The in situ observations of solidification and melting of an aluminum-silicon alloy (Al-12.6%Si) using an ultrasonic waveguide sensor are presented. The ultrasonic sensor consists of a conventional piezoelectric ultrasonic transducer, a cooling system and a titanium (Ti) rod as an ultrasonic waveguide. The sustainability of the Ti rod in the molten Al alloy is investigated by immersion tests for 1, 4, 8 and 16 h at 800 C. The formation of a layer consisting of globular TiAl 3 , disperse AlSi 2 Ti and -Al phases has been observed at the interface between the Ti and the Al alloy. Ultrasonic pulse-echo measurements of the Al alloy during solidification and melting have been performed using the ultrasonic sensor in temperature range from 200 to 800 C. The longitudinal wave velocity of the Al alloy shows a rapid and significant change from about 3900 to 5600 m/s around the eutectic point. An attempt to measure a solid/liquid interface of the Al alloy has been made at frequency of 2.25 MHz. The reflected echo from the interface undergoing directional solidification has been observed. The position and growth rate of the interface have also been determined from the reflected echo.
A high temperature ultrasonic sensor with a titanium buffer rod has been applied to the in situ monitoring of the solid-liquid interface of an aluminum alloy (Al-12.6%Si) during unidirectional solidification at 700°C. The ultrasonic sensor consists of a conventional piezoelectric transducer, a titanium buffer rod as an acoustic waveguide and a cooling system. Its length is approximately 300 mm. This ultrasonic sensor, because of the unique characteristics of titanium, provides not only good acoustic coupling to molten aluminum but also high-corrosion resistance. Pulse echo measurements in the molten aluminum alloy are performed using the sensor at 2.25 MHz. A clear reflected echo from a stable solid-liquid interface of the aluminum alloy has been successfully monitored. In addition, the reflected echo from the growing interface during unidirectional solidification has also been monitored. The growth rate of the interface was determined to be 0.12 mm/s from the monitored echo.
This paper presents a newly developed high temperature ultrasonic sensor and its application to in-situ observation of aluminum alloy during solidification and melting in temperature up to 800 ºC. The ultrasonic sensor mainly consists of a conventional piezoelectric transducer and a titanium buffer rod as an acoustic waveguide. The length is 300 mm. This sensor, owing to the unique characteristics of titanium, is highly expected to provide not only high acoustic coupling to molten aluminum but also high corrosion resistance. It is demonstrated that the titanium buffer rod has superior sustainability and wettability to the molten aluminum alloy. Using the ultrasonic sensor, the changes of the longitudinal velocity of the aluminum alloy during solidification and melting have been monitored as a function of temperature. Furthermore, a clear reflected echo from the solid-liquid interface of the aluminum alloy has been observed. The movement of the reflected echo due to the growth of the solid-liquid interface has also been monitored during cooling process. Thus, it is demonstrated that the developed ultrasonic sensor using a titanium rod is a promising tool for molten aluminum monitoring.
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