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ACTA AERONAUTICAET ASTRONAUTICA SINICA ›› 2022, Vol. 43 ›› Issue (2): 624680.doi: 10.7527/S1000-6893.2020.24680

• Special Topic of Advanced Aeronautical Materials Welding/Joining • Previous Articles     Next Articles

Microstructure characteristics of Ti/Al lap joints with pinless friction stir spot welding

LIU Hao, CHEN Yuhua, ZHANG Wentao   

  1. Jiangxi Key Laboratory of Forming and Joining Technology for Aerospace Components, Nanchang Hangkong University, Nanchang 330063, China
  • Received:2020-08-31 Revised:2020-09-10 Published:2020-11-27
  • Supported by:
    National Natural Science Foundation of China (51865035); Jiangxi Province Fund for Distinguished Young Scholars (2018ACB21016); Aeronautical Science Foundation of China (2017ZE56010)

Abstract: The dissimilar metals of Ti6Al4V titanium alloy and 2A12 aluminum alloy were joined by pinless friction stir lap spot welding. After welding, the low melting point aluminum alloy was melted by friction heat. The high melting point titanium alloy remained solid during the welding process and interacted with the aluminum alloy in the liquid state. Finally, at the Ti/Al interface formed a welded joint, and the tensile shear force of the joint reaches 19.20 kN. This paper studied the microstructure changes of the titanium alloy and aluminum alloy, and the characteristic morphology of the joint interface. The results indicate that due to the influence of friction heat and the downward pressure of the stirring head, the structures of the titanium alloy and aluminum alloy at the welding point changed significantly. On the titanium side mainly formed the thermal mechanically affected zone and the base material zone. Three areas formed on the aluminum side:the nugget zone, heat-affected zone, and base material zone. The grain size of heat-affected zone and nugget zone was larger than that of the base material zone, and its structure underwent a process from being heated for a long time to melt to complete melting. A uniform, dense and thin intermetallic compound layer formed at the interface of the lap joint, with the main component being TiAl3. The interface area of the joint changed obviously. There was a uniform interface layer in the middle part, and the layer gradually disappeared as it extended to both sides of the joint with the gathering of Cu at the edge. Compared with that by other Ti/Al lap joint welding methods, the tensile and shear strength of the joint obtained by pinless friction stir spot welding has been significantly improved.

Key words: titanium alloy, aluminum alloy, friction stir lap spot welding, tensile shear load, intermetallic compound

CLC Number: