Improving the strength-ductility synergy of bimodal-structure GO/ZK60 Magnesium matrix composites via structure optimization

Abstract

Bimodal-structured graphene oxide (GO)/ZK60 composites, consisting of GO-reinforced fine-grain (FG) zones and GO-free coarse-grain (CG) zones, were fabricated by powder thixoforming to conquer the strength-ductility trade-off by regulating partial remelting temperature. Results indicate that the grain size and volume fraction of CGs in the resultant GO/ZK60 composites continuously increase as the remelting temperature rises from 843 K to 873 K, while the grain size of FGs almost remains unchanged. The composite thixoformed at 853 K with moderate grain size and fraction of CGs exhibits an excellent synergy of strength and ductility. The yield strength, ultimate tensile strength and elongation are up to 192 MPa, 316 MPa, and 21.8 %, respectively, increased by 42.2 %, 18.8 % and 27.5 %, respectively, compared with those of the corresponding ZK60 matrix alloy. The increases of both grain size and fraction of CGs improve the deformation of the CGs by enhancing twinning deformation, as well as the co-deformation ability of FGs and CGs, thereby improving the strain hardening ability and blunting the cracks, which significantly increase the ductility. The strength of the bimodal GO/ZK60 composite is well predicted by a modified combining model considering the back stress strengthening. This work provides a promising route for improving the strength-ductility synergy of metal matrix composites.