In the present work, a 2-pole linear electromagnetic stirrer (LEMS) is developed to study
the effect of stirring during solidification of aluminium alloys. The stirrer design entails the
placement of a stack of coils around the mold to generate a primary motion that recirculates along
the longitudinal direction. The stirrer is first tested and validated by measuring the electromagnetic
forces on solid aluminum cylinders of different diameters as a function of excitation current. The
alloy to be stirred and solidified is placed in a cylindrical graphite mould located in the annulus of
the LEMS. A suitable cooling arrangement is provided at the bottom of the mould to extract heat
from the melt, in order to produce a rheocast billet inside the mould. Rheocasting experiments with
A356 aluminium-silicon alloy are performed using a stirring current of 250A, in order to assess the
effect of electromagnetic stirring on microstructure formation. The resulting microstructures and
cooling curves with stirring are compared with those obtained without stirring.
In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process design parameters such as cooling rate and stirring intensity, and in estimating the total solidification time. In the present work, a new method for estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al–Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with nondendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Scheil’s equation.
In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process parameters such as cooling rate, stirring intensity and in estimating the total solidification time. In the present work, a new method of estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al-Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with non-dendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Schiel equation.
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