TiAl alloy valve blank and preparation method thereof

Abstract

The invention discloses a TiAl alloy valve blank and a preparation method thereof, and belongs to the technical field of alloy material processing. The TiAl alloy valve blank preparation method comprises the steps that a TiAl alloy extrusion blank is prepared; the TiAl alloy extrusion blank is heated and placed in the preheated extrusion die to be extruded, and an extrusion part is obtained; and the extruded part is subjected to temperature compensation and die forging forming, and the TiAl alloy valve blank is obtained. According to the method, the TiAl alloy is processed under the condition of no sheath, the valve blank is prepared, and the problem that the forming difficulty of the TiAl alloy is large is effectively solved.

Description

Technical Field

[0001] The present application relates to the technical field of alloy material processing, and in particular to a TiAl alloy valve blank and a preparation method thereof. Background Art

[0002] The valve is a key hot end component of the internal combustion engine, used to control the flow of gas in and out, directly affecting the engine performance and life. Its service environment is complex and needs to withstand multiple tests such as high temperature, corrosion, and alternating loads. The temperature of the intake valve is about 300-450°C, and the temperature of the exhaust valve is as high as 700-850°C. Therefore, the valve material must have high hardness, heat resistance, impact resistance, corrosion resistance, non-deformation and light weight. γ-TiAl alloy has low density (about 4.0g / cm 3 ), high specific strength, high creep resistance and other advantages, and is considered to be an ideal lightweight structural material for high temperature environments of 600-900°C, especially in the fields of hot end components of internal combustion engines such as aerospace, high-end racing cars, and motorcycles.

[0003] However, as an intermetallic compound, TiAl alloy is extremely difficult to form at high temperatures, especially when preparing valves with thin rod diameters, which is difficult to obtain using conventional hot rolling processes. This seriously limits its application in the valve field. Summary of the invention

[0004] The main purpose of the present application is to provide a TiAl alloy valve blank and a preparation method thereof, aiming to solve the problem that TiAl alloy forming is difficult.

[0005] To achieve the above object, the present invention provides a method for preparing a TiAl alloy valve blank, comprising the following steps:

[0006] Preparing TiAl alloy extrusion billet;

[0007] The TiAl alloy extrusion blank is heated and placed in a preheated extrusion die for extrusion to obtain an extruded part;

[0008] The extruded part is subjected to supplementary temperature and die forging to obtain a TiAl alloy valve blank.

[0009] In one embodiment, the composition of the TiAl alloy extrusion billet includes, in atomic percentage, 40.0-46.0% Al, 1.0-5.0% Mn, 0-3.5% Nb, 0-1.0% W, 0-1.5% Mo, 0-0.3% B, 0-0.3% C, 0-0.3% Si, 0-0.1% Y, and the balance is Ti.

[0010] In one embodiment, the step of preparing the TiAl alloy extrusion billet comprises:

[0011] The TiAl alloy extrusion blank is prepared by vacuum induction melting; or,

[0012] The TiAl alloy extrusion blank is prepared by vacuum induction melting and hot rolling; or,

[0013] The TiAl alloy extrusion blank is prepared by duplex melting of vacuum induction melting and vacuum consumable electrode melting and hot rolling.

[0014] In one embodiment, the preheating temperature of the extrusion die is 300 - 600 °C;

[0015] and / or, the heating temperature for heating the TiAl alloy extrusion blank is 1240 - 1300 °C;

[0016] and / or, the supplementary heating temperature of the extruded part is 1240 - 1300 °C.

[0017] In one embodiment, the step of heating the TiAl alloy extrusion blank and placing it in the preheated extrusion die for extrusion includes:

[0018] Heating the TiAl alloy extrusion blank, and after coating with glass powder, placing it in the preheated extrusion die for extrusion.

[0019] In one embodiment, the rod diameter of the extruded part and / or the TiAl alloy valve blank is 4 - 6 mm.

