A method for preparing high-density crack-free Al-Cu alloy based on laser pulse shaping

Abstract

The application discloses a kind of preparation methods of high-density crack-free Al-Cu alloy based on laser pulse shaping, and Al-Cu alloy is easy to form low melting point eutectic due to wide solidification temperature range and can form solidification crack in the laser forming process.The application can control aluminum alloy powder bed preheating, powder melting and heat treatment effect by regulating laser power and exposure time of single laser pulse, effectively reduce residual thermal stress caused by large temperature gradient of molten pool and wide solidification range, inhibit the cracking of forming sample, and finally obtain high-density crack-free laser additive manufacturing Al-Cu alloy parts.The method uses laser pulse shaping to improve the forming quality of aluminum alloy during laser additive manufacturing, and obtains crack-free Al-Cu alloy parts.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing process innovation and relates to a method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping. Background Technology

[0002] Al-Cu high-strength aluminum alloys are characterized by low density, high strength, and good corrosion resistance, and are commonly used in aerospace, automotive, and transportation fields. Laser additive manufacturing of Al-Cu alloys can simplify the manufacturing process of complex parts, meeting the aerospace industry's demand for lightweight, high-strength, and complex structural components. However, during laser forming of Al-Cu alloys, the high cooling rate causes the liquid phase to shrink rapidly in the later stages of solidification, generating significant thermal stress and leading to crack formation. Summary of the Invention

[0003] Purpose of the invention: The technical problem to be solved by the present invention is to address the problem of cracking that easily occurs in the laser additive manufacturing process of Al-Cu alloys. The invention provides a method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping to eliminate thermal cracks, form a high-density, crack-free aluminum alloy sample, and improve the forming quality and performance of laser additive manufacturing of Al-Cu alloys.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping includes the following steps:

[0006] (1) Use computer-aided design software to establish a three-dimensional solid geometric model of the target part, and then use slicing software to slice the model into layers, plan the laser scanning path, and set the laser power and exposure time to discretize the three-dimensional solid into a series of two-dimensional data.

[0007] (2) Import the two-dimensional data from step (1) into the selective laser melting and forming equipment, melt and solidify the Al-Cu alloy powder layer by layer, and finally prepare a high-density, crack-free three-dimensional aluminum alloy solid part.

[0008] In step (2), laser pulse shaping technology is used to control the melting / solidification behavior of Al-Cu alloy powder, adjust the heating / cooling rate, effectively reduce thermal residual stress, and suppress cracking of the finished product. First, the alloy powder is preheated using a preheating pulse; then, the alloy powder is melted using a laser peak pulse; finally, the alloy is cooled and solidified using a post-pulse.

[0009] The preheating pulse refers to a low-power preheating peak before the maximum laser power peak exposure, which helps preheat the powder bed and reduce the temperature gradient of the molten pool during laser forming. The peak pulse, with its high energy input, completely melts the aluminum alloy powder, facilitating melt wetting and spreading. By rationally controlling the molten pool temperature and heat input, rapid melting and solidification of the material can be achieved, thereby improving the production efficiency of additive manufacturing. The post-pulse refers to a heat treatment peak with a longer exposure period and lower laser power after the maximum laser power peak exposure. It effectively controls the cooling and solidification of the molten pool, thus helping to control the residual thermal stress generated during cooling, acting as a heat treatment process. It also helps reduce the thermal temperature gradient during the rapid cooling of the molten pool, reducing residual stress and stress concentration, thereby suppressing hot cracking.

[0010] Preferably, in step (2), the Al-Cu alloy powder contains 3.08 to 4.93 wt.% Cu, 1.06 to 1.60 wt.% Zn, 0.20 to 1.10 wt.% Ni, with the balance being Al; the Al-Cu alloy powder has a particle size of 26 to 47 μm.

[0011] Preferably, in step (2), the ratio of the laser power of the preheating pulse to the laser peak pulse is 0.23 to 0.56.

[0012] Preferably, in step (2), the ratio of the laser power of the afterpulse to the laser peak pulse is 0.25 to 0.46.

