Microstructure and mechanical properties of multi-scale in-situ Mg2Si and CNTs hybrid reinforced AZ91D composites

Abstract

To optimize the mechanical properties of the Mg matrix composites, the carbon nanotubes (CNTs) and in-situ micro-Mg2Sim and nano-Mg2Sin hybrid reinforced composites were prepared by dispersion of nano-Sin and carboxylated CNTs on both surface of AZ91D and hydroxylated micro-Sim through hydrogen bonding and ball milling, and chemical reaction between the Mg matrix and Si particles occurred during spark plasma sintering (SPS). The multi-scale in-situ generated Mg2Si and nano-MgO formed at the CNTs/Mg interface enhance the interfacial bonding. As the ratio of CNTs/Mg2Si increases from 0.1 to 0.5vol.%, the mechanical properties of CNTs-Mg2Si/AZ91D composites gradually improve and then decrease. The 0.3CNTs-2.7Mg2Si/AZ91D composite has the best hardness (92.7 Hv), compressive ultimate strength (408.2 MPa), compressive yield strength (238.3 MPa), and elongation (24.5%) that are increased by 15.6%, 53.2%, 50.4%, and 2.9%, respectively compared with the AZ91D alloy, which is ascribed to the strong interface bonding between the matrix and multi-scale hybrid reinforcements that optimizes the synergetic strengthening of load transfer, thermal mismatch and Orowan mechanisms. An effective method is proposed to achieve the excellent performance of the Mg matrix composites.