Method for reducing grafting printing deformation of plate-shaped copper alloy parts

Abstract

The application discloses a method for reducing grafting printing deformation of a plate-shaped copper alloy part, and belongs to the grafting printing technical field.The printing method comprises the following steps: processing a countersunk hole on a pure copper substrate (avoiding a printing area) and locking the countersunk hole to a printing bottom plate by using a screw; printing parameters are as follows: a slice layer thickness is 0.03 mm, a laser power is 180-220 W, a scanning speed is 950-1050 mm / s, a chessboard grid scanning is adopted, and interlayer cooling is 10-20 s; first layer remelting and reinforcement are carried out during powder laying and printing; annealing treatment is carried out, that is, the temperature is kept at 600 DEG C for 2 h and then cooled; finally, the screw is removed to obtain a low-deformation plate-shaped part.The application improves the difference between the thermal expansion coefficients of the copper alloy and the pure copper substrate by using a specific copper alloy material, avoids the risk of deformation, and can also ensure good heat conduction performance and mechanical performance of the product; in addition, the printing process is combined, and residual stress is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graft printing, in particular to a method for reducing deformation of plate-shaped copper alloy parts in graft printing. BACKGROUND

[0002] Current research on copper alloy additive manufacturing is not uncommon. Liquid-cooled heat dissipation devices gradually become the core solution to solve the problem of high-power chip heat dissipation due to their excellent heat dissipation performance. The liquid-cooled heat dissipation device is a plate-shaped copper alloy part, which includes a base plate contacting the heat source and a fine heat dissipation structure connected thereto for contacting the cooling medium. The fine heat dissipation structure quickly transfers the heat transferred by the base plate to the cooling medium through contact with the cooling medium, thereby achieving rapid cooling of the heat generating components (such as chips). The fine heat dissipation structure requires higher mechanical properties, so it is generally made of copper alloy, not pure copper material.

[0003] For the combination of the base plate and the fine structure, simple machining cannot achieve integrated forming. From the perspective of processing difficulty and cost benefit, it is not desirable to use additive manufacturing to manufacture the whole. There is a problem that the possibility of defects on the large-area plate surface increases, and at the same time, the construction time and cost are greatly improved. Therefore, the method of grafting the fine structure on the machined base plate has gradually become the preferred solution, but a new problem has also arisen: as the grafting part of the fine structure and the base plate are different in processing method and material, they are prone to warping and deformation during grafting and heat treatment, which seriously affects the product quality.

[0004] The current improvement methods mainly include: (1) preheating the substrate at high temperature; (2) optimizing the scanning strategy according to the geometric shape of the specific part; (3) adding a support structure, which needs to balance the constraint effect and removability to avoid introducing new problems; edge constraint and gradual support are common strategies; (4) increasing the heat treatment fixture; (5) comprehensively applying multiple technologies, such as high-temperature preheating + optimized island scanning strategy + edge constraint support. Among the above methods, (1) the substrate preheating function is not available on all devices, and high-temperature preheating of the substrate can improve the adhesion between large-area substrates and grafting structures, but it cannot improve the problem of different internal residual stresses of different materials; (2) improving the scanning strategy according to the structure can avoid local deformation caused by heating for too long at the same position. However, when the grafting structure is too complex and local stress concentration occurs, changing the scanning strategy will not improve the situation. Moreover, when the process is mature, changing the scanning strategy may cause internal defects in the part; (3) adding a support structure is suitable for simple structure parts. For fine structures, the addition of supports may cause problems such as damage to the structure and residual support marks when removing the support constraint; (4) the heat treatment fixture is the most commonly used method to improve deformation. However, additional heat treatment fixtures need to be determined according to the structure; some structures do not support the use of fixtures, or additional custom design is required, increasing the difficulty and cost of work; (5) the existing technical solutions do not have universal applicability when used alone or in combination, and require changes in processing methods according to the structure, which increases the additional time cost or changes the performance. SUMMARY

