THERMAL-TREATMENT EFFECTS IN SIC/AL METAL-MATRIX COMPOSITES

A short-fibre-reinforced SiC/Al-7% Si-0.6% Mg composite has been subjected to thermal cycling and elevated temperature isothermal exposure treatments. The microstructure and residual mechanical properties have been determined as a function of these treatments. It was found that isothermal or cycling treatment at 350-degrees-C caused severe room-temperature strength degradation while treatment at 525-degrees-C caused little change. Strength changes are attributed principally to precipitation and dissolution effects and to transfer of magnesium from the matrix into the fibre/matrix interfacial reaction layer. There was no evidence of mechanical damage resulting from the cycling treatments.