Effect of testing environment on intergranular microsuperplasticity in an aluminum MMC

A correlation between the testing environment and the observed high temperature deformation characteristics of a Al 6090 (AlMgSiFeCu alloy) + 25 vol.% SiCp metal matrix composite (MMC) has been conducted. Post deformation observations were performed on similar material specimens tested in uniaxial tension to failure within either air or argon high temperature environments. Intragranular grain boundary whiskers that exhibited exceptionally high local superplastic-like elongations were observed when deformed in air at a temperature which was approximately 80% of, or greater than, the incipient melting point of the matrix and at a strain-rate of 4 × 10−4 s−1; whereas in a relatively pure argon environment under similar deformation conditions, the whiskering 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 thermodynamically most likely to be of a spinel compound, MgAl2O4.