Precipitation of Sr-rich and Fe-rich intermetallic compounds in Al alloys

The precipitation of intermetallic compounds (IMCs) in an aluminium alloy Al-7Si-0.4Mg (A356) was studied, making additions of Fe, Sr, and Mg. The experiment avoided metallographic techniques, using a novel experimental approach in which the outside surface of the cast metal was studied. Precipitation of IMCs was observed to occur on the surface of oxide bifilms in suspension in the liquid metal, occasionally as a Sr-rich IMC growth from one side and a Fe-rich IMC growth from the other, corroborating the structure of the bifilm as having two wetted outer sides. The bifilms onto which heavy IMCs had precipitated were observed by nanotomography to sediment rapidly, indicating a potential method of cleaning secondary metals from both bifilms and metals like Fe.