Effect Of Graphene Surface Loaded Metal On Properties Of Iron-based Powder Metallurgy Parts

Lightweight has become the trend of the development of the world automobile industry in recent years,especially the rapid promotion of new energy vehicles has put forward an urgent need for the lightweight of automobiles.Iron-based powder materials are the most widely used materials for automotive powder metallurgy parts.Improving the mechanical properties of iron-based powder metallurgy parts is of great significance for the lightweight of automobiles.Graphene is an ideal reinforcement for metal matrix composites.Considering that Fe is the element that forms carbides and there is a large difference in density with graphene.Therefore,the surface of graphene was modified by developing a suitable electroless copper plating process.The effect of electroless copper plating process and its parameters on the quality of copper plating layer on graphene surface was studied.The relationship between the process properties of iron-based composite powder and the mechanical properties of sintered body and graphene content was also studied.The main work and research results of this thesis are as follows:Firstly,The composition,morphology and structure of the copper plating layer on the surface of graphene under different electroless copper plating conditions were analyzed by means of ultra-deep-field microscopy,SEM,XRD and laser Raman spectroscopy.The results showed that the steps of purification-oxidation-sensitization-activation-reduction-plating were carried out with CH₃COCH₃ as purifying agent,H₂SO₄and HNO₃ as oxidant,SnCl₂ as sensitizer,PdCl₂ as activator and NaH₂PO₂·H₂O solution as reducing agent,and CuSO₄·5H₂O,C₄O₆H₄KNa,C₁₀H₁₄N₂Na₂O·2H₂O,C₁₀H₈N₂,Na₂CO₃ and HCHO are the main components of the electroless copper plating process,which can obtain a higher quality coating on the surface of graphene.It is a suitable process for electroless copper plating on graphene surface.The optimum process parameters for electroless plating are pH=12,plating time 40 min,temperature 50°C.Secondly,The optimum dispersion degree of modified graphene in pure iron powder under different mixing time was analyzed by SEM,and the optimum time for mixing powder was 0.5 h.The effect of the amount of graphene added on the process properties of the composite powder was studied.As a result,the addition of graphene resulted in a change in the process properties of the composite powder compared to the iron-based powder without the addition of graphene.Among them,the bulk density does not change much,and the fluidity and compressibility first increase and then decrease with the increase of graphene content,and there is an optimal amount of graphene added.When the graphene content is 0.15 wt.%,the fluidity and compressibility reached the maximum.Thirdly,The mechanical properties of the graphene-reinforced iron-based composite sintered body were measured by microhardness tester and electronic universal testing machine.The results show that the addition of graphene has a significant effect on the mechanical properties of iron-based composites.With the increase of graphene content,the density of composites shows a downward trend,but the change is not large;The hardness,tensile strength and yield strength of the composites increase first and then decrease with the increase of graphene content,and there is an optimal amount of graphene added.When the amount of graphene was 0.15 wt.%,the hardness,tensile strength and yield strength reach the maximum value,which is increased by 35%,31%and 36%,respectively,compared with the iron-based sintered material without graphene.If the amount of graphene is too large or too small,the impact toughness of the composite will be lowered.When the graphene content is 0.15 wt.%,the impact toughness of the composite reaches a maximum value,which is 60%higher than that of the iron-based powder sintered sample without graphene.Fourth,The microstructure and fracture of the composites were analyzed by metallographic microscope and scanning electron microscope.The mechanism of graphene reinforced iron-based powder materials was discussed.