Microstructures and Mechanical Properties of Ti-6Al-4V Alloy Processed by Multi-Process

To understand the relationship among the processes, mechanical properties and microstructures of the Ti-6Al-4V alloy processed by the different combinations of ring tolling, bulging and different heat treatments, the correlation between the alpha- and beta-phase morphologies, the strength and plasticity properties of tensile tests at ambient temperature and elevated temperature were investigated. Researches indicate that adding the second procedure, bulging, is necessary after the rolling process under the condition of the appropriate heat treatment. The tensile properties are closely related to the size and the volume fraction of the primary alpha-phase, the size and the thickness of the secondary alpha-phase. Furthermore, the bulging after heat treatment mainly affects firstly the size of primary alpha-phase, and the compositions of alpha- and beta-phase, secondarily the size and the quantity of the secondary platelet alpha-phase. The elongation decreases when the primary alpha-phase transforms from the small equiaxed to the thick multilateral shape. As the volume fraction of the primary alpha-phase decreases and the proportions of both untransformed beta structure and the dispersed secondary alpha-phase increase, the alloy strength increases. Fracture modes of the elevated temperature tensile fracture samples were determined as the ductile fracture. Poor plastic deformation ability is attributed to the casting micro-defects on the fracture surface.