TC11钛合金搅拌摩擦焊接头微观组织和力学性能研究

Friction stir welding test of TC11 titanium alloy was carried out under different rotational speeds, the microstructures and mechanical properties of the welded joints were analyzed, and the relationships among processing parameters, microstructures and properties of the joints were established. The results show that the SZ is characterized by β transformed microstructure, which contains grain boundary α phase, intragranular lamellar α+β phases and acicular α’ phase. The double strengthening is caused by the fine α phase and α+β phases as well as the presence of α’ phase, which leads to the highest hardness value in the SZ. The retained original α phase and β transformed microstructure are found in the HAZ and TMAZ, while the TMAZ shows the streamlined deformation characteristics. The proportion of β transformed microstructure in these zones is higher when closer to the SZ, and thus the strengthening effect is enhanced. The sizes of α phase and α+β phases increase and the content of α’ phase decreases with the rotational speed ascending, which results in the reduction of hardness value in the SZ. Similar to the law reflected from the hardness test, all the joints fracture in BM after tensile test, the tensile strength of the SZ under different rotational speeds are significantly higher than that of BM, and they decrease with the ascent of rotational speed. Besides, the fine α phase and α+β phases cause the higher elongation of SZ compared with that of BM, meaning that the SZ has good plasticity. With the rotational speed ascending, the elongation of SZ decreases owing to the increase of the sizes of α phase and α+β phases.