A process suitable for periodic electro-aided drawing of titanium alloys

Abstract

The application discloses a process suitable for periodic electric auxiliary stretching of titanium alloy, which comprises the following steps: performing normal-temperature tensile test on a sample on an electronic universal testing machine to obtain a tensile displacement amount of the sample material reaching a plastic section; performing pre-tensioning on the same sample under normal-temperature conditions on the same electronic universal testing machine, so that the sample reaches a corresponding tensile displacement amount and the sample material is in a plastic deformation stage; synchronously applying a pulse current with a continuous time length t1, a disconnect time length t2 and a cycle time length T=(t1+t2) to the sample, and the current density of the pulse current is J=αA / mm 2 , until the sample is fractured after experiencing N cycles of the pulse current. The application can significantly improve the elongation of the material by adopting the periodic pulse current with a small duty ratio to perform electric auxiliary stretching on the metal sample, the change of the microstructure of the material is extremely small, the time of the pulse current in the test process is significantly shortened, and the temperature rise of the material is also smaller.

Description

Technical Field

[0001] This invention relates to the field of electro-assisted forming technology, and in particular to a process suitable for the periodic electro-assisted stretching of titanium alloys. Background Technology

[0002] With the rapid development of equipment manufacturing in the aerospace field, the requirements for large, integral forgings with dimensional stability and excellent mechanical properties are becoming increasingly stringent. Therefore, expanding the application of titanium and titanium alloys in the aerospace field has become crucial. Titanium and titanium alloys not only possess advantages such as high temperature, low density, and high strength, but also exhibit excellent fracture toughness, creep resistance, fatigue resistance, thermal stability, and corrosion resistance. On the other hand, the narrow room temperature processing range, high deformation resistance, and poor formability of titanium alloys severely limit their application scope. However, traditional hot forming methods not only lead to complex microstructure changes in the samples, resulting in material properties failing to meet certain industry standards and being discarded, but also cause a decrease in die strength, surface oxidation of the samples, and severe energy loss. Therefore, developing a new forming technology to improve forming performance and efficiency is essential.

[0003] Currently, most electrically assisted tensile tests employ a continuous pulsed current process. This involves first applying a pulsed current to bring the specimen to its maximum temperature and stabilizing it for a period before starting the electronic universal testing machine for the tensile test. Just before the specimen fractures, necking occurs. According to the formula J = I / S (J: current density; I: pulsed current; S: cross-sectional area), when the current is constant, the decrease in cross-sectional area leads to a sharp increase in current density. Since current density is directly proportional to temperature, this ultimately results in a temperature rise. The specific temperature curve is shown below. Figure 4 As shown in (a), continuous electric assisted stretching introduces several defects and shortcomings. Firstly, uneven temperature and stress distribution lead to premature fracture and decreased elongation. Numerous researchers have confirmed the decrease in elongation of titanium alloys during continuous electric assisted stretching. Secondly, the rapid temperature increase before fracture inevitably causes complex microstructural changes within the titanium alloy, such as dynamic recovery, recrystallization, and phase transformation. Since the microstructure determines mechanical properties, the final performance may not meet industry requirements. Thirdly, the highest current density currently available for continuous electric assisted stretching is ≤25 A / mm². 2 Even lower, because high current density means high temperature. Once the temperature exceeds the phase transformation point of titanium alloy, the structure transforms into martensite, which is an irreversible process. Fourth: continuous electric assisted stretching consumes more energy. The pulse current must be turned on first and kept stable for a certain period of time. The pulse current is kept on throughout the entire stretching process, with a total duration of 236 seconds, which undoubtedly increases energy loss. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a process suitable for periodic electro-assisted stretching of titanium alloys, so as to improve the formability, forming efficiency and material properties of titanium alloy materials after forming.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A process for periodic electrically assisted stretching of titanium alloys includes the following steps:

[0007] S1. Perform a room temperature tensile test on the specimen on an electronic universal testing machine to obtain the stress-strain curve of the specimen and the tensile displacement of the specimen material when it reaches the plastic segment.

[0008] S2. The same specimens are pre-stretched at room temperature on the same electronic universal testing machine so that the specimens reach the corresponding tensile displacement and the specimen material is in the plastic deformation stage.

