Production of Al-Ce Casting Alloys Via Direct Reduction of Cerium Oxide

This proposal continues the development of aluminum alloy systems that use cerium as a primary alloying element at near eutectic compositions. Additional alloying elements can be used primarily to assist in the development of room-temperature mechanical properties. The cerium in the alloy stabilizes those properties at high temperatures (200-400°C). The primary intermetallic formed in the aluminum-rich region of the Al-Ce system is Al11Ce3.The as-cast microstructure of the binary alloy show a very fine interconnected eutectic and the pure aluminum phase. The scale of the laths can be as small as 100nm and do not exhibit preferential direction at standard cooling rates. These structures are stable at higher temperatures. The intermetallic is trapped by the zero solubility of cerium in the aluminum matrix. This trapping prevents the system from minimizing surface energy through diffusion, which blocks the alloys from traditional coarsening interactions. Currently, the alloys are produced using widely available aluminum base materials and cerium metal, which is generally imported from China, since they have facilities to produce cerium metal. Generally, even cerium metal that is imported from Europe or Canada has its origins in China. There is no cerium metal available in production quantities in the United States. In the best case, this leads to high costs of transportation, and in the worst case a potential for supply disruption. We propose to directly reduce aluminum oxides into molten metal using an aluminothermic reaction. Our recent experimental work demonstrated a proof of concept for that approach. Cerium oxides and carbonates were reduced to cerium and abundant Al11Ce3 intermetallic was formed. Post analyses of those samples showed a 40% reduction in strength, driven primarily by defects formed as byproducts of the reaction, typically MgO and MgAl2O4 which were not successfully removed. The proposed work will look at process variable such as melt temperature, level of Mg in the alloy, inclusion reduction techniques and cerium oxide size to scale the technology with no loss of strength.