[0005] Therefore, the present application provides a method for reducing the deformation of a plate-shaped copper alloy part during grafting printing, which solves the problem of stress imbalance between the grafting structure and the substrate after the grafting printing method is used to construct a new structure on the substrate, resulting in warping during printing and increased deformation during subsequent performance annealing, which affects the subsequent processing and assembly.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] A method for reducing the deformation of a plate-shaped copper alloy part during grafting printing, comprising the following steps:

[0008] S1, preparing a pure copper substrate, at least four countersunk holes are symmetrically processed on each substrate (the number of countersunk holes can be increased, such as six, when the length of the substrate exceeds 150 mm, and the positions of the countersunk holes are staggered from the area to be grafted and printed, and are preferably arranged at the periphery of the substrate);

[0009] S2, locking and fixing the substrate on the printing base plate through the countersunk screws;

[0010] Preferably, 1.5mm < substrate thickness < 3mm, M2 countersunk head screws are selected;

[0011] 3mm ≤ substrate thickness < 4mm, M3 countersunk head screws are selected;

[0012] S3, slice the model of the part to be grafted using Materialise slicing software, set the layer thickness to 0.03mm, and generate the corresponding slice file; use the upper surface of the substrate as the grafting printing surface to perform leveling and gas washing, and then print layer by layer on the substrate, with the first layer of the printed layer being remelted to increase adhesion and raise the substrate temperature (100-150°C), thereby avoiding local deformation of the substrate due to uneven temperature between the substrate and the printed layer;

[0013] A printing strategy of lower laser power + higher scanning speed (180-220W, 950-1050mm / s) is adopted, and higher laser power or slower scanning speed will cause heat accumulation;

[0014] Zonal scanning: adopt a chessboard scanning strategy to avoid local overheating (jump area scanning in the same layer to avoid repeated heat input in adjacent areas);

[0015] Interlayer cooling: increase the interlayer cooling time (10-20s) to reduce residual stress (adjust the software to set the interlayer jump interval time and prolong the interlayer cooling time);

[0016] S4, after printing, the entire part is sent to a vacuum atmosphere furnace for annealing treatment (the fixing screws are not removed), the temperature is raised to 600°C±3°C at a rate of 5-10°C / min, and then the temperature is maintained for 2h, then argon is filled to cool to 70°C±10°C, finally it is taken out and placed in the air to cool to room temperature, obtaining optimal thermal and mechanical properties. If the structure of the grafted printing part is too complex, the heating time can be appropriately prolonged (the heating rate is reduced) to avoid deformation caused by rapid stress release due to complex structure;

[0017] S5, after the entire part is completely cooled, the screws are removed, and the flatness of the substrate is detected.

[0018] The copper alloy powder comprises the following components by mass percentage:

[0019] Cr: 0.8-1.2%, Zr 0.1-0.3%, Ti 0.05-0.15%, nano-Al2O3 0.3-0.5%, and the balance of copper.

[0020] The characteristics of each element in the copper alloy powder are shown in Table 1.

[0021] Table 1 Characteristics of each element in the copper alloy powder

[0022]

[0023] Improvement mechanism of each element on thermal stress and deformation

[0024] ① Role of Cr

[0025] CTE matching: reduce the CTE of alloy from 17x10 -6 / ℃ of pure copper to about 15x10 -6 / ℃, reducing thermal mismatch with the substrate.

[0026] High temperature strength: precipitate Cr-rich phase (such as CrCu2) during aging process, inhibit high temperature deformation, and reduce stress concentration during cooling.

[0027] ② Synergistic effect of Zr and Ti

[0028] Grain boundary strengthening: Zr is segregated at grain boundaries, hindering dislocation movement and reducing residual stress accumulation.

[0029] Interface bonding: Ti preferentially reacts with the surface oxides of the substrate to form a metallurgical bonding layer, avoiding interface peeling.

[0030] ③ Dispersion effect of nano-Al2O3

[0031] Stress redistribution: nanoparticles act as local stress buffer points, dispersing stress concentration at the interface.

[0032] Deformation inhibition: hindering grain boundary migration at high temperature, reducing deformation caused by creep.

