Cold rolled machinability of TC6 titanium alloy plate

TC6 titanium alloy plate is a martensitic Ti-Al-Mo-Cr-Fe-Si system of α + β two-phase heat-strengthened titanium alloy with good comprehensive performance, its nominal composition is Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si, and its α / β transition temperature ranges from 960 to 1000℃. In addition to the advantages of ordinary titanium alloy such as high specific strength and good corrosion resistance, the alloy also has good comprehensive mechanical properties at room temperature and high temperature, and the service temperature can be as high as 450°C. It is often used in the manufacture of aero-engine blades, turbine disks and other important parts, and it can also be used in the manufacture of aircraft spacer frames, joints and other parts. A lot of work has been done domestically on the processing technology and performance optimization of TC6 titanium alloy forgings, castings, tubes and bars, etc., while less research has been done on TC6 alloy plates. The researchers have determined the basic process parameters of cold rolling processing of TC6 plates through the control of cold rolling processing process of TC6 plates, and studied the cold rolling processing performance of TC6 plates.

The experimental TC6 titanium alloy ingot is obtained by three times melting in vacuum self-consumption electric arc furnace, and its β-transition temperature is 975-985 ℃, and the specific chemical composition is (wt.%): Al6.2, Mo2.5, Cr1.4, Fe0.41, Si0.29, O0.10, Zr<0.01, C<0.01, N<0.01, and Ti remainder. The experimental TC6 ingots were opened in the β-phase region and forged into slabs in the α+β two-phase region. Slabs were hot rolled above the β-transition temperature to open billets, rolled to 3.5 mm in the α+β two-phase zone, and then cold rolled for work-hardening experiments after intermediate annealing and pickling. Processing rate of every 5% increase, from the head of the plate cut 200mm long piece of experimental material, the remaining plates continue to roll, so repeatedly rolled, sampling, until the plate edge cracks or surface cracks. Then the cut 200mm experimental material with different processing deformation was tested, and the thickness, width, edge crack, organization and mechanical properties of the experimental plates were tested.

The above experimental microstructure was observed on an Axiovert 200 MAT optical microscope and the mechanical properties were tested on an Instron 5885 tensile testing machine. The test results are as follows:
(1) From the cold rolling work hardening curve, it can be found that the tensile strength and yield strength increase with the increase of processing rate, while the elongation gradually decreases, which is mainly due to the increase of dislocation density with the increase of the processing rate of cold rolling and the intensification of work hardening. When the processing rate reaches about 27%, the tensile strength and yield strength curve tends to level, indicating that it enters the difficult deformation stage.
(2) TC6 titanium alloy plate maximum cold rolling processing rate can reach 30.3%, at this time the elongation of the material fell to 5.8%, the observation of the surface of the plate began to appear wrinkles and convexity, the edge of the cracks. Cold rolling processing rate of 30.3% when the width of the spread is 20mm.