A method for preparing large-size Ti6Al4V titanium alloy bars

Abstract

The present invention relates to a method for preparing large-size Ti6Al4V titanium alloy bars, comprising the following steps: S1, large-deformation blank forging in the β single-phase region: a total of 2 forging fires, each of which undergoes large-deformation upsetting and forging, followed by air cooling. S2, large-deformation diagonal drawing and stretching forging in the α+β two-phase region: a total of 1 to 2 forging fires, each of which undergoes large-deformation diagonal drawing and stretching forging, followed by air cooling. S3, small-deformation rapid upsetting and stretching forging in the β single-phase region: a total of 1 forging fire, the blank undergoes rapid upsetting and forging, followed by air cooling after forging; S4, small-deformation direct drawing forging in the α+β two-phase region: a total of 3 to 5 forging fires, the blank undergoes direct drawing and forging, followed by air cooling after forging, to obtain large-size Ti6Al4V titanium alloy bars. This method optimizes the hot working process and flow, reduces the number of forging fires, and improves the uniformity of the bar structure and the consistency of performance.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal processing and relates to a method for preparing large-size Ti6Al4V titanium alloy bars. Background Art

[0002] Ti6Al4V titanium alloy is currently the most widely used and researched alloy in the titanium alloy industry. It boasts excellent corrosion resistance, high specific strength, good toughness, and weldability, among other advantages. It is widely used in the aerospace industry for critical structural components such as aircraft pylons, wall panels, and fasteners. However, domestically produced large-scale Ti6Al4V bars suffer from numerous forging cycles, long processing cycles, and high costs, making them unable to meet the high reliability, stability, and cost requirements of civil aircraft. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and propose a method for preparing large-size Ti6Al4V titanium alloy bars. The method optimizes the hot working technology and process, reduces the number of forging fires, improves the uniformity of the bar structure and the consistency of performance, and cuts samples from the bar for hot deformation to verify the corresponding structure and performance of the bar after subsequent deformation. Ultimately, it can successfully produce low-cost, high-quality Ti6Al4V titanium alloy bars for civil aircraft with a tensile strength exceeding 949 MPa and a diameter of 200 mm ≤ Φ ≤ 450 mm.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing large-sized Ti6Al4V titanium alloy bars, characterized by comprising the following steps:

[0006] S1, β single phase region large deformation billet forging:

[0007] There are 2 forging passes in total, each pass is subjected to large deformation upsetting forging, and air cooling after forging.

[0008] S2, α+β two-phase region large deformation diagonal drawing forging:

[0009] There are 1 to 2 forging fires in total, and each fire is a large deformation diagonal stretching forging, and air cooling after forging.

[0010] S3, β single phase region small deformation rapid upsetting forging:

[0011] There is one forging fire in total, the blank is quickly upsetting and forged, and air-cooled after forging;

[0012] S4, α+β two-phase region small deformation direct drawing forging:

[0013] The forging process is performed for 3 to 5 times in total. The billet is straight-draw forged and air-cooled after forging to obtain large-size Ti6Al4V titanium alloy bars.

[0014] Furthermore, the preparation method further comprises sample upsetting forging:

[0015] The forging process is repeated once. The bar obtained in step S4 is selected to cut a sample, heated to the temperature of the α+β two-phase region and kept warm, and then subjected to upsetting forging after being taken out of the furnace. The sample is then air-cooled after forging.

[0016] Furthermore, the heating temperature of the sample upsetting forging is 940° C. to 980° C., the forging ratio is 2.0 to 3.0, and the upsetting rate is 20 mm / s to 50 mm / s.

[0017] Furthermore, the forging ratio of the large deformation amount is 3.0-5.0, and the forging ratio of the small deformation amount is less than 3.

[0018] Furthermore, in step S1, the heating temperature of the first fire is 1100°C to 1200°C, and the holding time is 11h to 13h; the heating temperature of the second fire is 1030°C to 1100°C, and the holding time is 9h to 11h; and the forging ratio of each fire is 3.0 to 5.0.