[0020] In one embodiment, the pressing force of the extrusion is 60 - 100 t, and the working feed speed is 1500 - 2000 rpm.

[0021] In one embodiment, the steps of die forging forming include:

[0022] Die forging the head cylinder of the extruded part into a valve disc.

[0023] In one embodiment, the die forging pressing force of the die forging forming is 40 - 80 t, and the working feed speed is 1500 - 2000 rpm.

[0024] The embodiment of the present application also provides a TiAl alloy valve blank, and the TiAl alloy valve blank is obtained by the TiAl alloy valve blank preparation method as described above.

[0025] One or more technical solutions proposed in the embodiments of the present application have at least the following technical effects: A method for preparing a TiAl alloy valve blank is provided. First, a TiAl alloy extrusion blank is prepared. During the preparation of the TiAl alloy extrusion blank, methods such as vacuum induction melting, vacuum induction melting and hot rolling, duplex melting of vacuum induction melting and vacuum consumable melting, and hot rolling can be used. Melting the TiAl alloy in a vacuum environment can effectively reduce the impurity and gas content in the alloy, improve the purity and uniformity of the material, thereby improving its mechanical properties and high-temperature properties, reducing surface defects of the cast rod such as cracks and pores, and further avoiding extrusion defects caused by surface quality problems. Extrusion can proceed smoothly without a jacket. Secondly, preheat the extrusion die, which can reduce the flow stress of the alloy during extrusion, reduce the frictional resistance of the die to the alloy, make the alloy easier to flow and deform, improve the extrusion efficiency and quality. During the extrusion of the heated TiAl alloy extrusion blank, the alloy is in a more suitable deformation temperature range, its plasticity is improved, and it can better adapt to complex deformation requirements, thus obtaining an extruded part with higher dimensional accuracy and more uniform structure. Finally, reheating the extruded part can keep it in good plasticity and deformation ability during die forging. Forming in a specific die during die forging can further improve its microstructure, density and performance uniformity, and finally obtain a high-quality TiAl alloy valve blank. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic flow chart of the method for preparing a TiAl alloy valve blank according to the solution of the embodiment of the present application;

[0027] Figure 2 It is a process flow chart related to Embodiment 1 of the present application;

[0028] Figure 3 It is a process flow chart related to Embodiment 2 of the present application;

[0029] Figure 4 It is an external view of the extruded part related to Embodiment 1 and 2 of the present application;

[0030] Figure 5 It is an external view of the valve blank related to Embodiment 1 and 2 of the present application.

[0031] The realization, functional characteristics and advantages of the purpose of the present application will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0033] Hereinafter, embodiments of the TiAl alloy valve blank and its preparation method of this application, which are specifically disclosed, will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter recited in the claims.

[0034] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0036] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0038] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application mean open-ended, and can also be closed-ended. For example, "comprising" and "including" can mean that other components not listed can also be included or contained, or can only include or contain the listed components.

[0039] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0040] To make the above objects, features, and advantages of this application more obvious and understandable, the technical solutions of this application will be further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, and should also include any other well-known changes within the scope of the rights required by this application.

[0041] As used herein, the term "one embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0042] To better understand the technical solutions of this application, the following will be described in detail in conjunction with the drawings of the specification and specific implementation manners.

[0043] In conventional technologies, as an intermetallic compound, TiAl alloy is extremely difficult to form at high temperatures. Especially when preparing valves with a small rod diameter, it is difficult to obtain using conventional hot rolling processes, which severely limits its application in the valve field.

