Oxidation of Aluminium Melts in Dry and Moist Atmospheres

The aluminium casthouse is responsible for substantial amounts of CO₂ emissions. Substituting low-emissions hydrogen for fossil fuels such as LNG and LPG would significantly reduce the climate impact of aluminium casting. Such a fuel-switch would also change the combustion products, eliminating CO₂ and increasing the amount of H₂O, potentially up to 100% in the case of oxy-fuel combustion. As a critical factor in aluminium casting is the loss of metal due to oxidation and dross formation, it will be necessary to have a good understanding of how the oxidation behaviour is influenced by the composition of the atmosphere. In this paper, we study how oxidation and dross formation on an AlSi7MgSr alloy changes for different atmospheres containing 40% H₂O versus 20% O₂. We find no temperature dependency of oxide and dross formation in the temperature range 670–750 °C. While inert process gas provides sufficient stirring for noticeable oxidation due to interactions with the laboratory air at the surface, the use of oxidising process gas significantly increases dross formation, by a factor of 3–4. Comparing dross formation with 40% H₂O versus 20% O₂, we find that 20% O₂ gives significantly more dross, despite the total molar amount of oxygen atoms being constant in these gas mixtures.