Preparation method for additive manufacturing heat-resistant AlCuNiZrTi alloy

Abstract

The invention discloses a preparation method of a heat-resistant AlCuNiZrTi alloy for additive manufacturing, and belongs to the technical field of metal additive manufacturing. The AlCuNiZrTi aluminum alloy powder comprises, by mass, 1-3% of Ni-Ti powder (the mass ratio of Ni to Ti is 1: 1), 0.5-1% of Zr powder and the balance 2219 aluminum alloy powder, the AlCuNiZrTi alloy powder is prepared through an in-situ synthesis method, and SLM forming is carried out. By introducing the Ni, Ti and Zr elements, the serious hot crack problem of the 2219 alloy in the selective laser melting additive manufacturing process is eliminated, meanwhile, the stability and mechanical property of the alloy in the high-temperature environment are improved, then the novel high-strength and heat-resistant aluminum alloy is obtained, and huge potential is shown in various high-temperature applications of SLM forming AlCuNiZrTi alloy.

Description

Technical Field

[0001] The present application relates to the technical field of metal additive manufacturing, and in particular to a method for preparing a heat-resistant AlCuNiZrTi alloy by additive manufacturing. Background Art

[0002] Selective laser melting (SLM) is an advanced metal additive manufacturing (AM) technology, also known as 3D printing technology, which uses a high-energy laser beam to melt metal powder layer by layer to produce complex 3D parts. Aluminum alloys are widely used in the automotive, aerospace and construction industries due to their light weight, high strength-to-weight ratio and good corrosion resistance. Three-dimensional objects are constructed by melting metal powder layer by layer using a high-energy laser beam. Complex 3D structures, including internal cavities, threads, mesh structures, etc., can be manufactured without the need for traditional machining molds. Since complex integral parts can be manufactured in one go, subsequent assembly processes can be reduced and the time for part manufacturing can be shortened, SLM can improve the utilization rate of raw materials compared to traditional cutting methods.

[0003] SLM of traditional high-strength aluminum alloys (such as 2xxx and 7xxx series alloys) has problems such as hot cracks, low mechanical properties, poor processability and formability. A common strategy to solve the crack problem is to promote columnar to equiaxed transformation (CET) during the SLM process. The Al3X (X = Zr, Sc, Ti, Nb, Ta) phase formed during AM solidification can seed new grains at the solidification front to achieve CET. Although the CET transformation can form high-strength aluminum alloys, the rapid heating and cooling during the SLM process inevitably produces residual stress. Therefore, annealing at the right temperature plays a vital role in eliminating residual stress. Some LPBF system suppliers recommend annealing at close to 300 o C. However, most aluminum alloys are annealed at 300 o C will lose strength due to grain coarsening and / or precipitate coarsening. In addition, due to the application of heat-resistant aluminum alloys at medium temperatures (250-450 o C) has great potential to replace titanium alloys, and people are increasingly interested in heat-resistant aluminum alloys. However, due to the rapid coarsening and dissolution of the strengthening phase at high temperatures, commercial casting and wrought aluminum alloys cannot be used in 200-450 o C temperature range. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a heat-resistant AlCuNiZrTi alloy by additive manufacturing, which can improve the heat resistance of the alloy.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: An additive manufacturing heat-resistant AlCuNiZrTi alloy material, wherein the components of the AlCuNiZrTi alloy material are by mass percentage: 1-3 wt.% Ni-Ti powder, 0.5-1 wt.% Zr powder, and the balance is 2219 aluminum alloy powder, and the mass ratio of Ni to Ti is 1:1.

[0006] The 2219 aluminum alloy powder is solid spherical, with a particle size of 15-53 μm; the Ni-Ti powder particles are solid spherical, with a particle size of 10 μm; the Zr powder particles are solid spherical, with a particle size of 15-53 μm.

[0007] The preparation method of the above-mentioned additive manufacturing heat-resistant AlCuNiZrTi alloy material includes the following steps: (1) Weigh the corresponding masses of Ni-Ti powder, Zr powder and 2219 aluminum alloy powder in proportion, and put the three powders into a pot mill for mixing; (2) Put the composite powder obtained in step (1) into a drying oven for drying; (3) Put the dried composite powder in step (2) into a metal additive manufacturing equipment for selective laser melting to form a sample; (4) Heat-treat the formed sample obtained in step (3).

[0008] Further, in step (1), the rotation speed of the pot mill is 100 revolutions per minute, the pot milling time is 3 hours, and the powder pot is vibrated for 10 minutes every 1 hour.

[0009] Further, in step (2), the drying oven is evacuated, the drying temperature is 80 °C, and the drying time is 6 hours.

