Microstructure and mechanical properties of carbon nano-onions reinforced Mg-based metal matrix composite prepared by friction-stir processing

Abstract

In consideration of the increasing demand for lightweight structural metal materials, it is essential to develop Mg-based metal matrix composite (MMC) with well-matched strength and ductility. In this study, carbon nano-onion (CNO) reinforced AZ31B Mg alloy MMC was successfully fabricated via friction stir processing (FSP). The microstructure and mechanical properties of the FSP CNO/AZ31B MMC were investigated. The obtained results showed that a homogeneous fine grain structure was achieved in the stir zone without gaps and microcracks. The grain refinement mechanisms were attributed to continuous and discontinuous dynamic recrystallization. The CNOs also played a critical role in the activation of {10−12} twinning behaviour. {10−12} twins can not only further refine the recrystallized grains but also reduce the basal texture intensity. The FSP CNO/AZ31B MMC exhibited enhanced yield strength due to the combined effects of grain boundary strengthening, dislocation strengthening, Orowan strengthening, and load bearing mechanism of reinforcements. Owing to the {10−12} twins and CNO induced back-stress strengthening, the FSP CNO/AZ31B MMC preformed improved strain hardening capacity. The yield strength and fracture elongation were enhanced by 14 % and 11.8 % compared with those of the matrix material, respectively, indicating that the strength and ductility were simultaneously improved due to the addition of CNO reinforcement.