Superplastic Behavior of Hyper-Eutectic Al-Si P/M Alloys Produced by Centrifugal Atomization Process

Rapidly solidified hyper-eutectic Al-25Si and Al-15Si pre-alloy powders have been produced at the cooling rate of 105-104°C/s using a centrifugal atomization process. The powders have been consolidated via hot extrusion with a reduction ratio of 110 at 490°C after vacuum hot pressing. Superplasticity of the P/M extruded bars has been investigated in the temperature range between 350 and 523°C. The values of maximum elongation of Al-25Si and Al-15Si P/M extruded bars are 154% and 307%, respectively. The above P/M extruded bars show the maximum elongation at a temperature just below the solidus line of the Al-Si alloys. A filament-like elongated microstructure is formed on the surface of the P/M extruded bar under the optimum condition of superplastic deformation. The formation of such a microstructure is considered to be based on the grain boundary sliding resulting from superplastic deformation. The elongation of the P/M extruded bar, which was directly extruded without pre-compaction of the powder by vacuum hot pressing, is larger than that of the extruded bar through vacuum hot pressing.