Fractional Solidification for Purification of Recycled Aluminium Alloys

Recycling Al is an up-to-date topic nowadays due to the economic benefits and sustainability, in fact recycling Al employs only 5% of the energy necessary for its extraction from bauxite ore, saving 9 ton of CO₂ per 1 tonne of Al recycled. In this research project the principles of fractional solidification have been applied to reduce the amount of impurities in model recycled Al alloys. A set-up based on isothermal squeezing of a semi-solid alloy has been developed and tested. The ultrasonic vibration applied to the semi-solid material has proven to enhance the purification achievable, up to 65% of reduction in the concentration. A number of potential impurities, such as Si, Ni, Cu, have been tested. The role of solute partitioning during the process has been evaluated and characterised by optical microscopy and modelling.