Microstructure And Performance Control Of Ti-Al Dissimilar Metal Butt Joints By MIG/TIG Double-side Arc Welding-brazing

For the problem of weld appearance,especially the appearance of weld back,and its incompatibility with interface characteristics,MIG/TIG double-side arc(DSA)welding-brazing was proposed to achieve Ti-Al dismillar metal butt welding-brazing joints.The microstructure of joints was studied and the relationship between the interface microstructure and interface properties was analyzed;the weld appearance achieved by MIG/TIG DSA welding-brazing was characterized by "form efficency" and the mechanical properties of the joint were evaluated;the optimum welding parameters were obtained by the compatible regulation of weld appearance and interface characteristics.The main research results are as follows:The system of MIG/TIG DSA welding-brazing was established and the high quality connection of Ti-Al dissimilar metals was realized.The effects of welding parameters on the joint quality were analyzed by the orthogonal test.Then the main controlling factors were identified and they were TIG current,MIG/TIG position and welding speed.For joints of Ti-Al dissmillar metal butt welding-brazing by MIG/TIG DSA welding-brazing,the microstructure of interface depended on welding heat input and the overlap degree of welding heat source.When the welding heat input or the overlap degree of welding heat source was low,TiAl3 was preferentially formed at the interface for its short time staying in high temperature,so the interface was only made of TiAl3;when the welding heat input or the overlap degree of welding heat source was high,the reaction 2Ti+TiAl3?3TiAl was generated at the interface for its long time staying in hightemperature,so the interface was made of TiAl and TiAl3;in terms of morphology,with the increase of welding heat input or the overlap degree of welding heat source,the thickness of interface increased and the lamellar interface was changed to the serrated or rodlike interface.In the thickness direction of the joint,the microstructure of interface was also significantly different.The Ti-Al IMC of the top and bottom was thicker and in form of serration or rod,even that a large number of IMC followed into the weld;the Ti-Al IMC of the middle was thinner and in form of layer or serration.For joints of Ti-Al dissmillar metal butt welding-brazing by MIG/TIG DSA welding-brazing,the interface properties were controlled by the morphology and thickness of Ti-Al IMC.When the interface was thin and in form of serration,the tensile strength without reinforcement was high and the fracture was located inside the weld;when the interface was too thick or in form of layer,the tensile strength without reinforcement was low.The "form efficency" was difined to characterize effects of weld appearance on joint quality.Under the appropriate process parameters,the form efficency was higher than 4%,so the weld appearance was good;when the welding heat input or the overlap degree of welding heat source was too low or too high,the form efficency was low,so the appearance of weld back was bad.The joint quality of Ti-Al dismillar metals butt welding-brazing by MIG/TIG DSA welding-brazing depended on weld appearance and interface properties.However,effects of welding parameters on weld appearance and interface properties were incompatible.The optimum welding parameters under the condition of this study,such as TIG current of 80A-90A,MIG/TIG position of-1mm,welding speed of 15mm/s,TIG position of 0mm-2mm,wire feeding speed of 9.5m/min-10m/min,MIG voltage of 13V-14V and MIG position of-0.2mm-0mm,were obtained by compatible regulation of weld appearance and interface characteristics.Under the optimum welding parameters,the average of tensile strength with reinforcement could reach 256.6MPa and the fracture was located inside the weld.