Aluminium alloys in a molten state at 700°C have a significant amount of hydrogen dissolved in them. If this is not treated, the resulting aluminium alloy would become highly porous on solidifying. Presently, argon rotary degassing is the primary method used for hydrogen removal. However, it is expensive and requires large amounts of energy. There is also a risk of contamination if the graphite impellers used in this process should break up.
Prof Dmitry Eskin (in the picture) of the Brunel Centre for Advanced Solidification Technology led a research project which discovered that using ultrasound was actually a preferable method, by a number of measures. Ultrasound processing uses less energy, produces less waste, and removes the most costly parts of the process, whilst achieving the same efficiency.
The team performed the pilot study using samples of up to 150kg. The tests confirmed earlier findings that a moving ultrasound probe could provide similar results to the traditional argon rotary degassing. They observed that using ultrasound led to a five-fold reduction in dross (waste material). Useable metal can be recovered from dross; however it requires electrolysis which is energy intensive and costly.
Prof Eskin’s research team now aims to find out ways to introduce ultrasound degassing in the earlier stages of the production process and also perform trials using larger quantities of up to half-tons.