A new method was used to investigate the effect of thermal cycling on the stress-free temperature of the macro-interface in castings consisting of an Al-12%Si alloy (A339) with a 16% v/o discontinuous Saffil [1] fiber reinforced region. Thin bimaterial strips, containing both the unreinforced alloy and composite, were sectioned from castings after being thermally cycled between 50°C and 275°C. Because these strips curl in response to thermal stress, like bimetal thermostats, it was possible to measure their deflection at different temperatures and thereby determine the temperature at which the thermal stress is nonexistent. It was found that this stress-free temperature increased with increasing numbers of thermal cycles and approached the maximum thermal cycle temperature. It is suggested that this is a result of dimensional changes experienced by the composite region during thermal cycling.