[0009] S3. A pulse current with a duration of t1, a disconnection time of t2, and a period of T = (t1 + t2) is synchronously applied to the sample. The current density of the pulse current is J = αA / mm². 2 The sample breaks after experiencing N cycles of pulsed current.

[0010] Furthermore, when the sample material is Ti60 titanium alloy, the duration of the pulse current in a single cycle is t1 = 4s, the disconnection time is t2 = 75s, the cycle length is T = (t1 + t2) = 79s, and the current density of the pulse current is J = 15A / mm². 2 The sample fractured after being subjected to five cycles of pulsed current.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] This invention employs periodic pulsed current with a small duty cycle to electrically assistedly stretch metal samples. Compared to existing continuous pulsed current assisted stretching, this significantly improves the elongation of the material while causing minimal changes to the material's microstructure. Furthermore, the duration of the pulsed current is significantly shortened during the same tensile test, resulting in a smaller temperature rise and greater energy efficiency, environmental friendliness, and sustainability. Under the same temperature rise, periodic pulsed current assisted stretching has a higher and wider application current range, providing a feasible technical solution for studying electrically assisted forming processes within a higher and wider current range. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the pulse frequency of the periodic pulse current used in this invention.

[0014] Figure 2The figures show the elongation curves of Ti60 titanium alloy samples obtained under two processes: periodic pulsed current assisted tensile and continuous pulsed current assisted tensile.

[0015] Figure 3 Metallographic images of Ti60 titanium alloy samples obtained after tensile tests under three conditions: room temperature, periodic pulsed current assistance, and continuous pulsed current assistance.

[0016] Figure 4 The temperature-tension time curves of Ti60 titanium alloy samples obtained under two processes: periodic pulsed current assisted tensioning and continuous pulsed current assisted tensioning. Detailed Implementation

[0017] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] Please see Figures 1 to 4 A process for periodic electrically assisted stretching of titanium alloys includes the following steps:

[0021] S1. Perform a room temperature tensile test on the specimen on an electronic universal testing machine to obtain the stress-strain curve of the specimen and the tensile displacement of the specimen material when it reaches the plastic segment.

[0022] S2. The same specimens are pre-stretched at room temperature on the same electronic universal testing machine so that the specimens reach the corresponding tensile displacement and the specimen material is in the plastic deformation stage.

[0023] S3. A pulse current with a duration of t1, a disconnection time of t2, and a period of T = (t1 + t2) is synchronously applied to the sample. The current density of the pulse current is J = αA / mm². 2 The sample breaks after experiencing N cycles of pulsed current.

[0024] The following uses Ti60 titanium alloy as an example to introduce the specific implementation process and the technical effects achieved by this process.

[0025] Through the controlled variable method and a finite number of orthogonal experiments, the pulse current parameters suitable for the periodic electro-assisted tensile testing of Ti60 titanium alloy were obtained as follows: the duration of the pulse current in a single cycle is t1 = 4s, the off-time is t2 = 75s, the cycle length is T = (t1 + t2) = 79s, the duty cycle is 4 / 79 ≈ 5%, and the pulse current density is J = 15A / mm². 2 The sample fractured after being subjected to five cycles of pulsed current.

[0026] The corresponding periodic electro-assisted stretching pulse frequency diagram for this parameter is as follows: Figure 1 As shown, the elongation curve of the material obtained by electro-assisted tensile testing using continuous pulsed current is as follows: Figure 2 As shown in (a), the elongation curve of the material obtained by electro-assisted tensile testing using this periodic pulsed current is as follows: Figure 2 As shown in (b). Experiments show that for the same Ti60 titanium alloy sample, at the same current density J = 15 A / mm², the results are satisfactory. 2 Under the conditions described, the elongation of continuous pulse current assisted stretching was 0.208, while the elongation of periodic pulse current assisted stretching was 0.284, representing an increase of 36.5%. Therefore, using periodic pulse current for stretching can significantly improve the elongation of titanium alloy materials.

