Ultrasonic in-situ monitoring of solidification and melting behaviors of an aluminum alloy

This paper presents a newly developed high temperature ultrasonic sensor (US) and its application to in-situ observation of Al alloy during solidification and melting in temperatures up to 800/spl deg/C. The US mainly consists of a conventional piezoelectric transducer and a Ti buffer rod as an acoustic waveguide. The length is 300 mm. This sensor, owing to the unique characteristics of Ti, is highly expected to provide not only high acoustic coupling to molten Al but also high corrosion resistance. It is demonstrated that the Ti buffer rod has superior sustainability and wettability to the molten Al alloy. Using the US, the changes of the longitudinal velocity of the Al 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 Al alloy has been observed. The movement of the reflected echo due to the growth of the solid-liquid interface has also been monitored during the cooling process. Thus, it is demonstrated that the developed US using a Ti rod is a promising tool for molten Al monitoring.