Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures

Three kinds of nanocrystalline materials, pure Al, Al-1.5Mg and Al-0.7Mg-1.0Cu, were compressive deformed at 300°C. In load-displacement curves, sharp drop of load after yielding was observed in Al-1.5Mg and Al-0.7Mg-1.0Cu alloys while slight increase of load in pure Al. The load drop results from effective grain boundary sliding, which indicates that alloying elements, Mg and/or Cu, assist the occurrence of grain boundary sliding. Plateau region where load is constantly sustained appeared following load drop, especially at strain rate of 1× 10^-3 s^-1 in Al-1.5Mg and Al-0.7Mg-1.0Cu alloys. During deformation in plateau region grains were highly refined from 100 nm to about 10 nm and then, the refined grains grew again up to 100 nm by subsequent deformation. All nanocrystalline Al alloys including pure Al showed strain softening phenomenon due to grain boundary sliding at 300°C regardless of strain rate.