[0019] Furthermore, the heating temperature of step S2 is 930° C. to 980° C., and the forging ratio per fire is 3.0 to 4.0.

[0020] Furthermore, the forging temperature of step S3 is 1030° C. to 1100° C., and the forging ratio is 1.5 to 3.0.

[0021] Furthermore, the heating temperature of step S4 is 930° C. to 970° C., and the forging ratio of each fire is 1.5 to 2.5.

[0022] Furthermore, the specification of the Ti6Al4V titanium alloy large-size bar is 200mm≤Φ≤450mm

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] From the perspective of material deformation, by designing the corresponding deformation amount after heating in different phase regions, the blanking stage is forged with a large deformation amount in the β single-phase region to fully break up the cast grains and refine the grain size; finally, in the forming stage, small deformation forging is performed in the α+β two-phase region. Through multiple small deformations, the stability of the process and the further refinement of the grains are guaranteed. This method optimizes the hot working process and process, reduces the number of forging fires, improves the uniformity of the bar structure and the consistency of performance, and cuts samples from the bar for hot deformation to verify the corresponding structure and performance of the bar after subsequent deformation. Ultimately, it is possible to successfully produce low-cost, high-quality Ti6Al4V titanium alloy bars for civil aircraft with a tensile strength exceeding 949Mpa and a diameter of 200mm≤Φ≤450mm.

[0025] Other features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the invention.

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 This is a macrostructure diagram of a Φ250mm large-size bar prepared in Example 1 of the present invention;

[0029] Figure 2 (a) is the microstructure of the edge of the Φ250 mm large-size bar prepared in Example 1 of the present invention;

[0030] Figure 2 (b) is the microstructure of the Φ250 mm large-size bar prepared in Example 1 of the present invention at r / 2;

[0031] Figure 2 (c) is a microstructure diagram of the core of a Φ250 mm large-size bar prepared in Example 1 of the present invention;

[0032] Figure 3 This is a macroscopic microstructure diagram of a Φ300 mm large-size bar prepared in Example 2 of the present invention;

[0033] Figure 4 (a) is the microstructure of the edge of the Φ300 mm large-size bar prepared in Example 2 of the present invention;

[0034] Figure 4(b) Microstructure diagram of the Φ300 mm large-size bar prepared in Example 2 of the present invention at r / 2

[0035] Figure 4 (c) is the microstructure of the core of the Φ300 mm large-size bar prepared in Example 2 of the present invention;

[0036] Figure 5 This is a macrostructure diagram of a Φ450mm large-size bar prepared in Example 3 of the present invention;

[0037] Figure 6 (a) is the microstructure of the edge of the Φ450 mm large-size bar prepared in Example 3 of the present invention;

[0038] Figure 6 (b) Microstructure of the Φ450 mm large-size bar prepared in Example 3 of the present invention at r / 2

[0039] Figure 6 (c) is the microstructure diagram of the core of the Φ450mm large-size bar prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0040] Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present invention. Rather, they are merely examples of arrangements consistent with certain aspects of the present invention as detailed in the appended claims.

[0041] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.

[0042] The present invention provides a method for preparing large-sized Ti6Al4V titanium alloy bars, which specifically comprises the following steps:

[0043] Step 1: Large deformation forging in β single phase region:

[0044] In the first fire, the ingot is heated to 1100℃~1200℃, air-cooled after two upsetting and two drawing, the forging ratio is controlled between 3.0~5.0, the holding time is 11h~13h, and the surface cracks of the billet are removed by grinding after forging and air cooling; in the second fire, the ingot is heated to 1030℃~1100℃, the holding time is 9h~11h, air-cooled after two upsetting and two drawing, the forging ratio is controlled between 3.0~5.0, and the surface cracks of the billet are removed by grinding after forging and air cooling.

[0045] Step 2: Diagonal forging with large deformation in the α+β two-phase region

[0046] The billet after the blanking forging in step 1 is heated to between 930°C and 980°C, and is forged for 1 to 2 times. Diagonal stretching forging is performed in each time. The forging ratio of each time is controlled between 2.0 and 4.0. The last forging is completed by air cooling.