[0033] Thermal conductivity performance balance strategy

[0034] ① Solid solubility control: Cr, Zr, Ti all maintain low solid solubility (<1.5% total), avoiding excessive electron scattering.

[0035] ② Second phase optimization: nano-Al2O3 size is controlled at 50-100 nm, ensuring dispersion distribution without blocking the thermal conductivity path.

[0036] In summary, in the present application, the composition of the copper alloy aims to reduce the difference in thermal expansion coefficient (CTE) between the copper alloy and pure copper, improve the high temperature strength of the copper alloy, reduce plastic deformation, and maintain good thermal conductivity (>300 W / mK).

[0037] Compared with the prior art, the present application has the beneficial effects of:

[0038] The application firstly improves the difference of thermal expansion coefficient between the copper alloy and the pure copper substrate by the composition and the amount of the copper alloy material, avoids the risk of deformation, and also ensures the good heat conduction performance and mechanical performance of the product; secondly, the printing process is improved to reduce the residual stress. In the application, the way of setting countersunk screw holes for fixing and restraining on the substrate is suitable for most of the substrate and the fine structure grafting printing scene, and does not affect the grafting printing process. The fixed restraint can make the grafting structure positioning more accurate, obtain better size accuracy, and can inhibit the stress deformation generated in the scanning process and the substrate deformation caused by the uneven stress release in the annealing process. It is not necessary to additionally increase the support and clamp, which ensures that the processing time is not increased while effectively reducing the construction cost, and does not affect the performance of the final part. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a schematic diagram of fixing and locking the substrate on the printing base plate by M3 countersunk screw.

[0040] In the figure: 1 is a printing base plate, 2 is a substrate, and 3 is a countersunk screw on the substrate. DETAILED DESCRIPTION

[0041] In order for those skilled in the art to more clearly and intuitively understand the application, the application will be further described below in conjunction with the drawings.

[0042] Example 1

[0043] The embodiment proposes a method for reducing the grafting printing deformation of plate-shaped copper alloy parts, which comprises the following steps:

[0044] S1, a pure copper substrate (length 110 mm, width 60 mm, thickness 3 mm) is prepared, and four countersunk screw holes are symmetrically processed on each substrate (the positions of the countersunk screw holes are staggered with the area to be grafting printed on the substrate, and in this embodiment, the four countersunk screw holes are arranged on the four corners of the substrate);

[0045] S2, the substrate is fixed and locked on the printing base plate by M3 countersunk screw, as shown in Figure 1 .

[0046] S3, the model of the part to be grafted is processed by using Materialise slicing software, the layer thickness is set to 0.03 mm, and the corresponding slice file is generated; the upper surface of the substrate is used as the grafting printing surface to perform leveling and gas washing preparation, and then copper alloy powder is printed layer by layer on the substrate, the first layer of the printing layer is remelted to increase the adhesion and make the substrate temperature rise (100-150°C), so as to avoid the local deformation of the substrate caused by the uneven temperature between the substrate and the printing layer;

[0047] Print strategy with lower power + higher scan speed (200 W + 1000 mm / s) to reduce heat accumulation;

[0048] Zoned scanning: Use a checkerboard scanning strategy to avoid local overheating (scan the same layer by jumping areas, avoid repeated heat input in adjacent areas);

[0049] Interlayer cooling: Increase the interlayer cooling time (10-20 s) to reduce residual stress (adjust the software settings to increase the interlayer cooling time by adjusting the interlayer jump interval time);

[0050] S4, After printing, the whole plate of parts is sent into a vacuum atmosphere furnace for annealing treatment (the fixing screws are not removed), the temperature is raised to 600℃ at a rate of 10℃ / min, and then the temperature is kept for 2h, then argon is filled to cool to 80℃, finally the whole plate of parts is taken out and placed in the air to cool to room temperature, to obtain the optimal thermal conductivity and mechanical properties;

[0051] S5, After the whole body is completely cooled, the screws are removed, and the flatness of the part substrate is detected;

[0052] In this embodiment, the copper alloy powder comprises the following components by mass percentage:

[0053] Cr: 1.0%, Zr 0.2%, Ti 0.10%, nano-Al2O3 0.4%, and the balance of copper.

