Trace alloying elements in secondary aluminium alloys

Secondary aluminium and alloys are getting wide acceptance world-wide since recycling process requires lower potential energy than primary aluminium production. The control of type and amount of trace elements during recycling operations can be either difficult and expensive. Furthermore, the role of trace elements in foundry metallurgy is not fully understood, even if it is sometimes a tool actually used to manipulate the microstructure of the alloys. Trace elements can be beneficial, as well as detrimental to the structure and properties of the alloy. Effects of Chromium and Bismuth additions to an AlSi9Cu3(Fe) secondary diecasting alloy on the microstructure and mechanical properties are investigated. The results indicate that the area fraction and the size of α-Alx(Fe,Mn,Cr)ySiz intermetallic compounds increases by increasing the Cr content, and this affects the ultimate tensile strength and the ductility of the alloy at the highest Cr level. Contrary, the Bi addition seems to not produce significantly changes in the microstructure and mechanical properties of the recycled AlSi9Cu3(Fe) alloy.