[0047] Step 3: Rapid upsetting and forging with small deformation in β single phase region

[0048] The billet forged in step 2 is heated to between 1030°C and 1100°C, and is quickly forged by upsetting and drawing after being taken out of the furnace. The forging ratio is controlled between 1.5 and 3.0. After forging, it is air-cooled and, after air-cooling to room temperature, the surface cracks and oxide scale of the billet are polished and removed.

[0049] Step 4: Direct drawing forging with small deformation in the α+β two-phase region

[0050] The billet after forging in step 3 is heated to between 930° C. and 970° C., and is straight-draw forged after being taken out of the furnace. The billet is straight-draw forged for 3 to 5 times, and the forging ratio of each time is controlled between 1.5 and 2.5. The billet is straight-draw forged, and air-cooled after forging to obtain a Ti6Al4V titanium alloy large-size bar with a diameter of Φ250 mm to Φ450 mm;

[0051] Step 5: Sample upsetting forging

[0052] Select the bar after step 4, cut a 50mm to 100mm thick sample from the bar, heat it to 940℃ to 980℃, control the forging ratio between 2.0 and 3.0, and the upsetting rate between 20mm / s and 50mm / s. Use air cooling after forging, and perform thermal deformation by cutting a sample from the bar to verify the corresponding structure and properties of the bar after subsequent deformation.

[0053] Example 1

[0054] Step 1: Large deformation forging in the β single phase region

[0055] A Ti6Al4V titanium alloy ingot weighing 7000kg was selected. The ingot was heated to 1100℃ for the first fire, kept warm for 12h, air-cooled after two upsetting and two drawing, with a forging ratio of 3.0. After forging and air cooling, the surface cracks of the billet were removed by grinding. The second fire was heated to 1100℃ for 9h, kept warm for 9h, air-cooled after two upsetting and two drawing, with a forging ratio of 4.0. After forging and air cooling, the surface cracks of the billet were removed by grinding.

[0056] Step 2: Diagonal forging with large deformation in the α+β two-phase region

[0057] The billet obtained in step 1 was heated to 950°C, kept at this temperature for 9 hours, forged twice, with a forging ratio of 4.0, and air-cooled after forging.

[0058] Step 3: Rapid upsetting and forging with small deformation in β single phase region

[0059] The blank obtained in step 2 is heated to 1030°C, and is quickly forged by upsetting and drawing after being taken out of the furnace. The forging ratio is controlled at 2.5. After forging, it is air-cooled, and after air-cooling to room temperature, the surface cracks and oxide scale of the blank are polished and removed.

[0060] Step 4: Direct drawing forging with small deformation in the α+β two-phase region

[0061] The billet after forging in step 3 is heated to 970°C and straight-draw forged after being taken out of the furnace. A total of 5 straight-draw forgings are performed on the billet. The forging ratio of the first 3 fires is controlled at 2.0, and the forging ratio of the last 2 fires is controlled at 1.5. Air cooling is used after forging to finally produce a large-size Ti6Al4V titanium alloy bar with a diameter of Φ250 mm.

[0062] Step 5: Sample upsetting forging

[0063] Select the bar prepared in step 4, cut a 100 mm thick sample from the bar, heat it to 940°C, control the forging ratio at 2.5, control the upsetting rate between 20 mm / s and 50 mm / s, and use air cooling after forging.

[0064] Example 2

[0065] Step 1: Large deformation forging in the β single phase region

[0066] A Ti6Al4V titanium alloy ingot weighing 7100kg was selected. In the first fire, the ingot was heated to 1150℃, kept warm for 11h, air-cooled after two upsetting and two drawing, with a forging ratio of 5. After forging and air cooling, the surface cracks of the billet were removed by grinding. In the second fire, the ingot was heated to 1070℃, kept warm for 10h, air-cooled after two upsetting and two drawing, with a forging ratio of 3. After forging and air cooling, the surface cracks of the billet were removed by grinding.

[0067] Step 2: Diagonal forging with large deformation in the α+β two-phase region

[0068] Heat the billet to 930℃, keep it at this temperature for 10h, forge it once, with a forging ratio of 3.0, and air cool it after forging.

