Effects of Solution-Treatment and Aging Temperature on Microstructure and Mechanical Properties of TC6 Titanium Alloy

Effects of solution-treatment and aging temperature on microstructure and mechanical properties of TC6 titanium alloy were investigated. The results show that when specimens are solution-treated is at 800 similar to 840 degrees C, primary a and metastable beta phases are form and they grow up with the increase of the temperature, which result in the slight increase of the strength and ductility. The metastable beta phase is also retained after solution-treatment at 880 degrees C though its stability is weakened, while at this moment double yield phenomenon is observed, which is attributed to stress-induced alpha '' orthorhombic martensite in the metastable beta phase. When specimens are solution-treated at 920 similar to 960 degrees C, primary alpha phase dissolves, and a large amount of fine acicular alpha '' orthorhombic martensite precipitate from the metastable beta phase; the strength increases and the ductility decreases,. The alloy is almost composed of coarse alpha' hexagonal martensite after solution treatment above the beta transus, which lead to the decrease in strength and the brittle fracture during tensile test. In terms of different aging temperatures for solution-treated specimens (880 degrees C /1.5 h/WQ), the main microstructural changes are the precipitation of secondary alpha phase from the metastable beta phase and its growth. Compared with solution-treated specimens, the specimens aged at 300 degrees C exhibit higher strength and lower ductility, and it can be seen that some secondary a phase and co phase have precipitated from the beta matrix. As the aging temperature increases to 400 degrees C, the maximum strength as well as minimum ductility is obtained. The specimens aged at 500 degrees C maintain the maximum strength, while the ductility is improved due to the sufficient diffusion of alloying elements. When the specimens are aged at 550 degrees C, they possess the optimum balance of strength and ductility. The primary alpha phase gradually gathers to grow up and the lamellar secondary alpha phase apparently disperses in the beta matrix after aging at 600 similar to 700 degrees C, which lead to the decrease in strength and the increase in ductility.