Morphology of primary α-Al dendrite and eutectoids as well as primary θ phase and size variation

and formation mechanism of semi-solid casting Al-Cu alloy containing 10% Cu

20% Cu and 40% Cu were investigated by SEM （scanning electron microscope）

OM （optical microscope）. The results reveal that primary α-Al phase with size of 50

8

0 μm exhibits near-equiaxed globular structure or rosette in semi-solid Al-10Cu and Al-20Cu alloy

while primary CuAl2 phase in semi-solid Al-40Cu alloy is fully converted from coarse long ribbon into particle or short rod with small length-diameter ratio or near-equiaxed particle with the average size lower than 80 μm

greatly improving the grain morphology. Compared with that by conventional casting

the microstructure of semi-solid casting Al-Cu alloy is significantly improved

fully meeting the demands of engineering application. Primary α-Al phase exhibits in-situ growth in semi-solid Al-Cu alloy in the condition of intensely stirring

which is responsible for the formation of near-equiaxed globular structure or rosette structure or small short rod and near-equaixed particle.