Preparation method of TA18 titanium alloy small-bore ultra-fine grain extruded pipe

Abstract

The application discloses a preparation method of a TA18 titanium alloy small-bore ultra-fine-grain extruded pipe, and the method comprises the following steps: firstly, a TA18 titanium alloy bar blank is mechanically processed to obtain a TA18 titanium alloy extruded blank; secondly, the TA18 titanium alloy extruded blank is covered with red copper to obtain a TA18 titanium alloy covered extruded blank; and thirdly, the TA18 titanium alloy covered extruded blank is heated by using a medium-frequency induction heating device and then is extruded to obtain the TA18 titanium alloy small-bore ultra-fine-grain extruded pipe. The batch preparation of the ultra-fine-grain TA18 titanium alloy is realized by controlling the heating mode, the heating temperature, the holding time, the extrusion ratio, the pressing speed and other process parameters of the extruded blank, the prepared TA18 titanium alloy small-bore ultra-fine-grain extruded pipe has high surface quality and good strength-plasticity matching, and is suitable for the preparation requirements of high-strength high-plasticity small-bore seamless pipe for an aero-engine pipeline system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium and titanium alloy pipe processing, and particularly relates to a preparation method of TA18 titanium alloy small-bore ultra-fine grain extruded pipe. BACKGROUND

[0002] The pipeline system in an advanced aircraft engine, such as a hydraulic, fuel, air conditioning and the like pipeline system, is known as the blood vessel of the aircraft, and its performance directly relates to the overall safety and service life of the aircraft. TA18 (Ti-3Al-2.5V) titanium alloy, as a preferred light-weight and pressure-resistant material for the pipeline of an aircraft engine, has been widely used in advanced engines at home and abroad. At present, the TA18 titanium alloy seamless pipe with a small caliber (Φ6mm-Φ20mm) used in the related models of the fourth-generation aircraft in China is all imported AMS 4946 standard class I pipe material from abroad. The pipe material has high strength (tensile strength = 862MPa-979MPa) and excellent room temperature plasticity (elongation ≥10%) and process performance, and can be cold-bent into shape. Based on the fact that the performance of a metal material is closely related to the grain size thereof, the strength, hardness, plasticity and toughness of fine-grained material are more superior than those of coarse-grained material, and therefore, grain refinement has become one of the important means to improve the performance of titanium alloy. Through analysis of the imported TA18 pipe material sample meeting the requirements of AMS 4946 standard class I, it is found that the pipe material has ultra-fine grain structure with a grain size <5μm, thereby realizing the dual improvement of the strength and plasticity of the alloy. At present, the small-caliber titanium seamless pipe process technology in China is not mature, and the equipment capacity is insufficient, and the prepared TA18 titanium alloy pipe material has a performance at the medium-strength (Rm≥620MPa) level, and the small-caliber high-strength and high-plastic TA18 pipe material required by the advanced engine pipeline system has not been mass-produced in China. The efficient and low-cost mass production of the ultra-fine grain high-performance TA18 titanium pipe has become a bottleneck restricting the performance improvement of the domestic aircraft engine.

