TC4 alloy based on forge piece and plasma arc additive manufacturing and preparation method of TC4 alloy

Abstract

The invention discloses a TC4 alloy based on forge pieces and plasma arc additive manufacturing and a preparation method of the TC4 alloy. The method comprises the steps that firstly, a TC4 alloy forge piece base material is prepared; secondly, the TC4 alloy obtained through forging is made into a TC4 alloy wire; and thirdly, a plasma arc is adopted as a heat source to heat the TC4 alloy wire, so that the TC4 alloy wire is formed on the surface of the TC4 alloy forge piece base material through plasma arc additive manufacturing, and the base material and additive composite TC4 alloy is obtained. According to the method, the TC4 alloy is prepared through the composite additive manufacturing process based on the lower-cost forge piece and the higher-flexibility plasma arc additive manufacturing, the comprehensive mechanical property, especially the tensile strength, of the TC4 alloy is improved, parts in various shapes are more easily formed, the preparation efficiency is improved while the preparation cost is reduced, and the method is suitable for the fields of aerospace and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy manufacturing, and particularly relates to a TC4 alloy based on forgings and plasma arc additive manufacturing and a preparation method thereof. Background Art

[0002] Titanium belongs to light metals. Its natural storage is second only to aluminum, iron, and magnesium, with broad development prospects. It is widely used in industrial production and is known as the "third metal" rising in the 21st century. The melting point of titanium is about 1668°C ± 5°C, and its linear expansion coefficient, thermal conductivity, and electrical conductivity are relatively low. The strength of pure titanium is relatively low, and its strength is generally increased through alloying. Titanium alloys have high specific strength and good high-temperature resistance, and are widely used in various fields such as aerospace, chemical industry, and automobiles. TC4 titanium alloy is a medium-strength α + β two-phase titanium alloy. Among them, about 6% of Al is used as an α-phase stabilizing element to strengthen the α-phase, and about 4% of V is used as a β-isomorphous element, which can retain the β-phase to room temperature, not only enhancing the heat treatment strengthening ability of the titanium alloy but also improving its plasticity. TC4 alloy is commonly used in traditional processing such as cutting, welding, and forging. After heat treatment, its tensile strength can reach up to 1173 MPa, and it has good thermal stability under high-temperature service conditions of 480°C, and the long-term working temperature can also reach 400°C, with excellent comprehensive performance.

