TA18 alloy, i.e. Ti-3A1-2.5V alloy, is a low-alloyed near-alpha titanium alloy, which not only has excellent room and high-temperature mechanical properties and corrosion resistance, but also has good cold and hot working properties as well as welding properties. As a result, the alloy has become the material of choice for aerospace piping systems. With the continuous development of the aerospace industry, the demand for TA18 alloy tubes with excellent performance continues to grow.
The raw materials used in the experiment are first-grade titanium sponge, A1-V intermediate alloy as well as Al beans and Al foils, which are melted in vacuum self-consumption electric arc furnace for several times to make Φ430mm TA18 alloy ingots. The ingot was opened in β-zone, precision forged into Φ130mm bar billet in α + β two-phase zone, and then extruded into Φ45mm×8mm alloy pipe billet in 2500t horizontal extruder. Through multi-pass cold rolling and surface treatment in two-roll LG and three-roll LD mills, and then annealed in a vacuum annealing furnace, it is prepared into Φ25mm×1.8mm, Φ22mm×1.6mm, Φ20mm×1.5mm, Φ18mm×1.3mm, Φ16mm×1.2mm, Φ14mm×1mm, Φ12mm×0.9mm, Φ 10mm×0.7mm, 8mm×0.6mm and Φ6mm×0.5mm.
The room temperature tensile property test of the pipes was carried out on a new Sansi 10t testing machine, and the test standard was ASTM E8 M. After the pipe specimens were ground and polished, the axial section of the specimens was corroded using an etchant, and the erosion time was 15-20 s. The microstructures of the specimens were observed with an optical microscope. The test results show that:
(1) when the cumulative deformation rate is not greater than 55%, and the inner diameter reduction rate and wall thickness reduction rate of the ratio of Q value control in 0.53 ~ 1.14, TA18 experimental pipe in the two-roll mill can be rolled smoothly, the inner and outer surfaces without cracks.
(2) TA18 experimental pipe processing state strength with the deformation rate increases gradually, but the deformation rate of the pipe plasticity of the impact of the existence of a critical value. When the deformation rate is lower than 44%, the deformation rate on the plasticity of the pipe processing state has little effect; when the deformation rate of more than 44%, the pipe plasticity with the deformation rate increases gradually decreased.
(3) With the increase of annealing temperature, the strength of TA18 experimental pipe gradually decreased, elongation gradually increased, while due to the deformation rate caused by the different work hardening effect is also reduced. When the deformation rate of 30% to 80%, recrystallization annealing can almost completely eliminate the effect of deformation rate on the mechanical properties of the pipe. But when the deformation rate is too small (23%), the plasticity of the pipe recrystallization state is still low, which is due to the deformation rate is too small pipe recrystallization grain size distribution is not uniform and caused by.
(4) When the deformation rate is 51% and the annealing regime is 550°C for 90 min, the mechanical properties of Φ12mm×0.9mm TA18 experimental pipe are: UTS=920MPa, YS=755MPa, El=14%.
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