Effects of high static magnetic field on the microstructure of Zn-Bi monotectic alloys during directional solidification process

Abstract Directional solidification of Zn-0.63 at% Bi monotectic alloys at different growth rates with and without a 5-T high static magnetic field (HSMF) was studied. Regardless of whether an HSMF was applied, the solid–liquid (S–L) interface changed in a consistent manner with increasing growth rate. The HSMF affected the S–L interface morphology and solidified microstructure by suppressing melt convection above the S–L interface. Two mechanisms led to the formation of strings of droplets. One was the Rayleigh instability of fibres caused by the bulk diffusion process as a result of the minimisation of the total interfacial energy of the system. The HSMF improved the stability of the fibre phase by reducing the interfacial energy, thereby helping to process material with a complete fibre-coupled growth structure, which has a greater specific surface area. The other was that constitutional instability at the S–L interface only existed when the growth rate was 3 µm/s under a 5-T HSMF. A revised stability-limit-diagram model was mapped to reveal solidification mechanism in monotectic systems. This work offers a new approach for processing functional monotectic alloy materials in the future.