Investigation On Ultrasonic Welding-riveting Technology Of C_f/PA6 Composites

Carbon fiber reinforced composite is being increasingly applied to automotive industry due to its good combination of low density,thermal stability and good mechanical property.The traditional ultrasonic welding joint has high shear strength and low peeling strength,so there is a great hidden danger of safety.Therefore,in order to synergistically improve the shear and peel strength of the ultrasonic welded joints,this study aimed at 30%C_f/PA6 composites,a new type of rivet with flange was developed.The ultrasonic welded-riveted 30%C_f/PA6 composite joints were fabricated.The macro-morphology,cross-sectional structure,failure model,shear strength,peel strength and the galvanic corrosion resistance were investigated.And the welding mechanism and the improvement mechanism of the mechanical properties of the welded-riveted joints were analyzed also.The following experimental results were obtained:The hybrid joining process of ultrasonic welding-riveting consists of five stages:Coulomb friction phase,upper workpieces riveting phase,lower workpieces riveting phase,melting phase and solidification phase of materials on the faying surface.The developed rivets with flange avoided the formation of flash in riveting site,resulted in the excellent mechanical interlocked between the flanges of the rivets and the workpieces and the formation of the weld around the rivets.Therefore,the shear strength,peel strength and energy absorption ability of hybrid joints were improved.Compared with shear strength,ultrasonic welding-riveting process improved the peel strength more significantly.The optimal ultrasonic welding parameters ware 2.5s welding time and 0.38MPa welding pressure.The robust ultrasonic welded-riveted hybrid joints produced with the optimal ultrasonic welding parameters increased the shear strength,peel strength by?29.9%and?39.2%respectively compared with the ultrasonic welded joints.Accordingly,the energy absorption ability of the joints was increased by?87.2%under shear load and?244.6%under peel load respectively also.The improvement of the shear and peel strengths of the hybrid joints attributed the combination effect of the mechanical interlock between the rivet flange and the workpieces and the weld around the rivets.The shape of the rivets had a significant effect on the mechanical properties of the ultrasonic welded-riveted C_f/PA 6 composites.The thicker the tail flange,the higher the shear strength and peel strength of the welded-riveted joints.The notch in the tail flange increased the shear strength of the welded-riveted joints but was not conducive to the improvement of the peel strength.The double-flange rivet can achieve the synergistic improvement of the shear strength and peel strength of the welded-riveted joint.Therefore,it is a new type of rivet that improves the mechanical properties of ultrasonic welded joints.The galvanic corrosion resistance of the welded-riveted hybrid joints and the riveted joints produced with the aluminum anode protection rivets were improved.The improvement mechanism is the preferential corrosion of the aluminum anode.For riveted joints,at least 3%of the weight of the rivet was required to be wrapped around the surface of the rivet to achieve the desired protection effect.For welded-riveted hybrid joints produced with aluminum anode protection rivets,although they exhibited higher corrosion resistance than bare welded-riveted joints without aluminum anode in1-3 weeks of salt water immersion test,the severe joints strength degradation in the fourth week indicated that this method had certain limitations.Therefore,it is necessary to further improve in the future work.