Titanium and titanium 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. GR5 titanium alloy contains 6% α-phase stabilizing element Al and 4% β-phase stabilizing 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. , Can be processed into bar, profile, plate, forging and other semi-finished products, more and more popular.
At present, the domestic research mainly focuses on the high temperature performance, creep performance and thermal stability of GR5 titanium alloy, and there are few studies on how to formulate a reasonable heat treatment process to meet its actual performance. Through the heat treatment of GR5 titanium alloy plate by different processes, it is of great theoretical and practical significance to study the influence of heat treatment process on the structure and mechanical properties of materials.
Sponge titanium, high-purity aluminum (99.99%) and aluminum-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 titanium alloy rod was prepared by three times of reflow melting, rolled into a 3mm thick titanium plate, and subjected to stress relief annealing treatment at 650°C×4h. The stress-relieved and annealed plates are 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 aging ( 980℃×1h, water cooling +580℃×8h, furnace cooling). The heat-treated samples were tested for tensile properties.
After annealing, the GR5 titanium alloy is cooled in the furnace and recrystallization occurs in both phases. 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. 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 α-sheet decreases, the straight α-sheet is distorted, and the continuous β-phase boundary is destroyed, forming a thin sheet or basket-like α, β-phase from the high-temperature region for rapid cooling. 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, titanium The overall performance of the alloy is improved.