An effect of the rotation speed on microstructure and mechanical properties of the friction stir welded 2060-T8 Al-Li alloy

In the present paper, a study of the 2060-T8 Al-Li alloy friction stir welded using the rotation speed range of 600–1000 rpm at a constant welding speed of 300 mm/min is summarized. The effect of rotation speed on microstructure and mechanical properties of the joint was investigated. The results show that with the rotation speed increasing, material in the thermo-mechanically affected zone (TMAZ) on the retreating side (RS) is extended increasingly to the weld nugget zone (WNZ). The microhardness of the WNZ is much lower than that of the base material (BM), consequently all joints were fractured in the WNZ. The maximum tensile strength of the joint is 440 MPa. The maximum strength was achieved at the rotation speed of 800 rpm. However, the maximum elongation is only 2.8%. A model is constructed to explain the mechanism of initiation and propagation of the crack in a joint of the considered material systems. Compared to the BM with various precipitates, only small amounts of T1, β′ and δ′ were detected in the WNZ. This leads to the reduction of mechanical properties. It was established that the grain refinement and the dislocation strengthening are the dominant strengthening mechanisms for the WNZ.