STRESS-FREE TEMPERATURE OF THE MACRO-INTERFACE IN SELECTIVELY REINFORCED ALUMINUM CASTINGS

A new method was used to investigate the effect of thermal cycling on the stress-free temperature of the macro-interface in castings consist ing 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 degrees C and 275 degrees C. Because these strips curl in response to thermal stress, like bimetal thermos tats, it was possible to measure their deflection at different tempera tures and thereby determine the temperature at which the thermal stres s is nonexistent. It was found that this stress-free temperature incre ased with increasing numbers of thermal cycles and approached the maxi mum thermal cycle temperature. It is suggested that this is a result o f dimensional changes experienced by the composite region during therm al cycling.