Cold Heading Fasteners, Microstructure And Properties Of Ti-3Al-5Mo-4.5V Titanium Alloy

Cold heading fasteners, microstructure and properties of Ti-3Al-5Mo-4.5V titanium alloy

Ti-3Al-5Mo-4.5V titanium alloy (BT16) by the Russian Institute of light alloy development, is a high strength, model of typical alpha + beta phase titanium alloy with excellent mechanical properties and cold heading forming, the alloy of the main semi-finished products is rolling and drawing state 4 ~ 10mm wire and bar diameter, through the cold heading can produce screws, bolts and rivets and other aerospace fastener.

Titanium alloy BT16 characteristics are as follows: a small amount of Al containing more beta stable elements (MO) and beta phase stability coefficient K beta up to 0.8, beta phase content is about 25% ~ 30%, annealing or quenching state has a high plasticity, and solid solution plus aging alloy with higher strength and plastic does not reduce significantly. The main transition of titanium alloy during heat treatment by alpha 'phase, "alpha beta phase and quench aging. Russia uses annealed BT16 alloy wire for cold heading fasteners aviation. The annealing process, microstructure, phase structure and mechanical properties of BT16 titanium alloy have been studied by many scholars both at home and abroad.

The BT16 alloy is used to manufacture the cold deformation strengthening fastener, the working hours and the lowest cost can be used in the indefinite period of 160 degrees C, and the working temperature of the fastening piece which is made by the solid solution aging BT16 alloy is up to 350. Provide a theoretical basis and experimental data for the further research and optimization of BT16 titanium alloy and application and scientific research personnel by using optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of BT16 titanium alloy in the production process of microstructure evolution and heat treatment craft influence on the mechanical properties of alloy wire material.

In the experiment, 6.5mm titanium alloy wire with a diameter of BT16. The preparation process of alloy wire as follows: ingot billet, forging, rolling, open. Firstly, the two vacuum consumable electrode melting furnace to obtain the diameter 210mm BT16 titanium alloy ingot, and cogging, start temperature for 1150, end temperature control in 800 DEG C, after hot forging into diameter 7.5mm wire. Finally, annealing treatment: 780 DEG C for 2h, furnace cooling to 550 DEG C, and then air cooling. The annealed wire surface polishing, for cold heading test.

Chemical composition of BT16 titanium alloy Type Al Mo V C Fe Si Zr O N H Test 2.8 5.2 4.5 0.02 0.05 0.08 0.10 0.08 0.02 0.001 Standard 1.8~3.8 4.5~5.5 4.0~5.0 ≤0.10 ≤0.25 ≤0.15 ≤0.30 ≤0.15 ≤0.05 ≤0.015 To use Leica DM2500M is set through the reflection optical microscopy (OM), JEOL JEM - 2100 transmission electron microscopy (TEM) and jeol JSEM - 7001F type high resolution scanning electron microscopy (SEM) of BT16 titanium alloy wire material and the cold upsetting specimens were observed and analyzed. Chemical etching agent ratio for 2.5mLHf3mLHNO35mLHCl89.5mLH2O. The test results are as follows: (1) BT16 alloy wire annealing system is: 760 ~ 830 degrees C, 2h + 550 C, air cooling. Income wire mechanical properties of sigma B is 870 ~ 935 MPa, and the elongation is 22% ~ 25%, the psi for 62% to 65%, the cold upsetting deformation reached 80%. After annealing microstructure by primary equiaxed alpha phases, small strip alpha phase and intergranular beta phase. (2) solid solution Kong Leng + after aging treatment, microstructure by irregular equiaxed primary alpha phase and precipitation of acicular alpha 'phase of the beta phase composition; solid solution (quenching) + after aging, alloy by axis alpha phase and intergranular beta phase constitution of the duplex microstructure, namely primary alpha phase, intergranular beta phase and beta phase precipitates within the acicular alpha' phase composition.