Study on the structural evolution of Al–15Sn–1Cu alloys solidified at different electromagnetic vibration frequencies

For most alloys, columnar grains can lead to solidification defects and mechanical property anisotropy, making it a significant challenge in metallurgical sciences to promote columnar-to-equiaxed transition and control segregation. This study investigated the effects of convection induced by electromagnetic vibration frequency on the evolution of the directional solidification structure of Al–15Sn–1Cu alloys. The experimental results revealed that as the electromagnetic vibration frequency decreased from 100 to 1 Hz, the solidification front shape gradually transformed from sloping to planar. Moreover, the number of equiaxed grains increased as the frequency decreased, ultimately leading to the columnar-to-equiaxed transition at 1 Hz. The numerical results indicated that the formation of the planar solidification front can be attributed to a more uniform solute distribution and temperature oscillations. Additionally, the oscillatory flow-induced back-and-forth solute transport distance increases with decreasing frequency. Consequently, dendrite fragmentation is promoted as inter-dendrite solute fluctuations increase. The columnar-to-equiaxed transition occurs when the growth of columnar dendrites is completely blocked by equiaxed grains grown from the dendrite fragmentation ahead of them. Furthermore, owing to solute homogenisation and refinement of the solidification structure, a fine and uniform distribution of Sn phases in the Al matrix was achieved at 1 Hz. This study elucidates the effects of oscillatory convection driven by electromagnetic vibration on the temperature, solute transport behaviour, and directional solidification structure. These findings provide critical insights and practical guidelines for the production of fine and uniform equiaxed grain structures using electromagnetic vibration.