[0013] Preferably, in step (2), the preheating pulse includes two single laser pulse peaks, the laser peak pulse is a single laser pulse peak, and the post pulse includes two single laser pulse peaks; the five single laser pulse peaks of the preheating pulse, the laser peak pulse, and the post pulse are distributed in a normal shape to achieve precise control of the preheating, melting, and heat treatment of the aluminum alloy powder bed during the material forming process.

[0014] Preferably, in step (2), the peak laser pulse power is 44 to 72 W.

[0015] Preferably, the exposure time for each single laser pulse peak is 100–500 μs.

[0016] Preferably, in step (2), the Al-Cu alloy powder is laid with a thickness of 30 to 50 μm.

[0017] Preferably, in step (2), the laser pulse scanning interval is 50-60 μm, and a point scanning strategy is adopted.

[0018] Preferably, in step (2), the selective laser melting equipment used includes an Nd:YAG fiber laser (maximum power of 100W), a powder supply system, a protective atmosphere device, a computer control system, and a cooling circulation system; before forming, the forming cavity is sealed by a sealing device, evacuated, and high-purity Ar gas is introduced as a protective atmosphere to keep the oxygen content below 40ppm.

[0019] The laser additive manufacturing process is as follows: (a) The powder spreading device spreads aluminum alloy powder onto the forming substrate to form a powder bed. (b) The laser system controls laser pulses to scan and form exposure points with different laser powers and exposure times, and repeats the same laser pulse for each exposure point to form a preheating, melting and heat treatment process of the aluminum alloy powder and forming sample, producing a two-dimensional plane of solid part; then the forming cylinder drive system drives the forming cylinder to move down by one powder layer thickness, and the powder spreading device spreads a new powder bed; (c) Repeat step (b) until a solid aluminum alloy sample is formed layer by layer.

[0020] The above parameters are the optimal parameters. Based on the different microstructures and properties of Al-Cu alloys, the process parameters of the laser additive manufacturing process and the laser power and exposure time of the pulse shaping settings can be reasonably adjusted and optimized to successfully prepare aluminum alloy material forming samples with good forming quality and excellent comprehensive performance.

[0021] Beneficial effects:

[0022] (1) In the process of laser additive manufacturing, the present invention utilizes pulse shaping to control the laser energy distribution during the sample preparation process, thereby reducing the residual thermal stress generated by the large temperature gradient of the molten pool in the Al-Cu alloy during the additive manufacturing process, suppressing the cracking of the formed sample, and realizing the laser additive manufacturing of crack-free high-strength aluminum alloy.

[0023] (2) This invention only requires a simple change to the laser energy distribution used in the laser additive manufacturing process, without damaging its original function and structure. Laser pulse shaping has a higher energy utilization rate, which can reduce energy consumption, reduce production costs, and improve the forming quality and stability of Al-Cu alloys prepared by laser additive manufacturing.

[0024] (3) Compared with traditional casting, forging, welding, powder metallurgy, and subtractive machining methods, this invention innovatively uses laser additive manufacturing to prepare high-strength aluminum alloy components, which greatly improves the design freedom of parts and makes it possible to manufacture complex high-strength aluminum alloy components with topology optimization and biomimetic design. The formed parts are suitable for aerospace, medical and health and other fields with small batch, high forming quality, lightweight, customization and complexity requirements. Attached Figure Description

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0026] Figure 1 This is a schematic diagram of the laser pulse during the laser additive manufacturing process of the present invention.

[0027] Figure 2 This is an optical image of the laser additive manufacturing Al-Cu alloy obtained in Example 1 of the present invention.

[0028] Figure 3 This is an optical image of the laser additive manufacturing Al-Cu alloy obtained in Example 2 of the present invention.

[0029] Figure 4 This is an optical image of the laser additive manufacturing Al-Cu alloy obtained in Example 3 of the present invention.

[0030] Figure 5 This is an optical image of the laser additive manufacturing microstructure of Al-Cu alloy obtained in Comparative Example 1 of this invention.

