Study On The Joining Method Of Carbon Fiber Reinforced Thermoplastic Resin Matrix Composite And 6061-T6 Aluminum Alloy

With automobile lightening and more and more carbon fiber reinforced composites used in automobile,the joining between aluminum alloy and carbon fiber reinforced composites is one of the difficult problems to be solved.In this paper,2mm thick 6061 Aluminum Alloy sheet and 2.3mm thick short carbon fiber reinforced thermoplastic composites sheet respectively joined by adhesive bonding,friction stir spot welding and laser welding is investigated.Strength test,fracture analysis,and metallographic test are adopted to study the feasibility of these three mothods and the factors on the joints’ shape and mechanical properties.By adhesive bonding,Henkel E-120 HP epoxy adhesive and Aluminum Alloy have a good interface binding force,the joint strength mainly depends on the adhesive strength between CFRTP and CFRTP as well as the parent material.The mechanical properties of the joint can be greatly improved by the plasma treatment on CFRTP,and the shear strength of the joint can reach 3500 N.However,the curing time of the glued connection takes up to 7 days.By friction stir spot welding,and the suitable stir head is necessary to weld CFRTP and Aluminum Alloy.The tensile shear strength is between 500N-1000 N,but the surface of the aluminum plate is inevitably left with dents and burrs.The mechanical properties of the backfilled friction stir spot welding are related to the factors such as the pressing time,the holding time,the press-in depth and the speed of the joint.Under the conditions of this experiment,the mechanical properties of backfilled friction stir spot welding joints are poor,and the tensile shear strength is not more than 1000 N.The fracture morphology of the joint can be divided into deformation zone,transition zone,adhesion zone and heat affected zone.The joint mechanism mainly includes mechanical chimerism and adhesion.By laser welding,aluminum alloy surface roughness after shot peening treatment significantly improved,upper surface of aluminum alloy with shot peening treatment is conducive to the absorption of laser welding,so that the power interval becomes larger,while weld fine and uniform.However,the mechanical properties of the joints after shot peening on lower surface of aluminum alloy is decreased.The content of polar bonds increased on the surface of aluminum alloy after anodization,which is beneficial to improve the interface bonding ability of the aluminum alloy and CFRTP,and the joint performance is greatly improved.When the welding power is 1400 W,the tensile shear force of the joint reaches 983 N.After tensile fracture,it was observed that the CFRTP on aluminum alloy increased gradually along the direction of laser welding,and the CFRTP contained short carbon fibers.The central position of the bonded CFRTP at the fracture interface of the aluminum alloy contains a dense hole.There are obvious depressions on the fracture interface of CFRTP.There are obvious directional tears and non-directional tear at both ends of the concave,and there are scattered short carbon fibers in the center of the depression.Through metallographic experiment,it is found that there is little difference in the weld interface between the joints of the alcohol washing treatment and shot peening treatment on the lower surface of aluminum plate,the boundary is relatively smooth,and there are tiny sawtooth shaped mechanical chimeras.With anodic anodization on the lower surface of the aluminum plate,the boundary of the metallographic weld of the joint is wavy,and the wavy at the edge is reduced.By laser welding,aluminum alloy after anodic oxidation surface treatment is welded with 1400 W power.With the increase of the number of welds from 1 to 3,CFRTP melt more,the bonding area on Aluminum Alloy is bigger,the mechanical property of the joint is higher,the fracture mode is the interface fracture.In 3 welds,the tensile shear of joint gets the maximum value 2380 N.When the welds are 4 and 5,the heat input of laser welding increase.The melting of CFRTP is too much,which leads to the decrease of mechanical properties of the base metal.The fracture mode is the fracture of the base material,so the tensile shear force decreases.