Effects of cryogenic and annealing treatment on microstructure and properties of friction stir welded TA15 joints

Abstract

Cryogenic treatment is an effective method that can improve the material's performance by changing the microstructure, such as shrinking the crystal lattice. It is usually used in combination with the annealing treatment of the material. In this article, the effects of cryogenic and annealing treatment on the microstructure and mechanical properties of TA15 friction stir welded joints are investigated. The results show that the base material's microstructure has no noticeable change after cryogenic and annealing treatment. However, the microstructure of the stirred zone has an apparent structural transformation. It indicates a selected influence of cryogenic and annealing treatment on the microstructure under severe plastic deformation of the friction stir welding. The weight fraction of the α phase increases from 78.7% to 84.8%, and the aspect ratio of the β phase becomes smaller. These changes improve the mechanical properties of the friction stir welded joints. The ultimate tensile strength and elongation of the TA15 welded joints treated by cryogenic and annealing treatment are 943.4 MPa and 5.5%.