Electrically-assisted solidification of pure aluminum: Experiment and mechanism

Abstract

Integral die-casting technology is a promising lightweight solution widely used in automobiles due to its advantages of near-net shape forming. To solve the traditional aluminum alloy die-casting defects, electrically-assisted (EA) die-casting is regarded as a potential method to improve the microstructure of traditional casting. The electromagnetic and electrothermal effects during EA solidification of pure aluminum are investigated through numerical simulation and experiment by loading varied current density, duty ratio, and frequency. The results show that the mechanical strength of pure aluminum using EA solidification increased by 64.6 % compared with the traditional method, which is attributed to the improved equiaxiality and refinement of grains. As the current density increases, the material strength initially rises to the peak at the current density of 2.27 A/mm² and then begins to decline. Besides, the material strength increases with an increase in current frequency and decreases with an increase in duty ratio. The above phenomena are attributed to the competitive action of electromagnetic and electrothermal effects. On the one hand, the current-induced Lorentz force and electromagnetic oscillations cause shear effects on the pure aluminum particles, inhibiting the grain coarsening and refining the grains. However, the current-induced Joule heating (electrothermal effect) can promote grain growth, which is opposite to the electromagnetic effect. The opposite action of electromagnetic and electrothermal effects leads to the material strength first increasing and then decreasing with increased current density. The findings provide a theoretical basis for optimizing EA solidification processes, enabling improvements in mechanical properties and expanding applications in lightweight automotive.