EFFECT OF TESTING ENVIRONMENT ON INTERGRANULAR MICROSUPERPLASTICITY IN AN ALUMINUM MMC

A correlation between the testing environment and the observed high te mperature deformation characteristics of a Al 6090 (Al-Mg-Si-Fe-Cu all oy) + 25 vol.% SiCp metal matrix composite (MMC) has been conducted. P ost deformation observations were performed on similar material specim ens tested in uniaxial tension to failure within either air or argon h igh temperature environments. Intragranular grain boundary whiskers th at exhibited exceptionally high local superplastic-like elongations we re observed when deformed in air at a temperature which was approximat ely 80% of, or greater than, the incipient melting point of the matrix and at a strain-rate of 4 x 10(-4) s(-1) whereas in a relatively pure argon environment under similar deformation conditions, the whiskerin g phenomenon (i.e. microsuperplastic whiskering, MSPW) at failure was not observed. Differential thermal analysis of the MMC microstructure verified that the observed MSPW behavior was a solid-state deformation process rather than being related to the presence of a liquid or semi -solid. The chemical constitution of the observed whiskers is thermody namically most likely to be of a spinel compound, MgAl2O4.