Modification of Al–Mg–Si casting aluminum alloys by liquid phase processing with nanosecond electromagnetic pulses

Abstract

The AA 511 alloy of the Al–Mg–Si system was used as an example to demonstrate that aluminum melt irradiation with nanosecond electromagnetic pulses (NEPs) leads to a significant change in the nature of structure formation during crystallization. It was found that an increase in the frequency of melt irradiation with NEPs is accompanied by the refinement of the alloy structural components, while the greatest grain size reduction of the α-solid solution and intergranular inclusions of the eutectic Mg2Si phase is observed at a NEPs frequency f = 1000 Hz. An increase in the NEPs frequency leads to a significant increase in the concentration of magnesium in the α-solid solution and the fragmentation of Mg2Si phase intergranular inclusions, which is released in the form of compact isolated inclusions when the melt is irradiated at a frequency of 1000 Hz. It was shown that melt processing with NEPs leads to an increase in the Brinell hardness of as-cast specimens, as well as to a significant increase in the microhardness of α-solid solution grains (from 38.21 HV in the initial state to 61.85 HV after irradiation with a frequency of 1000 Hz). It was 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 – molten metal» interface, which causes a modifying effect on the alloy structure due to a decrease in the critical size of crystal nuclei.