For applying an alternating magnetic field (AMF) in materials processing it is of high significance to understand the physical mechanisms behind the change in diffusivity in the AMF. In this work, the effect of the AMF on interdiffusion in a Ni-Cr alloy was investigated with a diffusion couple. The interdiffusion coefficient was found to increase with increasing AMF intensity. The faster diffusivity is a consequence of the enhancement of the dislocation density in the diffusion couples that was confirmed by the broadening of X-ray diffraction peaks. The higher dislocation density is attributed to the magnetoplastic effect (MPE). Theoretical considerations on the relation of MPE, dislocation density and diffusivity are in agreement with the experimental results.

The final mechanical properties of alloys are significantly influenced by the secondary dendrite arm spacing (SDAS). The application of a steady magnetic field (SMF) during solidification is a novel method to control the SDAS, however, the nature of the change in SDAS under an SMF is still an open question. In this work, dendrite coarsening in the Al4.5 mass%Cu alloy in an SMF and its effect on microsegregation were investigated experimentally by the quenching technique. The coarsening experiments showed that the SDAS increased in an SMF, which was mainly attributed to the thermoelectric magnetic convection (TEMC) while the change in solid/liquid interfacial tension in the SMF played an adverse role. Further, the variation of the microsegregation level in the SMF was examined by composition measurements. It was shown that the segregation ratio increased in the SMF, which could be ascribed to the reduction of diffusivity in the solid phase and the enlargement of SDAS in the SMF. Using a modified analytical model developed by Voller, the microsegregation levels with and without an SMF were predicted, which was in agreement with the experimental results.

The microsegregation behavior of the Al-4.5 wt%Cu alloy solidified at different cooling rates under the alternating magnetic field (AMF) was investigated. The experimental results showed that the amount of non-equilibrium eutectics in the interdendritic region decreased upon applying the AMF at the same cooling rate. The change in microsegregation could be explained quantificationally by the modifications of dendritic coarsening, solid-state back diffusion and convection in the AMF. The enhanced diffusivity in the solid owing to the AMF was beneficial for the improvement in microsegregation compared to the cases without an AMF. In contrast, the enhanced dendritic coarsening and forced convection in the AMF were found to aggravate the microsegregation level. Considering the contributions of the changes in above factors, an increase in solid diffusivity was found to be primarily responsible for the reduced microsegregation in the AMF. In addition, the microsegregation in the AMF was modeled using the analytical model developed by Voller. The calculated and experimental results were in reasonable agreement.