Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. However, the imposition of a rotating (RMF) or a travelling magnetic field (TMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface. Previous investigations considered the use of time-modulated rotating magnetic field to control the heat and mass transfer at the solidification front to avoid segregation effects.
This present study examines the directional solidification of AlSi7 alloys from a water cooled copper chill. A rotating magnetic field are used to agitate the melt. Different magnetic field intensities and time-modulated magnetic fields were considered to show the impact of diverse flow conditions on the resulting mechanical properties. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were realized. Our results reveal the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields demonstrated their capability to homogenize both the grain size distribution and the corresponding mechanical properties.