[0010] Further, the process parameters of the selective laser melting in step (3) are: the laser power is 150-300 W, the scanning speed is 700-1500 mm / s, the scanning spacing is 90 mm, the powder spreading thickness is 30 mm, the substrate is an aluminum alloy substrate, the substrate preheating temperature is 200 o °C, the scanning angle of adjacent powder layers rotates 67°, the forming chamber uses argon, and the oxygen content is less than 100 ppm.

[0011] Further, the heat treatment temperature in step (4) is 300 o °C to 450 o °C, and the heat treatment time is 200 h.

[0012] The present invention addsitively manufactures an AlCuNiZrTi alloy through selective laser melting (SLM) technology, and analyzes its precipitated phases and mechanical properties. In addition, the evolution of precipitated phases during high-temperature heat treatment and their effects on mechanical properties are systematically studied. Through the synergistic effect of Zr and Ti elements, during the SLM forming process, when the molten pool temperature is 600 - 800 °C, Al3(Zr,Ti) can be in-situ generated. When the molten pool temperature is 1000 - 1700 °C, molten Ni reacts with the Al matrix to generate Al7Cu4Ni, which can improve the heat resistance of 2219 aluminum alloy. The present invention also conducts post-heat treatment research on the AlCuNiZrTi alloy. Long-term heat exposure of the specimen at 300 - 400 °C can induce high-density and large-volume L12-Al3(Zr,Ti), improving the stability and mechanical properties of the alloy in high-temperature environments.

[0013] The advantages of the present invention are as follows: By introducing Zr and Ti elements into 2219 alloy, L12-Al3(Zr,Ti) is in-situ generated during the forming process. This phase serves as a nucleating agent, promoting the transformation of columnar grains to equiaxed grains and eliminating the serious hot cracking problem of 2219 alloy during selective laser melting additive manufacturing. On this basis, Ni element is introduced into the alloy, and the rapid cooling characteristic of SLM is used to refine the heat-resistant Al7Cu4Ni phase. During the heat exposure process, the coarsening rate of this phase is relatively low, and it can inhibit the growth of grains, maintaining the fine-grained advantage after selective laser melting. The precipitation of L12-Al3X (X = Zr, Ti) elements during the heat exposure process plays an additional strengthening role, thereby obtaining a new type of high-strength and heat-resistant aluminum alloy. Description of the Drawings

[0014] Figure 1 SEM morphology of AlCuNiZrTi powder used in the present invention and particle size analysis diagram of powder particles: (a) SEM image of AlCuNiZrTi powder; (b) particle size distribution of AlCuNiZrTi powder.

[0015] Figure 2 Metallographic micrographs of SLM-formed 2219 (a) and AlCuNiZrTi alloy specimens (b) in Example 1 of the present invention.

[0016] Figure 3 Hardness change trends of 2219 and AlCuNiZrTi alloy specimens in Example 1 of the present invention at 300 - 450 °C.

[0017] Figure 4The stress-strain curve (a) and the corresponding tensile strength, yield strength, and elongation values (b) of the SLM-formed AlCuNiTiZr alloy specimen after selected heat treatment in Example 1 of the present invention.

[0018] Figure 5 XRD patterns of the SLM-formed AlCuNiZrTi alloy in the as-received state and different heat treatment states in Example 1 of the present invention. Detailed implementation manners

[0019] To make the above features and advantages of the present invention more obvious and understandable, specific examples are given below for detailed description. Unless otherwise specified, the methods of the present invention are conventional methods in the art.

[0020] The composition of the 2219 aluminum alloy powder used in the following examples and comparative examples is specifically shown in Table 1. The 2219 aluminum alloy powder is a solid sphere with a particle size of 15 - 53 μm and is prepared by gas atomization.

