirring

Application of electromagnetic stirring (EMS) during continuous casting shears off the dendrites from the solidification front to produce billets with a non-dendritic microstructure. In the present study, a systematic approach to the scaling analysis of momentum, energy and species conservation equations pertaining to the case of the solidification of a binary alloy in the presence of EMS is outlined. With suitable choices of non-dimensionalizing parameters, the governing equations coupled with appropriate boundary conditions are first scaled, and then the relative significance of various terms appearing in them are analysed. In the physical domain two regions are identified, one where the electromagnetic forces play a dominant role in the momentum equations, and the other where the inertia and viscous effects play major roles. Using the scaling predictions, the influence of various processing parameters on the system variables can be utilized for the selection of appropriate electromagnetic forces to shear off the dendrites from the solidification area. For the sake of assessment of the scaling analysis, the predictions are validated against corresponding computational results.

Modeling of transport phenomena in continuous casting of non-dendritic billets

A macroscopic model for simulating the phase change process and transport of solid fraction is developed for the case of solidification during direct chill continuous casting of a non-dendritic Al-alloy billet, in presence of electromagnetic stirring. Maxwell’s equations are solved to obtain the electromagnetic force field, which is incorporated in the momentum conservation equations as body force source terms. Thereafter, the complete set of equivalent single-phase governing equations (mass, momentum, energy, species conservation and transport of solid fraction) are solved using a pressure-based finite volume method. A variable viscosity approach is employed to model fluid flow in presence of phase change. The model is first validated against some experimental and numerical results available in the literature, pertaining to the case of conventional continuous casting without any externally imposed stirring. The model predicts the temperature, velocity, species and most importantly, the solid fraction distribution in the mold. These predictions are then used for studying the influence of initial superheat, stirring intensity and cooling rate on the macroscopic behavior of the system.

Channel segregation during solidification and the effects of an alternating traveling magnetic field

The model proposed by Felicelli, Heinrich, and Poirier is used to simulate the solidification of a small two-dimensional domain of Pb-10 wt pct Sn alloy in the presence of electromagnetic stirring by different traveling fields, with or without gravity. Results show (a) enrichment of the bulk liquid by mush solute draining; (b) spontaneous formation of vertical channels, acting as ducts, significantly modified by the electromagnetic flow; and possibly (c) a finer periodic structure of subchannels. Only the last feature is sensitive to the mesh size and permeability value. Scaling analysis is used to balance Darcy, buoyancy, and electromagnetic phenomena. Attention is focused on the gradient zone at the solidification front. Electromagnetic forces can change the flow structure in the bulk liquid. In this way, they modify the pressure differences at the solidification front, changing the channel segregation pattern. Although they cannot eliminate the channels, they can control their positions and partly prevent the unsteadiness of buoyancy effects.

Influence of permeability on the grain refinement induced by forced convection in copper-base alloys

Copper-base alloys, Cu–1wt%Ni–1wt%Pb–0.2wt%P and Cu–4wt%Zn–4wt%Sn–4wt%Pb, exhibiting different solid fraction evolutions, have been solidified in the presence of electromagnetic stirring. The influence of the permeability of the dendritic network on the liquid penetration in the mushy zone, and thus on grain refinement, has been analyzed with the help of numerical simulation.

Effects of a magnetically forced convection during the crystallization in mould of aluminium alloys

The role of natural and forced convection during solidification of aluminium alloys in a toroidal mould was studied. The forced convection was generated by application of a time-varying electromagnetic field. Maps of electromagnetic body forces and velocity fields were obtained for various positions of the solidification front. Temperature measurements made it possible to follow the evolution of the temperature distribution inside the solidifying melt with time. These experiments were performed in the absence and presence of electromagnetic stirring. A discussion is presented relating the crystallographical findings to the heat and fluid flow patterns.

Effects of electromagnetic stirring during the controlled solidification of tin

The role of natural and forced convections during solidification of pure tin in an annular crucible was studied. The forced convection was generated by electromagnetic stirring. Maps of electromagnetic body forces and velocity fields were obtained for various stirring intensities and various positions of the solidification front. Temperature measurements made it possible to follow the evolution of the solidification front with time. These experiments were carried out from various degrees of superheat both in the absence and presence of electromagnetic stirring. A discussion is presented relating the metallurgical findings (macrostructure) to the heat and fluid flow measurements.