A laser additive manufacturing method for titanium / aluminum composite structures based on variable component high entropy transition layer

Abstract

A laser additive manufacturing method for titanium / aluminum composite structures based on a variable-component high-entropy transition layer belongs to the field of dissimilar material composite laser additive manufacturing technology. It utilizes a multi-channel powder feeding laser melting deposition technique for additive manufacturing of titanium / aluminum dissimilar metal parts. The laser acts as a heat source to melt the simultaneously introduced powders. By adjusting the rotational speed of the multi-channel powder feeding barrel, the variable-component high-entropy alloy transition layer can be customized and the multi-metal powder can be mixed online in real time with high uniformity. Compared to traditional mechanical connection, welding, and bonding methods, the entire composite manufacturing process can be automated, significantly improving production efficiency, achieving excellent repeatability, simplifying process operations, and reducing production costs. The resulting defect-free joints meet the requirements for integrated manufacturing of high-performance heterogeneous metal composite structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing of heterogeneous material composites, and specifically relates to a laser additive manufacturing method for a titanium / aluminum composite structure based on a variable component high entropy transition layer design. Background Art

[0002] Titanium alloy is a structural material with excellent comprehensive properties, characterized by low density, high specific strength, good corrosion resistance, and excellent high-temperature strength and low-temperature toughness. It is widely used in important fields such as aerospace, weaponry, and rail transportation. However, the application of single titanium alloys is limited by their single function, high price, and poor processing performance. Aluminum alloys have attracted widespread attention due to their light weight, high strength, excellent corrosion resistance, low price, good processability, and electrical and thermal conductivity. 7075 aluminum alloy is an Al-Zn-Mg-Cu high-strength aluminum alloy with high specific strength and strong corrosion resistance. It is one of the most widely used high-strength aluminum alloys for aircraft structural components. However, in certain special service environments, a structure is often required to possess multiple functions and performance, and a single material cannot meet the requirements. Combining titanium alloys with aluminum alloys to form titanium / aluminum composite structures can fully utilize the characteristics and advantages of both materials, further expanding the application potential of composite structures.

[0003] Titanium / aluminum dissimilar metal composite structural parts have the advantages of high strength and corrosion resistance of titanium alloys and lightweight and high specific strength of aluminum alloys. They are also conducive to reducing the consumption of precious metals, reducing the overall design and manufacturing costs of parts, and realizing the integration of the structure and function / performance of parts. Therefore, the demand for manufacturing titanium / aluminum dissimilar metal composite structures is becoming more and more urgent. For example, aircraft cabin heat sinks, aircraft engine edge covers, and high-speed train carriages all adopt aluminum / titanium dissimilar metal composite structure designs. However, the technical bottleneck of dissimilar metal connection is the poor interface quality in the transition zone, resulting in low bonding strength, which seriously limits the reliability of titanium / aluminum integrated composite structures in high-performance key aviation equipment.

[0004] Dissimilar metals are more difficult to join than homogeneous metals due to metallurgical incompatibility, interfacial reactions that easily produce brittle intermetallic compound layers, and large differences in thermal expansion / contraction coefficients of dissimilar metals that lead to stress cracking. The thermal expansion coefficient of 7075 aluminum alloy is 23.6×10 -6 K -1 , while the thermal expansion coefficient of TC4 titanium alloy is 8.6×10 -6 K -1The thermal expansion coefficient of 7075 aluminum alloy is about 2.5 times that of TC4 titanium alloy. Therefore, the deformation problem at the joint during the connection process is relatively serious. The melting point of titanium alloy is about 1000℃ higher than that of aluminum alloy. When the temperature reaches the melting point of titanium, a large amount of aluminum and aluminum alloy elements will be burned and evaporated. The thermal conductivity of aluminum alloy is about 20 times that of titanium alloy. The absorption rate of titanium alloy to laser is about 8 times that of aluminum alloy. Therefore, titanium alloy and aluminum alloy will have large residual stress after welding, which is easy to cause defects such as joint deformation and cracks, seriously reducing the bonding strength at the joint interface.

