A process for laser marking high-contrast QR codes on aluminum alloy surfaces

Abstract

The present invention discloses a process for laser marking a high-contrast QR code on an aluminum alloy surface, comprising the following steps: S1: the aluminum plate needs to be cleaned with alcohol and then ultrasonically cleaned for 20 minutes before use; S2: the laser uses a MOPA structure fiber laser, and the field lens is selected to be 140×140 mm in size; S3: the aluminum plate to be marked is placed flat on the marking platform, and the focal length of the field lens is adjusted by adjusting the laser optical path load-bearing bracket up and down to ensure that the defocus amount of the marking experiment does not exceed ±0.1 mm. The present invention utilizes a MOPA structure nanosecond pulse fiber laser with adjustable pulse width and high peak power. By adjusting the parameters, a high-contrast QR code can be obtained at a low pulse width, and the surface roughness is low, and the appearance is delicate and beautiful, thereby achieving laser precision marking of high-contrast QR codes on aluminum alloy surfaces.

Description

Technical Field

[0001] The present invention relates to the technical field of laser marking on aluminum alloy surfaces, and in particular to a process for laser marking a high-contrast two-dimensional code on an aluminum alloy surface. Background Art

[0002] It's become a trend for companies to mark QR codes on metal products, parts, and decorative items for anti-counterfeiting, traceability, and promotional purposes. Aluminum alloy, due to its dense oxide film, has a very low laser absorption rate of approximately 0.8%. Currently, the most commonly used lasers for marking QR codes on aluminum alloy surfaces are Q-switched lasers and solid-state Nd:YAG lasers. The marked QR codes are all off-white. Because aluminum alloy itself is silvery-white and highly reflective, the marked QR codes are difficult or even impossible to identify. Existing technical solutions: Ultrafast lasers can be used to mark black graphics on aluminum alloy surfaces. Q-switched lasers and Nd:YAG solid-state lasers can be used to mark gray QR codes.

[0003] Most current research on laser marking QR codes on aluminum alloy surfaces has shown that using ultrafast lasers (femtosecond and picosecond lasers) for low-efficiency marking can produce high-contrast, high-color-difference QR codes. However, due to their high price and low efficiency, they are difficult to apply in industry. Conventional Q-switched, solid-state nanosecond lasers have not achieved high contrast when exploring parameter marking of high-contrast QR codes, and can only form grayish-white QR codes, which makes subsequent industrial identification difficult. In addition, the surface roughness is high, and the marked QR codes are not aesthetically pleasing. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a process method for laser marking a high-contrast two-dimensional code on the surface of an aluminum alloy.

[0005] The present invention proposes a process for laser marking a high-contrast two-dimensional code on an aluminum alloy surface, comprising the following steps:

[0006] S1: The aluminum plate needs to be cleaned with wine and then ultrasonically cleaned for 20 minutes before use;

[0007] S2: The laser uses a MOPA structure fiber laser, and the field lens size is 140×140mm;

[0008] S3: Place the aluminum plate to be marked flat on the marking platform, and adjust the focal length of the field lens by moving the laser optical path bearing bracket up and down to ensure that the defocus of the marking experiment does not exceed ±0.1mm, and the focal length is 254mm;

[0009] S4: Turn on the red light indicator positioning, determine the required marking position on the aluminum plate surface, edit a 12×12mm square in the marking software, and input the following laser parameters for marking white: pulse width 9ns, pulse frequency 850KHz, scanning speed 700mm / s, fill spacing 0.04mm, and average power 12W. Edit a 10×10mm QR code in the marking software, input the laser parameters for marking the QR code, conduct a single-factor marking experiment, and explore the optimal parameter combination. Place the QR code layer on the top layer, ensuring that the white bottom layer is marked first and then the QR code.

[0010] S5: Click the Start Marking button to laser mark the QR code. The marked QR code is captured by a CCD industrial camera, and a grayscale image is taken for contrast measurement. The optimal marking process parameters are selected through grayscale image comparison and analysis.

