Critical Assessment 36: Assessing differences between the use of cerium and scandium in aluminium alloying

Key factors affecting an application of two rare-earth metals cerium and scandium as alloying elements in aluminium are critically assessed. Having similar abundance in the Earth's crust, their cost and consumption differ by three to four orders of magnitude. The spectacular increment of alloy strength, achieved by scandium through the coherent, nano-scale, L1(2)-ordered Al3Sc precipitates is faced by the prohibitive cost barrier. For cerium, the low cost is accompanied by rather limited strengthening effects: negligible solid-state solubility of cerium in aluminium makes age hardening ineffective so the alloy strength depends on the Al11Ce3 eutectic phase, formed during solidification. As a result, there are still no commercial aluminium alloys with large-scale applications that take advantage of cerium, scandium or their combination.