(西北工业大学 应用物理系，西安 710072)
摘 要: 将20 kHz、500 W的高强超声分别引入亚共晶Al-5%Si合金凝固过程的不同阶段，探索了超声场对于初生α(Al)相和枝晶间组织形成的作用机制。结果表明：超声作用下凝固组织中气孔率显著降低，初生α(Al)相从“粗大枝晶”演变为“等轴或碎断枝晶”，枝晶间组织也呈现出细化趋势。在液相阶段施加超声，可以改善熔体中晶胚与杂质的润湿程度，促进晶粒细化。若在初生相形核和长大阶段施加超声，空化效应引发的晶体形核以及空化引起的枝晶碎断是超声场细化初生α(Al)相的主要机制。在共晶转变阶段施加超声，力学效应则是枝晶碎断的主要原因。在凝固过程的不同阶段施加超声，均能提高Al-5%Si合金的显微硬度和屈服强度。
关键字: 超声场；共晶凝固；动态形核；空化效应；组织形成；力学性能
（Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract:High-intensity ultrasound at a resonant frequency of 20kHz and power of 500 W was introduced into different solidification stages of hypoeutectic Al-5%Si alloy, and the formation mechanism of primary α(Al) phase and its interdendritic structure was explored. The results show that porosity in the solidified structure reduces remarkably, and the primary α(Al) phase transforms from coarse dendrites under static into equiaxed grains or fragmented dendrites by introducing power ultrasound during different solidification stages. Meanwhile, the interdendritic structure is also refined by ultrasound. When the power ultrasound is applied into liquid phase, it accelerates the nucleation of primary α(Al) phase by enhancing wetting status between the crystal embryos and impurities in the alloy melt. If ultrasound is employed during nucleation and growth of primary α(Al) phase, the cavitation-induced nucleation and cavitation-induced fragmentation take the responsibility of most remarkable grain refinement. Once the ultrasound is introduced in eutectic transformation, the dendritic fragmentation results from mechanical effect accounted for the reducing in grain size of primary α(Al) phase. Both microhardness and yield strength can be improved after ultrasound is applied at each solidification stage of Al-5%Si alloy, indicating that applying power ultrasound is an effective way to moderate the mechanical properties of Al-Si alloys.
Key words: ultrasonic field; eutectic solidification; dynamic nucleation; cavitation effect; structure formation; mechanical property
