Grain Refinement of Casting Aluminum Alloys of the Al–Mg–Si System by Processing the Liquid Phase Using Nanosecond Electromagnetic Pulses

In this paper, using the AA 511 alloy of the Al–Mg–Si system as an example, it is shown that the irradiation of aluminum melts with nanosecond electromagnetic pulses (NEPs) leads to a significant change in the nature of structure formation during crystallization, contributing to the refinement of the structural components of the alloy and the redistribution of alloying elements in them. It has been established that an increase in the frequency of irradiation of NEP melts is accompanied by the refinement of the structural components of the alloy, while the greatest degree of decrease in the grain size of the α-solid solution and intergranular inclusions of the eutectic Mg2Si phase is observed at an NEP frequency of 1000 Hz. An increase in the NEP frequency leads to a significant increase in the concentration of magnesium in the α-solid solution and the fragmentation of intergranular inclusions of the Mg2Si phase, which, when the melt is irradiated at a frequency of 1000 Hz, is released in the form of compact isolated inclusions. The processing of melts with NEPs leads to an increase in the Brinell hardness of the specimens in the cast state, as well as to a significant increase in the microhardness of the grains of the α-solid solution (from 38.21 in the initial state to 61.85 HV 0.001 after irradiation with a frequency of 1000 Hz). It is assumed that the effect of a pulsed electromagnetic field leads to a decrease in the critical values of the Gibbs free energy required to initiate nucleation processes and to a decrease in the surface tension at the “growing crystal–metal melt” interface, which causes a modifying effect on the alloy structure due to a decrease in the critical size nuclei of crystallization.