The Cu-C and Al-Cu-C phase diagrams were determined at 1550 degrees C to 2300 degrees C by chemical and X-ray diffraction analyses of alloys saturated with carbon within sealed graphite crucibles. Isothermal sections for the ternary system were determined at intervals of 150 degrees C over the range of temperatures investigated. The univariant points in atomic percent on the 1700 degrees C, 1850 degrees C, and 2000 degrees C isotherms are 70.7Al-28.9Cu-0.4C, 74.4Al-24.0Cu-1.6C, and 78.3Al-17.0Cu-4.7C, respectively, as determined by metallographic examination of rapidly cooled alloys. Graphite and Al4C3 (decomposition temperature 2156 degrees C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved carbon in the liquid Al-Cu-C solutions in equilibrium with C, as calculated from the experimental solubilities, is¯ G c e = - RT lnx =y 2[176,860 - 55.42T - (224,200 - 110.84T)x] +z 2[237,000 - 48.61T] +yz[320,510 - 36.77T + (30,180 + 35.10T)z + (51,570 - 74.13T)yz + (246,400 - 88.04T)yz 2 - 60,000], J/g atom where R is the gas constant,T is the temperature in K, andx, y, andz are the atomic fractions of C, Al, and Cu, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A14C3.