STIRRING CONDITIONS AND GRAIN REFINEMENT IN Al-Cu ALLOYS BY RHEOCASTING.

An investigation is reported on stirring conditions and grain refinement of Al-Cu alloys containing 10, 24 and 30 mass% copper with high ductility at elevated temperatures in the vacuum rheocasting in which the alloy is violently agitated at very high rotation speeds of a stirrer inserted in the solid-liquid coexisting zone. The results are as follows. The average size of primary solid particles in these alloys is consistently decreased with the increase in rotation speed from 20 to 67 rev/s at a cooling rate of 0. 42 K/s. The primary solid particle sizes of 67 rev/s are 90 plus or minus 29 mu m in Al-10%Cu, 61 plus or minus 32 mu m in Al-24%Cu and 46 plus or minus 14 mu m in Al-30%Cu. The primary solid particle is more refined into 41 plus or minus 12 mu m in diameter at a stirrer speed of 67 rev/s by addition of grain refiners of 0. 5 mass% Ti and 0. 1 mass% B to Al-24%Cu. It also becomes smaller in the rheocasting of A1-10%Cu and A1-24%Cu alloys in a crucible with ribs machined along the surface of cylindrical wall. The values of elongation at 773 K are 91% in Al-24%Cu and 71% in Al-30%Cu at an initial strain rate of 1. 19 multiplied by 10** minus **3s** minus **1.