DAMAGE OF 6061 SICW COMPOSITE BY THERMAL CYCLING/

The unreinforced 6061 alloy and a 6061/SiC composite, at the beginning in the T6 temper, were submitted to thermal cycling (up to 2000 cycle s) in the temperature ranges 25-180 degrees C and 25-220 degrees C. Th e microstructure of these materials was studied by scanning electron m icroscopy and mercury intrusion porosimetry. Mechanical and thermomech anical properties were also investigated. Tensile strength, hardness, Charpy impact resistance, fracture toughness, density, specimen dimens ions and thermal expansion were compared before and after thermal cycl ing. The unreinforced alloy showed an increase of ductility with cycli ng. This behaviour was chiefly due to overageing and partial annealing . The composite material, following the thermal treatment, did not onl y undergo overageing and annealing of its metal matrix; void coalescen ce, crack formation and reinforcement debonding were also observed. Th e development of these defects basically resulted in a marked decrease of tensile strength, yield strength, Charpy impact energy and fractur e toughness.