Accurate quantification of lithium in aluminium-lithium alloys with electron energy-loss spectrometry

The composition of the Al3Li (δ)' metastable precipitation-hardening phase is an important factor in understanding the strengthening behaviour of Al-Li base alloys. The procedure for using electron energy-loss spectrometry in a transmission electron microscope for accurate quantification of the Li content of δ' is established. All factors that can affect the accuracy of the analysis procedure are considered, namely: the specimen preparation, the mode of operation of the microscope, the identification of spectra from through-thickness regions of the specimen, the calibration of the Li / Al partial cross-section ratio, the deconvolution of the spectra and the background extrapolation scheme. The composition of the δ' phase in the temperature range 155-290 °C is determined, and the non-stoichiometry of this phase is clearly shown.