Thermal stability of metastable Mg-30% Ti-2% Al-0.9% Mn (wt.%) alloy synthesised by PVD

The objective of this work is the study of the thermal stability of the Mg-30% Ti-2% Al-0.9% Mn (wt.%) alloy produced by physical vapour deposition (PVD). For this purpose differential scanning calorimetry and transmission electron microscopy techniques have been used. The alloy, in the as-deposited condition, is a solid solution of the alloying elements in the magnesium matrix, which induces a strong decrease in lattice parameters. The microstructure is characterised by elongated grains oriented in the deposit growth direction. After a differential scanning calorimetry experiment, the breakdown of the solid solution occurs. The precipitation phenomenon takes place by three exothermal reactions. As in Mg-Ti alloys, the two first peaks are associated with the titanium precipitation within the grains. The third transformation is due to the precipitation at grain boundaries of spherical Ti3Al particles. At higher temperatures, above 720 K, an increase in heat flow takes place and it is related to the strong oxidation of the magnesium matrix.