[0003] Since the 1990s, material processing and preparation technology has shown a development trend of pursuing short process, low consumption, high flexibility, environmental friendliness, and integrated control of forming and organizational performance. Especially in the field of aerospace, high-end equipment such as launch vehicles, manned spacecraft, and aero engines are developing towards large-scale, lightweight, complex, and integrated structural and functional design and manufacturing. The formed parts require high precision, high performance, high flexibility, rapid response, and complex forming structures, which puts forward more stringent requirements and challenges for processing and manufacturing processes. Although various traditional manufacturing technologies such as casting, forging, welding, and powder metallurgy have been tried to reach their limits, due to the fundamental limitations of their respective technical principles, it is still difficult to meet this extreme demand, which has become a bottleneck restricting the overall development of aerospace technology. As a new technology for rapid free forming of high-performance dense metal parts, plasma arc fuse additive manufacturing technology provides a new technical approach to solve the problem of meeting multiple needs at the same time. In the process of preparing parts, it can not only provide a large degree of freedom in shape, but also take into account the size of parts to a certain extent. It has broad application prospects in the high-performance direct forming and rapid repair of complex integral components in the fields of aerospace, ship machinery, energy and power. However, additive manufacturing technology still faces the problem of not being able to balance processing efficiency and cost. Combining the advantages of additive manufacturing technology in forming complex structures and direct near-net-shape forming with the advantages of traditional manufacturing technology in terms of high efficiency, low cost, high precision and excellent surface quality can form the best manufacturing strategy. Plasma arc fuse additive manufacturing can achieve high-performance combination of homogeneous and heterogeneous materials, and can also add fine structures to parts manufactured by traditional technologies such as casting, forging and machining, and make them have mechanical properties comparable to those of integral manufacturing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of TC4 alloy based on forging and plasma arc additive manufacturing in view of the shortcomings of the above-mentioned prior art. The method prepares TC4 alloy based on a composite additive process of forging and plasma arc additive manufacturing, improves the comprehensive mechanical properties of TC4 alloy, and is easier to form parts with various shapes, while also improving the utilization rate of raw materials and preparation efficiency, solving the problem that the cost and efficiency of the existing processing methods cannot be taken into account at the same time.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a preparation method of TC4 alloy based on forging and plasma arc additive manufacturing, characterized in that the method comprises the following steps: Step 1, preparing a TC4 alloy forging substrate; the size of the TC4 alloy forging substrate is 150 mm to 200 mm in width × length × thickness of 250 mm to 300 mm × 30 mm to 50 mm; Step 2: The forged TC4 alloy is made into TC4 alloy wire with a diameter of 1.2 mm to 2.0 mm; the TC4 alloy wire is composed of the following elements by mass percentage: H 0.0025% - 0.0035%, O 0.085% - 0.089%, N 0.0015% - 0.0025%, C 0.0075% - 0.0085%, Fe 0.025% - 0.035%, V 4.15% - 4.25%, Al 6.35% - 6.39%, and the balance is Ti; Step 3: Using a plasma arc as a heat source to heat the TC4 alloy wire in Step 2, so that the TC4 alloy wire is formed on the surface of the TC4 alloy forging substrate prepared in Step 1 by plasma arc additive manufacturing, and a TC4 alloy with a substrate and additive composite is obtained; the plasma arc current used in the plasma arc additive manufacturing is 125 A - 135 A, the voltage is 16 V - 17 V, the wire feeding speed is 1500 mm / min - 2500 mm / min, and the feeding speed is 150 mm / min - 250 mm / min.

[0006] Since most of the TC4 alloy parts applied in the aerospace field are forgings, and considering that the process characteristics of plasma arc additive manufacturing require a certain thickness of substrate, the present invention selects a TC4 alloy forging as the substrate. The preparation cost of the TC4 alloy forging is relatively lower and the preparation efficiency is higher than that of other types of profiles, reducing the preparation cost. And the plasma arc additive manufacturing improves the freedom of the preparation method. The combination of the two takes into account the cost and efficiency issues of the preparation method. At the same time, the cyclic thermal cycle during the plasma arc additive manufacturing process is equivalent to performing multiple heat treatments, and due to the relatively high cooling rate, more secondary α phases are formed during the additive process. And due to different processes, there are differences in the structure and properties between the TC4 alloy forging substrate and the additive. Therefore, during the tensile process of the TC4 alloy with a substrate and additive composite, the non-uniform change of stress will be caused by the existence of non-uniform structures, thus having better tensile properties.

[0007] The above preparation method of TC4 alloy based on forging and plasma arc additive manufacturing is characterized in that the TC4 alloy forging substrate in Step 1 is composed of the following elements by mass percentage: H 0.0018% - 0.0020%, O 0.12% - 0.16%, N 0.005% - 0.015%, C 0.015% - 0.025%, Si 0.025% - 0.035%, Fe 0.025% - 0.035%, V 4.15% - 4.25%, Al 6.35% - 6.37%, and the balance is Ti.

[0008] The above-mentioned preparation method of TC4 alloy based on forgings and plasma arc additive manufacturing is characterized in that the preparation process of the TC4 alloy wire in step two is as follows: first, the TC4 alloy forging is rolled into a bar with a diameter of 60 mm to 90 mm, and then drawn through 5 to 7 passes, and each pass includes annealing and pickling processes to obtain a TC4 alloy wire with a diameter of 1.2 mm to 2.0 mm.

[0009] The above-mentioned preparation method of TC4 alloy based on forgings and plasma arc additive manufacturing is characterized in that the annealing is in-line annealing.