[0003] The small diameter seamless titanium tube with diameter less than 20 mm is usually produced by cold working method of "billet + breakdown rolling + multi-pass finishing rolling". The use of small diameter tube billet can greatly reduce the subsequent rolling passes, reduce the multi-pass accumulation of material defects, improve the production efficiency and effectively improve the flaw detection qualified rate of finished tube. Therefore, obtaining small diameter TA18 titanium alloy tube billet with fine grains is the key to solve the above-mentioned problems in preparation of high-performance TA18 tube. The existing preparation methods of titanium tube billet mainly include extrusion, piercing and bar machining. The smallest tube billet specifications that can be obtained are Φ32 mm × 4 mm extruded tube, Φ32 mm pierced tube and Φ20 mm bar machined tube. There is no information showing that conventional extrusion and piercing methods can prepare Φ30 mm or less titanium alloy billet tube; although the bar machining method can prepare Φ25 mm or less billet tube, the machining process causes great waste of raw materials, reduces the yield of tube and increases the production cost, which is not suitable for batch production of tube. At the same time, the grain size of the tube billet prepared by the existing tube billet production method is also large. The extruded titanium tube is processed in the α+β phase zone, usually obtains "α 等轴 +α 条 +β 转 " basket organization, the grain size span is large, usually about 5 μm~50 μm; the temperature of the cross piercing is higher than the phase transition point, usually obtains "α 针 +β 转 " Widmanstatten organization with obvious β grain boundary, usually the β grain size is >100 μm; the TA18 alloy bar machined by forging usually can be processed in the α+β phase zone, and the obtained organization is usually equiaxed organization with average size >10 μm. Chinese invention patent (authorized publication number: CN102974645B) adopts conventional process of 800℃~1000℃, 1.5h~3h holding to extrude Φ45 mm × 4.5 mm TA18 titanium alloy tube billet. Although the patent does not mention the tube billet organization, the extruded billet must be recrystallized at a temperature above 200℃ for a long time, which will make the recrystallized grains grow to more than 20 μm.

[0004] At present, the preparation process of ultra-fine grain material mainly includes extrusion, rolling, spinning, powder metallurgy and other types. The most common "equal channel angular extrusion / equal channel angular extrusion" technology and "reciprocating extrusion" technology are all severe plastic deformation technologies realized by extrusion process. However, the "severe deformation extrusion technology" needs to use large-tonnage equipment and complex dies to realize the preparation of small-size (cross-sectional diameter / diagonal line less than 10mm) rods or profiles, which has many processing passes, complex preparation process, complex die mechanism, poor material applicability and high production cost, and is only suitable for laboratory-level small amount of short pipe preparation, and cannot be applied to the batch preparation of TA18 titanium pipe. "High pressure torsion", "accumulative roll bonding", "powerful spinning", "powder metallurgy + amorphous crystallization method" are all material fine-grain strengthening processes by non-severe plastic deformation. Among them, "high pressure torsion" is mainly used for laboratory preparation of small-size cylindrical and disc-shaped samples, and the strain uniformity of the billet deformation is poor, which cannot be used for pipe production. "Accumulative roll bonding" is a high-efficiency method for preparing fine-grained plates by cumulative large deformation, which can prepare materials with grain size less than 1um, but due to the limitation of pipe rolling equipment structure and material cold rolling plasticity, it cannot be used for TA18 pipe preparation. "Powerful spinning" is a near-net forming method for pipe, which is characterized by continuous deformation of local points of the pipe. The cumulative large deformation rate causes the grains to be crushed and crystallized, but this method is mainly suitable for thin-walled pipes with a diameter greater than 30mm, and the die cost is high. TA18 titanium alloy has low ultimate reduction rate and is prone to cracking during cold spinning, so it is not suitable. "Powder metallurgy + amorphous crystallization method" is a special fine-grain method suitable for multi-component and poor plasticity metals. The whole processing process adopts hot working method, the die form is single, and the production cost is high, which cannot be used for batch production of pipes.

[0005] In summary, the existing process technology in China cannot realize the batch and stable preparation of TA18 titanium alloy small-diameter ultra-fine grain pipe blanks. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a preparation method of TA18 titanium alloy small-diameter ultra-fine grain extruded pipe to solve the problems of the prior art. The method realizes the batch preparation of ultra-fine grain TA18 titanium alloy by controlling the heating method, heating temperature, holding time and extrusion ratio, pressing speed and other process parameters of the extruded billet. The prepared TA18 titanium alloy small-diameter ultra-fine grain extruded pipe has high surface quality and good strength and plasticity matching, and is suitable for the preparation requirements of high-strength and high-plasticity small-diameter seamless pipe for aircraft engine pipeline system.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a preparation method of TA18 titanium alloy small-diameter ultra-fine grain extruded pipe, characterized in that the method comprises the following steps:

