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Sheet metal forming limit diagram (FLD) is a comprehensive index used to evaluate sheet metal formability. In this paper, the forming limit curves of GH605 sheet materials with 0.2 mm and 2.5 mm thickness under three different heat treatment conditions were obtained by numerical simulation of bulging. Then, the simulated forming limit results of the three materials with 0.2 mm thickness were compared with the experimental results. The results show that the simulated FLDs can be in good agreement with the experimental FLDs. The influences of work hardening index (n value) and anisotropy index (r value) on the forming limit are analysed from the view of material property difference. The comprehensive simulated and experimental results show that the formability of the sheets after the two kinds of solution treatment is significantly better than that of the annealed sheets. The forming limit curve increases with the increase of n value and r value, and the influence of n value on the forming limit curve is more significant than that of r value. The forming limit diagram established by numerical simulation can provide a theoretical basis for material development and process selection.

In order to study the effect of hole extrusion strengthening process on the fatigue performance of Ti2AlNb alloy, a simulation analysis model of residual stress of hole strengthening process was established. The distribution law of surface residual stress and strengthening mechanism after hole extrusion process were discussed. In this work, the hole extrusion experiments were carried out. The high temperature and low cycle fatigue performance of the compressed and un-compressed specimens were tested respectively. Meanwhile, the microstructure characteristics of the fatigue fracture of the two specimens were compared. The results show that the hole extrusion process can produce a strong residual compressive stress layer around the small hole, which effectively delays and inhibits the initiation and propagation of fatigue cracks, and significantly improves the high temperature and low cycle fatigue performance of Ti2AlNb specimens.

The effect of grain size and crystal orientation on the tensile deformation behavior of Ti-3Al-4.5V-5Mo titanium alloy was studied by using scanning electron scanning electron, X diffraction instrument and theoretical calculation. The results of tensile test of the wires in different states have verified that there are obvious macroscopic yield points on true stress-true strain curves of 720-840 ℃ annealing structures, and then a stress drop occurs. When the crystal orientation of α phase all shows fiber texture of different wires, the grain size determines the macroscopic yield stress of the wire. The larger the grain size is, the lower macroscopic yield stress is. Compared with fiber texture, the existence of fiber texture of α phase generates larger plastic deformation in α phase, the internal stress in β phase, increased, and the macroscopic yield strength of the alloy decreased.

The effect of surface integrity on the hot fatigue performance of Ti2AlNb alloy was investigated. A turning process was used to prepare the standard specimens for hot fatigue tests. The surface integrity characterization and axial fatigue tests were performed. The results show that the influence of surface roughness on the hot fatigue performance of the Ti2AlNb alloy is a secondary factor. The compressive residual stress and enhanced microhardness in the surface layer has a significant effect on the hot fatigue life and they are dominant in the hot fatigue behavior of the Ti2AlNb alloy. Through the investigation on the characteristics of the fatigue fractures, the fatigue propagation process was significantly suppressed because of the strong residual compressive stress and microhardness distribution on the surface layer of the Ti2AlNb specimen. [ABSTRACT FROM AUTHOR]