[0005] Conventional melting welding methods are still unable to completely suppress the formation of brittle intermetallic compounds at the interface of heterogeneous materials, while methods such as friction welding and brazing have difficulty in reliably connecting large-scale, large-section, and complex-shaped composite structures. In view of the requirements of the harsh service environment of aviation equipment for high-performance / multifunctional components, it is difficult to connect titanium / aluminum dissimilar metal parts using traditional welding technology, which seriously restricts the widespread application and stable service of titanium / aluminum dissimilar metal parts in actual production. Therefore, the design and preparation of a suitable intermediate interface transition layer can suppress the formation of brittle intermetallic compounds in the interface area and achieve a significant improvement in the connection strength of the titanium-aluminum heterogeneous metal interface, which is of great significance to the reliable service of titanium / aluminum composite structures.

[0006] Laser melting deposition technology holds broad application prospects due to its advantages, including concentrated energy density, rapid cooling rate, small heat-affected zone, and flexible deposition layer composition. This technology uses a high-energy laser beam as the energy source to melt synchronously delivered multi-layer alloy powder raw materials, stacking them layer by layer to form three-dimensional solid components. Parameters such as energy input, heating position, material system, and interface gradient composition can be precisely controlled online and in real time, enabling customized design and flexible manufacturing of alloy components in the intermediate interface transition layer.

[0007] In summary, there is an urgent need to invent a laser additive manufacturing method for titanium / aluminum composite structures based on a variable component high entropy transition layer design, which can not only meet the requirements of high performance and multi-function, but also realize the integrated manufacturing of large and complex shaped components, and promote the rapid development of my country in the field of laser additive manufacturing of heterogeneous material components with integrated functional performance. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a laser additive manufacturing method for titanium / aluminum composite structures based on a variable component high entropy transition layer design. This method is particularly suitable for the integrated laser additive manufacturing of large and complex bimetallic structural parts with integrated functions and performance.

[0009] This invention proposes a method for integrated additive manufacturing of titanium / aluminum dissimilar metals using a variable-component high-entropy alloy cladding layer as an interface transition. This method utilizes laser melting deposition, a variable-component high-entropy layer transition, and high-quality additive manufacturing of titanium / aluminum dissimilar metals. By designing a high-entropy alloy interface buffer layer, high-strength transition layers with minimal metallurgical defects are achieved, meeting the requirements for integrated manufacturing of high-performance heterogeneous metal composite structures.

[0010] The technical objectives of the present invention are achieved through the following technical solutions:

[0011] A laser additive manufacturing method for a titanium / aluminum composite structure based on a variable component high entropy transition layer comprises the following steps:

[0012] (1) Titanium alloy is selected as the substrate, and the laser is focused and adjusted by the laser melting deposition additive manufacturing head (hereinafter referred to as the laser head) of the laser so that it melts the laser melting deposition powder delivered by the feeding device and deposits the titanium alloy part on the titanium alloy substrate as the titanium alloy bottom layer;

[0013] (2) On the surface of the deposited titanium alloy, laser melting and depositing a variable component high entropy alloy interface buffer layer, the interface buffer layer is divided into a first interface buffer layer portion and a remaining interface buffer layer portion. When the first interface buffer layer portion is laser melted and deposited, the deposited titanium alloy bottom layer is melted to a certain degree, and the molten titanium alloy and the laser melt-deposited liquid high entropy alloy are mixed to form a common molten pool. After cooling and solidification, the first layer of the interface buffer layer portion is formed. The titanium alloy portion and the interface buffer layer are connected by melting and solidification, and then the remaining interface buffer layer portion is subjected to laser melting deposition additive manufacturing;

[0014] (3) Laser melting and depositing aluminum alloy on the high entropy alloy interface buffer layer to prepare the aluminum alloy part. When the first layer of the aluminum alloy part is laser melted and deposited, the high entropy alloy interface buffer layer melts to a certain degree, and the molten high entropy interface buffer layer mixes with the laser melt-deposited liquid aluminum alloy to form a common molten pool. After cooling and solidification, the first layer of the aluminum alloy part is formed. The high entropy alloy interface buffer layer and the aluminum alloy part are connected by melting and solidification, and then the remaining aluminum alloy part is laser melted and deposited for additive manufacturing.

