Preparation,Microstructures And Properties Of AZ91D Magnesium Matrix Composites With Graphene Nanoplates

As a new type of carbon material,graphene have great application potential in various fields due to their unique two-dimensional structure and excellent performance.Adding graphene as reinforcements to the magnesium alloys not only improves the mechanical properties,but also improves the thermal and electrical properties of the magnesium alloys.At present,the preparation technologies of graphene reinforced magnesium matrix composite are severely limited due to the complexity of the process,high cost and difficulty in mass production.It can be seen that it is necessary to develop a low-cost,high-yield preparation technique for graphene reinforced magnesium matrix composite.In this paper,graphene nanoplates（GNPs）and AZ91D magnesium alloy chips were mixed by V-type mixing method.Then,different contents of GNPs（0.3%,0.6%,0.9%,mass fraction）reinforced AZ91D magnesium matrix composites were prepared by thixomolding.The effects of different contents of GNPs on the microstructure and mechanical properties of the composites were studied,and the optimal content of GNPs was obtained.Subsequently,the optimal addition amount of GNPs was selected,and GNPs reinforced AZ91D magnesium matrix composites were prepared by electromagnetic stirring.The microstructure and properties of the composites were studied.This work provided a reference for the preparation and application of graphene reinforced magnesium matrix composites.The microstructure of AZ91D-chips fixed GNPs was characterized by scanning electron microscopy.The microstructure of the composites was characterized by optical microscope,scanning electron microscopy,energy spectrum analysis,transmission electron microscopy and X-ray diffractometer.The mechanical properties of the composites were tested by various tests such as density test,hardness test and tensile test.The main results are as follows:After the V-type mixing,the sheet-like GNPs adhered firmly to the surface of the AZ91D magnesium alloy chips,and the mixing effect was good.The V-type mixing and the addition of GNPs did not affect the size of the AZ91D magnesium alloy chips.The microstructure of the GNPs reinforced AZ91D magnesium matrix composite prepared by the thixomolding consists ofα-Mg phase and eutectic structure(α-Mg+β-Mg₁₇Al₁₂).GNPs are uniformly dispersed in the matrix and exists in the form of a black stripe,tightly bound to the matrix,maintaining the structural integrity of the GNPs.With the increases of GNPs content,the average grain size of the composites gradually decreases,the density increases,the porosity decreases,and the hardness and tensile properties first increase and then decrease.When the amount of GNPs added is 0.6wt.%,the mechanical properties of the composites are the best.The hardness,tensile strength and elongation are 92.3HV,245MPa and 3.9%,respectively,which are 36%,40%and 86%higher than the matrix.The microstructure of the GNPs reinforced AZ91D magnesium matrix composite prepared by electromagnetic stirring consists ofα-Mg phase and eutectic structure(α-Mg+β-Mg₁₇Al₁₂).GNPs are successfully dispersed uniformly in the magnesium matrix.The average grain size of the composite is 84%lower than that of the base alloy.With the addition of GNPs,the density,hardness,tensile strength and elongation of composites are improved.The hardness,tensile strength and elongation of the composites were 77.0 HV,162MPa and 3.9%,respectively,which were 18%,19%and 86%higher than the matrix.