Rolling Process Of High Strength TA18 Titanium Alloy Pipe For Aviation

TA18 alloy, Ti-3A1-2.5V alloy, is a low-alloyed near-α titanium alloy, which not only has excellent room temperature, high temperature mechanical properties and corrosion resistance, but also has good cold and hot processing properties and welding performance. Therefore, this alloy has become the material of choice for aerospace piping systems. With the continuous development of the aerospace industry, the demand for TA18 alloy pipes with excellent performance continues to grow.
At present, domestic production of TA18 pipe with a strength of 860MPa through cold rolling technology is not yet mature. Tubes are prone to cracking during the rolling process, and the high strength and high plasticity of the finished tubes are difficult to guarantee at the same time. Therefore, domestic demand for high-strength and high-toughness TA18 alloy tubes has always been dependent on imports.
Researchers have tried to produce TA18 pipes of different specifications to study the effects of the ratio Q of the internal diameter reduction ratio to the wall thickness reduction ratio, the cumulative deformation rate ε, and the annealing temperature on the microstructure and properties of the finished tube, thereby optimizing the alloy processing technology , To provide technical guidance and reference for the localization of high-strength and high-toughness TA18 alloy tubes.
The experimental raw materials are made of first-grade sponge titanium, A1-V intermediate alloy, Al beans and Al foil, which are melted by vacuum consumable arc furnace for many times to make Φ430mm TA18 alloy ingot. The ingot is blanked in the β zone, finely forged into a Φ130mm bar billet in the α + β two-phase zone, and then extruded into a Φ45mm × 8mm alloy tube billet on a 2500t horizontal extruder. Through multi-pass cold rolling and surface treatment on two-roll LG and three-roll LD rolling mills, and then annealing in a vacuum annealing furnace, it is prepared into Φ25mm × 1.8mm, Φ22mm × 1.6mm, Φ20mm × 1.5mm, Φ18mm × Finished pipes of 10 specifications of 1.3mm, Φ16mm × 1.2mm, Φ14mm × 1mm, Φ12mm × 0.9mm, Φ10mm × 0.7mm, 8mm × 0.6mm and Φ6mm × 0.5㎜.
The room temperature tensile test of the pipe is carried out on the new Sansi 10t testing machine, the test standard is ASTM E8 M. After the pipe sample is ground and polished, the axial section of the sample is corroded with an etchant, and the erosion time is 15-20s. Observe the microstructure of the sample with an optical microscope. The results showed that:
(1) When the cumulative deformation rate is not more than 55%, and the ratio of the reduction ratio of the inner diameter reduction ratio to the wall thickness reduction ratio is controlled at 0.53 to 1.14, the TA18 experimental pipe can be smoothly rolled on the two-roll mill, inside and outside No cracks on the surface.
(2) The strength of the processed state of the TA18 experimental pipe gradually increased with the increase of the deformation rate, but the influence of the deformation rate on the plasticity of the pipe has a critical value. When the deformation rate is lower than 44%, the deformation rate has little effect on the plasticity of the processed state of the pipe; when the deformation rate exceeds 44%, the plasticity of the pipe gradually decreases with the increase of the deformation rate.
(3) With the increase of annealing temperature, the strength of TA18 test tube gradually decreases, the elongation rate gradually increases, and the work hardening effect due to different deformation rates also decreases. When the deformation rate is 30% to 80%, recrystallization annealing can almost completely eliminate the influence of the deformation rate on the mechanical properties of the pipe. However, when the deformation rate is too small (23%), the plasticity of the tube recrystallization state is still low, which is caused by the uneven distribution of the recrystallization grain size of the tube.
(4) When the deformation rate is 51%, the annealing system is 550 ℃, 90min, the mechanical properties of Φ12mm × 0.9mm TA18 test tube are: UTS = 920MPa, YS = 755MPa, El = 14%.