[0015] The above-mentioned laser additive manufacturing method for titanium / aluminum composite structures based on a variable component high entropy transition layer, wherein:

[0016] Preferably, the titanium alloy is produced using laser melting deposition with 10 to 15 layers, the high-entropy alloy interface buffer layer is produced using 20 to 30 layers, and the aluminum alloy is produced using 20 to 30 layers. The number of layers determines the height of the final deposited specimen and is determined based on the tensile specimen height.

[0017] The process parameters for each layer of laser melting deposition are:

[0018] Titanium alloy part: laser power 1000-3500W, scanning speed 5-15mm / s, powder feeding rate 0.7-2.0r / min, overlap rate 30%-75%, carrier gas flow rate 3.5-5.0L / min, spot diameter 2-4mm, defocus distance -4-4cm, laser head interlayer lift 0.3-1.0mm, oxygen content ≤50ppm;

[0019] High-entropy alloy interface buffer layer: laser power 2000-5000W, scanning speed 5-15mm / s, powder feeding rate of each barrel of the multi-channel powder feeding barrel is 0.5-2.0r / min, overlap rate is 30%-75%, carrier gas flow rate is 2.5-4.5L / min, spot diameter is 2-4mm, defocus distance is -4-4cm, laser head interlayer elevation is 0.3-0.7mm, oxygen content is ≤50ppm;

[0020] Aluminum alloy part: laser power 2500~5000W, scanning speed 7~12mm / s, powder feeding rate 0.7~1.5r / min, overlap rate 50%, carrier gas flow 3.5~5.0L / min, spot diameter 2~4mm, defocus amount -4~4cm, laser head interlayer elevation 0.3~1.0mm, oxygen content ≤30ppm.

[0021] The high entropy alloy interface buffer layer system is AlCoCrFeNi 2.1 , AlTiV (molar ratio of 0.8:0.8:1), AlTiVSi (molar ratio of 0.8:0.8:1:1), AlTiVNbSi (molar ratio of 0.8:0.8:1:1:1), AlTiVCrNi (molar ratio of 0.8:0.8:1:1:1) and AlTiCoCuV (molar ratio of 0.8:0.8:1:0.5:1) and other high entropy alloys.

[0022] The laser melting deposition feed material is powder material.

[0023] The powder feeder device is a multi-channel powder feeding system, which can respectively realize the customized design of the variable component high entropy alloy composition system and the online real-time mixing of pure metal powder.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention adopts a multi-channel powder feeding laser melting deposition technology to perform additive manufacturing of titanium / aluminum dissimilar metal parts. The laser is used as a heat source to melt the powders introduced synchronously. By adjusting the rotation speed of the multi-channel powder feeding barrel, the customized design of the variable component high entropy alloy transition layer (for example: powder barrel 1 is filled with pure Al powder - powder barrel 2 is filled with pure Ti powder - powder barrel 3 is filled with pure V powder - powder barrel 4 is filled with pure Nb powder - powder barrel 5 is filled with pure Si powder) and the multi-metal powder is mixed online in real time with high uniformity.

[0026] (2) The present invention uses a high entropy alloy as an interface buffer layer. The four major effects of high entropy alloys include high entropy effect, hysteresis diffusion effect, lattice distortion effect and "cocktail" effect. Among them, the "high entropy effect" makes it easy for the interface layer of the transition zone of dissimilar metals to form a simple solid solution rather than a brittle intermetallic compound; the "hysteresis diffusion effect" makes the diffusion of titanium atoms and aluminum atoms in the high entropy alloy relatively slow, reducing the probability of titanium atoms and aluminum atoms meeting in the transition layer and inhibiting the formation of TiAl-based brittle intermetallic compounds; the "lattice distortion" effect can cause solid solution strengthening, and the "cocktail" effect improves the performance of the alloy, ultimately significantly improving the bonding strength at the titanium / aluminum interface.

