MICROSTRUCTURE CONTROL OF INTERMETALLIC CUAL AND HYPEREUTECTIC AL-SI ALLOYS BY STIRRING SYNTHESIS

An investigation was made on the microstructure refinement of Cu-37%Al and Al-17%Si alloys by the vacuum stirring synthesis. In this method the molten alloys were allowed to flow down onto a polygonal rotor that rotated at a high speed up to 167 s-1 about the horizontal shaft in a heat-controlled vessel, the rotor spatered the molten alloys, many initial grains formed in the spattered droplets were refined with repeating a collision against the rotor surface and the inner wall of the vessel by the stirring action of the rotor rotating at high speed, and finally the alloys with slurrying of gathered semi-solidified droplets were poured down into a metallic mold through a taphole at the bottom of the vessel. Considerable refinement of microstructure was accomplished by the present stirring synthesis process as compared with the microstructures formed by conventional casting processes. The average grain size was about 20-mu-m in the Cu-37%Al alloy made by the stirring synthesis at a rotation speed of 167 s-1, although the grain size was 300 to 1000 mu-m in the alloy conventionally cast without rotation of rotor. The average silicon grain size was about 16-mu-m in the Al-17%Si alloy made by the stirring synthesis at a rotation speed of 167 s-1, and it was 89-mu-m in the alloy rheocast at a rotation speed of 70 s-1.