[0021] Table 1 Chemical composition of 2219 aluminum alloy powder (mass fraction / %) Example 1 Preparation of AlCuNiZrTi alloy: (1) Add 2 wt% Ni-Ti powder (Ni: 1 wt%, Ti: 1 wt%) and 0.8 wt.% Zr powder to the 2219 aluminum alloy powder. The composition and content of the 2219 aluminum alloy powder are shown in Table 1. The Ni-Ti powder particles are solid spheres with a particle size of 10 μm, and the Zr powder particles are solid spheres with a particle size of 15 - 53 μm. Put the obtained mixed powder into a planetary ball mill for mechanical powder mixing. The rotation speed of the planetary ball mill is 100 revolutions per minute, and the ball milling time is 3 hours. Every 1 hour, vibrate the powder tank for 10 minutes; (2) Put the composite powder obtained in step (1) into a drying oven for drying treatment. The drying oven is evacuated, the drying temperature is 80 °C, and the drying time is 8 hours; (3) Perform selective laser melting forming on the dried composite powder to obtain AlCuNiZrTi alloy. The forming process parameters are: laser power is 200 W, scanning speed is 1500 mm / s, scanning spacing is 90 mm, powder layer thickness is 30 mm, the substrate is an aluminum alloy substrate, the substrate preheating temperature is 200 °C, the scanning angle of adjacent powder layers rotates 67°, and the forming chamber uses argon with an oxygen content less than 100 ppm; (4)Heat treatment: The AlCuNiZrTi alloy was heat-treated. The hardness of the AlCuNiZrTi alloy was 125 HV, and the prepared samples were heat-treated at 300 °C, 350 °C, and 400 °C in an air furnace respectively. To study the heat resistance of the AlCuNiZrTi alloy, the exposure time at 300 °C and 350 °C was 200 hours. The Vickers hardness of the specimens with different heat treatment processes was measured by a microhardness tester with a load of 150 gf and a dwell time of 10 s, and the average value of 8 points was taken as the test result.

[0022] The tensile test was carried out along the vertical building direction of each SLM-formed alloy specimen. The sample size was 60 mm (length) × 10 mm (width) × 1.5 mm (thickness), and it was processed from the SLM-formed specimen by electrical discharge machining (EDM). The test was carried out on an Instron 2384 machine equipped with an extensometer. The tensile experiment was carried out at room temperature with a tensile rate of 0.6 mm / min. Three specimens to be tested were prepared for each group to ensure data accuracy.

[0023] Mechanical properties of the formed AlCuNiZrTi tensile specimen (without heat treatment): tensile strength was 398.1 Mpa, yield strength was 278.3 Mpa, and elongation was 17.9%. Mechanical properties of the 350 °C / 200 h specimen: tensile strength was 347.1 Mpa, yield strength was 310.8 Mpa, and elongation was 17.9%. All XRD scans were carried out on the plane of the vertical building direction of the SLM-formed alloy specimen, and the results are shown in Table 2. It can still maintain its mechanical properties stable after 200 h of thermal exposure at 300 - 350 °C. Instead of decreasing, the yield strength of the specimen increased from the initial state of 278.3 MPa to 310.8 MPa after 350 °C / 200 h of thermal exposure.

[0024] Comparative Example 1 The comparative example was pure 2219 alloy powder without adding Ni-Ti powder and Zr powder. Other steps were the same as in Example 1, and the hardness of the obtained 2219 alloy was 90 HV.

[0025] The morphology and particle size analysis of the AlCuNiTiZr powder obtained in step (1) of Example 1 are as Figure 1 shown in (a, b). The metallographic micrographs of the 2219 alloy and AlCuNiTiZr alloy specimens are as Figure 2 shown in (a, b). The hardness change trends of the 2219 and AlCuNiZrTi alloy specimens at 300 - 400 °C are as Figure 3 shown. The stress-strain curves and the corresponding tensile strength, yield strength, and elongation values of the SLM-formed AlCuNiTiZr alloy specimens after selected heat treatment are as Figure 4As shown, the XRD of the SLM-formed AlCuNiZrTi alloy in the as-formed state and different heat treatment states is as follows Figure 5 As shown

[0026] As Figure 3 shown, when the heat treatment temperature is 300 °C, the hardness value of the 2219 alloy specimen decreases from 90.7 HV to 68.6 HV after 4000 min. Due to the rapid coarsening of the θ' phase in this environment, the hardness drops significantly. During the heat treatment of the AlCuNiTiZr alloy specimen, when the temperature exceeds 300 o °C, due to the elimination of dislocations, the hardness will decrease within the first 0.5 h at all temperatures. When the temperature is 300 °C and 350 °C, the hardness shows a wavy upward trend. After holding for 1 h at 300 °C and 350 °C, the hardness values of the samples decrease from 125 HV to 102 HV and 106.2 HV respectively. Then, instead of remaining stable or decreasing, the hardness increases. After 200 h of exposure, the hardness values at 300 °C and 350 °C are 112.3 HV and 116.2 HV respectively, both higher than the hardness values after 1 h, indicating that the microstructure has high stability at high temperatures of 300 °C and 350 °C. It should be noted that in terms of hardness, the values during the 350 °C treatment are always higher than those during the 300 °C treatment. For the AlCuNiTiZr alloy specimen at 400 °C, the hardness drops from 125 HV in the initial state to 107.7 HV within 1 h, then starts to rise until it reaches a peak of 113.2 HV after 6 h, and then drops rapidly