[0054] The mechanical property detection standard of the part substrate refers to GB / T 228.1:

[0055] (1) Install the sample

[0056] Clamp the sample in the test machine clamp, ensure axial centering, and avoid eccentric load.

[0057] The clamping force is moderate to prevent the sample from slipping or being damaged.

[0058] (2) Preload

[0059] Apply a small initial load (such as 1% of the expected maximum force) to eliminate the gap and adjust the extensometer zero point.

[0060] (3) Load test

[0061] Rate control:

[0062] Elastic stage: control by stress rate (such as 1-10 MPa / s, ISO 6892-1 method A).

[0063] Plastic stage: switchable strain rate (such as 0.0025-0.025 s -1 ).

[0064] Continuous recording: load-displacement data are collected simultaneously until specimen failure.

[0065] (4) Post-Fracture Measurement

[0066] The specimen is removed, the fractured portions are rejoined, and the post-fracture gauge length (L u ) and the minimum diameter / width at the neck are measured.

[0067] Example 2

[0068] The difference between this embodiment and Example 1 is that the cooling rate during annealing is 5℃ / min; the printing power is 180W, and the scanning speed is 1050 mm / s.

[0069] In this embodiment, the copper alloy powder comprises the following components in mass percentage:

[0070] Cr: 0.8%, Zr 0.1%, Ti 0.05%, nano-Al2O3 0.3%, and the balance of copper.

[0071] Example 3

[0072] The difference between this embodiment and Example 1 is that the size of the substrate is 110mm long, 60mm wide, and 2mm thick, and is fixed on the printing base plate using M2 countersunk screws; the printing power is 220W, and the scanning speed is 950 mm / s.

[0073] In this embodiment, the copper alloy powder comprises the following components in mass percentage:

[0074] Cr: 1.2%, Zr 0.3%, Ti 0.15%, nano-Al2O3 0.5%, and the balance of copper.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that Cr is removed from the copper alloy powder, i.e., the copper alloy powder comprises the following components in mass percentage:

[0077] Zr 0.2%, Ti 0.1%, nano-Al2O3 0.4%, and the balance of Cu.

[0078] From the effect of graft printing on a pure copper substrate using the above-mentioned copper alloy powder, the thermal deformation of the substrate increases, affecting the flatness; at the same time, the mechanical properties are affected, and the absence of Cr reduces the solid solution of the copper alloy powder, and the thermal conductivity is improved.

[0079] Comparative Example 2

[0080] The difference between the present comparative example and Example 1 is only that the addition amount of Cr in the copper alloy powder is increased, i.e. the copper alloy powder comprises the following components in mass percentage:

[0081] Cr 1.5%, Zr 0.2%, Ti 0.1%, nano-Al203 0.4%, balance Cu.

[0082] From the effect of graft printing on the pure copper substrate using the above copper alloy powder, the excessive Cr is solid-solved in the matrix, increases the free electron scattering rate, hinders the heat conduction path, and thus affects the heat conduction performance; and the excessive Cr leads to an increase in brittleness, affecting the mechanical performance.

[0083] Comparative Example 3

[0084] The difference between the present comparative example and Example 1 is only that the Zr and Ti in the copper alloy powder are removed, i.e. the copper alloy powder comprises the following components in mass percentage:

[0085] Cr 1.0%, nano-Al203 0.4%, balance Cu.

[0086] From the effect of graft printing on the pure copper substrate using the above copper alloy powder, the absence of Zr and Ti causes the residual stress to accumulate in the grafting part, and the interface adhesion effect is poor; the interface bonding quality is significantly reduced due to the relatively coarse grain formation and obvious interface residual stress accumulation, and the interface is prone to cracking.

[0087] Comparative Example 4

[0088] The difference between the present comparative example and Example 1 is only that the addition amount of Zr in the copper alloy powder is increased, i.e. the copper alloy powder comprises the following components in mass percentage:

[0089] Cr 1.0%, Zr 0.4%, Ti 0.1%, nano-Al203 0.4%, balance Cu.