[0031] Figure 6 This is an optical image of the laser additive manufacturing microstructure of Al-Cu alloy obtained in Comparative Example 2 of the present invention.

[0032] Figure 7 This is an optical image of the laser additive manufacturing microstructure of Al-Cu alloy obtained in Comparative Example 3 of the present invention.

[0033] Figure 8 This is an optical image of the laser additive manufacturing Al-Cu alloy obtained in Comparative Example 4 of the present invention.

[0034] Figure 9 This is an optical image of the laser additive manufacturing Al-Cu alloy obtained in Comparative Example 5 of the present invention. Detailed Implementation

[0035] The present invention can be better understood from the following embodiments.

[0036] In the following examples and comparative examples, the Al-Cu alloy powder used contained Cu with a content of 3.08–4.93 wt.%, Zn with a content of 1.06–1.60 wt.%, Ni with a content of 0.20–1.10 wt.%, and the balance being Al; the particle size of the Al-Cu alloy powder was 26–47 μm.

[0037] Laser pulse shaping technology is used to control the melting / solidification behavior of Al-Cu alloy powder, adjust the heating / cooling rate, effectively reduce thermal residual stress, and suppress cracking of the finished product. For example... Figure 1As shown, firstly, a lower-power preheating pulse is used before the exposure at the maximum laser power peak to preheat the aluminum alloy powder bed, thereby reducing the temperature gradient of the molten pool during laser forming. Then, a peak pulse is used, with high energy input, to completely melt the aluminum alloy powder, ensuring thorough wetting and spreading of the molten aluminum alloy powder. Finally, a longer exposure period and a lower laser power follow-up pulse are used after the maximum laser power peak exposure. This effectively controls the cooling and solidification rate of the molten pool, helps reduce the thermal temperature gradient during rapid cooling, controls the formation and stress concentration of residual thermal stress during cooling, suppresses hot cracking, and achieves a heat treatment effect. Therefore, by adjusting the laser power and exposure time of a single laser pulse, the effects of preheating the aluminum alloy powder bed, powder melting, and heat treatment can be achieved, effectively reducing residual thermal stress caused by a large molten pool temperature gradient, suppressing cracking of the formed sample, and ultimately obtaining a highly dense, crack-free Al-Cu alloy part.

[0038] Example 1

[0039] (1) A three-dimensional solid geometric model of the target part was established using computer-aided design software and exported as an STL file. Then, the model was sliced ​​using slicing software, and the laser scanning path and laser process parameters were set. The laser process parameters were set as follows: peak pulse power 44W, laser power ratio of pre-pulse / peak pulse 0.23 and 0.46, laser power ratio of post-pulse / peak pulse 0.42 and 0.25, respectively, i.e., pulse laser power of 10W, 20W, 44W, 18W and 11W, exposure time of adjacent laser peaks 100μs, 250μs, 250μs, 500μs and 200μs, layer thickness 30μm, scanning interval 60μm, and point scanning strategy was adopted.

[0040] (2) Import the slice file obtained in step (1) into the computer control system of the selective laser melting forming equipment, and place the Al-Cu alloy powder in the equipment for forming. The selective laser melting equipment uses an Nd:YAG fiber laser (maximum power of 100W), and before forming, the forming cavity is sealed by a sealing device, evacuated and high-purity Ar gas is introduced as a protective atmosphere to ensure that the oxygen content in the forming chamber is less than 40ppm.

[0041] (3) The laser additive manufacturing process is as follows: (a) The powder spreading device spreads aluminum alloy powder onto the forming substrate to form a powder bed. (b) The laser system controls the laser pulse to scan and form exposure points with different laser power and exposure time, and repeats the same laser pulse for each exposure point to form a preheating, melting and heat treatment process of aluminum alloy powder and forming sample, producing a two-dimensional plane of solid part; then the forming cylinder drive system drives the forming cylinder to move down by one powder layer thickness, and the powder spreading device spreads a new powder bed; (c) Repeat step (b) until a solid aluminum alloy sample is formed layer by layer.