[0027] Figure 4 shows that the yield strength (YS), ultimate tensile strength (UTS), and elongation (El) of the SLM-formed AlCuNiTiZr alloy are 278.3 MPa, 398.1 MPa, and 7% respectively. After heat treatment at 300 o °C, 350 o °C, and 400 o °C for 3 h, the elongation of the alloy is improved and increases with the increase in temperature. The results show that compared with 3 h, the yield strength is improved after 200 h of thermal exposure at 300 o °C and 350 o °C. Especially under the condition of 350 o °C / 200 h, the yield strength of the sample reaches 310.8 MPa. Compared with the as-formed specimen and the 350 o °C / 3 h state, not only does the strength not decrease, but it further increases. In addition, 350 oThe elongation of the C / 200h sample is 7%, which is the same as that of the as-formed sample, indicating that while maintaining a certain plasticity, a significant strength improvement has been achieved.

[0028] Figure 5 XRD patterns of AlCuNiTiZr alloy samples in the as-formed state and different heat treatment states are shown. It can be seen that diffraction peaks corresponding to α-Al, Al7Cu4Ni, and L12 - Al3(Zr, Ti) are detected in the as-formed samples, indicating that Al7Cu4Ni is formed after introducing Ni during the SLM process. From the intensity of the Al7Cu4Ni diffraction peak, it can be seen that after heat treatment at 300 o C - 400 o °C for 3 h, the proportion of Al7Cu4Ni increases. In addition, a new diffraction peak corresponding to the "θ' phase" appears only in the samples heat-treated at 300 o °C and 350 o °C / 3 h, while a stable θ phase is detected in the samples heat-treated at 400 o °C / 3 h. When the as-formed sample is thermally exposed at 300 o °C for 200 h, the diffraction peak of the θ' phase still exists, indicating that the θ' phase exhibits stronger thermal stability in this alloy. After thermal exposure at 350 °C for 200 h, the intensity of the diffraction peak of the θ′ phase decreases significantly, indicating that the θ′ phase has coarsened or transformed into the thermodynamically stable θ phase.

[0029] Table 2 Tensile properties of SLM-formed AlCuNiZrTi alloy in different states The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. An additively manufactured heat-resistant AlCuNiZrTi alloy material, characterized in that: The components of the AlCuNiZrTi alloy material are as follows by mass percentage: 1-3 wt.% Ni-Ti powder, 0.5-1 wt.% Zr powder, and the balance is 2219 aluminum alloy powder, and the mass ratio of Ni to Ti in the Ni-Ti powder is 1:

1.

2. The additively manufactured heat-resistant AlCuNiZrTi alloy material according to claim 1, characterized in that: The 2219 aluminum alloy powder is a solid sphere with a particle size of 15 to 53 μm; the Ni-Ti powder particles are a solid sphere with a particle size of 10 μm; and the Zr powder particles are a solid sphere with a particle size of 15 to 53 μm.

3. The method for preparing a heat-resistant AlCuNiZrTi alloy material by additive manufacturing according to claim 1, characterized in that: The steps include: (1) Weigh out Ni-Ti powder, Zr powder and 2219 aluminum alloy powder in proportion, and mix the three powders in a pot mill; (2) placing the composite powder obtained in step (1) into a drying oven for drying; (3) placing the composite powder dried in step (2) into a metal additive manufacturing device for laser selective melting to obtain a sample; (4) Heat treating the molded sample obtained in step (3).

4. The preparation method according to claim 3, characterized in that: In step (1), the rotation speed of the jar mill is 100 rpm, the jar milling time is 3 hours, and the powder jar is vibrated for 10 minutes every hour.

5. The preparation method according to claim 1, characterized in that: In step (2), the drying box is evacuated, the drying temperature is 80° C., and the drying time is 6 hours.

6. The preparation method according to claim 3, characterized in that: The process parameters of laser selective melting in step (3) are: laser power of 150-350W, scanning speed of 700-1500mm / s, scanning spacing of 90mm, powder thickness of 30mm, substrate of aluminum alloy, substrate preheating temperature of 200 o C, the scanning angle of adjacent powder layers is rotated by 67°, and the molding chamber uses argon gas with an oxygen content of less than 100ppm.

7. The preparation method according to claim 3, characterized in that: The temperature of the heat treatment in step (4) is 300 o C~450 o C, the heat treatment time is 200h.

8. An additively manufactured heat-resistant AlCuNiZrTi alloy material, characterized in that: It is prepared by the method according to any one of claims 3 to 7.

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