Abstract:This work provides an overview of the aluminum (Al) recycling process, from the scrap upgrading to the melting process. Innovations and new trends regarding the Al recycling technologies are highlighted. Aluminum recycling offers advantages in terms of environmental and economic benefits. The presence of deleterious impurities in recycled Al alloys is increasing and this is the main drawback if compared to primary alloys. The continuous growth of undesired elements can be mitigated by different technologies, preliminary operations and treatments, and by the optimization of the melting process. Downgrading and dilution are possible solutions to reduce the rate of impurities, but they are not sustainable if the final use of Al alloy continuously increases. The main objectives in the development of the Al recycling are shown and discussed. In particular, the evolution of preliminary treatments of the scrap, as sorting, comminution and de-coating, is reported and a review of the melting technologies is also presented. However, the choice of performing preliminary operations to the melting stage, thus improving the operating conditions during the furnace running, is a trade-off between costs and process efficiency.

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The precipitation of primary Fe-bearing compounds in a secondary AlSi9Cu3(Fe) alloy has been investigated over three levels of iron (0.80, 1.00, 1.20 mass%) and manganese (0.25, 0.40, 0.55 mass%), and two levels of chromium (0.06, 0.10 mass%), as well as different cooling rates (2, 10, 20 °C min-1). Differential scanning calorimetry and metallographic techniques have been used in order to quantitatively evaluate the nucleation temperature and the phase fraction of sludge particles. The temperature of sludge formation increases by increasing the initial concentrations of Fe, Mn and Cr, while an increase in the cooling rate shifts the sludge nucleation towards lower temperature. The amount of sludge particles increases progressively with the sludge factor but even more by decreasing the cooling rate. The combination of Fe, Mn and Cr levels, as well as cooling rate, allows to determine a threshold value that prevents the sludge formation. In the analysed range of composition and cooling conditions, functional equations have been developed in order to accurately predict the precipitation temperature and the phase fraction of sludge in AlSi9Cu3(Fe) die-casting alloys

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