[0042] (4) After forming is completed, the part and the substrate are separated by wire cutting to obtain the Al-Cu alloy sample. The Al-Cu alloy block sample is ground and polished according to the standard metallographic sample preparation method. Its optical image is shown below. Figure 2 As shown, the Al-Cu alloy sample has good forming quality, with no obvious cracks or pores, and a density of 99.8%.

[0043] Example 2

[0044] (1) A three-dimensional solid geometric model of the target part was established using computer-aided design software and exported as an STL file. Then, the model was sliced ​​using slicing software, and the laser scanning path and laser process parameters were set. The laser process parameters were set as follows: peak pulse power 58W, laser power ratio of pre-pulse / peak pulse 0.26 and 0.53, laser power ratio of post-pulse / peak pulse 0.44 and 0.28, respectively, i.e., pulse laser power of 15W, 30W, 58W, 25W and 16W, exposure time of adjacent laser peaks 100μs, 230μs, 200μs, 480μs and 200μs, layer thickness 40μm, scanning interval 55μm, and point scanning strategy was adopted.

[0045] (2) Import the slice file obtained in step (1) into the computer control system of the selective laser melting forming equipment, and place the Al-Cu alloy powder in the equipment for forming. The selective laser melting equipment uses an Nd:YAG fiber laser (maximum power of 100W), and before forming, the forming cavity is sealed by a sealing device, evacuated and high-purity Ar gas is introduced as a protective atmosphere to ensure that the oxygen content in the forming chamber is less than 40ppm.

[0046] (3) The laser additive manufacturing process is as follows: (a) The powder spreading device spreads aluminum alloy powder onto the forming substrate to form a powder bed. (b) The laser system controls the laser pulse to scan and form exposure points with different laser power and exposure time, and repeats the same laser pulse for each exposure point to form a preheating, melting and heat treatment process of aluminum alloy powder and forming sample, producing a two-dimensional plane of solid part; then the forming cylinder drive system drives the forming cylinder to move down by one powder layer thickness, and the powder spreading device spreads a new powder bed; (c) Repeat step (b) until a solid aluminum alloy forming sample is obtained by forming layer by layer.

[0047] (4) After forming is completed, the part and the substrate are separated by wire cutting to obtain the Al-Cu alloy sample. The Al-Cu alloy block sample is ground and polished according to the standard metallographic sample preparation method. Its optical image is shown below. Figure 3 As shown, no obvious cracks were observed in the Al-Cu alloy sample, although a small number of micropores were present. It exhibited good forming quality and a density of 99.6%.

[0048] Example 3

[0049] (1) A three-dimensional solid geometric model of the target part was established using computer-aided design software and exported as an STL file. Then, the model was sliced ​​layer by layer using slicing software, and the laser scanning path and laser process parameters were set. The laser process parameters were set as follows: peak pulse power 72W, laser power ratio of pre-pulse / peak pulse 0.28 and 0.56, laser power ratio of post-pulse / peak pulse 0.46 and 0.32, i.e., pulse laser power of 20W, 40W, 72W, 33W and 23W respectively, exposure time of adjacent laser peaks 100μs, 200μs, 180μs, 400μs and 200μs, layer thickness 50μm, scanning interval 50μm, and point scanning strategy was adopted.

[0050] (2) Import the slice file obtained in step (1) into the computer control system of the selective laser melting forming equipment, and place the Al-Cu alloy powder in the equipment for forming. The selective laser melting equipment uses an Nd:YAG fiber laser (maximum power of 100W), and before forming, the forming cavity is sealed by a sealing device, evacuated and high-purity Ar gas is introduced as a protective atmosphere to ensure that the oxygen content in the forming chamber is less than 40ppm.