[0044] In the embodiment of the present application, first, a TiAl alloy extrusion blank is prepared. During the preparation of the TiAl alloy extrusion blank, methods such as vacuum induction melting, vacuum induction melting and hot rolling, double melting of vacuum induction melting and vacuum consumable melting, and hot rolling can be used. Melting the TiAl alloy in a vacuum environment can effectively reduce the impurity and gas content in the alloy, improve the purity and uniformity of the material, thereby improving its mechanical properties and high-temperature properties, reducing the surface defects of the cast rod, such as cracks and pores, and further avoiding extrusion defects caused by surface quality problems. Extrusion can proceed smoothly without a jacket; then, the extrusion die is preheated. This can reduce the flow stress of the alloy during extrusion, reduce the frictional resistance of the die to the alloy, make the alloy flow and deform more easily, improve the extrusion efficiency and quality. During the extrusion process of the heated TiAl alloy extrusion blank, the alloy is in a more suitable deformation temperature range, its plasticity is improved, and it can better adapt to complex deformation requirements, thereby obtaining an extruded part with higher dimensional accuracy and more uniform structure; then, the extruded part is reheated to enable it to maintain good plasticity and deformation ability during die forging. Forming in a specific die during die forging can further improve its microstructure, increase density and performance uniformity, and finally obtain a high-quality TiAl alloy valve blank.

[0045] The first aspect of the embodiment of the present application provides a method for preparing a TiAl alloy valve blank, referring to Figure 1 , including the following steps:

[0046] Step S10, preparing a TiAl alloy extrusion blank;

[0047] In a feasible embodiment, a TiAl alloy extrusion blank required for extrusion is prepared. Among them, the TiAl alloy extrusion blank required for extrusion can be prepared by methods such as vacuum induction melting, vacuum induction melting and hot rolling, double melting of vacuum induction melting and vacuum consumable melting, and hot rolling.

[0048] Optionally, high-purity titanium, aluminum and other alloy element raw materials are selected, proportioned according to a certain ratio, and the raw materials are placed in a vacuum induction furnace. Under high temperature and vacuum or low-pressure environment, the raw materials are melted using the principle of electromagnetic induction, and then the melted alloy liquid is poured into a preheated mold. After cooling and solidifying, a cast rod is formed and used as an extrusion blank.

[0049] In a feasible embodiment, step S10, the step of preparing a TiAl alloy extrusion blank includes any one of the following:

[0050] Step S11, preparing the TiAl alloy extrusion blank by vacuum induction melting;

[0051] In a feasible embodiment, vacuum induction melting is a melting method carried out in a vacuum environment, which can effectively reduce the impurity and gas content in the alloy, improve the purity and uniformity of the material, thereby improving its mechanical properties and high-temperature properties. At the same time, vacuum induction melting can avoid the mixing of impurities and gases, reduce surface defects of the ingot, such as cracks, pores, etc., and thus avoid extrusion defects caused by surface quality problems. Extrusion can proceed smoothly without a jacket.

[0052] Step S12: Prepare a TiAl alloy extrusion blank through vacuum induction melting and hot rolling.

[0053] In a feasible embodiment, select raw materials of high-purity titanium, aluminum and other alloying elements, mix them in a certain proportion, place the raw materials in a vacuum induction furnace, and use the principle of electromagnetic induction to melt the raw materials under high temperature and vacuum or low-pressure environment. Then pour the molten alloy liquid into a preheated mold, cool and solidify to form an ingot. Then roll the heated ingot through a rolling mill to deform it into a bar of the required size and shape, which is used as an extrusion blank.

[0054] In this embodiment, heating makes the ingot have better plasticity during the rolling process, which can better meet the deformation requirements. During the rolling process, the material undergoes repeated plastic deformation, which helps to refine the grains, improve the strength and toughness of the material, make the structure of the material more uniform, and reduce segregation and defects.

[0055] Step S13: Prepare a TiAl alloy extrusion blank through duplex melting of vacuum induction melting and vacuum consumable electrode melting and hot rolling.

[0056] In a feasible embodiment, select raw materials of high-purity titanium, aluminum and other alloying elements, mix them in a certain proportion, place the raw materials in a vacuum induction furnace to melt them into electrodes, and then melt the obtained electrodes in a vacuum consumable electrode furnace. Through the contact self-consumption melting of the electrodes and the molten pool, a pure ingot is obtained. Then heat the ingot and forge it through forging equipment to make it undergo preliminary deformation. Then hot-roll the forged blank to finally form the required bar, which is used as an extrusion blank.

