Improved Processing For Direct Reduction of Cerium Precursors for the Production of Al-Ce Alloys

This project seeks to build on a Phase 1 effort to reduce the cost and supply barriers to the implementation of Al-Ce alloys in defense and commercial applications using direct reduction of cerium precursors in molten aluminum. A successful project will eliminate the need for foreign sources of cerium metal and exploit the cost differences between pure cerium and its oxide, currently a factor of three. Al-Ce alloys have good mechanical properties at high temperatures and are easy to cast-good fluidity and no hot tearing through the later stages of freezing. In alloy systems that use cerium in combination with common aluminum alloying elements such as silicon, magnesium and/or copper, the casting characteristics are generally better than the aluminum-copper system. In the Al-Mg-Ce, Al-Zn-Ce and Al-Mg-Zn-Ce systems the alloys do not require a post casting heat treatment to develop properties because of the combined effects of dispersion strengthening by the Al-Ce intermetallic and solid solution strengthening by the magnesium and or zinc. A new class of Al-Ce alloys is being investigated that gain additional strengthening through post casting heat treatment. These alloys contain other alloying elements such as Ni, Mn and Si that improve room temperature strength and may offer advantages at elevated temperatures such as reduced coefficients of thermal expansion. In our Phase 1 effort we learned that the success of conversion of cerium precursors is dependent on the dwell time of those precursors in the melt as controlled by the mixing RPM and delay between the additions and the degassing and melt cleaning procedures. We attempted to use production de-gassing equipment for this work. That equipment is incapable of sufficient RPM to ensure good mixing and is designed for concurrent mixing along with alloy de-gassing and cleaning. In Phase 2 we propose to use specially designed equipment to do a two-stage treatment. In stage one we will do vortex mixing based on mixing speeds roughly determined in the Phase 1 program as modified based on the actual equipment mechanics, followed immediately by a degassing-cleaning stage with reduced RPM’s and the use of cleaning gasses. The alloy produced will be used to produce castings and test pieces for internal and external testing. We will optimize mixing time, RPM and determine best gasses to be used in the degassing/cleaning stage. We will characterize the alloy and compare with alloy produced using metallic cerium additions. Other alloying additions will be done pre and post cerium additions to determine relative efficiency of the cerium conversion in the presence of anticipated final alloy compositions as determined by us and our customers. The alloy will be tested in both casting form as well as in atomized powder for selective laser sintering and consolidated powder.