Influence of Strain Rate and Temperature on Mechanical Properties and Fracture Mechanism of Dispersion Strengthened Al-12Al4C3 System

Abstract

In the presented work the change in fracture for the Al-12Al4C3 system was investigated and analysed at temperatures from 20 to 400 °C and strain rates from 2.5·10–5 to 10–1 s–1. At room temperature 20 °C, during tensile testing at strain rates in the tested region, the strain is first controlled by work hardening, expressed by the exponent n. In the second generally smaller part the deformation is limited by local straining and forming the neck. There is a marked decrease of plastic properties for the strain rate ε& = 2.5·10–5 s–1 with the growth of temperature in the investigated region. It is explained by changes in the micromechanism of deformation and fracture. Fracture surface shows the transition from ductile fracture with dimples at 20 °C, to intercrystalline fractures, with the growth of the temperature, an indication of exhausted grain boundary plasticity. The intercrystalline fracture initiation tends, it is supposed, to be localized in triple points. At temperatures 400 °C, and ε& = 10–1 s–1 there is a marked growth of plastic properties. The first part of the strain characterized by work hardening is very short. After the short growth of the stress to maximum, a deformation mechanism, showing presence of thermally and mechanically activated dynamic recovery processes takes place. The strain is this way uniform all over the body of the test piece. The fracture process ends with the increase of cavities and transcrystalline fracture with deep pimples.