[0090] From the effect of graft printing on the pure copper substrate using the above copper alloy powder, the excessive addition of Zr can slightly improve the strength, but significantly reduces the plasticity and toughness, and the excessive brittle intermetallic compound (such as Cu5Zr) leads to grain boundary stress concentration, especially the elongation is greatly affected.

[0091] Comparative Example 5

[0092] The difference between the present comparative example and Example 1 is only that the nano-Al203 in the copper alloy powder is removed, i.e. the copper alloy powder comprises the following components in mass percentage:

[0093] Cr 1.0%, Zr 0.2%, Ti 0.1%, balance Cu.

[0094] From the effect of using the above-mentioned copper alloy powder for graft printing on a pure copper substrate, the lack of nano-Al2O3 leads to a lack of stress buffering and strengthening phase, and high-temperature creep is intensified, resulting in a decrease in the mechanical properties of the formed part.

[0095] Comparative Example 6

[0096] In this comparative example, the only difference from Example 1 is that the nano-Al2O3 in the copper alloy powder is added in excess, i.e., the copper alloy powder comprises the following mass percentage of components:

[0097] Cr 1.0%, Zr 0.2%, Ti 0.1%, nano-Al2O3 0.8%, and the balance Cu.

[0098] From the effect of using the above-mentioned copper alloy powder for graft printing on a pure copper substrate, the excess nano-Al2O3 particles agglomerate, forming local stress concentration points and promoting cracks.

[0099] Comparative Example 7

[0100] This comparative example proposes a method for graft printing on a substrate, which differs from Example 1 in that when printing on a copper substrate, no fixed constraints are added, and then during the annealing process, a flat clamp is used to fix the substrate, and the rest is the same as Example 1. From the final effect, the substrate lacks fixed constraints during the printing stage and has already deformed greatly. The use of a flat clamp during the subsequent annealing process cannot completely suppress the deformation tendency and repair the deformation during the printing stage, and the final sample is severely warped.

[0101] Comparative Example 8

[0102] This comparative example proposes a method for graft printing on a substrate, which differs from Example 1 in that it uses a printing strategy with a laser power of 250 w for printing. From the effect of using the above-mentioned copper alloy powder for graft printing on a pure copper substrate, the excessive laser power leads to excessive heat accumulation, which affects the flatness of the copper substrate.

[0103] Comparative Example 9

[0104] This comparative example proposes a method for graft printing on a substrate, which differs from Example 1 in that it uses a printing strategy with a scanning speed of 900 mm / s for printing. From the effect of using the above-mentioned copper alloy powder for graft printing on a pure copper substrate, the excessively slow scanning speed also leads to excessive heat accumulation, which affects the flatness of the copper substrate.

[0105] Comparative Example 10

[0106] The comparative example proposes a method for graft printing on a substrate, which is different from example 1 in that no remelting operation is performed during printing, and the copper substrate is not preheated. From the effect of graft printing on a pure copper substrate using the above-mentioned copper alloy powder, the thermal difference between the pure copper substrate and the base is large, the residual stress release is inconsistent, which leads to a large stress difference in the first few layers during printing, the middle of the bottom plate is arched, and the overall mechanical properties are affected.

[0107] The products obtained by graft printing in each example and comparative example are subjected to mechanical property detection, and the results are shown in Table 2.

[0108] Table 2 Mechanical property detection results of products obtained by printing in each example and comparative example

[0109]

[0110] From the results of examples and comparative examples 1-6 in Table 2, it can be seen that the amount of each component in the copper alloy powder plays an important role in the deformation of the plate-shaped copper alloy part during graft printing, especially the influence on flatness and mechanical properties. In addition, from the structure of comparative example 7, the substrate is fixed with the printing bottom plate by using a countersunk screw in the present application, which effectively prevents the thermal stress deformation of the substrate. This method does not affect the printing process and heat treatment process of the part, so it does not have a negative impact on the mechanical properties and thermal conductivity of the plate-shaped copper alloy part. From the results of comparative examples 8-10, by changing the laser power, scanning speed and whether to use remelting, the heat accumulation during product printing is too large, which leads to the generation of deformation.

