A Positron Emission Particle Tracking (PEPT) Study of Inclusions in Liquid Aluminium Alloy

Abstract

Inclusions have a detrimental effect upon casting properties but it is known empirically that a slow liquid metal flow has a beneficial effect by reducing the number of inclusions entering the casting. Positron Emission Particle Tracking (PEPT) is a method that can be used to track the path taken by radioactive particles, and can be used to follow the behaviour of inclusions as they make their way from a furnace, along the launder and into the casting. A new PEPT camera geometry was developed and used to track radioactively labelled γ-alumina particles, in the region of 600 μm size. The camera detectors were arranged radially around a launder, into which was poured 150 kg of liquid Al alloy, the radioactive particles being released at intervals during the pour. The positron camera was 0.7 m in length and 0.1 m2 in cross-sectional area, and this matched the dimensions of an industrial launder. A model of inclusion behaviour in a flowing liquid Al alloy was also developed, and the Positron Imaging system described was used to validate this model.