[0010] The above-mentioned preparation method of TC4 alloy based on forgings and plasma arc additive manufacturing is characterized in that the pickling is surface pickling of the drawn blank after annealing with HF and H2SO4. The above-mentioned preparation method of TC4 alloy based on forgings and plasma arc additive manufacturing is characterized in that before forming in step three, the oxide film on the surface of the TC4 alloy forging substrate is removed, then it is washed 1 to 3 times with anhydrous ethanol and acetone respectively, and then dried.

[0011] Meanwhile, the present invention also discloses a TC4 alloy prepared by the method as described above.

[0012] The present invention has the following advantages compared with the prior art: 1. Based on forgings and plasma arc additive manufacturing, the present invention prepares TC4 alloy through a composite additive process. Compared with the TC4 alloy prepared by traditional methods, the TC4 alloy with substrate and additive composite has better comprehensive mechanical properties and higher tensile strength.

[0013] 2. Compared with traditional preparation methods, the method of the present invention for manufacturing TC4 alloy based on forgings and plasma arc additive manufacturing is more flexible. Various shaped structures can be prepared on the forgings according to actual needs, and TC4 alloy parts with diverse structures can be obtained, broadening the application fields of TC4 alloy.

[0014] 3. Compared with the traditional forging and machining method, the present invention uses TC4 alloy wire as raw material to form and prepare TC4 alloy on the TC4 alloy forging substrate, with higher material utilization rate and higher preparation efficiency.

[0015] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram showing the division of the deposition area, bonding area and substrate area of the TC4 alloy prepared in Example 2 of the present invention.

[0017] Figure 2It is the microstructure morphology diagram of the substrate area in the TC4 alloy prepared in Example 2 of the present invention.

[0018] Figure 3 It is the microstructure morphology diagram of the bonding area in the TC4 alloy prepared in Example 2 of the present invention.

[0019] Figure 4 It is the microstructure morphology diagram of the additive area in the TC4 alloy prepared in Example 2 of the present invention.

[0020] Figure 5 It is the stress-strain curve diagram of the deposited area, bonding area and substrate area samples of the TC4 alloy prepared in Example 2 of the present invention at room temperature.

[0021] Figure 6 It is the stress-strain curve diagram of the bonding area samples of the TC4 alloy prepared in Examples 1 to 3 of the present invention at room temperature. Detailed implementation manners

[0022] Example 1 This example includes the following steps: Step 1: Prepare a TC4 alloy forging substrate with a size of width×length×thickness of 150 mm×250 mm×30 mm; the TC4 alloy forging substrate is composed of the following elements by mass percentage: H 0.002%, O 0.16%, N 0.015%, C 0.008%, Si 0.035%, Fe 0.035%, V 4.25%, Al 6.37%, and the balance is Ti; Step 2: First roll the TC4 alloy forging into a bar with a diameter of 90 mm, and then perform 5 passes of drawing. Each pass includes on-line annealing and a surface pickling process for the drawn blank after annealing using HF and H2SO4 to obtain a TC4 alloy wire with a diameter of 1.2 mm; the TC4 alloy wire is composed of the following elements by mass percentage: H 0.003%, O 0.087%, N 0.002%, C 0.008%, Fe 0.03%, V 4.2%, Al 6.37%, and the balance is Ti; Step 3: Grind the TC4 alloy forging substrate prepared in Step 1 to remove the surface oxide film, then clean it 3 times with anhydrous ethanol and acetone respectively, and then dry it; Feed the TC4 alloy wire in Step 2 using a wire feeding mechanism, and use a plasma arc as the heat source for heating. Under the condition that the protective atmosphere is Ar gas, the TC4 alloy wire is formed on the surface of the dried TC4 alloy forging substrate by plasma arc additive manufacturing to obtain a TC4 alloy with a substrate and additive composite, denoted as Sample 1. The plasma arc used in the plasma arc additive manufacturing has a current of 125 A, a voltage of 16 V, a wire feeding speed of 1500 mm / min, and a feeding speed of 150 mm / min.

