Preparation,Microstructure And Properties Of MgO@GNPs/AZ91 Magnesium Matrix Composites

Magnesium matrix composites have the characteristics of light weight,high specific strength,specific stiffness and excellent vibration damping performance.They have good application prospects in aerospace,automotive industry,3C products and other fields.Graphene nanosheets(GNPs)have high strength,high modulus and good wear resistance.They are ideal reinforcements for magnesium matrix composites.However,the dispersion and interfacial bonding ability of GNPs in magnesium matrix still need to be improved.Surface modification of GNPs can not only maintain the excellent properties of GNPs,but also improve the dispersion and interface bonding ability of GNPs.Combined with the appropriate preparation process,the microstructure and properties of mag nesium matrix composites can be significantly improved.In this paper,AZ91 magnesium alloy is used as matrix,GNPs is used as reinforcement,GNPs is surface modified(coated with MgO),the modified GNPs(MgO@GNPs)and AZ91 magnesium alloy are uniformly mix ed by ball milling process,and MgO@GNPs/AZ91 magnesium alloy composite is prepared by vacuum hot pressing sintering process.The composites were tested and characterized by optical microscope,scanning electron microscope,transmission electron microscope,electronic density balance,X-ray diffractometer and electronic universal tensile testing machine.The surface modification process and vacuum hot pressing sintering process of GNPs were studied,and the effects of MgO@GNPs content and mass ratio of MgO to GNPs on the microstructure,density and mechanical properties of MgO@GNPs/AZ91 composite were explored.GNPs were modified by non covalent bond by uniform precipitation method.Flake MgO particles were evenly distributed on the surface of GNPs,and the average diameter of MgO particles was 98 nm.The interface between MgO and GNPs is well bonded,and there are no defects such as holes and separation at the interface.The effects of vacuum hot pressing temperature on the microstructure,density and hardness of MgO@GNPs/AZ91 composites were studied.With the increase of hot pressing temperature,the density of the composite increases and the porosity of the composite decreases.When the vacuum hot pressing temperature is 490?,the density of MgO@GNPs/AZ91 is 98.37% and the hardness is 65.7 HV.The effects of MgO@GNPs content on the microstructure,density and mechanical properties of MgO@GNPs/AZ91 composites were studied.MgO@GNPs is uniformly distributed at the boundary of AZ91 particles,which inhibits the diffusion of atoms during hot pressing.When the content of MgO@GNPs is 0.3 wt.%,the composite has the best comprehensive mechanical properties,with the density of 98.82%,hardness of 67.9 HV,compressive strength,tensile strength and yield strength of 430 MPa,198 MPa and 117 MPa,respectively.MgO@GNPs bonded well with AZ91 matrix,and no holes and gaps were observed.The effects of the mass ratio of MgO to GNPs on the microstructure,density and mechanical properties of MgO@GNPs/AZ91 composites were studied.The comprehensive mechanical properties of composites reinforced with different MgO to GNPs ratios are higher than those of GNPs/AZ91 composites and MgO/AZ91 composites.When the mass ratio of MgO to GNP s is 1: 1,MgO@GNPs is evenly distributed in the matrix,and its comprehensive mechanical properties are the best.Its hardness,compressive strength,tensile strength and yield strength are increased by 3.6%,4.9%,39.4% and 13.6%respectively compared with GNPs/AZ91.