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

The substitution behavior of additional elements in the L1(2)-type met astable 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 cont aining delta' phase are expected to be a new class of structural mater ials with low density and high specific strength. In the conventional Al-Li alloys the contents of aluminum are higher than the stoichiometr y of 75 mol%Al and the precipitation of the Al3Li phase is effective i n increasing the mechanical strength of Al-Li alloys. A prediction met hod has been developed for the substitution behavior of ternary elemen ts and the type of defect structures of the Al3Li phase at off stoichi ometric compositions and the pseudoground state. The substitution type defect (or antistructure type defect) is found to be preferred, and m ost of transition metals substitute only for Li atoms at all compositi ons investigated. Ca and Sr are predicted to be useful as low-density alloying elements for improving the properties of Al-Li alloys based o n the results of the present investigation.