[0027] like Figure 3 As shown, tensile tests were conducted on the same specimens using three tensile methods: room temperature, periodic pulsed current assisted, and continuous pulsed current assisted. The tensile specimens were then surface-etched using the same polishing method and the same batch of etchant. Corresponding metallographic images were then obtained at the same magnification and scale, as shown in the figures. Figure 3 (a) Figure 3 (b) and Figure 3As shown in (c), the microstructure of periodically electrically assisted stretching is almost identical to that of room-temperature stretching, both exhibiting an elongated state. However, the microstructure of continuous electrically assisted stretching has changed; the microstructure is no longer elongated along the stretching direction but rather closer to a regular shape, with spheroidization occurring under the combined effects of temperature and drift electrons. Therefore, periodically electrically assisted stretching has an extremely small impact on the microstructure of the material.

[0028] like Figure 4 As shown, identical Ti60 titanium alloy samples were subjected to the same current density J = 15 A / mm². 2 Continuous pulsed current assisted tensile tests and periodic pulsed current assisted tensile tests were conducted separately. In the continuous pulsed current assisted tensile test, the duration of the pulsed current was 236 s; while in the periodic pulsed current assisted tensile test, the duration of the pulsed current was only 5 × 4 s = 20 s. Since the materials, current densities, and testing instruments were identical, the energy consumption per unit time was the same. The energy consumption of continuous pulsed current assisted tensile testing was 11.8 times that of periodic pulsed current assisted tensile testing. Therefore, the periodic pulsed current assisted tensile testing process is more energy-efficient, environmentally friendly, and green.

[0029] At the same time, from Figure 4 As can be seen from the data, the same Ti60 titanium alloy sample at the same current density J = 15 A / mm²... 2 Continuous pulsed current assisted tensile tests and periodic pulsed current assisted tensile tests were conducted separately. The temperature rise in the continuous pulsed current assisted tensile test reached 500℃, while the temperature rise in the periodic pulsed current assisted tensile test was only 150℃. Therefore, the temperature rise in the continuous pulsed current assisted tensile test is 3.33 times that in the periodic pulsed current assisted tensile test, and the temperature rise in the periodic pulsed current assisted tensile test is smaller.

[0030] Because the temperature rise during periodic electro-assisted stretching is small, the pulse current range for periodic electro-assisted stretching is wider. For example, for the same Ti60 titanium alloy sample, at the same current density J = 15 A / mm², 2 The continuous pulsed current assisted tensile test had a temperature of 500℃, while the temperature rise in the periodic pulsed current assisted tensile test was only 150℃; the current density in the periodic pulsed current assisted tensile test was J = 37 A / mm². 2 Only when the temperature rises can it reach 500℃, such as Figure 4 As shown in (c). Therefore, the current range for periodic pulsed current assisted stretching is 2.47 times that for continuous pulsed current assisted stretching. If the current density range for continuous electric assisted stretching is 0–25 A / mm... 2 Therefore, the current density range for periodic electrically assisted stretching can be 0–61 A / mm. 2Thus, periodic electric-assisted stretching allows for the study of electric-assisted forming processes within a higher and wider current range.

[0031] Obviously, since most metallic materials have similar electrical heating characteristics to Ti60 titanium alloy, as well as similar heating-enhanced elongation properties, by setting appropriate pulse duration and disconnection duration to obtain pulse current with corresponding periodic frequency, a similar periodic pulse current-assisted process can be used to improve the elongation of the material, effectively save energy, and improve forming efficiency and overall forming performance.

[0032] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0033] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A process suitable for periodic electrically assisted stretching of titanium alloys, characterized in that, Includes the following steps: S1. Perform a room temperature tensile test on the specimen on an electronic universal testing machine to obtain the stress-strain curve of the specimen and the tensile displacement of the specimen material when it reaches the plastic segment. S2. The same specimens are pre-stretched at room temperature on the same electronic universal testing machine so that the specimens reach the corresponding tensile displacement and the specimen material is in the plastic deformation stage. S3. A pulse current with a duration of t1, a disconnection time of t2, and a period of T = (t1 + t2) is synchronously applied to the sample. The current density of the pulse current is J = αA / mm². 2 The sample breaks after experiencing N cycles of pulsed current. The sample material was Ti60 titanium alloy. The duration of a single-cycle pulse current was t1 = 4 s, the disconnection time was t2 = 75 s, the cycle length was T = (t1 + t2) = 79 s, and the pulse current density was J = 15 A / mm². 2 The sample fractured after being subjected to five cycles of pulsed current.

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