[0008] Step one, TA18 titanium alloy bar is machined to obtain TA18 titanium alloy extrusion billet;

[0009] Step two, the TA18 titanium alloy extrusion billet obtained in step one is covered with red copper to obtain TA18 titanium alloy covered extrusion billet;

[0010] Step three, the TA18 titanium alloy covered extrusion billet obtained in step two is heated to 800-845 DEG C by medium frequency induction and kept for 5-10 min, and after taking out, high temperature lubricant is applied, and then placed on the extruder for extrusion to obtain TA18 titanium alloy small diameter ultra-fine grain extruded pipe; the extrusion ratio is controlled to be 10.7-26.4 and the extrusion speed is 120-150 mm / s during the extrusion.

[0011] The preparation method of the TA18 titanium alloy small diameter ultra-fine grain extruded pipe has the characteristics that the TA18 titanium alloy bar in step one is a forged bar, a rolled bar or an extruded bar meeting the A1 level requirement in GB / T 5193 "Titanium and Titanium Alloy Machining Product Ultrasonic Inspection Method".

[0012] The preparation method of the TA18 titanium alloy small diameter ultra-fine grain extruded pipe has the characteristics that the TA18 titanium alloy small diameter ultra-fine grain extruded pipe in step three has a microstructure of ultra-fine grains, and the average grain size is 1-4 μm.

[0013] The preparation method of the TA18 titanium alloy small diameter ultra-fine grain extruded pipe has the characteristics that the TA18 titanium alloy small diameter ultra-fine grain extruded pipe in step three has a specification of (16-25 mm) x (3-4.5 mm) in outer diameter x wall thickness.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] 1. The TA18 titanium alloy bar is coated, heated and extruded, the process parameters such as heating mode, heating temperature, holding time, extrusion ratio and pressing speed of the extrusion billet are controlled to realize batch production of ultra-fine grain TA18 titanium alloy, specifically, the short-time medium frequency induction heating mode is used to control the grain size of the extrusion billet, and the large deformation and high speed extrusion process is used to further break the grains, so that the TA18 titanium alloy small diameter ultra-fine grain extruded pipe prepared has high surface quality and good strength-plasticity matching, and is suitable for the preparation requirements of high-strength high-plastic small diameter seamless pipe for aero-engine pipeline system.

[0016] 2. The present application uses a red copper single sleeve, and extrudes below the eutectic temperature, so that the sleeve process is simple, the surface of the product TA18 extruded pipe is free of low-melting eutectic contaminants, and subsequent surface treatment is easy.

[0017] 3、The application can realize the production of the ultra-fine grain TA18 extruded pipe with the grain size of 1-4 microns by using the conventional horizontal or vertical extruder, the processing method is simple, does not depend on the equipment and die, effectively improves the yield and reduces the cost, and is suitable for batch production of the TA18 titanium alloy small-diameter ultra-fine grain extruded pipe.

[0018] 4、The raw material TA18 rod used in the application is derived from forged rod, rolled rod or extruded rod, the selection range is wide, and the application range of the application is expanded.

[0019] The technical scheme of the application will be further described in detail below with the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The SEM microstructure diagram of the TA18 titanium alloy small-diameter ultra-fine grain extruded pipe prepared in the embodiment 1 of the application.

[0021] Figure 2 The SEM microstructure diagram of the TA18 titanium alloy small-diameter ultra-fine grain extruded pipe prepared in the embodiment 2 of the application.