[0069] Step 3: Rapid upsetting and forging with small deformation in β single phase region

[0070] The blank is heated to 1050℃, and then taken out of the furnace for rapid forging by upsetting and drawing. The forging ratio is controlled at 1.5. After forging, it is air-cooled and then polished to remove cracks and oxide scale on the surface of the blank after air-cooling to room temperature.

[0071] Step 4: Direct drawing forging with small deformation in the α+β two-phase region

[0072] The billet after forging in step 3 is heated to 930°C and straight-draw forged after being taken out of the furnace. The billet is straight-draw forged for 4 times in total. The forging ratio of the first 2 times is controlled at 2.5, and the forging ratio of the last 2 times is controlled at 1.5. Air cooling is used after forging to finally produce a large-size Ti6Al4V titanium alloy bar with a diameter of Φ300 mm.

[0073] Step 5: Sample upsetting forging

[0074] Select the bar after step 4, cut a 70mm thick specimen from the bar, heat it to 960℃, control the forging ratio at 3.0, control the upsetting rate between 20mm / s and 50mm / s, and use air cooling after forging.

[0075] Example 3

[0076] Step 1: Large deformation forging in the β single phase region

[0077] A Ti6Al4V titanium alloy ingot weighing 7000kg was selected. In the first fire, the ingot was heated to 1200℃, kept at this temperature for 13h, air-cooled after two upsetting and two drawing, with a forging ratio of 4.0. After forging and air cooling, the surface cracks of the billet were removed by grinding. In the second fire, the ingot was heated to 1030℃, kept at this temperature for 9.5h, air-cooled after two upsetting and two drawing, with a forging ratio of 5.0. After forging and air cooling, the surface cracks of the billet were removed by grinding.

[0078] Step 2: Diagonal forging with large deformation in the α+β two-phase region

[0079] The billet obtained in step 1 was heated to 980°C, kept at this temperature for 9.5 hours, forged once, with a forging ratio of 3.0, and air-cooled after forging.

[0080] Step 3: Rapid upsetting and forging with small deformation in β single phase region

[0081] The billet obtained in step 2 is heated to 1100°C, and after being taken out of the furnace, the billet is subjected to rapid forging by upsetting and drawing, with the forging ratio controlled at 1.8. After forging, it is air-cooled, and after air-cooling to room temperature, the surface cracks and oxide scale of the billet are polished and removed.

[0082] Step 4: Direct drawing forging with small deformation in the α+β two-phase region

[0083] The billet after forging in step 3 is heated to 940°C and straight-draw forged after being taken out of the furnace. The billet is straight-draw forged for 3 times in total. The forging ratio of the first 2 times is controlled at 1.8, and the forging ratio of the last time is controlled at 1.5. Air cooling is used after forging to finally produce Ti6Al4V titanium alloy civilian large-size bars with a diameter of Φ450mm.

[0084] Step 5: Sample upsetting forging

[0085] Select the bar prepared in step 4, cut a 50 mm thick sample from the bar, heat it to 980°C, control the forging ratio at 2.0, control the upsetting rate between 20 mm / s and 50 mm / s, and use air cooling after forging.

[0086] Figure 1 、 Figure 3 、 Figure 5 The low-magnification microstructures of Ti6Al4V titanium alloy bars with specifications of Φ250mm, Φ300mm and Φ450mm prepared by this process are shown in Figure 1. Figure 1 、 Figure 3 、 Figure 5 All positions of the tissue are uniformly blurred at medium and low magnifications; Figure 2 、 Figure 4 、 Figure 6 The microstructures of Ti6Al4V titanium alloy rods with specifications of Φ250mm, Φ300mm, and Φ450mm at the edge, r / 2, and core are respectively. It can be seen that the structure is composed of equiaxed and strip-shaped primary α phase structures, and the difference between different positions is very small. Therefore, the Ti6Al4V titanium alloy rods prepared in this application have good organizational uniformity at all positions and the rods are very uniform.

