Effect Of Physical Field On Microstructure And Hardness Of Graphene-magnesium-matrix Composites And Computational Study

Graphene nanoplates(GNPs)have become an ideal reinforcing phase material due to their unique two-dimensional structure and excellent mechanical properties,and have great potential in the preparation of composite materials.However,due to the large surface area and poor wettability,it is easy to agglomerate in magnesium matrix composites and is difficult to disperse uniformly in the matrix,and it is still difficult to prepare GNPs-magnesium matrix composites with good performance.Therefore,it is necessary to develop a method to uniformly disperse GNPs in the magnesium matrix.In this paper,the distribution of GNPs in magnesium alloys under the action of external physical fields(magnetic field and electric field)is mainly studied by combining experimental and computational methods.Before the experiment,GNPs and magnesium chips need to be mixed with ultrasonic waves to improve the wettability between graphene layers,and after completion,the mixture of GNPs and magnesium chips is placed between the AZ31 B magnesium plate layers by multi-layer stacking,and it is melted by stirring casting,and finally solidified in a magnetic field atmosphere to obtain AZ31 B,Mf-AZ31 B,0.5GNPs-AZ31 B and Mf+GNPs-AZ31 B composites.The resulting samples are characterized using a variety of means.Through the results of SEM and XRD,it can be seen that the action of magnetic field inhibits the precipitation of β-Al12Mg17,so that Al solid solution in the α-Mg matrix.The results of energy spectrum analysis showed that the magnetic field could uniformly disperse GNPs in the magnesium matrix.The results of Raman spectroscopy showed that the magnetic field changed the distribution of GNPs in the magnesium matrix,and its phase distribution in the matrix was more chaotic.The metallographic diagram and grain size calculation results of OM show that the grains of AZ31 B and 0.5% GNPs-AZ31 B are effectively refined by the action of magnetic field.The nanoindentation test proves that the magnetic field can increase the hardness and Young’s modulus of magnesium alloy materials.By establishing a model of Armchair GNPs and Zigzag GNPs vertically embedded in the Mg(100)interface,the influence of different electric field directions on the GNPs/Mg composite model was explored using first-principles calculations.The comparison of the geometric model with structural optimization shows that the action of the electric field will cause the Mg atoms in the system to shift from the GNPs,and when the electric field direction is along the Y axis,the structure of the GNPs changes and the phenomenon of folding occurs.The calculation results of adsorption energy and state density were analyzed,and after the electric field was applied,the adsorption energy and pseudogap energy of the vertically embedded GNPs and Mg(100)interface increased,and the adsorption effect in the system was enhanced.The results of charge density and differential charge density show that the electric field will increase the charge density and differential charge density between GNPs and Mg atoms,expand the charge transfer range,and expand the adsorption to the entire surface of GNPs.