Simulation of Solidification Defects for Prediction of Dross Formation in Aluminum 5182 Remelt Secondary Ingot

In aluminum recycling about 4% on average is lost on oxidation and dross. However, large percent of remelt secondary ingots (RSI) produce much more dross after remelting. It is rather surprising that no dross can be detected in the RSI, but after remelting some parts of apparently ‘healthy’ aluminum can give up to 80% of dross. This raises question how dross gets formed. Recent research proposes that the formation of dross after remelting of the RSI is closely related to the solidification process in the ingot, specifically the formation of shrinkage porosity, hydrogen porosity, and hot tearing. Under these circumstances, dross comes from oxidized surfaces of those defects. In this paper, simulations of the RSI cooling down show susceptibility of ingots towards shrinkage porosity and hot tearing, which are in accordance with experimental findings. Simulations also show that dross is more likely to form with increased temperature of the mold and increased thickness of the ingot. The only efficient solution for the problem of dross formation, however, seems to be a change in geometry of the mold.