Enhanced Degradation in Grain Refinement of Inoculated 2024 Al Alloy in Steady Magnetic field

Abstract

The grain refinement of 2024 Al alloy inoculated with Al-5Ti-1B master alloy in a steady magnetic field (SMF) was investigated. It was shown that the degradation in grain refinement was enhanced and a cellular–dendritic transition of equiaxed primary α-Al grains occurred under the SMF. Employing a differential scanning calorimeter, the nucleation temperature of primary α-Al phase was found to decrease in the SMF, i.e., the undercooling was enhanced, and the kinetics of phase transformation was modified in the SMF. The enhanced degradation in grain refinement and increase in undercooling are attributed to the modified solid/liquid interfacial free energy and the delay of formation of critical nucleus due to the retarded migration rate of atoms in the liquid phase in the SMF. The cellular–dendritic transition of primary α-Al grains is ascribed to the modified constitutional undercooling at the solid/liquid interface, which results from the change in solute distribution by the damped convection and retarded diffusivity in the SMF. Additionally, the increase in growth dimension and the modified solid/liquid interfacial free energy under the SMF are also responsible for the enhanced constitutional undercooling and the cellular–dendritic transition.