The preparation method of seamless titanium alloy pipes for aircraft engines includes the following steps:
1) The ingot is forged into an intermediate bar
Titanium sponge ingot with titanium mass fraction of not less than 99.6% after melting is heated to 1000 ~ 1100℃, and after holding heat for 4 ~ 6h, open forging with deformation of 60 ~ 80% is carried out. After the open forging is completed, two rounds of forging are carried out, and no less than five times of upsetting are carried out in each forging, and the bar is rounded after the upsetting is completed.
2) The middle bar is extruded into a tube blank
Drill a through hole suitable for the inner hole of the extrusion tube billet in the center of the middle bar, and cover the outer surface of the middle bar, the inner surface of the through hole and the end with a thickness of 1.0 ~ 2.0mm copper sheet, and then heat it to 700 ~ 750℃ for 1 ~ 3h, and then send it to the extruder to extrude the tube billet, and the extrusion speed is controlled at 50 ~ 55mm/s; The extruded tube billet is heat treated at 650 ~ 700℃ for 30 ~ 45min. After the heat treatment is completed, the residual copper skin on the surface of the tube billet is removed by soaking in HNO3 acid washing solution with a volume concentration of 30 ~ 60%, and the folding, cracks and pits on the surface of the tube billet are removed.
3) Opening and rolling of tube billet
The tube billet with no defects on the outside surface is sent to the two-high billet rolling mill at room temperature for 2 ~ 3 times of billet rolling, and the deformation of each pass is 45 ~ 65%. After the first two billet rolling, the inner hole of the pipe is treated by the boring tool. After the rolling is completed, the oil adhering to the surface of the pipe is removed and cleaned with acid washing solution. Under vacuum conditions of 1.0×10-2 ~ 1.0×100Pa and pressure rise rate ≤2.0Pa/h, heat treatment at 600 ~ 700℃ for 0.5 ~ 2.0h, and then cooling with the furnace to below 200℃ for air cooling, check and remove the surface defects;
4) Intermediate pipe rolling
The tube billet after billet rolling was cold rolled continuously on the multi-roll cold rolling machine for 2 ~ 3 times. The deformation amount of each cold rolling was controlled within 10.0 ~ 30.0%, and the total deformation amount of each 2 ~ 3 consecutive passes was controlled within 40.0 ~ 60.0%. After cold rolling, the oil adhering to the surface of the tube was removed and cleaned with acid washing solution. Then, under the vacuum conditions of 1.0×10-2 ~ 1.0×100Pa and pressure rise rate ≤2.0Pa/h, heat treatment at 650 ~ 700℃ for 0.5 ~ 2.0h, after the heat treatment is completed, the furnace is cooled to below 200℃ for air cooling, and the intermediate pipe is obtained after checking and removing the surface defects;
5) Finished pipe rolling
The intermediate pipe was cold rolled for 2 to 3 consecutive times, the deformation of each cold rolling was controlled within 10.0 ~ 30.0%, and the total deformation was 35.0 ~ 60.0%. After cold rolling, the oil adhering to the surface of the pipe was removed and cleaned with acid wash solution. Then, under the vacuum conditions of 1.0×10-2 ~ 1.0×100Pa and pressure rise rate ≤2.0Pa/h, heat treatment at 500 ~ 550℃ for 1.0 ~ 1.5h, and after the heat treatment is completed, the furnace is cooled to below 200℃ for air cooling to obtain the finished pipe.
