Solidification characteristics of Al–9·6Mg alloy solidified under high pressure (4 GPa)

Abstract

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 β-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=8·495 Å. Evolution mechanism of microstructures and phases was studied in the present paper. Furthermore, Mg concentration in α-Al phase has increased by 42%. Correspondingly, the lattice constant of α-Al phase has increased by 0·44%. The nanohardness of α-Al phase in the alloy increased under high pressure, whereas that of the elastic modulus decreased.

Keywords:

• HIGH PRESSURE
• AL-9.6MG ALLOY
• MICROSTRUCTURES
• METASTABLE PHASE
• NANOHARDNESS
• ELASTIC MODULUS