THE ELECTRONIC CONTRIBUTION TO METASTABILITY IN AGE-HARDENING AL-LI ALLOYS - A SOFT-X-RAY EMISSION STUDY

A commercial 2091 aluminium-lithium alloy was subjected to various agi ng treatments to produce different metastable precipitates. The nature of the precipitates was deduced from differential thermal analysis an d by reference to the literature. The Al L(2,3) and the Li K beta spec tra were recorded. The average energy of the Al L(2,3) emission band f rom the matrix was taken to be a measure of the overall energy of the valence electrons, and a direct correlation was established between th e valence electron energy and the hardness of the alloy. The Li K beta spectra from lithium concentrated in the precipitates showed consider able structure not present in the spectrum from the pure metal, and wh ich is related to covalency in the Al-Li bonds.