[0087] The room temperature tensile properties of Ti6Al4V titanium alloy bars with test specifications of Φ250mm, Φ300mm, and Φ450mm in the LT and L directions are shown in Table 1. It can be seen from Table 1 that the differences in the tensile properties of the LT and L directions are small.

[0088] After the upsetting forging of the Ti6Al4V titanium alloy bar specimen in step 5, its room temperature tensile properties were tested. The results are shown in Table 2. It can be seen from Table 2 that all indicators of the tensile properties in the LT direction have been improved, and the improvement is large, which verifies the excellent mechanical properties of the bar from the opposite side. Among them, Rm, Rp0.2, A, and Z are the tensile strength, yield strength, elongation, and cross-sectional reduction rate in the room temperature tensile properties, respectively.

[0089] Table 1. Room temperature tensile properties of Ti6Al4V titanium alloy large-size bars

[0090]

[0091]

[0092] Table 2. Room temperature tensile properties of Ti6Al4V titanium alloy bar specimens after upsetting

[0093]

[0094] From the perspective of material deformation, by designing the corresponding deformation amounts after heating in different phase regions, large deformation forging is performed in the β single-phase region during the cogging stage to fully break up the as-cast grains and refine the grain size. Finally, small deformation forging is performed in the α+β two-phase region during the forming stage. Through multiple small deformations, process stability and further grain refinement are ensured. By using Ti6Al4V titanium alloy bar specimens subjected to large deformation upsetting forging, the corresponding microstructure and properties after further deformation in subsequent processes are predicted, and the quality reliability of the bars is reversely verified. Ultimately, low-cost, high-quality Ti6Al4V titanium alloy bars with a tensile strength exceeding 950 MPa and a diameter of 200 mm ≤ Φ ≤ 450 mm for civil aircraft were successfully produced.

[0095] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0096] It should be understood that the present invention is not limited to the above description and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing large-sized Ti6Al4V titanium alloy bars, characterized in that: The steps include: S1, β single phase region large deformation billet forging: There are 2 forging fires in total, each of which is subjected to large deformation upsetting forging, and air cooling after forging; S2, α+β two-phase region large deformation diagonal drawing forging: The forging process is 1 to 2 times in total, and each time a large deformation diagonal stretching forging is performed, followed by air cooling after forging. S3, β single phase region small deformation rapid upsetting forging: There is one forging fire in total, the blank is quickly upsetting and forged, and air-cooled after forging; S4, α+β two-phase region small deformation direct drawing forging: The forging process is repeated 3 to 5 times, and the billet is straight-drawn forged and air-cooled after forging to obtain large-size Ti6Al4V titanium alloy bars. Among them, the forging ratio of the large deformation amount is 3.0-5.0, and the forging ratio of the small deformation amount is less than 3.

2. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: The preparation method further comprises upsetting and forging the sample: The forging process is repeated once. The bar obtained in step S4 is selected to cut a sample, heated to the temperature of the α+β two-phase region and kept warm, and then subjected to upsetting forging after being taken out of the furnace. The sample is then air-cooled after forging.

3. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 2, characterized in that: The heating temperature of the sample upsetting forging is 940° C. to 980° C., the forging ratio is 2.0 to 3.0, and the upsetting rate is 20 mm / s to 50 mm / s.

4. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: In step S1, the heating temperature of the first fire is 1100°C to 1200°C, and the holding time is 11h to 13h; the heating temperature of the second fire is 1030°C to 1100°C, and the holding time is 9h to 11h; the forging ratio of each fire is 3.0 to 5.

0.

5. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: The heating temperature of step S2 is 930° C. to 980° C., and the forging ratio per fire is 3.0 to 4.

0.

6. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: The forging temperature of step S3 is 1030° C. to 1100° C., and the forging ratio is 1.5 to 3.

0.

7. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: The heating temperature of step S4 is 930° C. to 970° C., and the forging ratio of each fire is 1.5 to 2.

5.

8. The method for preparing large-sized Ti6Al4V titanium alloy bars according to claim 1, characterized in that: The specifications of the Ti6Al4V titanium alloy large-size bar are 200mm≤Φ≤450mm.

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