  The valence states of Mg-Al alloys are compared to those of reference
materials (pure Mg and Al metals, and intermetallics). Two methods based on
X-ray emission spectroscopy are proposed to determine the phases and their
proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys
and the Mg valence spectra of the Al-rich alloys; second, by fitting with a
linear combination of the reference spectra the Al spectra of the Al-rich
alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine
that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and Mg
and Al12Mg17 are present in the 62.5-100 wt% Al composition range. In the
43.9-62.5% Al range, the alloy is single phase and an underestimation of the Al
content of the alloy can be estimated from the comparison of the bandwidth of
the alloy spectrum to the bandwidths of the reference spectra.

Materials Science