[0057] In this embodiment, processing is carried out in a vacuum environment through vacuum induction plus vacuum consumable electrode melting, which can effectively remove impurities and gases in the material, further improve the purity of the material. The self-consumption melting of the electrodes can reduce internal defects and improve the density of the material. The duplex melting process can make the composition and structure of the material more uniform, improve the stability of performance, and combine forging and hot-rolling processes to refine the grains and improve the strength and toughness of the material.

[0058] In a feasible embodiment, the composition of the TiAl alloy in atomic percentage includes: 40.0 - 46.0% of Al, 1.0 - 5.0% of Mn, 0 - 3.5% of Nb, 0 - 1.0% of W, 0 - 1.5% of Mo, 0 - 0.3% of B, 0 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, and the balance is Ti.

[0059] Optionally, the main system of the TiAl alloy is Ti - Al - Mn - X, where X is at least one of the elements Mo, W, and Nb. By adding elements Mo, W, and / or Nb, the hot deformability of the TiAl alloy at high temperatures can be effectively improved, the hot working window of the TiAl alloy can be broadened, and at the same time, the good oxidation resistance of the TiAl alloy can be ensured. Therefore, the requirements for forging conditions can be reduced, and a relatively simple non - encapsulated forging method can be adopted, reducing the forging cost.

[0060] Optionally, in atomic percentage, the composition of the TiAl alloy includes 41.0 - 44.0% of Al, 4.0 - 5.0% of Mn, and the balance is Ti. The Al content in the range of 41.0 - 44.0% enables the alloy to maintain the basic properties of the TiAl alloy, and by adding an appropriate amount of Mn element, the strength and toughness of the alloy can be improved, and its oxidation resistance and creep resistance at high temperatures can be improved.

[0061] Optionally, in atomic percentage, the composition of the TiAl alloy includes 41.0 - 46.0% of Al, 1.0 - 5.0% of Mn, 2.0 - 3.5% of Nb, 0.1 - 0.3% of B, 0.1 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, and the balance is Ti. By adding elements such as Nb, B, and C, the high - temperature performance of the alloy is significantly improved. Among them, Nb can improve the high - temperature strength and creep resistance of the alloy, B and C can refine the grains and improve the high - temperature stability and oxidation resistance of the alloy, and the addition of Y element can further improve the oxidation resistance of the alloy, enabling it to better resist oxidation corrosion in a high - temperature environment and extending its service life.

[0062] Optionally, in atomic percentage, the composition of the TiAl alloy includes 40.0 - 44.0% of Al, 1.0 - 4.0% of Mn, 0.2 - 1.0% of Mo, 0.1 - 0.3% of B, 0.1 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, and the balance is Ti. The addition of Mo can improve the high - temperature strength and creep resistance of the alloy, enabling it to withstand a large load in a high - temperature environment, while the addition of B and C elements helps to refine the grains and improve the creep resistance of the alloy, enabling it to still maintain good performance under long - term high - temperature load.

[0063] Optionally, by atomic percentage, the composition of the TiAl alloy includes 41.0 - 46.0% of Al, 1.0 - 4.0% of Mn, 0.1 - 1.0% of W, 0.1 - 0.3% of B, 0.1 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, with the balance being Ti. The addition of W element can significantly improve the high-temperature strength and creep resistance of the alloy, making it have better stability and load-bearing capacity in high-temperature environments, while the addition of B and C elements can improve the oxidation resistance of the alloy, enabling it to better resist oxidation corrosion at high temperatures.

[0064] Optionally, by atomic percentage, the composition of the TiAl alloy includes 41.0 - 46.0% of Al, 1.0 - 4.0% of Mn, 0.3 - 1.5% of Mo, 0.1 - 1.0% of W, 0.1 - 0.3% of B, 0.1 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, with the balance being Ti. By adding two elements, Mo and W, the high-temperature performance of the alloy is further improved. Both Mo and W can improve the high-temperature strength and creep resistance of the alloy, making it have better stability and load-bearing capacity in high-temperature environments, while the addition of B and C elements can improve the oxidation resistance of the alloy, enabling it to better resist oxidation corrosion at high temperatures.

