Ultrasonic solidification mechanism and optimized application performances of ternary Mg_71.5Zn_26.1Y_2.4 alloy

One dimensional (1D) and three dimensional (3D) ultrasound sources were applied to the solidification process of Mg_71.5Zn_26.1Y_2.4 alloy. The acoustic spectra were in-situ measured, based on which the cavitation intensities and dynamic solidification mechanism were further investigated. With the increase of ultrasonic dimension and amplitude, the primary Mg₃Zn₆Y phase was significantly refined from petals to nearly pentagonal shape. The sound field measurements showed that the transient cavitation played a decisive role in generating a high local undercooling, which facilitated the formation of icosahedral clusters and promoted the nucleation of primary Mg₃Zn₆Y phase. The morphological transition of (α-Mg+Mg₃Zn₆Y) eutectic from lamellar to anomalous structure occurred under 3D ultrasonic condition. The stable cavitation took the main responsibility because the high pressure excited by nonlinearly oscillating bubbles induced the preferential nucleation of α-Mg phase rather than Mg₃Zn₆Y phase. As compared with its static values, the tensile strength and compression plasticity of this alloy were increased by the factors of 1.9 and 2.1, and its corrosion resistance was also improved with the corrosion current density decreased by one order of magnitude.