The solidification of A1-20 wt% Mn alloy was investigated under pressures u
p to 6 GPa, It was found that the solidification products under pressures b
elow 4 GPa were about the same, composed mainly of Al and Al6Mn. A new Al-M
n phase with needle like morphology and Al nanocrystallites in size less th
an 20 nm were obtained in the quenched alloy at 6 GPa. Structure analysis b
y transmission electron microscopy and x-ray diffraction indicated that the
new phase had a C-center othorhombic unit cell with lattice constants of a
= 0.7565(4) nm, b = 1.2965(6) nm, and c = 0.7801(6) nm, The composition wa
s determined to be Al77.5Mn22.5 by election probe microanalysis. The phase
evolution during solidification under different pressures was discussed. Ou
r experimental results show that the pressure, as a basic thermodynamic var
iable like temperature, may play an important role on the solidification of
the alloy.