[0065] In this embodiment, the alloy used in this application itself has a certain effective hot working window, providing material support for the extrusion forming of the TiAl alloy valve with a thin rod diameter.

[0066] Step S20: Heat the TiAl alloy extrusion blank and place it in a preheated extrusion die for extrusion to obtain an extruded part.

[0067] In a feasible embodiment, preheat the extrusion die, heat the TiAl alloy extrusion blank, and place it in the preheated extrusion die for extrusion to obtain an extruded part.

[0068] Optionally, the extrusion die is prepared from tungsten steel or H13 die steel.

[0069] Optionally, the preheating temperature of the extrusion die is 300 to 600 °C. For example, the preheating temperature of the extrusion die is 300 °C, 320 °C, 340 °C, 360 °C, 380 °C, 400 °C, 420 °C, 440 °C, 460 °C, 480 °C, 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, etc. By preheating the extrusion die in advance, the problem that the valve stem part cannot be extruded smoothly due to the rapid cooling of the extruded blank in contact with the extrusion die can be effectively avoided. At the same time, it can also reduce the flow stress of the alloy during extrusion, reduce the frictional resistance of the die to the alloy, make the alloy easier to flow and deform, and improve the extrusion efficiency and quality. If the preheating temperature is too high, the metallographic structure of the die material will change, resulting in a decrease in the hardness and strength of the die, thereby reducing the service life of the die. At the same time, the high temperature may also cause oxide scale to form on the die surface, further weakening the performance of the die, consuming more energy, and increasing production costs. Therefore, the embodiments of the present application determine that the preheating temperature of the extrusion die is 300 to 600 °C.

[0070] In a feasible embodiment, the heating temperature for heating the TiAl alloy extrusion blank is 1240 to 1300 °C. For example, the heating temperature of the TiAl alloy extrusion blank is 1240 °C, 1245 °C, 1250 °C, 1255 °C, 1260 °C, 1265 °C, 1270 °C, 1275 °C, 1280 °C, 1285 °C, 1290 °C, 1295 °C, 1300 °C, etc. If the heating temperature of the TiAl alloy is too high, it may cause abnormal grain growth of the TiAl alloy, forming a coarse grain structure, which will reduce the strength and toughness of the material, making it prone to cracks and fractures during subsequent processing and use. And at high temperatures, the TiAl alloy is prone to react with oxygen, nitrogen, etc. in the air, resulting in surface oxidation and gas absorption, forming defects such as oxide scale and pores, affecting the surface quality and internal density of the extruded part. If the heating temperature of the TiAl alloy is too low, the plasticity of the TiAl alloy will be reduced, and defects such as cracking and fracture are likely to occur during extrusion, reducing the yield and quality of the extruded part. Therefore, the embodiments of the present application determine that the heating temperature for heating the TiAl alloy extrusion blank is 1240 to 1300 °C.

[0071] In a feasible embodiment, step S20, the steps of heating the TiAl alloy extrusion blank and placing it in the preheated extrusion die for extrusion include:

[0072] Step S21, heating the TiAl alloy extrusion blank, and after coating with glass powder, placing it in the preheated extrusion die for extrusion.

[0073] In a feasible embodiment, a TiAl alloy extrusion blank is heated to 1240 - 1300 °C and quickly coated with a layer of glass powder, and then a cylindrical-headed extrusion part with a rod diameter of 4 - 6 mm is quickly extruded under set hot extrusion parameters.

[0074] In this embodiment, by coating a layer of glass powder with heat insulation, lubrication, and force transmission functions on the heated extrusion blank, the cracking tendency caused by the direct contact between the high-temperature TiAl alloy extrusion blank and the extrusion concave die and convex die is reduced.

