Preparation And Properties Of Cold Sprayed Graphene/Aluminum Composites Coating On Magnesium Alloys

Magnesium and its alloys have many characteristics,such as low density,high specific strength,specific stiffness,specific elastic modulus,excellent casting and machinability,and are widely used in automotive automation,aerospace,medical equipment,biological materials and other fields.However,low standard electrode potential and loose porous surface oxide film make magnesium and its alloys easy to be corroded in wet water environment.How to improve the corrosion resistance of magnesium and its alloys and prolong the service life of its products has become a hot topic in the field of materials research.Graphene-reinforced Al matrix composites coating and Al₂O₃-graphene multiphase strengthen composites coating were prepared by cold spraying technology.The microstructure and interface structure,composition and microstructure were analyzed and characterized utilized SEM,XRD,Raman equipment.The preparation of various types of coating corrosion resistant properties was studied in corrosion environment,and the friction and wear behavior was evaluated under the room temperature environment.The main research works are as follows:1?Graphene encapsulated Al powders prepared by in situ reduction method was directly used for cold spraying,obtaining a graphene-reinforced Al matrix composites coating with more compact structure and better performance.Cross-sectional analysis revealed that compared with the pure Al powders,the graphene encapsulated Al powders were more severely deformed,and the resulting was denser coating and its porosity was reduced by over 80%.The hardness of the graphene-reinforced Al matrix composites coating was increased by 40%,and its full immersion time was prolonged by nearly three times in3.5wt.%Na Cl solutions.However,the graphene increases the pitting sensitivity of the Al coating;so,the enhanced corrosion resistance of the graphene-reinforced Al matrix composites coating is mainly attributed to the improvement of its structure densification.Moreover,the results of friction and wear tests show that the graphene-reinforced Al matrix composites coating has higher wear resistance than the aluminum-based coating.2?On the basis of the above work,we mixed 20wt.%Al₂O₃ with graphene encapsulated aluminum powder,and changed the graphene content of coated aluminum powder.Al₂O₃-graphene/aluminum matrix multiphase reinforced composites coating with different composition ratios were prepared on the surface of AZ31B magnesium alloy by low-pressure cold spraying.Corrosion tests show that multiphase reinforced composites coating has better corrosion resistance,higher impedance spectrum resistance fitting value,stronger repassivation capacity;In the corrosive environment,the immersion time of composites coating was at least 20 days and the fitting value of the composites coating was found to be higher by impedance spectrum resistance fitting.It was due to its longitudinally accelerated pitting corrosion mechanism changed to tangential superficial corrosion by graphene.3?The friction and wear behavior of multiphase reinforced composites coating was studied at room temperature.In the process of friction and wear test under different loads,the friction coefficient of Al/0.2G composites coating was lower than that of Al coating,and showed different wear mechanisms.During the test,Al coating produced a large number of abrasive chips,which showed serious abrasive wear and large width of abrasive marks.However,the surface of Al/0.2G composites coating is smooth,without obvious furrow and debris formation,and the width of abrasion marks is smaller.It shows that the self-lubricating property of graphene can improve the wear resistance of the matrix.