[0022] Figure 3 The SEM microstructure diagram of the TA18 titanium alloy small-diameter ultra-fine grain extruded pipe prepared in the embodiment 3 of the application. DETAILED DESCRIPTION

[0023] Embodiment 1

[0024] The embodiment includes the following steps:

[0025] Step one, the TA18 titanium alloy rod blank is mechanically processed to obtain the TA18 titanium alloy extruded blank with the specification of outer diameter x inner diameter x length of 60mm x 19mm x 200mm; the TA18 titanium alloy rod blank is a forged rod meeting the A1 level requirement in GB / T 5193 'Titanium and Titanium Alloy Processing Product Ultrasonic Inspection Method', and the entry end of the TA18 titanium alloy extruded blank needs to be provided with a 20mm long inverted right angle edge and a 45° bevel;

[0026] Step two, the outer surface of the TA18 titanium alloy extruded blank obtained in step one is coated with a thickness of 0.8mm thick purple copper plate, and the inner wall is coated with a 19mm x 1mm diameter x wall thickness purple copper tube to obtain a TA18 titanium alloy coated extruded blank with an outer diameter of less than 65mm;

[0027] Step three, the TA18 titanium alloy cladding extrusion billet obtained in step two is heated to 845 DEG C by medium frequency induction and kept for 5 min, after taking out, smearing high temperature lubricant, placing on the extruder to carry out extrusion, obtaining the TA18 titanium alloy small caliber ultra-fine grain extruded pipe with 25mm*4.5mm of outer diameter*wall thickness; the extrusion process adopts the extrusion cylinder with 65mm of diameter, controlling the extrusion ratio to be 10.7, and the extrusion speed is 150mm / s.

[0028] The TA18 titanium alloy small caliber ultra-fine grain extruded pipe obtained in the embodiment is put into a resistance furnace for heat treatment at 680 DEG C for 10 min, and then microstructure detection is carried out, and the result is shown in Figure 1 .

[0029] Figure 1 The SEM microstructure diagram of the TA18 titanium alloy small caliber ultra-fine grain extruded pipe prepared in the embodiment can be seen from Figure 1 , the microstructure of the TA18 titanium alloy small caliber ultra-fine grain extruded pipe is ultra-fine grain, and the average grain size is 4.01um.

[0030] Example 2

[0031] The embodiment includes the following steps:

[0032] Step one, the TA18 titanium alloy rod billet is mechanically processed to obtain the TA18 titanium alloy extrusion billet with 60mm*15mm*200mm of outer diameter*inner diameter*length; the TA18 titanium alloy rod billet is a rolling bar meeting the A1 level requirement in GB / T 5193 "Titanium and Titanium Alloy Machining Product Ultrasonic Inspection Method", and the entry end of the TA18 titanium alloy extrusion billet needs to be processed with 20mm of inverted right angle edge length and 45 DEG of bevel angle;

[0033] Step two, the outer surface of the TA18 titanium alloy extrusion billet obtained in step one is cladded with a copper plate with 0.8mm of thickness, and the inner wall is cladded with a copper pipe with 15mm*1mm of diameter*wall thickness, to obtain the TA18 titanium alloy cladding extrusion billet with less than 65mm of outer diameter;

[0034] Step three, the TA18 titanium alloy cladding extrusion billet obtained in step two is heated to 820 DEG C by medium frequency induction and kept for 10 min, after taking out, smearing high temperature lubricant, placing on the extruder to carry out extrusion, obtaining the TA18 titanium alloy small caliber ultra-fine grain extruded pipe with 20mm*4mm of outer diameter*wall thickness; the extrusion process adopts the extrusion cylinder with 65mm of diameter, controlling the extrusion ratio to be 15.9, and the extrusion speed is 130mm / s.

[0035] The TA18 titanium alloy small-bore ultra-fine grain extruded pipe obtained in the embodiment is loaded into a resistance furnace and heat treated at 680 DEG C for 10 min, and then microstructure detection is performed, and the results are shown in Table 2. Figure 2

[0036] Figure 2 The SEM microstructure diagram of the TA18 titanium alloy small-bore ultra-fine grain extruded pipe prepared in the embodiment can be seen from Table 4. Figure 2 It can be seen that the microstructure of the TA18 titanium alloy small-bore ultra-fine grain extruded pipe is ultra-fine grain, and the average grain size is 2.04 μm.

