Microstructure And Properties Of Ti/Al Laminated Composites By Ultrasonic Consolidation And Electropulsing Post-treatment

The ultrasonic consolidation?UC?technology uses high power ultrasonic as the energy source,conducts the conversion of sound energy to mechanical energy through the transducer,utilizing the ultrasonic energy field and the thermal field formed by the local temperature rise from the vibration of metal foil,to achieve fast and high quality solid state joining of the same or dissimilar metal materials.In this paper,Al1100 foils and TA1 foils were used as raw materials to prepare Ti/Al laminated composite materials under three different parameter conditions by UC technique.The microstructure and the formation mechanism of the interface after the consolidation process were explored,meanwhile,the peeling,tensile properties and fracture of Ti/Al laminated composites under different process parameters were also discussed.Research was carried out to establish the relationship between process,micorstructure and performance.Based on that,the ultrasonic consolidation samples were post-processed by high energy electro-pulsing treatment?EPT?with different current density,the microstructure and mechanical properties were characterized,and the effect of different current density on the performance of the samples was investigated.Research showed that:The ultrasonic bonding Ti/Al specimen had a good interfacial bonding and no new phase was formed.With the increase of amplitude and positive pressure,the plastic deformation intensified,he degree of interface bending and the density of line welding increased,the dislocation density in the center of the Al layer got lower and lower than that of the cold rolling condition,while the change trend of dislocation density at the interface was opposite.The original Copper,Brass,Goss etc.cold rolling texture components disappeared and recrystallization R texture induced,grain size increased and secondary recrystallization grains appeared.Different oriented texture was formed in the interface region,including the Goss texture,the{111}<110>_TD shear texture and the<111>//TD,<110>//RD oriented texture,which was related to the stress condition of the consolidation process and the influence of the ultrasonic energy.TEM observed that,under low amplitude,the Ti/Al interface was straight without defect,and there were equiaxed grains with sub-grain boundary in the aluminum side,while a large number of dislocation rings on the side of the titanium.There was an orientation relationship at the Ti/Al interface:[210]_Ti//[001]_Al,{002}_Ti//{200}_Al,proving that the dynamic recrystallization grain growth of aluminum enabled metallurgical bonding of the interface.With the increase of amplitude,the interface was sharply bent,amorphous alumina and nano-crystalline Al were distributed continuously along the interface,and the nano-crystalline Ti appeared in the local region.The change of consolidation parameters had little effect on the hardness of Ti layer,and the average value varied between 150¹55HV.With the increase of the amplitude and pressure,the dislocation density increasing in the dynamic recrystallized grain at the interface of the Al layer induced hardness value increasing,while the aggravated recovery degree of the center region induced hardness value decreasing.The interfacial bonding quality was enhanced and the adhesion area,the maximum peeling load and peeling work all got increased.The micromorphology of the peeling fracture showed that the number of dimples increased,the size became smaller,the width and height of the tearing edge increased,and the Al atom in the bottom of the dimple was raised.The results of tensile test showed that with the increase of the amplitude and pressure,the hardening degree of the Ti/Al interface was increased,it was easier to crack during the tensile process,and the ultimate tensile strength was reduced by 23%,while the center region generated recovery,which led to the lengthening of the uniform plastic deformation stage of the sample.The necking of the Al layer,and the small dimples in the fracture interface of the Al and Ti layers,the wavy stripes in the spallation section,and the shear tear morphology were observed in the typical tensile fracture.The work hardening occurred on the Ti side of the spallation zone,and the ratio of the adherent Al atoms decreased significantly compared with the unseparated interface.The morphology and line density of samples after EPT treatment did not change,and there was no inter-diffusion observed between them.With the increase of the current density,the diffraction peak of Al crystal plane narrowed and dislocation density decreased,the overall hardness of the Al layer decreased in varying degrees,and the difference of the hardness between the interface and the center region gradually decreased,the Ti layer had obvious softening only when the current density reaches 90.2A/mm²,the tensile strength of EPT samples was relatively stable,but the fracture strain and the strain-hardening exponent had a significant increase compared with that before the treatment.It was observed in the tensile crack that the interlayer cracking decreased,and the adherent Al atom of the cracking interface increased,which proved that the EPT treatment enhanced the coordinated deformability of the Ti/Al interface.