[0023] Example 2 The difference between this example and Example 1 is that: in Step 3, the plasma arc used in the plasma arc additive manufacturing has a current of 135 A, a voltage of 17 V, a wire feeding speed of 2500 mm / min, and a feeding speed of 250 mm / min, to obtain a TC4 alloy with a substrate and additive composite, denoted as Sample 2.

[0024] Example 3 The difference between this example and Example 1 is that: in Step 3, the plasma arc used in the plasma arc additive manufacturing has a current of 130 A, a voltage of 16.5 V, a wire feeding speed of 2000 mm / min, and a feeding speed of 200 mm / min, to obtain a TC4 alloy with a substrate and additive composite, denoted as Sample 3.

[0025] Example 4 The difference between this example and Example 1 is that: the size of the TC4 alloy forging substrate prepared in Step 1 is width × length × thickness = 200 mm × 300 mm × 50 mm; in Step 2, the TC4 alloy forging is rolled into a bar with a diameter of 60 mm, and then drawn through 7 passes, and each pass includes in-line annealing and surface pickling of the drawn blank after annealing using HF and H2SO4 to obtain a TC4 alloy wire with a diameter of 2.0 mm, to obtain a TC4 alloy with a substrate and additive composite.

[0026] Perform performance tests on the TC4 alloys with substrates and additives composite, namely Samples 1 - 3, prepared in Examples 1 - 3 of the present invention.

[0027] Figure 1 It is a schematic diagram of the division of the deposition zone, bonding zone, and substrate zone of the TC4 alloy prepared in Example 2 of the present invention. Among them, LDZ is the deposition zone (abbreviated as L in the figure), that is, the area where the TC4 alloy wire is uniformly formed on the TC4 alloy forging substrate; HAZ is the bonding zone (abbreviated as W + L in the figure), that is, the area near the surface of the TC4 alloy forging substrate where it is formed; WSZ is the substrate zone (abbreviated as W in the figure), that is, the area of the TC4 alloy forging substrate far from the bonding zone and the deposition zone. The division of the deposition zone, bonding zone, and substrate zone in the samples of the other examples is the same as that of Sample 2.

[0028] Figure 2 This is the microstructural morphology diagram of the substrate area in the TC4 alloy prepared in Example 2 of the present invention. Among them, Figure (a) is a low-magnification diagram, and Figure (b) is a high-magnification diagram. From Figure 2 it can be seen that the microstructure of the substrate area is a duplex structure composed of lamellar α-phase and equiaxed α-phase. Since the substrate areas are all far from the bonding area and are little affected by heat, the microstructures of the substrate areas in the samples of each example are roughly the same.

[0029] Figure 3 This is the microstructural morphology diagram of the bonding area in the TC4 alloy prepared in Example 2 of the present invention. Among them, Figures (a) to (c) represent the microstructural morphology diagrams of the bonding area gradually from the substrate area to the additive area. The microstructural morphology of the bonding area near the substrate area in Figure (a) is close to the substrate structure. As it approaches the additive area, the equiaxed phase morphology gradually disappears in the microstructural morphology of the bonding area near the additive area in Figure (c) and is gradually replaced by slender α-phase. Figure (b) is between the two; from Figure 3 it can be seen that the structure of the bonding area shows a transitional change from the substrate area to the additive area, mainly due to the temperature difference in the bonding area during the plasma arc additive manufacturing process.

[0030] Figure 4 This is the microstructural morphology diagram of the additive area in the TC4 alloy prepared in Example 2 of the present invention. Among them, Figure (a) is a low-magnification diagram, and Figure (b) is a high-magnification diagram. From Figure 4 it can be seen that, similar to the structure of the traditional additive area, it macroscopically shows epitaxially grown β columnar crystals, and the microstructure is a basketweave structure morphology.

[0031] Figure 5 This is the stress-strain curve diagram at room temperature of the specimens in the deposition area, bonding area, and substrate area of the TC4 alloy prepared in Example 2 of the present invention. From Figure 5 it can be seen that the tensile strength of W+L, that is, the specimen in the bonding area, is better than that of W, that is, the specimen in the substrate area, and L, that is, the specimen in the deposition area. The reason is that slender α-phase and secondary α-phase are formed in the bonding area due to a relatively high cooling rate, indicating that the tensile strength of the TC4 alloy prepared by the composite additive process of the present invention is superior to that of the substrate of the TC4 alloy forging prepared by forging.

