Study On Corrosion Degradation Behavior Of Graphene Composite Mg-based Materials

Magnesium alloy has been widely used in automobile manufacturing,electronic products,aerospace and other fields due to its high specific strength stiffness,good toughness,strong electronic shielding ability and high thermal conductivity.Magnesium matrix composites（MMCs）not only maintain the advantages of light magnesium alloy,but also further improve their wear resistance,strength and toughness.In addition,MMCs have been widely used as degradable materials for human bone transplantation due to their good biocompatibility and biodegradability.However,the low electrode potential and poor corrosion resistance of magnesium will cause the premature loss of the structural properties of MMCs in human body.Therefore,the study on the corrosion properties and corrosion mechanism of MMCs can provide a reference for improving the application of MMCs in biodegradable materials for human bone transplantation.Graphene nanoplapelets（Gnps）have good biocompatibility and cellular compatibility,and can adsorb human bone cells,which is beneficial to human bone growth,and is an ideal enhancement of MMCs.In this paper,semi-solid injection molding process was used to prepare Gnps composite magnesium based materials.Metallographic microscope and scanning electron microscope were used to characterize the structure and composition of Gnps composite magnesium based materials before and after corrosion.Electrochemical testing method was adopted.The corrosion performance of the composite is tested by weight loss method and hydrogen evolution method in the modified Simulated Body Fluid（SBF）,the influence of the Gnps content and distribution,and the holding time of solution treatment and aging treatment on the corrosion degradation behavior of the composite is studied.And the microscopic mechanism of composite corrosion was verified through first-principles calculation and exploration.The main contents are as follows:（1）The corrosion and degradation behavior of Gnps composite magnesium based material prepared by semi-solid injection molding process in simulated body fluid of SBF was studied.The experimental results show that the microstructure of Gnps composite Mg-based materials prepared by semi-solid injection molding process is refined,and the degree of refinement increases first and then decreases with the increase of Gnps content.By adjusting the process parameters in the semi-solid injection molding preparation process,the Gnps were uniformly dispersed into the matrix material,and the corrosion performance of the composite exceeded that of the matrix material.（2）To study the corrosion and degradation behavior of Gnps composite Mg-based materials in SBF simulated body fluid under solution treatment.The experimental results show that the second phase in the matrix is gradually integrated into the matrix after the solution treatment,which makes the corrosion performance of the composite exceed that of the as-cast material.The corrosion performance of Gnps composite magnesium based materials gradually increased with the extension of solution holding time.When the holding time reached 24 h,the corrosion rate of the composite materials gradually leveled off.At the same holding time,the composite material with 0.6 wt.%Gnps had the best corrosion performance,and the matrix material had the worst corrosion performance.（3）To study the corrosion and degradation behavior of Gnps composite Mg-based materials in SBF simulated body fluid under aging treatment.The experimental results show that after aging treatment,the second phase precipitates in the grain boundary and grain interior in the form of lamellar and short rod,respectively.After aging treatment,the corrosion performance of the composite decreases.With the extension of aging insulation time,the corrosion performance of the composite gradually decreased.When the insulation time reached 48 h,the corrosion rate of the composite gradually became stable.When the insulation time was 72 h,the corrosion rate of the composite was almost the same as that of48 h.Under the same heat preservation time,the composite with Gnps content of 0.6 wt.%still had the best corrosion performance,and the matrix material had the worst corrosion performance.（4）The surface energy and electron work function of different crystal faces of magnesium crystal and the electron work function of different crystal faces of Mg₁₇Al₁₂ with different atoms as terminal faces are calculated by first principles.The calculated results show that most of the work functions of Mg₁₇Al₁₂ are higher than those of the Mg crystal and are relatively stable compared with the Mg crystal.As a cathode phase in corrosion,it can accelerate the corrosion of magnesium matrix.