Solidification Characteristics Of Al-9.6mg Alloy Solidified Under High Pressure (4 Gpa)

The present paper studies influences of high pressure up to 4 GPa at 1273 K on the microstructures and the phases of Al-9.6Mg alloy by means of optical microscopy (OM), X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results showed that fine dendrite with long primary arm formed at 4 GPa in comparison with the coarse discontinuous dendrite under normal pressure. Specially, a new high pressure metastable phase, Al(63.7)Mg(36.3), was produced besides a small amount of beta-Al3Mg2 phases at 4 GPa, which was not found in other solidification conditions. Al(63.7) Mg(36.3) phase has bcc structure with the lattice constant a = 58.495 angstrom. Evolution mechanism of microstructures and phases was studied in the present paper. Furthermore, Mg concentration in alpha-Al phase has increased by 42%. Correspondingly, the lattice constant of alpha-Al phase has increased by 0.44%. The nanohardness of alpha-Al phase in the alloy increased under high pressure, whereas that of the elastic modulus decreased.