[0051] (3) The laser additive manufacturing process is as follows: (a) The powder spreading device spreads aluminum alloy powder onto the forming substrate to form a powder bed. (b) The laser system controls the laser pulse to scan and form exposure points with different laser power and exposure time, and repeats the same laser pulse for each exposure point to form a preheating, melting and heat treatment process of aluminum alloy powder and forming sample, producing a two-dimensional plane of solid part; then the forming cylinder drive system drives the forming cylinder to move down by one powder layer thickness, and the powder spreading device spreads a new powder bed; (c) Repeat step (b) until a solid aluminum alloy forming sample is obtained by forming layer by layer.

[0052] (4) After forming is completed, the part and the substrate are separated by wire cutting to obtain the Al-Cu alloy sample. The Al-Cu alloy block sample is ground and polished according to the standard metallographic sample preparation method. Its optical image is shown below. Figure 4 As shown, a small number of micropores can be found in the Al-Cu alloy sample, with a density of 99.5%.

[0053] Optical images of the samples prepared in Examples 1, 2, and 3 show that controlling the laser power and exposure time of a single laser pulse during laser additive manufacturing can effectively control the preheating, melting, and heat treatment of the aluminum alloy powder bed, thereby reducing the temperature gradient of the molten pool in the formed sample, reducing residual thermal stress, avoiding stress concentration, and thus inhibiting cracking of the formed sample.

[0054] Comparative Example 1

[0055] Comparative Example 1 follows the same basic steps as Example 1, except that laser pulse shaping is not used in the laser additive manufacturing process. Instead, a Gaussian beam is used to perform laser additive manufacturing on aluminum alloy powder. The laser process parameters are set as follows: laser power 44W, scanning speed 300mm / s, scanning spacing 60μm, layer thickness 30μm, and point scanning strategy is adopted.

[0056] Hot cracks parallel to the forming direction were observed in laser-formed Al-Cu alloy samples, spanning multiple molten pools and penetrating the entire sample. Unmelted porosity was also present in the samples, with a density of 98.1%. Figure 5 This is because the solid-liquid coexistence zone with high crack sensitivity exists for a long time during solidification. At high scanning speeds, the cooling rate is high, and the liquid phase at the end of solidification does not have enough time to fill, resulting in crack formation. At the same time, the laser energy input is low, and the aluminum alloy powder is not completely melted, forming irregular unmelted pores, thus resulting in poor laser formability.

[0057] Comparative Example 2

[0058] Comparative Example 2 followed the same basic steps as Example 2, the only difference being that the laser power ratio of the pre-pulse / peak pulse was 0.10 and 0.75, and the laser power ratio of the post-pulse / peak pulse was 0.70 and 0.12, i.e., the pulsed laser powers were 6W, 44W, 58W, 41W, and 7W, respectively. A small number of cracks were still observed in the laser-formed Al-Cu alloy samples. Figure 6 The density was slightly improved to 98.8%. This was because the laser power variation between the preheating pulse and the post-pulse was too large, resulting in uneven heating of the aluminum alloy powder during the forming process. This failed to achieve the desired preheating effect on the aluminum alloy powder and the heat treatment effect on the formed sample, leading to stress concentration inside the molten pool and the generation of cracks.

[0059] Comparative Example 3

[0060] The basic steps of Comparative Example 3 were the same as those of Example 1, the only difference being that the peak laser pulse power during laser additive manufacturing was less than 44W. In this comparative example, the peak pulse power was 20W, the laser power ratio of the pre-pulse to the peak pulse was 0.23 and 0.46, and the laser power ratio of the post-pulse to the peak pulse was 0.42 and 0.25, i.e., the pulsed laser powers were 5W, 9W, 20W, 8W, and 5W, respectively. A large number of unfused pores and unmelted powder residue were observed in the laser-formed Al-Cu alloy sample, and its compactness decreased to 97.3%. Figure 7 This is because the peak pulse power is too small, the aluminum alloy powder is not completely melted, and the temperature of the molten pool decreases, which leads to an increase in melt viscosity, a decrease in wetting and spreading performance, the formation of unmelted pores, and ultimately a reduction in the forming quality of the aluminum alloy.