[0027] (3) The present invention is used to manufacture titanium / aluminum dissimilar material composite components in an integrated manner. Compared with traditional mechanical connection, welding and bonding methods, the entire composite manufacturing process can be automated, significantly improve production efficiency, have good repeatability, simplify process operations, and save production costs. The resulting joints without obvious defects meet the integrated manufacturing requirements of high-performance heterogeneous metal composite structures.

[0028] (4) The present invention can be used to manufacture titanium / aluminum dissimilar metal parts in an integrated manner using laser melting deposition additive manufacturing technology according to the above scheme. The present invention can also be widely promoted in the field of composite manufacturing of other dissimilar metal parts such as titanium / steel, titanium / copper, aluminum / magnesium, aluminum / steel, and titanium / nickel. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the customized design of the variable component high entropy alloy transition layer and the online real-time uniform powder mixing process proposed in the present invention based on the five-way powder feeding system. In order to achieve highly uniform mixing of multi-metal powders, the present invention adds a single spiral conduit powder mixer between the multi-way powder feeder and the laser head.

[0030] Figure 2Schematic diagram of the structure of the laser melting deposition additive manufacturing process for titanium / aluminum dissimilar metal parts proposed in the present invention; (a) is a schematic diagram of the laser melting deposition process of TC4 on a TC4 substrate, (b) is a schematic diagram of the process of continuing to deposit a high-entropy alloy interface buffer layer on the deposited TC4, and (c) is a schematic diagram of the process of depositing 7075 aluminum alloy on the deposited interface buffer layer; in the figure: 1-laser beam; 2-laser melting deposition manufacturing head; 3-feeding device; 4-TC4 titanium alloy substrate; 5-TC4 titanium alloy bottom layer; 6-high-entropy alloy interface buffer layer; 7-7075 aluminum alloy surface layer.

[0031] Figure 3 The titanium / aluminum composite structure specimens were manufactured by laser additive manufacturing using the traditional method without adding a high-entropy alloy transition layer. Due to the large differences in physical parameters, there were very obvious cracks and melt collapse defects.

[0032] Figure 4 The titanium / aluminum composite structure specimen with a variable component high entropy alloy transition layer prepared based on the method of the present invention successfully achieved defect-free connection of titanium / aluminum dissimilar metals, and the macroscopic contour of the specimen was square without collapse defects. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the specific content and implementation scheme of the present invention are further explained below in conjunction with the accompanying drawings and specific embodiments.

[0034] Example

[0035] A laser additive manufacturing method for titanium / aluminum composite structures based on variable component high entropy transition layers, such as Figure 1 The specific operations are as follows:

[0036] The present invention involves a laser melting deposition additive manufacturing test of titanium / aluminum dissimilar metal parts. The substrate is TC4 titanium alloy with a size of 50mm×50mm×4mm. The interface buffer layer material is AlTiVNbSi (molar ratio of 0.8:0.8:1:1:1) high entropy alloy. Laser melting deposition additive manufacturing technology is used for the integrated manufacturing of titanium / aluminum dissimilar metal parts. The laser melting deposition system used in the test consists of a six-axis robot KR60-HA produced by KUKA, a YSL-10000-KC laser produced by IPG (maximum output power of 10KW), an RC / PGF / D multi-barrel powder feeder produced by Zhongke Yuchen, an Ar gas flexible sealed cabin, and an air-protected optical powder feeding nozzle.

[0037] Titanium alloys are relatively active, and prolonged exposure to air will form a protective film on their surface. Therefore, surface pretreatment is required before testing. This test pre-polishes the titanium alloy substrate with 600-grit metallographic sandpaper to remove the oxide film on the titanium alloy substrate until the metallic luster is exposed. The substrate is then wiped clean of oil and dirt on the surface with 75% anhydrous ethanol and dried. After the oxide film is removed, the test should be conducted within 2 hours to prevent the formation of a new oxide film.

