Ultrasound processing of metal alloys is an environmental friendly and promising green technology for liquid metal degassing and microstructural refinement. However many fundamental issues in this field are still not fully understood, because of the difficulties in direct observation of the dynamic behaviours caused by ultrasound inside liquid metal and semisolid metals during the solidification processes. In this paper, we report a systematic study using the ultrafast synchrotron X-ray imaging (up to 271,554 frame per second) technique available at the Advanced Photon Source, USA and Diamond Light Source, UK to investigate the dynamic interactions between the ultrasonic bubbles/acoustic flow and the solidifying phases in a Bi-8%Zn alloy. The experimental results were complimented by numerical modelling. The chaotic bubble implosion and dynamic bubble oscillations were revealed in-situ for the first time in liquid metal and semisolid metal. The fragmentation of the solidifying Zn phases and breaking up of the liquid-solid interface by ultrasonic bubbles and enhanced acoustic flow were clearly demonstrated and agreed very well with the theoretical calculations. The research provides unambiguous experimental evidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure fragmentation and refinement in solidification under ultrasound.

中文翻译：

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超声凝固过程中微结构碎裂的超快同步加速器X射线成像研究

金属合金的超声处理是一种环境友好且有前途的液态金属脱气和微结构细化绿色技术。然而，由于在凝固过程中液态金属和半固态金属内部由超声波引起的动态行为难以直接观察，因此该领域的许多基本问题仍未完全了解。在本文中，我们报告了一项系统研究，该研究使用美国 Advanced Photon Source 和英国 Diamond Light Source 提供的超快同步加速器 X 射线成像（高达每秒 271,554 帧）技术来研究超声波气泡之间的动态相互作用/ Bi-8% Zn 合金中的声流和凝固相。数值模拟对实验结果进行了补充。首次在液态金属和半固态金属中原位揭示了混沌气泡内爆和动态气泡振荡。超声气泡和增强的声流导致凝固的 Zn 相的碎裂和液固界面的破裂被清楚地证明，并且与理论计算非常吻合。该研究为阐明超声凝固过程中微观结构破碎和细化的主要机制提供了明确的实验证据和可靠的理论解释。超声气泡和增强的声流导致凝固的 Zn 相的碎裂和液-固界面的破裂被清楚地证明，并且与理论计算非常吻合。该研究为阐明超声凝固过程中微观结构破碎和细化的主要机制提供了明确的实验证据和可靠的理论解释。超声气泡和增强的声流导致凝固的 Zn 相的碎裂和液固界面的破裂被清楚地证明，并且与理论计算非常吻合。该研究为阐明超声凝固过程中微观结构破碎和细化的主要机制提供了明确的实验证据和可靠的理论解释。