[0032] Figure 6 This is the stress-strain curve diagram at room temperature of the specimens in the bonding area of the TC4 alloy prepared in Examples 1 to 3 of the present invention. From Figure 6It can be seen that the tensile strength of Sample 2 is superior to that of Sample 1 and Sample 3. Since the linear energy density corresponding to Sample 2 under its process parameters is 550.4 J / mm, which is lower than that of Sample 1 (800 J / mm) and Sample 3 (650 J / mm), with a low linear energy density, the substrate conducts heat quickly, a large number of slender α-phases are formed in the bonding zone, and the number of secondary α-phases formed due to heat accumulation in the later stage increases, making the tensile strength of Sample 2 superior to that of Sample 1 and Sample 3.

[0033] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments based on the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of TC4 alloy based on forgings and plasma arc additive manufacturing, characterized in that The method comprises the following steps: Step 1, preparing a TC4 alloy forging substrate; the size of the TC4 alloy forging substrate is width×length×thickness = 150 mm to 200 mm×250 mm to 300 mm×30 mm to 50 mm; Step 2, making the forged TC4 alloy into a TC4 alloy wire with a diameter of 1.2 mm to 2.0 mm; the TC4 alloy wire is composed of the following elements by mass percentage: H 0.0025% to 0.0035%, O 0.085% to 0.089%, N 0.0015% to 0.0025%, C 0.0075% to 0.0085%, Fe 0.025% to 0.035%, V 4.15% to 4.25%, Al 6.35% to 6.39%, and the balance is Ti; Step 3, using a plasma arc as a heat source to heat the TC4 alloy wire in Step 2, so that the TC4 alloy wire is formed on the surface of the TC4 alloy forging substrate prepared in Step 1 by plasma arc additive manufacturing to obtain a TC4 alloy with a substrate and additive composite; the plasma arc current used in the plasma arc additive manufacturing is 125 A to 135 A, the voltage is 16 V to 17 V, the wire feeding speed is 1500 mm / min to 2500 mm / min, and the feeding speed is 150 mm / min to 250 mm / min.

2. The preparation method of a TC4 alloy based on forgings and plasma arc additive manufacturing according to claim 1, characterized in that The TC4 alloy forging substrate in Step 1 is composed of the following elements by mass percentage: H 0.0018% to 0.0020%, O 0.12% to 0.16%, N 0.005% to 0.015%, C 0.015% to 0.025%, Si 0.025% to 0.035%, Fe 0.025% to 0.035%, V 4.15% to 4.25%, Al 6.35% to 6.37%, and the balance is Ti.

3. The preparation method of a TC4 alloy based on forgings and plasma arc additive manufacturing according to claim 1, characterized in that, The preparation process of the TC4 alloy wire in Step 2 is as follows: first, rolling the TC4 alloy forging into a bar with a diameter of 60 mm to 90 mm, and then subjecting it to 5 to 7 passes of drawing, and each pass includes annealing and pickling processes to obtain a TC4 alloy wire with a diameter of 1.2 mm to 2.0 mm.

4. A preparation method of a TC4 alloy based on forgings and plasma arc additive manufacturing according to claim 3, characterized in that The annealing is online annealing.

5. The preparation method of a TC4 alloy based on forgings and plasma arc additive manufacturing according to claim 3, characterized in that, The pickling is surface pickling of the drawn blank after annealing with HF and H2SO4.

6. A preparation method of a TC4 alloy based on forgings and plasma arc additive manufacturing according to claim 1, characterized in that, Before forming in Step 3, first remove the oxide film on the surface of the TC4 alloy forging substrate, then clean it 1 to 3 times with anhydrous ethanol and acetone respectively, and then dry it.

7. A TC4 alloy prepared by the method according to any one of claims 1 to 6.

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