Cold rolling machinability of TC6 titanium alloy sheet

TC6 titanium alloy plate is a kind of martensiform Ti-Al-Mo-Cr-Fe-Si system α+β two phase thermal strength titanium alloy, whose nominal composition is Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si, and the α/β transition temperature is in the range of 960 ~ 1000℃.In addition to the advantages of high specific strength and good corrosion resistance of ordinary titanium alloy, the alloy also has good comprehensive mechanical properties of room and high temperature. The operating temperature can be as high as 450℃. It is often used in the manufacture of important components such as aero-engine blades and turbine discs, and can also be used in the manufacture of aircraft frames, joints and other parts. Domestic of TC6 titanium alloy forgings, castings, optimizing the processing technology and properties of tube rod has done a lot of work, and less on the study of TC6 alloy plate, cold rolling process of the board of scientific research personnel of TC6 control, determine the basic process parameters of TC6 plate cold rolling, cold rolling process performance of TC6 plate is studied.

The TC6 titanium alloy ingot was obtained by three times smelting in a vacuum consumable arc furnace. The β transition temperature of the ingot was 975 ~ 985℃. The concrete fraction was (wt.%) :Al6.2, Mo2.5, Cr1.4, Fe0.41, Si0.29, O0.10, Zr < 0.01, C < 0.01, N < 0.01, Ti allowance. In the experiment, the blank of TC6 ingot was opened in β phase zone, and the blank was forged into α+β phase zone. After hot rolling above β transition temperature, the slab was rolled to 3.5mm in α+β two-phase zone. After intermediate annealing and pickling, the cold-rolling work hardening experiment was carried out. When the processing rate increases by 5%, a 200mm long piece of experimental material is cut from the head of the plate, and the remaining plate continues to be rolled, so repeated rolling, sampling, until the edge crack or surface crack of the plate appears. Then the cut 200mm experimental materials with different processing deformities were tested to test the thickness, width, edge crack, structure and mechanical properties of the experimental board.

The microstructure of the experiment was observed by Axiovert 200 MAT optical microscope, and the mechanical properties were tested by Instron5885 tensile tester. The test results are as follows:

(1) From the work hardening curve of cold rolling, it can be found that the tensile strength and yield strength increase with the increase of the processing rate, while the elongation gradually decreases. This is mainly because the dislocation density increases with the increase of the processing rate of cold rolling, and the work hardening intensification. When the processing rate reaches about 27%, the curve of tensile strength and yield strength tends to level, indicating that it enters the stage of difficult deformation.

(2) The maximum cold-rolling processing rate of TC6 titanium alloy plate can reach 30.3%. At this time, the elongation of the material decreases to 5.8%. It is observed that the surface of the plate begins to wrinkle and protrude, and the edge cracks appear. The width is 20mm when the cold rolling processing rate reaches 30.3%.