SUBSTITUTION BEHAVIOR OF ADDITIONAL ELEMENTS IN THE LI2-TYPE AL3LI METASTABLE PHASE IN AL-LI ALLOYS

The substitution behavior of additional elements in the L1(2)-type metastable intermetallic compound of Al3Li (delta' phase) is investigated for the Al-Li alloy design based on the relative internal energies of the Al3Li phase with various defect structures. The Al-Li alloys containing delta' phase are expected to be a new class of structural materials with low density and high specific strength. In the conventional Al-Li alloys the contents of aluminum are higher than the stoichiometry of 75 mol%Al and the precipitation of the Al3Li phase is effective in increasing the mechanical strength of Al-Li alloys. A prediction method has been developed for the substitution behavior of ternary elements and the type of defect structures of the Al3Li phase at off stoichiometric compositions and the pseudoground state. The substitution type defect (or antistructure type defect) is found to be preferred, and most of transition metals substitute only for Li atoms at all compositions investigated. Ca and Sr are predicted to be useful as low-density alloying elements for improving the properties of Al-Li alloys based on the results of the present investigation.