Evolution of Precipitated Phases during Ageing in High Alloyed Mg-Al Based Alloys

The artificial ageing treatments have been performed in the commercial magnesium alloys AZ80 (Mg-8.2Al-0.5Zn) with different grain size in the temperature interval 150-250 °C. The comprehensive microstructure observations through ageing were carried out by light microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Solid solution decomposition proceeds in non-deformed materials by two modes of precipitated γ – Mg17Al12 phase: discontinuous (grain boundary) and continuous (intragranular) precipitation. A competitive formation of precipitation is influenced by either initial grain size or applied cold deformation before ageing. The electrical resistivity measurements have allowed evaluating some kinetic parameters of precipitated γ - Mg17Al12 phase. The good agreements of the obtained volume fractions of γ - Mg17Al12 phase after different ageing time by electrical resistivity and a XRD technique were observed.