Surface etched graphene nanoplatelets and their heterogeneous interface to reinforce magnesium alloys for high strength and ductility

Surface etched graphene nanoplatelets (SEGs) were obtained by KOH etching of reduced graphene oxides, and the etching degree was controlled by KOH addition. Nano-sized pores with diameters mainly around 1 nm and 4 nm were created on the surface carbon layer of SEGs. During the composite preparation, the nanopores on SEGs provided nucleation sites and suppressed the growth of Mg crystal, which led to Mg nanograins. The mechanical deformation (hot extrusion) and nanocrystalline structures promoted Mg amorphization transition on the interface. The absorbed and residual oxygen on SEGs reacted with Mg into MgO nanoparticles. These nanoparticles (Mg nanograins, MgO nanograins and amorphous Mg) respectively had coherent, semi-coherent and incoherent interface with Mg matrix, which caused dislocations and lattice mismatch regions along the interface. The resulting heterogeneous interface of SEGs/nanoparticles/Mg matrix built a nano-micro hierarchical structure, which largely enhanced the strength and ductility of SEGs/ZK61 composites. The SEG-4/ZK61 composite exhibited optimum mechanical performance with yield strength of 236 MPa, ultimate tensile strength of 337 MPa, and especially elongation of 32 %. This work develops nanopore-modified graphene to reinforce Mg alloys, which might provide a design guideline for high performance metal matrix composites.