Research On Improving Bonding Strength Of CFRP And Aluminum Alloy By Plasma Pretreatment

Carbon fiber reinforced polymer(CFRP)has excellent properties such as high specific strength,fatigue resistance,corrosion resistance,energy absorption,shock absorption and so on,and is widely used in the fields of aerospace,automobiles and the like.However,the application range of CFRP is limited due to the defects of low surface energy,poor wettability,low bonding strength and the like caused by the resin and surface contaminants of the surface layer.Therefore,in order to solve the problem of poor bonding performance of CFRP,the surface of CFRP is often pretreated before bonding.An atmospheric pressure dielectric barrier discharge plasma jet was proposed to improve the adhesion of CFRP materials.A self-made dielectric barrier electrode device was used to generate plasma.The principle of plasma generation,characteristics of plasma jet and discharge parameters were discussed.It was determined that the use of high purity helium and oxygen as discharge gases at atmospheric pressure resulted in a uniformly stable plasma jet suitable for CFRP modification.The discharge voltage for surface pretreatment of CFRP was determined to be 3.74 k V,and the oxygen mixing ratio was between 0% and 1.5%.The influence of plasma on the physical and chemical properties and wettability of CFRP surface was analyzed.It is found that plasma can etch the surface of carbon fiber composites and change its chemical composition,which can improve the surface wettability rapidly.Performing surface pretreatment through pure helium plasma jet to determine that the process parameters are 10mm/s,the treatment distance is 3mm,and the treatment times are 10.Considering the problems of low concentration of active particles and low modification efficiency in single gas discharge,in order to further improve the modification effect,plasma jet was produced by mixing different proportion of oxygen into high-purity helium to pretreat the surface of CFRP.The effects of different proportion of oxygen on jet length and jet temperature were determined.The optimum proportion of oxygen was 0.75%.The results show that mixed oxygen plasma can further improve the wettability of the surface of CFRP.In order to determine the process parameters of plasma treated CFRP and the effect of plasma on the bonding properties of CFRP before and after oxygen mixing,the bonding strength of CFRP and aluminum alloy joints treated by plasma jet with different process parameters and different oxygen mixing ratios were tested.The results show that the failure mode changes from untreated interface failure to cohesive failure,and the bonding strength of CFRP is further improved by oxygen mixing plasma compared with pure helium plasma.In addition,due to the fact that the bonding structure can be used in a wet and hot environment,the wet and hot aging test of the bonding joint is carried out to evaluate the durability of the bonding joint in the wet and hot environment.