Effect of Grain Refinement on the Dendrite Coherency Point during Solidification of the A319 Aluminum Alloy

Dendrite coherency is important to the formation of the solidification structure and castability of alloys. The effects of grain refinement on the dendrite coherency in A319 aluminum alloy have been studied using the two-thermocouple thermal analysis technique in the solidifying sample. The fraction solid at the dendrite coherency point (f(s)(DCP)) in the A319 alloy increases with increasing Al-5Ti-1B grain refiner, and varies from 16 to 21 pct when the amount of Al-5Ti-1B in the alloy is in the range of 0 to 4.6 wt pct. The results also indicate that the grain refinement increases the temperature interval of coherency (T-N - T-DCP) and coherency time (t(DCP)) and it can postpone dendrite coherency. These changes were interpreted based on the dendrite growth rate, the growth restriction factor, and the microstructure.