Titanium and its alloys are widely used in aerospace, automotive, chemical and marine industries due to their advantages of low density, high specific strength and good corrosion resistance. TC4 titanium alloy contains 6% α-phase-stable element Al and 4% β-phase-stable element V. It belongs to the typical α + β type two-phase thermally strong titanium alloy of Ti-Al-V series and has good mechanical properties and technological properties. It can be processed into the supply of semi-finished products such as bars, profiles, plates, forgings, etc., and is more and more popular. At present, the domestic research mainly focuses on the high-temperature performance, creep performance and thermal stability of TC4 titanium alloy, and there is relatively little research on how to formulate a reasonable heat treatment process to meet its actual performance. In this paper, it is of great theoretical and practical significance to study the influence of the heat treatment process on the microstructure and mechanical properties of the TC4 alloy sheet by different processes.
Sponge titanium, high-purity aluminium (99.99%) and aluminium-vanadium alloy are smelted in a vacuum water-cooled copper crucible non-consumable electric arc furnace at a certain ratio, electromagnetic field stirring, argon protection. The alloy composition after smelting is (mass fraction,%): 6.29Al, 4.14V, 0.029Fe, 0.023C, 0.19o, and the balance is Ti. In order to ensure the uniformity of the chemical composition of the sample, the TC4 alloy bar was prepared by three times of reflow melting, rolled into a plate with a thickness of 3 mm, and subjected to stress relief annealing treatment at 650 ° C × 4h. The stress-relieved and annealed sheet is processed into microstructure observation samples and tensile samples, and different heat treatments are carried out: annealing (790 ℃ × 3h), solution quenching (980 ℃ × 1h, water cooling), solution ageing ( 980 ℃ × 1h, water cooling + 580 ℃ × 8h, furnace cooling). The heat-treated samples were tested for tensile properties.
After annealing, the TC4 alloy is cooled in the furnace and both phases recrystallize. The α-phase is recrystallized, and small polygonal crystal grains are precipitated in the deformed matrix, and the secondary α is precipitated in the recrystallized β-phase, and the α-phase structure is distributed on the matrix of the β-transformed structure, and the structure is relatively uniform. Since the internal stress is eliminated, the plasticity and tissue stability are improved, but the strength and hardness are reduced. After solution quenching, the aspect ratio of the alpha sheet is reduced, the straight alpha sheet is distorted, and the continuous beta phase boundary is destroyed, forming a thin sheet or basket-like alpha, beta phase from the high-temperature region, rapid cooling is too late Forming the α phase and forming the metastable β phase. The microstructure at room temperature is martensite α '' and metastable β phase. The strength and hardness are improved, but the plasticity is reduced more. After solution aging, the martensite α ”and metastable β phases are partially decomposed and transformed into stable and dispersed α phases and β phases, whose strength and hardness are higher than that of furnace cooling, but the plasticity is lower than that of furnace cooling The overall performance of the alloy has been improved.
没有评论:
发表评论