Dendrite coherency point: determination and significance

Measurements of the rheological properties of solidifying alloys have shown that the fraction solid at which dendrite coherency is reached varies systematically as a function of both alloy and solidification parameters. The coherency point of the alloys under investigation was determined in two different ways. Each method is based on indirect measurements of a physical property of the material which is assumed to undergo a significant liquid-solid transition at the dendrite coherency point. The coherency fraction solid for Al-Cu-Si alloys was found to decrease with increasing solute concentration. AA601 was found to have a higher coherency fraction solid than binary Al-7 wt%Si. Increasing the cooling rate was found to increase the coherency fraction solid of the alloys, as measured with the thermal analysis technique. Variation between the coherency fraction solids determined by rheological and thermal analysis methods are considered to be related to the different coherency criterion used in each experimental method. 15 refs., 6 figs