  Differential thermal analysis has been conducted for the Al-Cu-Co alloys with
the composition range of 15 at.% Co and 10 to 30 at.% Cu, and 25 at.% Co and
2.5 to 20 at.% Co. The features of the formation of solid phases have been
studied during the crystallization in a crucible in the conditions of slow
cooling (rate of cooling to 1 K s-1) at normal pressure. On the state diagram
of the Al-Cu-Co system with 15 at.% Co and 25 at.% Cu the concentration
sections have been built, which allows to determine the concentration ranges
from which different phases are formed during the first stage of
crystallization. Along the boundaries of different phase regions, extrema are
observed on the liquidus line. The observed extrema on the liquidus lines and
concentration dependences of undercooling are associated with change in the
chemical short-range order at the considered concentrations both in the liquid
and solid states.
