Hot Deformation Behavior and Microstructures Evolution of GNP-Reinforced Fine-Grained Mg Composites

Graphene nanoplates (GNPs)-reinforced magnesium matrix composites have been attracted great attention. However, knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium (GNPs/Mg) composite. In this study, the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion. The hot deformation behavior, microstructure evolution and dynamic recrystallization (DRX) mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction (EBSD). The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s(-1). The strain compensated power law equation was established to describe the hot deformation behavior of the composites. The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol, respectively, suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep. The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement. The grain size increases with the decrease in Zener-Hollomn (Z) parameter, which can be well fitted by power-law relationship. With the increase in grain size and decrease in Z parameter, the geometrically necessary dislocation density decreases, which shows the approximately power-law relationship. A random and weak texture was formed after hot compression. The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s(-1) and 573 K/0.001 s(-1), respectively.