Effect of High-Energy Ultrasound and Mixed Rare Earths Modification on Microstructure of Semisolid AlSi11Cu3 Alloy

In this paper, semisolid AlSi11Cu3 alloys with mixed rare earths (Pr + Ce) were fabricated via ultrasonic vibration treatment (UVT). The effects of ultrasonic vibration treatment parameters (temperature, time) and the contents of mixed rare earths were studied. The results showed that alpha-Al was refined in semisolid AlSi11Cu3 alloy with the addition of mixed rare earths. Rounder and uniformly distributed alpha-Al grains were detected when UVT temperature, time, and power were 600 degrees C, 90 s, and 2.1 kW, respectively. With the addition of 0.6 wt% of mixed rare earths, the average grain size of alpha-Al grains was reduced to 14.7 mu m with a shape factor of 0.83, indicating that the mixed rare earths had an excellent refinement effect on alpha-Al. These changes can be attributed to the modification of rare earths, cavitation effect and acoustic streaming effect of high-energy ultrasound. The main function of cavitation effect is to make the bubbles in the melt burst and produce an instantaneous impact force, which can break the massive dendritic structure and achieve the effect of grain refinement. Under the action of acoustic flow, the broken dendrites are evenly distributed in the solution, forming new nucleation sources and promoting nucleation. Under the combined action of these two effects and rare earth modification, the aim of refining alpha-Al grain is realized.