DENDRITE COHERENCY DURING EQUIAXED SOLIDIFICATION IN BINARY ALUMINUM-ALLOYS

Dendrite coherency, or dendrite impingement, is important to the forma tion of the solidification structure and castability of alloys. Dendri te coherency in the systems Al-xMn, Al-xCu, Al-xFe, and Al-xSi (x = 0 to 5 wt pct) has been studied by continuous torque measurement in soli difying samples. The fraction solid at the dendrite coherency point, f s, varies with the alloy system and the solute concentration in the a lloy, from 18 to 56 pet for the present alloys investigated. An increa se in solute concentration decreases the coherency fraction solid, fs . An alloy system with a large slope of the liquidus line has a high c oherency fraction solid. A theoretical approach has been developed to account for the effects of the alloy system and solute concentration o n the dendrite coherency in the alloy. The grain sizes of the alloys w ere evaluated using the parameters at coherency point.