Joint Performance Improvement Method Applicable To Laser Direct Joining Of CFRTP And Al Based On The Surface Modification

Carbon fiber reinforced thermoplastic composites(CFRTP)not only have the advantages of light weight,high strength,but also their resin matrix have the characteristics of repeated melting and consolidation,which is easy to realize the formed CFPTP parts and aluminum alloy(Al)and other metal parts under local heating conditions for connection.Lasers have a concentrated energy density and can heat up quickly,which is an important way to realize fast connection between CFRTP and metal.However,the physical and chemical properties of CFRTP and metals are very different,and the reactivity and affinity with CFRTP resin matrix and metals is weak.As a result,the bonding strength of CFRTP and metal laser direct joint is low,which is an urgent problem to be solved in engineering application of CFRTP and metal laser direct joining technology.To solve this problem,the performance enhancement of CFRTP/Al laser direct joining is studied by enhancing the interface reactivity and increasing the contact area between CFRTP and Al.The main research contents and conclusions are as follows:(1)The enhancement mechanism of silane coupling agent to CFRTP/metal laser direct joining interfaces was studied.And the bonding process of active group of silane coupling agent and CFRTP was analyzed,which is affected by temperature.We found that the enhancement effect is mainly related to the bonding effect of CFRTP and silane coupling agent and the thermal stability of the active group.KH570 with better thermal stability may obtain better interface enhancement effect.(2)The variable power experiments of laser direct joining between CFRTP and Al treated with silane coupling agent were carried out.The effects of silane coupling agents with different active groups on the interfacial bonding were investigated at different interfacial bonding temperatures.The results show that improving the physical entanglement between silane coupling agent and CFRTP is the key to enhance the strength of the joint.When silane coupling agent has long chain active groups and can self-aggregate to form a crosslinking structure which is stable at high temperature,strong physical entanglement and good joint strength can be obtained.(3)Laser direct joining experiments on CFRTP and Al which has many microgrooves on its surface,and tensile shear fracture simulation of the joint were carried out.The bearing capacity of the microstructural characteristics in the shear process of the joint was analyzed.And the enhancing effect of microgroove depth-width ratio and groove spacing on interface bonding of laser direct joining.The results show that the microstructure of A1 surface significantly improves the shear strength of the joint.Compared with the untreated joint,the maximum shear strength is increased by to about 8.27 times.In a certain range,the enhancement effect increases first and then decreases with the increase of the depth-width ratio of the microstructure,and decreases with the increase of the groove spacing.(4)In order to further improve the joint performance of CFRTP and A1 laser direct joining,a synergistic reinforcement process considering both mechanical anchoring and physical and chemical interaction was proposed in this paper,That is,the CFRTP/Al interface synergistic enhancement process,which uses silane coupling agent to treat A1 surface to improve interface reactivity,and uses A1 surface prefabricated microstructure to increase interface contact area.Experiments were carried out to analyze the effect of this method on interface bonding and joint strength improvement.It was found that the shear strength of the joint treated with the synergistic reinforcement technology was up to about 38.2 MPa,and the joint strength was increased by about 9.32 times compared with the untreated joint.The above research proposed a highly applicable CFRTP/Al interface synergistic strengthening process,thus further improving the joint performance.The research work has reference value for improving the connection strength between CFRTP and metal dissimilar material structures.