Study On Promotion Of Interface Adhesion By Ultrasonic Vibration For Adhesively Bonded CFRP/Al Alloy Joints

Adhesively bonded carbon fiber reinforced-polymer composites(CFRP)/aluminum alloy joint is more and more widely used in the automobile industry,and the interface bonding strength of the adhesive joint is one of the important factors that determine the strength of the whole joint.The insufficient interface bonding strength limits the larger application of CFRP and aluminum alloy materials in the automobile lightweight process.The traditional adhesive bonding processes of CFRP / Al alloy are to treat the surface of the adherend before bonding,and the effect of the surface treatment for the complex structure is not good.The use of ultrasonic vibration to strengthen the interface bonding of joints is a new process that significantly increases the strength of whole joints.However,the new process is not mature and needs to be further optimized.And the mechanism of ultrasound significantly improving the strength of the interface bonding is not clear,so it is urgent to study the influence by ultrasound on the micro bonding and chemical bonding at the bonding interface to explain the reason of ultrasound significantly improving the joint strength.Firstly,the process was optimized,including sandpaper grinding in pretreatment and the main parameters of the ultrasonic vibration.The results showed that the bonding strength was the highest when the 400 mesh sandpaper was used to sand the Al adherend.After the parameters of the main variables influencing the ultrasonic vibration were further optimized by the orthogonal test,the bonding strength and stability increased by 40% and 60%,respectively.The failure mode of joints without ultrasonic action was interface failure.However,it was no longer a single interface failure and the adhesive layer tears with ultrasonic action.Ultrasonic vibration improves the interface bonding between Al palte and the adhesive layer,which significantly improves the strength and stability of joints.Then,the mechanism of ultrasonic vibration strengthening interface bonding was explored from the point of view of interface microphysical bonding.The interface morphology was characterized by Field Emission Scanning Electron Microscopy.The results showed that the application of ultrasonic vibration can significantly reduce the micro pore defects at the interface between the adhesive and the adherend,and make the micro bonding more compact.The promoting effect of ultrasonic vibration on penetration of the elements at the interface was studied by Energy Dispersive X-Ray Spectrometer.The results showed that the ultrasonic vibration enhanced the penetration of elements at the bonding interface and made the bonding quality more reliable.And the reason that ultrasonic can less pore defect at interface was studied.It was found that the contact angle of adhesive on CFRP laminate and Al adherend were reduced by 16.3% and 14.8% by ultrasonic vibration,respectively,which showed that the ultrasonic vibration improves the wettability of adhesive on adherend in the bonding process.Then the promoting effect of ultrasound on the groove-filling at interface was studied.The results showed that the ultrasonic vibration induced the flow and penetration of the adhesive on the uneven surface of the adherend at the bonding interface,thus promoting the mechanical properties at the interface.Finally,the promoting effect of ultrasonic vibration on the chemical bonding at the bonding interface was studied.The change of the binding energy of the main elements at the interface was characterized by X-Ray Photoelectron Spectroscopy.Under the application of ultrasonic vibration,a chemical reaction occurred to form chemical bonds.The high-frequency impact between the adhesive and the Al adherend at the interface caused by the ultrasonic vibration strengthened the attack of electrophilic Al+ on O-of the epoxy group,so the opening of the epoxy group was promoted to allow Al to react with-O-C to form Al-O-C.In this thesis,based on the engineering background of extensive application of CFRP and aluminum alloy materials,aiming at the problem of insufficient interface bonding strength of current adhesively bonded CFRP/Al joint,the new technology of ultrasonic strengthening bonding interface was optimized,and the mechanism of ultrasonic strengthening interface bonding was analyzed systematically.This study have important reference significance for the continuous optimization of the new technology and for the further study of interface bonding mechanism.