[0038] like Figure 2 As shown in (a), 10 to 15 layers of TC4 titanium alloy are first deposited on the titanium alloy substrate. The process parameters are: laser power of 1500 W, scanning speed of 10 mm / s, powder feeding rate of 1.0 r / min, overlap rate of 50%, carrier gas flow rate of 4.7 L / min, spot diameter of 4 mm, defocusing amount of 4 cm, laser head interlayer elevation of 0.5 mm, and oxygen content ≤50 ppm.

[0039] After the titanium alloy is partially laser melted and deposited, Figure 2 As shown in Figure (b), 20 to 30 layers of AlTiVNbSi (0.8:0.8:1:1:1) high-entropy alloy interface buffer layer are laser melted and deposited. First, the 5-way powder feeder system and the single-tube spiral powder mixing device are respectively turned on to pre-mix and feed 5 kinds of pure metal powders according to the ratio of Al:Ti:V:Nb:Si = 0.8:0.8:1:1:1. When the first layer of the interface buffer layer is laser melted and deposited, the deposited titanium alloy undergoes a certain degree of melting. The molten titanium alloy mixes with the liquid interface buffer layer deposited by laser melting to form a common molten pool. After cooling and solidification, the first layer of the interface buffer layer is formed. The titanium alloy part and the interface buffer layer are connected by melting and solidification, and then the remaining interface buffer layer is deposited. The process parameters are: laser power of 3000W, scanning speed of 7mm / s, powder feeding rates of 5-way powder feeding barrels are 0.8r / min, 0.8r / min, 1.0r / min, 1.0r / min, 1.0r / min respectively, overlap rate is 50%, carrier gas flow rate is 3.0L / min, spot diameter is 4mm, defocus amount is 4cm, laser head interlayer lifting amount is 0.3~0.5mm, oxygen content is ≤50ppm.

[0040] After the laser melting deposition of the high entropy alloy interface buffer layer is completed, Figure 2As shown in Figure (c), 20 to 30 layers of AA7075 high-strength aluminum alloy are deposited by laser melting. During the laser melting deposition of the first aluminum alloy layer, the deposited interface buffer layer melts to a certain degree. The melted interface buffer layer mixes with the laser melt-deposited liquid aluminum alloy to form a common molten pool. After cooling and solidification, the first layer of aluminum alloy is formed. The interface buffer layer and the aluminum alloy are connected by melting and solidification. Finally, the laser melting deposition of the remaining aluminum alloy layers is continued to complete the entire titanium / aluminum dissimilar metal part. The process parameters are: laser power 3500W, scanning speed 10mm / s, powder feed rate 1.2r / min, overlap ratio 50%, carrier gas flow rate 4.5L / min, spot diameter 4mm, defocus distance 4cm, laser head interlayer lift 0.4mm, and oxygen content ≤100ppm.

[0041] like Figure 3 , the titanium / aluminum composite structure specimens manufactured by laser additive manufacturing without adding high entropy alloy transition layer by traditional method have very obvious cracks and melt collapse defects due to the large difference in physical parameters. Figure 4 As shown, a titanium / aluminum composite structure specimen with a variable-component high-entropy alloy transition layer prepared using the method of the present invention successfully achieved defect-free joining of the titanium / aluminum dissimilar metals, with the specimen's macroscopic profile being square and free of collapse defects. The defect-free joints produced by the preparation method of the present invention meet the requirements for integrated manufacturing of high-performance heterogeneous metal composite structures, significantly outperforming traditional methods.

[0042] In addition, the present invention also carried out the 2.1 The alloy was tested for titanium / aluminum connection, but it was found that the connection effect was not good and cracks occurred. Therefore, it is preferred to prepare the interface buffer layer part with a high entropy alloy composed of approximately equimolar proportions.

