Impact of forced flow on the solidification structure of wrought aluminium alloys by means of AC magnetic

AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification. Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions, that an accurate tuning of the magnetic field parameters can avoid segregation effects and homogenize the mechanical properties. The present study examines the directional solidification of commercial wrought aluminium alloys from a water-cooled copper chill. Rotating magnetic fields were used to agitate the melt.
Our results demonstrate the potential of magnetic fields to control the grain size, the formation of segregation freckle and the morphology and distribution of pores, especially for use time modulated rotating fields.