Pulsed/steady electromagnetic field modulation of melt viscosity and solidification in rare earth-aluminum alloys: Mechanistic insights beyond La-ZL114

Abstract

Regulating the magnetohydrodynamic behavior of molten metals during solidification stands as a high-quality, high-efficiency material manufacture strategy in the context of global carbon neutrality and lightweight materials development. Magnetic viscosity exerts a significant influence on mold filling capacity, defect formation, and microstructure evolution by modulating thermal, mass, and momentum transfer processes. This paper investigates how pulsed and steady magnetic fields regulate the viscosity of rare earth-containing Al-Si alloy melts (with 0.4 wt% La) to control both their casting fluidity and solidification microstructures, employing an electromagnetic field high-temperature viscometer, electromagnetic field confocal laser scanning microscope and the electromagnetic casting physic simulation. The results shown that the melt viscosity at 650 °C increases from 0.08 Pa·s to 0.092 Pa·s under a 60 mT steady magnetic field, while the casting fluidity length decreases by 19.34 %. This can be attributed to the magnetic damping effect. Under a pulsed magnetic field, the alloy casting fluidity length increases 23.74 %, Concurrently, both α-Al phases and rare earth phases are uniformly distributed and refined, with the α-Al grain refinement reaching 20.57 %. It is worth noting that the molten oscillation induced by the Lorentz force leads to the formation of dispersed microporosity / blowholes. In contrast, a stable magnetic field is effective in removing blowholes as most of them are concentrate in the upper part of the melt. A quantitative relationship between magnetic viscosity, temperature, and magnetic flux density is established, unlocking new potential for the precise tailoring of additive manufacturing and complex casting components through the coupled regulation of electromagnetic and solidification parameters.