[0037] Example 3

[0038] The embodiment comprises the following steps:

[0039] Step one, a TA18 titanium alloy extruded billet with a specification of outer diameter x inner diameter x length of 60 mm x 13 mm x 120 mm is obtained by machining a TA18 titanium alloy bar; the TA18 titanium alloy bar is an extruded bar meeting the A1 level requirement in GB / T 5193 "Titanium and Titanium Alloy Machining Product Ultrasonic Inspection Method", and the entry end of the TA18 titanium alloy extruded billet needs to be provided with a 20 mm long inverted right angle edge and a 45 DEG inclined angle;

[0040] Step two, the outer surface of the TA18 titanium alloy extruded billet obtained in step one is coated with a thickness δ of 0.8 mm of red copper plate, and the inner wall is coated with a red copper pipe with a specification of diameter x wall thickness of 13 mm x 1 mm, to obtain a TA18 titanium alloy coated extruded billet with an outer diameter less than 65 mm;

[0041] Step three, the TA18 titanium alloy coated extruded billet obtained in step two is heated to 800 DEG C by using a medium frequency induction and is kept for 10 min, and after being taken out, a high-temperature lubricant is applied and placed on an extruder for extrusion to obtain a TA18 titanium alloy small-bore ultra-fine grain extruded pipe with an outer diameter x wall thickness of 16 mm x 3 mm; a diameter of 65 mm of the extrusion cylinder is used in the extrusion process, and the extrusion ratio is controlled to be 26.4, and the extrusion speed is 120 mm / s.

[0042] The TA18 titanium alloy small-bore ultra-fine grain extruded pipe obtained in the embodiment is loaded into a resistance furnace and heat treated at 680 DEG C for 10 min, and then microstructure detection is performed, and the results are shown in Table 2. Figure 3

[0043] Figure 3 The SEM microstructure diagram of the TA18 titanium alloy small-bore ultra-fine grain extruded pipe prepared in the embodiment can be seen from Table 4. Figure 3 It can be seen that the microstructure of the TA18 titanium alloy small-bore ultra-fine grain extruded pipe is ultra-fine grain, and the average grain size is 2.04 μm. ​​

[0044] The above merely illustrates the preferred embodiments of the present application, but is not intended to limit the present application. Any simple modification, change and equivalent variation of the above embodiments according to the spirit of the present application shall still fall within the protection scope of the present application.

Claims

1. A method for preparing a small-bore ultra-fine-grained extruded pipe of TA18 titanium alloy, characterized in that, The method comprises the following steps: Step one, the TA18 titanium alloy bar is mechanically processed to obtain TA18 titanium alloy extrusion blank; Step two, the TA18 titanium alloy extrusion blank obtained in step one is coated with red copper to obtain TA18 titanium alloy coated extrusion blank; Step three, the TA18 titanium alloy coated extrusion blank obtained in step two is heated to 800-845 DEG C by medium frequency induction and kept for 5-10 min, then taken out, smeared with high temperature lubricant, placed on the extruder for extrusion to obtain TA18 titanium alloy small diameter ultra-fine grain extruded pipe; the extrusion ratio is controlled to be 10.7-26.4 and the extrusion speed is 120-150 mm / s during the extrusion; the microstructure of the TA18 titanium alloy small diameter ultra-fine grain extruded pipe is ultra-fine grain, and the average grain size is 1-4 um; the specification of the TA18 titanium alloy small diameter ultra-fine grain extruded pipe is (16-25) mm* (3-4.5) mm.

2. The preparation method of a TA18 titanium alloy small-bore ultra-fine grain extruded pipe according to claim 1, characterized in that, The TA18 titanium alloy bar in step one is a forged bar, a rolled bar or an extruded bar meeting the A1 level requirement in GB / T 5193 'Titanium and Titanium Alloy Processing Product Ultrasonic Inspection Method'.

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