[0075] Optionally, the pressing force for extrusion is 60 - 100 t. For example, the pressing force for extrusion is 60 t, 62 t, 64 t, 66 t, 68 t, 70 t, 72 t, 74 t, 76 t, 78 t, 80 t, 82 t, 84 t, 86 t, 88 t, 90 t, 92 t, 94 t, 96 t, 98 t, 100 t, etc. If the pressing force for extrusion is too large, it will accelerate the wear and damage of the die, shorten the service life of the die, increase production costs, and in extreme cases, excessive pressure may cause defects inside the material, such as cracks. If the pressing force is insufficient, it may cause difficulties in the flow of the material in the die, unable to completely fill the die, thus affecting the shape and dimensional accuracy of the extrusion part and resulting in defects such as scratches and pits on the surface of the extrusion part. Therefore, the pressing force for extrusion in the embodiment of this application is determined to be 60 - 100 t.

[0076] Optionally, the working feed speed for extrusion is 1500 - 2000 rpm. For example, the working feed speed is 1500 rpm, 1550 rpm, 1600 rpm, 1650 rpm, 1700 rpm, 1750 rpm, 1800 rpm, 1850 rpm, 1900 rpm, 1950 rpm, 2000 rpm, etc. If the working feed speed is too high, it may cause an increase in frictional heat during the extrusion process, raising the temperature of the die and the material, which may affect the properties of the material and the life of the die, and may cause defects such as ripples and chatter marks on the surface of the extrusion part, reducing the surface quality. If the working feed speed is too small, it may reduce the extrusion speed, thus reducing production efficiency, increasing production costs, and causing the material to stay in the die for too long, with too fast a cooling speed, affecting the fluidity and deformation degree of the material, and resulting in a decrease in the dimensional accuracy and surface quality of the extrusion part. Therefore, the working feed speed for extrusion in the embodiment of this application is determined to be 1500 - 2000 rpm.

[0077] Step S30: Perform supplementary heating on the extrusion part and form it by die forging to obtain a TiAl alloy valve blank.

[0078] In a feasible embodiment, the extruded part is reheated, and the cylindrical part of the extruded part is die-forged into a valve disc to obtain a TiAl alloy valve blank. Since titanium aluminide has better plasticity at high temperatures and can better adapt to complex deformation requirements, reheating can ensure that the extruded part is within a suitable temperature range during die forging, thereby improving its plasticity and reducing the occurrence of defects such as cracking and fracture.

[0079] Optionally, the reheating temperature of the extruded part is 1240 - 1300 °C. For example, the reheating temperature of the extruded part is 1240 °C, 1245 °C, 1250 °C, 1255 °C, 1260 °C, 1265 °C, 1270 °C, 1275 °C, 1280 °C, 1285 °C, 1290 °C, 1295 °C, 1300 °C, etc.

[0080] Optionally, the die-forging pressure for die-forging forming is 40 - 80 t. For example, the die-forging pressure for die-forging forming is 40 t, 42 t, 44 t, 46 t, 48 t, 50 t, 52 t, 54 t, 56 t, 58 t, 60 t, 62 t, 64 t, 66 t, 68 t, 70 t, 72 t, 74 t, 76 t, 78 t, 80 t, etc. If the die-forging pressure is too large, it will accelerate the wear and damage of the die, shorten the service life of the die, increase production costs. At the same time, in extreme cases, excessive pressure may cause defects such as cracks inside the material. If the pressure is insufficient, it may cause difficulties in the flow of the material in the die, unable to completely fill the die, thus affecting the shape and dimensional accuracy of the product and resulting in defects such as scratches and pits on the product surface. Therefore, in the embodiment of the present application, the die-forging pressure for die-forging forming is determined to be 60 - 100 t.

