Measurement of Liquid Permeability in the Mushy Zones of Aluminum-Copper Alloys

Measurements of liquid permeability in the mushy zones of Al-15.42 pct Cu and Al-8.68 pet Cu alloy samples were performed isothermally just above the eutectic temperature, using eutectic liquid as the fluid. A modified method was developed to determine the specific permeability as a function of time (Ks) during the test from the data collected on these alloys. Factors affecting permeability measurements are discussed. The permeabilties are observed to vary throughout the experiment. This is attributed to microstructural coarsening and channeling that occur in the sample during the experiment. Coarsening rates are determined for the isothermal coarsening tests without fluid flow, and the results are observed to be less than the rates indicated from permeability tests where fluid flow is present. Careful measurement of the volume fraction of liquid (g(L)) shows that g(L) decreases during the test. The permeability is then related to the microstructure of the sample using the Kozeny-Carman equation. The correlation between the measured Ks,g(L) and specific solid surface area (S(V)) improves markedly when compared to previous studies, when microstructural parameters at the initial stage of the test are used.