Effects of super-high pressure on microstructures, nano-mechanical behaviors and corrosion properties of Mg–Al alloys

• The area fraction of Mg matrix is increased with increasing the pressure.
• Al concentration is increased in Mg17Al12 compound after high pressure treatment.
• Both the hardness and Young’s modulus are increased with increasing the pressure.
• The corrosion properties of SHP-2 GPa-800 sample are improved greatly.
• The high corrosion resistance is related to the formation of fine oxide film.

The aim of this study was to investigate the effects of super-high pressure solidification (2 and 4 GPa) on microstructures, nano-mechanical behaviors and corrosion properties of Mg-30 wt.% Al alloy. The lattice parameter (a) of Mg matrix is decreased and the c/a value is increased owing to the increased Al concentration in Mg matrix. In contrast to the as-cast sample or other super-high pressure samples, the Mg matrix is more homogeneous and the net-like eutectic phase becomes finer after super-high pressure solidification at 800 °C under 2 GPa. In addition, the area fraction of eutectic phase is reduced with increasing the exterior pressure and temperature during the solidification, whilst the Al concentration in both the Mg matrix and the eutectic phase are enhanced. The nanoindentation results indicate that both the hardness and Young’s modulus are sensitive to the solidification pressure and temperature. The Tafel curves and electrochemical impedance spectroscopes results reveal the corrosion properties of the sample at 800 °C under 2 GPa are remarkably improved due to the formation of a compact and continuous oxide layer.