[0081] Optionally, the feed speed for die-forging forming is 1500 - 2000 rpm. For example, the feed speed is 1500 rpm, 1550 rpm, 1600 rpm, 1650 rpm, 1700 rpm, 1750 rpm, 1800 rpm, 1850 rpm, 1900 rpm, 1950 rpm, 2000 rpm, etc. If the feed speed is too high, it may cause an increase in frictional heat during die forging, raising the temperature of the die and the material, which may affect the properties of the material and the life of the die, and may cause defects such as ripples and chatter marks on the product surface, reducing the surface quality. If the feed speed is too low, it may reduce the die-forging speed, thereby reducing production efficiency, increasing production costs, and causing the material to stay in the die for too long, with too fast a cooling rate, affecting the fluidity and deformation degree of the material, resulting in a decrease in the dimensional accuracy and surface quality of the product. Therefore, in the embodiment of the present application, the feed speed for die-forging forming is determined to be 1500 - 2000 rpm.

[0082] In this embodiment, first, a TiAl alloy extrusion blank is prepared. During the preparation of the TiAl alloy extrusion blank, methods such as vacuum induction melting, vacuum induction melting and hot rolling, duplex melting of vacuum induction melting and vacuum consumable melting, and hot rolling can be used. Melting the TiAl alloy in a vacuum environment can effectively reduce the impurity and gas content in the alloy, improve the purity and uniformity of the material, thereby improving its mechanical properties and high-temperature properties, reducing surface defects of the casting rod such as cracks and pores, and further avoiding extrusion defects caused by surface quality problems. Extrusion can proceed smoothly without a jacket; then preheat the extrusion die, which can reduce the flow stress of the alloy during extrusion, reduce the frictional resistance of the die to the alloy, make the alloy flow and deform more easily, improve the extrusion efficiency and quality. During the extrusion of the preheated TiAl alloy extrusion blank, the alloy is in a more suitable deformation temperature range, its plasticity is improved, and it can better adapt to complex deformation requirements, thereby obtaining an extruded part with higher dimensional accuracy and more uniform structure; then heating the extruded part can keep it in good plasticity and deformation ability during die forging. Forming in a specific die during die forging can further improve its microstructure, increase density and performance uniformity, and finally obtain a high-quality TiAl alloy valve blank.

[0083] To enable those skilled in the art to clearly understand the details and operations of the above embodiments of the present application, and to significantly reflect the progressive performance of the embodiments of the present application, the above technical solutions are illustrated by multiple embodiments below.

[0084] Embodiment 1:

[0085] Refer to Figure 2 the process shown to process the valve blank of TiAl alloy.

[0086] (1) Use a vacuum induction melting furnace to melt and cast a series of cylindrical extrusion blanks with a diameter of 50 mm in height, where the alloy composition is Ti-44Al-3Mn-0.8Mo-0.1B-0.1C (at.%).

[0087] (2) Heat the extrusion blank (at 1300 °C). After the extrusion blank reaches the temperature, quickly coat a layer of glass powder on the surface, and place it in a preheated (500 °C) extrusion die for extrusion to obtain an extruded part with a cylindrical head and a rod diameter of 6 mm. Among them, the pressing force is 60 t, and the working feed speed is 2000 rpm;

[0088] (3) Heat the extruded part (at 1270 °C), and forge the cylindrical head of the extruded part into a valve disk to obtain a valve blank with a rod diameter of 6 mm. Among them, the die forging pressing force is 50 t, and the working feed speed is 2000 rpm.

[0089] Example 2

[0090] Refer to Figure 3 the process shown to machine the valve blanks of TiAl alloy.