[0111] The present application combines the thermal deformation law of the edge of the plate, reduces the possibility of warping of the plate during heat treatment through corner constraint, reduces the flatness tolerance of the plate by 90-95%, and controls the flatness to ≤0.1mm; the present application selects the copper alloy powder and the printing process to maximize the stability of the final performance of the part. After treatment, the density of the part reaches 99.99%, the tensile strength is above 550MPa, the yield strength is above 450MPa, and the thermal conductivity is above 300W / mK, which meets the performance requirements of thermal conductive parts.

[0112] The above description of the examples is to facilitate the understanding and application of the present application by ordinary skilled persons in the technical field. Those skilled in the art can easily make various modifications to these examples, and apply the general principles described herein to other examples without creative labor. Therefore, the present application is not limited to the examples herein, and any improvements and modifications of the present application made by those skilled in the art based on the disclosure of the present application should be within the scope of protection of the present application.

Claims

1. A method for reducing deformation during grafting and printing of plate-shaped copper alloy parts, characterized in that, Includes the following steps: S1. Prepare a pure copper substrate. On each substrate, at least four countersunk screw holes are symmetrically machined. The positions of the countersunk screw holes are staggered from the area to be grafted and printed. S2. Secure the substrate to the printing base plate using countersunk screws; S3. Use Materialise slicing software to slice the model of the part to be grafted, set the layer thickness to 0.03mm, and generate the corresponding slice file; use the upper surface of the substrate as the grafting printing surface to prepare for leveling and gas washing, and then lay copper alloy powder layer by layer on the substrate for printing, and remelt the first layer of the printed layer. The copper alloy powder comprises the following components in weight percentage: Cr: 0.8-1.2%, Zr: 0.1-0.3%, Ti: 0.05-0.15%, nano Al2O3: 0.3-0.5%, and the balance being copper; The laser power for printing is 180~220W, the scanning speed is 950~1050 mm / s, a checkerboard scanning strategy is adopted, and the interlayer cooling time is set to 10~20s. S4. After printing, the entire part is sent into a vacuum atmosphere furnace along with the printing base plate for annealing. The temperature is raised to 600℃±3℃ at a rate of 5~10℃ / min, held for 2 hours, then argon gas is used to cool it to 70℃±10℃. Finally, it is taken out and placed in the air to cool to room temperature. S5. After the whole thing has completely cooled down, remove the screws to get the plate-shaped copper alloy part.

2. The method for reducing deformation during grafting and printing of plate-shaped copper alloy parts as described in claim 1, characterized in that, The copper alloy powder comprises the following components by mass percentage: Cr: 1.0%, Zr: 0.2%, Ti: 0.10%, nano Al2O3: 0.4%, and the balance being copper.

3. The method for reducing deformation during grafting printing of plate-shaped copper alloy parts as described in claim 1, characterized in that, The countersunk screw holes are located at the four corners of the substrate.

4. The method for reducing deformation during grafting printing of plate-shaped copper alloy parts as described in claim 1, characterized in that, When 1.5mm < substrate thickness < 3mm, M2 countersunk screws should be selected.

5. The method for reducing deformation during grafting printing of plate-shaped copper alloy parts as described in claim 1, characterized in that, When the substrate thickness is 3mm or less and 4mm or less, M3 countersunk screws should be selected.

6. The method for reducing deformation during grafting printing of plate-shaped copper alloy parts as described in claim 1, characterized in that, Remelting causes the substrate temperature to rise to 100~150°C.

7. The application of the method according to any one of claims 1 to 6 in the preparation of a liquid-cooled heat sink.

8. The application as described in claim 7, characterized in that, The liquid-cooled heat sink includes a copper substrate and a copper alloy heat dissipation structure, which is constructed by grafting printing.

9. The product obtained by the method according to any one of claims 1 to 6.

10. The product as described in claim 9, characterized in that, The product is a liquid-cooled radiator with a density of 99.99%, a tensile strength of over 550MPa, a yield strength of over 450MPa, and a thermal conductivity of over 300W / mK.

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