超声凝固条件下二元Al-12.6%Si共晶合金的组织演变机制研究

Three-dimensional (3D) ultrasounds were introduced into liquid Al-12.6%Si eutectic alloy to explore its dynamic solidification and structural evolution mechanisms. Under static solidification, a typical eutectic microstructure was composed of irregular flake (Si) and dendritic matrix α(Al) phases. Once 3D ultrasounds were applied, the undercooling increase caused by ultrasonic cavitation promoted the independent nucleation of eutectic (Si) and α(Al) phases. Meanwhile, the uniform temperature field and solute field secured by acoustic streaming made these two eutectic phases grow isotropically. As a result, a divorced eutectic structure formed, consisting of the blocky (Si) and globular α(Al) phase. The high-frequency vibration effect of ultrasound increased the twinning probability of the Si phase, leading to lots of multiple twin (Si) phases with intercrossing interfaces. The intensive ultrasound reduced interfacial energy between (Si) and α(Al) phases and enhanced the quantity of parallel growth-oriented crystalline planes, which improved the microhardness of ultrasonicated binary Al-12.6%Si eutectic alloy.