[0091] (1) Use a vacuum induction melting furnace to melt and cast an ingot with a size of . Among them, the alloy composition is Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C (at.%). The ingot is directly rolled into a bar with a diameter of 16 mm by a Y-type rolling mill in multiple passes at one time. Among them, the initial rolling deformation temperature is 1380 °C. Then, the rolled bar is cut into several cylindrical extrusion blanks with a diameter of and a height of 50 mm;

[0092] (2) Heat the extrusion blank (1280 °C). After the extrusion blank reaches the temperature, quickly coat a layer of glass powder on the surface, and place it in a preheated (450 °C) extrusion die for extrusion to obtain an extrusion part with a cylindrical head and a rod diameter of 6 mm. Among them, the pressing force is 60 t, and the working feed speed is 2000 rpm;

[0093] (3) Compensate the temperature of the extrusion part (1260 °C), and forge the cylindrical head of the extrusion part into a valve disc to obtain a valve blank with a rod diameter of 6 mm. Among them, the forging pressing force is 40 t, and the working feed speed is 2000 rpm.

[0094] Perform sandblasting treatment on the surfaces of the extrusion parts obtained in the above Examples 1 and 2 to obtain the extrusion parts as shown in Figure 4 . It can be seen that the rod diameters of the extrusion parts all meet the requirements. Perform sandblasting treatment on the surfaces of the valve blanks of Examples 1 and 2 to obtain the valve blanks as shown in Figure 5 .

[0095] The above are only the preferred embodiments of this application, and do not limit the patent scope of this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included in the patent protection scope of this application.

Claims

1. A method for preparing a TiAl alloy valve blank, characterized in that, The preparation method comprises the following steps: Preparing a TiAl alloy extrusion blank; Heating the TiAl alloy extrusion blank and placing it in a preheated extrusion die for extrusion to obtain an extruded part; Performing supplementary heating on the extruded part and performing die forging to form a TiAl alloy valve blank.

2. The method for preparing the TiAl alloy valve blank according to claim 1, wherein, In atomic percentage, the composition of the TiAl alloy comprises: 40.0 - 46.0% of Al, 1.0 - 5.0% of Mn, 0 - 3.5% of Nb, 0 - 1.0% of W, 0 - 1.5% of Mo, 0 - 0.3% of B, 0 - 0.3% of C, 0 - 0.3% of Si, 0 - 0.1% of Y, and the balance is Ti.

3. The preparation method of the TiAl alloy valve blank according to claim 1, characterized in that, The steps for preparing the TiAl alloy extrusion blank comprise: Preparing the TiAl alloy extrusion blank by vacuum induction melting; or, Preparing the TiAl alloy extrusion blank by vacuum induction melting and hot rolling; or, Preparing the TiAl alloy extrusion blank by duplex melting of vacuum induction melting and vacuum consumable electrode melting and hot rolling.

4. The method for preparing a TiAl alloy valve blank according to claim 1, wherein The preheating temperature of the extrusion die is 300 - 600 °C; And / or, the heating temperature for heating the TiAl alloy extrusion blank is 1240 - 1300 °C; And / or, the supplementary heating temperature of the extruded part is 1240 - 1300 °C.

5. The method for preparing the TiAl alloy valve blank according to claim 1, characterized in that, The step of heating the TiAl alloy extrusion blank and placing it in a preheated extrusion die for extrusion comprises: Heating the TiAl alloy extrusion blank and placing it in a preheated extrusion die for extrusion after coating with glass powder.

6. The method for preparing a TiAl alloy valve blank according to claim 1 or 5, characterized in that, The pressing force of the extrusion is 60 - 100 t, and the working feed speed is 1500 - 2000 rpm.

7. The method for preparing a TiAl alloy valve blank according to claim 1, characterized in that, The rod diameter of the extruded part and / or the TiAl alloy valve blank is 4 - 6 mm.

8. The method for preparing a TiAl alloy valve blank according to claim 1, characterized in that, The step of die forging comprises: Die forging the head cylinder of the extruded part into a valve disc.

9. The method for preparing a TiAl alloy valve blank according to claim 1 or 8, characterized in that, The die forging pressing force of the die forging is 40 - 80 t, and the working feed speed is 1500 - 2000 rpm.

10. A TiAl alloy valve blank, characterized in that, The TiAl alloy valve blank is obtained by the TiAl alloy valve blank preparation method as described in any one of claims 1 to 9.

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