Abstract: A rapidly solidified Al-17Si alloy was pre- pared by the ultrasonic gas atomization and extrusion method.Its superplasticity was studied under constant cross-head speed tensile test condi- tion over the temperature range of 450℃ to 550℃ and strain rate range of 1.67×10~(-4) to 6.17× 10~(-2) s~(-1).The superplastic behaviour of the as-extruded and the thermomechanically treated samples was compared.It was found that the thermomechanical treatment was essential to achieving superplastic deformation.A maximum elongation of 445% was obtained at test tempera- ture of 550℃ and strain rate of 6.17×10~(-4) s~(-1). The microstructures before and after deformation were studied using OM,SEM and TEM.Void for- mation on the primary Si phase interfaces was found to have detrimental effect on superplasticity. It was also noted that the primary Si phase coarsened rapidly during superplastic deformation. The micromechanisms of superplasticity,phase coarsening and void formation were discussed.

Key words: superplasticity, rapid solidification, AI-Si alloy