MICROSTRUCTURAL CONTROL OF INTERMETALLIC CUAL-BASED AND HYPEREUTECTIC AL-SI ALLOYS BY STIRRING SYNTHESIS METHOD

An investigation was made on the microstructural refinement of Cu-37%Al and Al-17%Si alloys by the vacuum stirring synthesis. In this process, a molten alloy was spattered by a polygonal rotor rotating at a high speed up to 167 s-1 in a heat-controlled vessel. Many primary crystals formed in the spattered droplets were refined with repeating a collision between the rotor surface and the inner wall of the vessel by the stirring action of the rotating rotor. Finally, the slurry of gathered semi-solidified droplets was poured down into a metallic mold. Remarkable refinement of microstructure was achieved by the present stirring synthesis process as compared with the microstructures formed by conventional casting processes. The mean size of primary crystals was about 20 mum in the Cu-37%Al alloy made by the stirring synthesis at a rotation speed of 167 s-1, while the primary crystal size in the alloy cast conventionally without stirring was 300 to 1000 mum. The mean size of primary silicon crystals was about 16 mum in the Al-17%Si alloy made by the stirring synthesis at a rotation speed of 167 s-1, and it was 89 mum in the alloy rheocast at a rotation speed of 70 s-1.