Dynamic Response of Residual Stresses due to Rapid Temperature Changes in Kaowool Reinforced AA339 Aluminum

Abstract

The residual stresses in the matrix of an AA339 aluminum/ 23%(vol.) Kaowool short fibre composite were measured by x-ray diffraction at 100°C, after rapid heating and cooling at 200°C/min between 100°C and 300°C. A special heating stage was developed, with a very low thermal expansion to minimize systematic errors due to specimen alignment and a very low thermal mass to permit rapid temperature changes. A linear position sensitive detector enabled diffraction peak profiles to be measured in 5 seconds. Rapid cooling from 300°C produced high residual stresses at 100°C which subsequently relaxed. After a slow thermal cycle (5°C/min heating and cooling) the stresses at 100°C were smaller and stable. Many subsequent rapid thermal cycles were required to establish the higher stresses and this behaviour is attributed to the development of a fine precipitate dispersion with a transition from coherent precipitates to incoherent ones. These results cannot be explained purely by dislocation mechanisms.