| Ti/Al dissimilar metal composite structure has become one of the key technologies that need to be broken through due to its light weight and high strength.In this study,the Ti/Al dissimilar metals were welded by hot-diped Al-Si brazing technology and“Friction stir spot welding and brazing”composite welding technology.The process parameters?aluminizing process and welding process?were studied.The influence of the performance was explained by the fracture analysis.The fracture mechanism of the friction stir spot-weld hybrid joint was analyzed.The friction stir spot welding-brazing?FSSW-B?hybrid welded joint and mixing are compared and analyzed.The mechanical properties of Friction Stir Spot Brazing?FSSB?joints were quantified and the auxiliary effects of brazing were quantified.At the same time,the microstructure and interface structure of the joints were analyzed by SEM and EDS,and the formation mechanism of the FSSW-B-joint was studied and the strengthening mechanism of the hybrid joint was revealed.Research indicates:The tensile shear strength of FSSW-B hybrid joints increased first and then decreased with the increase of the rotation speed and holding time of the tool,while the effect of aluminizing time on the hybrid joints showed a gradual decline trend,when the aluminizing time,the rotation speed was 1180 rpm and the holding time was 18 s,the strength of the joint reached a maximum of 15.8 kN,which was 13.9%higher than the current level.The tensile shear resistance of FSSB joints increases first and then decreases with the decrease of Si content or the increase of weld holding time.When the Si content is 8wt%and the holding time is 30s,the strength of FSSB joint reaches 11.5kN.The value provides a feasible reference for the keyless hole spot welding connection of Ti/Al dissimilar metals.The strength of the brazing zone in the FSSW-B hybrid joint accounts for 40.35%of the strength of the hybrid joint.The brazing aid can significantly strengthen the joint.The Ti/Al dissimilar metal friction stir spot welding-brazing hybrid welded joint is mainly brittle fracture during the shearing process.The fracture mode of the joint is mainly the shear fracture along the interface between the two plates and the breakage of the weld nugget.The shear fracture along the interface between the two plates mainly occurs in the brazing zone,and the fracture mainly occurs in the aluminized layer,brazing.After the zone is completely fractured,the spot weld zone begins to fracture,and the fracture mode is mainly the weld nugget breaks off.In the spot welding area of FSSW-B hybrid joint,due to the lubricating effect of Zn on the shaped flowing metal,the Ti/Al dissimilar metal in the bonding zone has a large degree of mixing,and the inter-diffusion phenomenon of Ti and Al is obvious.The Hook interface structure is mainly a discontinuous layer.In the lamellaer TiAl phase,the vicinity of the bonding zone is mainly a dispersed TiAl phase.The TiAl phase is transformed from the primary phase TiAl3,and its distribution state has obvious strengthening effect on the joint,which is mainly represented by the diffusion strengthening of the bonding zone and the strengthening of the Hook interface zone.The interface structure of the brazing zone near the position of the pin is mainly Al substrates/Al0.403Zn0.597inter-metallic compoundlayer/??Al?/Ti7Al5Si12/Ti substrates,and the interface structure away from the pin is mainly Al substrates/Al0.403Zn0.597 inter-metallic compound layer/Zn layer/Al0.403Zn0.597 inter-metallic compound layer/??Al?/Ti7Al5Si12/Ti substrates.During the aluminizing process,Si can significantly inhibit the dissolution of Ti into the aluminizing solution,and form a Ti7Al5Si12 compound layer and a surface aluminized layer on the surface of the titanium alloy,while the Si element is segregated in the aluminized layer to become the diffusion channel of Zn atoms,a large amount of Zn atoms diffuse into the aluminized layer,and exerts a significant solid solution strengthening effect on the aluminized layer,and the strength of the brazing zone is improved.The strengthening mechanism of FSSW-B hybrid joint is mainly TiAl phase strengthening,solid solution strengthening of aluminized layer and brazing assisted strengthening. |
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