Interface formation and properties of friction spot welded joints of AA5754 and Ti6Al4V alloys

• Interface formation and properties of friction spot welded joints of AA5754 and Ti6Al4V were investigated.
• The joint interface was mainly composed of a TiAl3 intermetallic layer
• Minimizing the brittle intermetallic phase was demonstrated to be critical to achieve high strength Ti/Al dissimilar joints
• Reaction controlled mechanism were successfully used to express the TiAl3 growth kinetics

This study aims to understand the influence of dwell time on the microstructure of the interface and lap shear strength of friction spot welded joints of AA5754 and Ti6Al4V alloys. The interface reaction layer consists mainly of TiAl3 intermetallic compound. It was noticed that dwell time significantly influences the diffusion process during the friction spot welding, thereby modifying the thickness of the interface and thus affecting the mechanical performance of the joints. Minimizing or optimizing the brittle TiAl3 phase was demonstrated to be the key issue to achieve high strength Ti/Al dissimilar joints. The intermetallic compound growth kinetics was also examined showing that an incubation time of approximately 2.7 s is necessary before it nucleates at the Ti/Al interface and grows laterally to form a continuous layer. Afterwards, the TiAl3 layer grows toward the Al during thickening with a corresponding growth rate of k = 2.92 × 10− 7 m/s. These results are critical to understand the microstructure–properties relationship and contribute with additional improvements on the joint performance.

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