In situ monitoring of solid-liquid interface of aluminum alloy using high-temperature ultrasonic sensor

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 degrees 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 0.12mm/s from the monitored echo.