Tensile Deformation and Fracture Behaviour of Pure Aluminum and Aluminum Alloy at Cryogenic Temperatures

Abstract

Effect of cryogenic temperature on tensile deformation and fracture behaviours of pure aluminum and aluminum alloy was investigated in the present experiment mainly in view of certain parameters controlling the deformation process and microstructures of the test materials. The results indicate that the work-hardening and impurity or alloying addition seem to increase the athermal component of the yield strength more than the thermal part in pure aluminum. Sensitivity of flow stress to strain rate change of the work-hardened 1050 aluminum was larger than that of fully annealed specimen for the temperature range from 300 K down to 4 K, however, the sensitivity was relatively lowered at 4 K and 300 K corresponding to the variation of the deformation mode at respective temperatures. A typical serrated yielding was observed for the load-elongation curves in accordance with the specific test conditions below about 20 K. The occurence of serration of pure aluminum specimens were clearly influenced by not only strain rate or test temperatures but microstructures. The effect of stress, microstructures, impurities and test temperature on the dislocation mechanism of the deformation was also discussed in view-point of the activation volume and activation energy for the plastic flow of pure aluminum and aluminum alloy.