[0061] Comparative Example 4

[0062] Comparative Example 4 follows the same basic steps as Example 3, except that the peak laser melting power during laser additive manufacturing is greater than 72W. In this comparative example, the peak pulse power is 95W, the laser power ratio of pre-pulse / peak pulse is 0.28 and 0.56, and the laser power ratio of post-pulse / peak pulse is 0.46 and 0.32, i.e., the pulsed laser powers are 27W, 53W, 95W, 44W, and 30W, respectively. A large number of circular pores were observed in the laser-formed Al-Cu alloy sample, and its compactness decreased to 97.3%. Figure 8 This is because the laser peak power is too high, causing low-melting-point elements in the aluminum alloy to vaporize during laser forming. These elements do not overflow from the molten pool in time during rapid solidification, resulting in circular pores.

[0063] Comparative Example 5

[0064] Comparative Example 5 follows the same basic steps as Example 3, the only difference being that the five single laser pulse peaks—the preheating pulse, the laser peak pulse, and the post-pulse—during the laser additive manufacturing process exhibit a non-normal distribution. In this comparative example, the pulsed laser powers were 40W, 20W, 72W, 23W, and 33W, respectively. A small number of cracks and interlayer porosity were still observed in the laser-formed Al-Cu alloy sample, with a compactness of 98.7%. Figure 9 This is because the non-normal distribution of laser energy during laser forming causes uneven temperature distribution in the molten pool, resulting in a large temperature gradient. This leads to discontinuity in temperature and thermal stress between different layers, which easily causes stress concentration, reduces the interlayer bonding strength, and affects the overall compactness of the aluminum alloy sample.

[0065] This invention provides a method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping, characterized in that, Includes the following steps: (1) Use computer-aided design software to establish a three-dimensional solid geometric model of the target part, and then use slicing software to slice the model into layers, plan the laser scanning path and set the laser power and exposure time to discretize the three-dimensional solid into a series of two-dimensional data. (2) Import the two-dimensional data from step (1) into the selective laser melting and forming equipment, melt and solidify the Al-Cu alloy powder layer by layer, and finally prepare a high-density, crack-free three-dimensional aluminum alloy solid part. In step (2), laser pulse shaping technology is used to control the melting / solidification behavior of Al-Cu alloy powder. First, the alloy powder is preheated with a preheating pulse. Then, the alloy powder is melted with a laser peak pulse. Finally, the alloy is cooled and solidified with a post-pulse. In step (2), the laser power ratio of the preheating pulse to the laser peak pulse is 0.23~0.56; In step (2), the ratio of the laser power of the afterpulse to the laser peak pulse is 0.25 to 0.46; In step (2), the peak laser pulse power is 44~72 W; In step (2), the preheating pulse includes two single laser pulse peaks, the laser peak pulse is a single laser pulse peak, and the post pulse includes two single laser pulse peaks; the five single laser pulse peaks of the preheating pulse, the laser peak pulse, and the post pulse are distributed in a normal shape. The exposure time for each single laser pulse peak is 100~500 μs.

2. The method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping according to claim 1, characterized in that, In step (2), the Al-Cu alloy powder contains 3.08~4.93 wt.% Cu, 1.06~1.60 wt.% Zn, 0.20~1.10 wt.% Ni, and the balance is Al; the particle size of the Al-Cu alloy powder is 26~47 μm.

3. The method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping according to claim 1, characterized in that, In step (2), the Al-Cu alloy powder is laid with a thickness of 30~50 μm.

4. The method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping according to claim 1, characterized in that, In step (2), the laser pulse scanning interval is 50~60 μm, and a point scanning strategy is adopted.

5. The method for preparing a high-density, crack-free Al-Cu alloy based on laser pulse shaping according to claim 1, characterized in that, In step (2), the selective laser melting equipment used includes an Nd:YAG fiber laser, a powder supply system, a protective atmosphere device, a computer control system, and a cooling circulation system. Before forming, the forming cavity is sealed by a sealing device, evacuated, and high-purity Ar gas is introduced as a protective atmosphere to keep the oxygen content below 40ppm.

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