Process And Mechanism Research On Ultrasonic-assisted Brazing Between TA15 Titanium Alloy And C_f/Al Composites

The development of aerospace technology puts forward higher requirements for the lightweight and comprehensive performance of materials.The single performance of traditional materials can no longer meet the needs of this field,so composite materials have emerged.Carbon fiber reinforced aluminum matrix composites?C_f/Al?have excellent performance such as high specific strength and stiffness,low thermal expansion coefficient,good dimensional stability,etc.,and have been applied to components such as missiles,rockets,satellites,antennas,missiles,space shuttles,etc..The good strength in high temperature and excellent mechanical properties of TA15 titanium alloy also make it have broad application prospects.The joining of the two materials can be applied to the missile rudder components.As a fluxless brazing technology,ultrasonic-assisted brazing can effectively remove the oxide film on the surface of the aluminum substrate and titanium alloy,and it has been used widely in the welding of the materials with poor wettability.Therefore,this thesis is proposed to study the wettability between the base metal and Zn5Al filler meatl under the ultrasound,and research the process of the aluminum immersion treatments on the surface of TA15.Finally,the ultrasonic-assisted brazing technology is used in the joining between the TA15 and the C_f/Al,and the joint satisfying the strength requirement is obtained.Firstly,the model of the solder pool under ultrasonic excitation was calculated by simulation software.In the analyses of the harmonic response and transient process of the solder pool,it was found that the amplitude of the two sides of the solder pool was 24?m,which was twice of that of the middle position.The simulation of the sound pressure field inside the solder pool also confirmed that the sound pressure value?=40 MPa?on both sides of the solder pool was still twice as large as that of the middle position.Therefore,the base metal samples in the wetting test must be placed on both sides of the solder pool to achieve better wetting effect.The wettability test between the base metal and the filler metal showed that the interface of TA15 can not get wetted or reacted which formed an interfacial bonding layer,but the C_f/Al formed an interfacial bonding layer with the filler metal,it was found that the Al element in the filler metal achieved an effective transition,and the carbon fiber is also incorporated into the filler metal.Since TA15 is difficult to form an interface wetting with the solder,aluminum immersion treatments was used.It was found that a short ultrasonic time can remove oxide film and promote the formation of the interface reaction layer,and the increase of the holding time is beneficial to the growth of the interface reaction layer.The XRD analysis after corrosion of the aluminum-impregnated sample showed that the composition of the interfacial reaction layer was only TiAl₃ intermetallic compound.The titanium alloy of TA15 was welded by the molten aluminum.It was found that the TiAl₃ intermetallic compound in the joint continuously filled the weld area with the prolonging of the holding time,and the joint was completely covered by TiAl₃ when the holding time reached 30 min.The strength of the joint is also increased by the increase of the number of TiAl₃ particles.The shear strength of the joint for 20 minutes reached 120 MPa,which exceeds the shear strength of pure aluminum.Ultrasonic-assisted brazing of the aluminum-impregnated TA15 was carried out by Zn5Al solder,it was found that the increase of ultrasonic time and amplitude can promote the dissolution of the aluminum-impregnated layer to the solder,and the TiAl₃ particles in the interface were incorporated into the solder.The shear strength of the joints under different parameters exceeded 60 MPa,and the shear strength of the amplitude of 6?m for 10 s was the highest,reaching 112 MPa.Ultrasonic-assisted brazing was used to join the aluminum-impregnated TA15titanium alloy and C_f/Al composites.The joints obtained were well bonded.TiAl₃particles and carbon fibers were mixed into the solder on both sides of the joint,forming a composite joint.The increase of the ultrasonic time and amplitude is beneficial to the formation of the composite joint.The shear strength of the joint with an amplitude of 6?m for 10 s reached 70.42 MPa,which met the strength requirements proposed in the background.The fracture location was on the side of the composite interface and the filler was found in the fracture.The XRD analysis showed no carbon fiber was in the filler.