In this study, the authors show how to build an experiment that can impose rotating magnetic stirring during the solidification of a cylindrical cast with thermal data acquisition. Several experiments with increasing frequency and magnetic intensity were conducted. The discontinuous solidification curves of the castings were acquired by means of a thermocouple connected to a high resolution data recording system. It was found that the grain refinement is obtained by resorting to increasingly higher frequencies and intensities of the magnetic field. The dispersion of the grain size decreases in line with magnetic intensity and frequency. The thermal analysis revealed that important solidification events are conditioned by the magnetic field. Several proposals for grain refinement justification are advanced.
In this work the authors show how to build a semi-industrial scale macrothermal analysis experimental apparatus for low pressure aluminium casting AA 354 with quasi-unidirectional solidification. Several thermocouples were connected to a multichannel electronic device allowing a sampling rate up to 10 Hz; the thermocouples were installed in the mould at different locations to acquire the discontinuous cooling curves at those same locations. With this type of experiment and appropriate mathematical procedures it was possible to build a reasonable response surface T5f(x, t) and the respective derivatives: LT/Lt and LT/Lx. Exponential polynomials were applied for modelling the curves and linear interpolation to relate the several cooling curves. Mathematical tools applied to the modelled curves allowed the authors to identify different solidification events and correlate them with the specific thermal gradient, cooling conditions and solidification fronts phenomena such as columnar to equiaxed transition of a aluminium grains. Growth velocity of proeutectic aluminium a and eutectic fronts were also determined.
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