[0043] Finally, it should be noted that the above is an exemplary description of the present invention. It should be noted that without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other technicians in this field without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A laser additive manufacturing method for titanium / aluminum composite structures based on a variable component high entropy transition layer, characterized in that The steps are as follows: (1) Titanium alloy is selected as the substrate. The laser is focused and adjusted by the laser melting deposition additive manufacturing head of the laser so that it melts the laser melting deposition powder delivered by the feeding device and deposits the titanium alloy part on the titanium alloy substrate as the titanium alloy bottom layer. The laser melting deposition feeding material is powder material, and the powder feeder device is a multi-channel powder feeding system. (2) On the surface of the deposited titanium alloy, a variable component high entropy alloy interface buffer layer is continuously laser melted and deposited. The interface buffer layer is divided into a first interface buffer layer portion and a remaining interface buffer layer portion. When the first interface buffer layer portion is laser melted and deposited, the deposited titanium alloy bottom layer is melted to a certain degree, and the molten titanium alloy and the laser melt-deposited liquid high entropy alloy are mixed to form a common molten pool. After cooling and solidification, the first layer of the interface buffer layer portion is formed. The titanium alloy portion and the interface buffer layer are connected by melting and solidification, and then the remaining interface buffer layer portion is laser melted and deposited for additive manufacturing. The high entropy alloy interface buffer layer system is selected from AlCoCrFeNi 2.1 , AlTiV with a molar ratio of 0.8:0.8:1, AlTiVSi with a molar ratio of 0.8:0.8:1:1, AlTiVNbSi with a molar ratio of 0.8:0.8:1:1:1, AlTiVCrNi with a molar ratio of 0.8:0.8:1:1:1, and AlTiCoCuV high entropy alloy with a molar ratio of 0.8:0.8:1:0.5:1; the process parameters for laser melting deposition to manufacture the high entropy alloy interface buffer layer are: laser power 2000~5000W, scanning speed 5~15mm / s, powder feeding rate of each barrel of multi-channel powder feeding barrel 0.5~2.0r / min, overlap rate 30%~75%, carrier gas flow rate 2.5~4.5L / min, spot diameter 2~4mm, defocus distance -4~4cm, laser head interlayer lift 0.3~0.7mm, oxygen content ≤50ppm; (3) Laser melting and depositing aluminum alloy on the high entropy alloy interface buffer layer to prepare the aluminum alloy part. When the first layer of the aluminum alloy part is laser melted and deposited, the high entropy alloy interface buffer layer melts to a certain degree, and the melted high entropy interface buffer layer mixes with the laser melt-deposited liquid aluminum alloy to form a common molten pool. After cooling and solidification, the first layer of the aluminum alloy part is formed. The high entropy alloy interface buffer layer and the aluminum alloy part are connected by melting and solidification, and then the remaining aluminum alloy part is laser melted and deposited for additive manufacturing.

2. The laser additive manufacturing method for titanium / aluminum composite structure based on variable component high entropy transition layer according to claim 1 is characterized in that The number of layers of the titanium alloy laser melting deposition additive manufacturing is 10 to 15 layers, the number of layers of the high entropy alloy interface buffer layer laser melting deposition additive manufacturing is 20 to 30 layers, and the number of layers of the aluminum alloy laser melting deposition additive manufacturing is 20 to 30 layers.

3. The laser additive manufacturing method for titanium / aluminum composite structure based on variable component high entropy transition layer according to claim 1 is characterized in that The process parameters for laser melting deposition to manufacture the titanium alloy bottom layer are: laser power 1000~3500W, scanning speed 5~15mm / s, powder feeding rate 0.7~2.0r / min, overlap rate 30%~75%, carrier gas flow rate 3.5~5.0L / min, spot diameter 2~4mm, defocus amount -4~4cm, laser head interlayer elevation 0.3~1.0mm, oxygen content ≤50ppm.

4. The laser additive manufacturing method for titanium / aluminum composite structures based on a variable component high entropy transition layer according to claim 1 is characterized in that The process parameters for laser melting deposition to manufacture aluminum alloy parts are: laser power 2500~5000W, scanning speed 7~12 mm / s, powder feeding rate 0.7~1.5r / min, overlap rate 50%, carrier gas flow rate 3.5~5.0L / min, spot diameter 2~4mm, defocus amount -4~4cm, laser head interlayer elevation 0.3~1.0mm, and oxygen content ≤30ppm.

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