[0011] Preferably, the aluminum plate used is an Al 1060 aluminum plate with a thickness of 1 mm, a size of 100×100 mm, a metallic bright white color, and no surface coating.

[0012] Preferably, after the laser marking is completed, a grayscale picture of the QR code image is captured, and a picture of the marked area taken by the industrial camera is captured in the software corresponding to the camera, and the grayscale value of the image is obtained through the software.

[0013] The beneficial effects of the present invention are:

[0014] The present invention utilizes a MOPA structure nanosecond pulse fiber laser with adjustable pulse width and high peak power. By adjusting the parameters, a high-contrast two-dimensional code can be obtained at a low pulse width, and the surface roughness is low, the appearance is delicate and beautiful, and the laser precision marking of a high-contrast two-dimensional code on the aluminum alloy surface is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing the process parameter settings for laser marking a high-contrast QR code on an aluminum alloy surface in a process method for laser marking a high-contrast QR code on an aluminum alloy surface proposed by the present invention;

[0016] Figure 2 This is a diagram showing the actual effect of the unmarked and marked white bottom QR codes before and after the process of laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention;

[0017] Figure 3 This is a table of process parameters for laser marking a white bottom layer of a process method for laser marking a high-contrast QR code on an aluminum alloy surface proposed by the present invention;

[0018] Figure 4This is a diagram showing the actual effects of QR codes marked with different waveforms and the regularity of image contrast changes in a process for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention;

[0019] Figure 5 This is a diagram showing the effect of the pulse waveform on the micromorphology of the process for laser marking high-contrast two-dimensional codes on aluminum alloy surfaces proposed by the present invention;

[0020] Figure 6 This is a grayscale image and contrast change image of the QR code marked at different average powers and pulse widths of 1ns, 2ns, and 4ns for a process method for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention;

[0021] Figure 7 This is a diagram showing the effect of laser power on the microscopic morphology of a high-contrast two-dimensional code on an aluminum alloy surface laser marking process proposed by the present invention;

[0022] Figure 8 Grayscale images and contrast change diagrams of the QR codes marked at different scanning speeds and pulse widths of 1ns, 2ns, and 4ns for a process method for laser marking high-contrast QR codes on aluminum alloy surfaces proposed in this invention;

[0023] Figure 9 This is a diagram showing the effect of scanning speed on the microscopic morphology of a high-contrast two-dimensional code on the surface of an aluminum alloy laser marking process proposed by the present invention;

[0024] Figure 10 Grayscale images and contrast variation diagrams of the QR codes marked at different filling intervals at pulse widths of 1ns, 2ns, and 4ns using a process for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention.

[0025] Figure 11 This is a diagram showing the effect of filling spacing on microscopic morphology in a process for laser marking high-contrast two-dimensional codes on aluminum alloy surfaces proposed by the present invention;

[0026] Figure 12 This is a process for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention, showing the actual effects of marking QR codes on different grades of aluminum alloys at pulse widths of 1ns, 2ns, and 4ns respectively;

[0027] Figure 13 This is a process for laser marking high-contrast QR codes on aluminum alloy surfaces proposed in the present invention, showing image contrast ratios of QR codes marked on different aluminum alloys at pulse widths of 1ns, 2ns, and 4ns.

[0028] Figure 14The SEM images of the black QR code area at different magnifications of the process method for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention are as follows;

[0029] Figure 15 This is a diagram of the grayscale value collection and microscopic morphology observation area of ​​the process method for laser marking high-contrast QR codes on aluminum alloy surfaces proposed by the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] Reference Figure 1-15 A process for laser marking a high-contrast QR code on an aluminum alloy surface comprises the following steps:

[0032] S1: The aluminum plate needs to be cleaned with wine and then ultrasonically cleaned for 20 minutes before use;

[0033] S2: The laser uses a MOPA structure fiber laser, and the field lens size is 140×140mm;

[0034] S3: Place the aluminum plate to be marked flat on the marking platform, and adjust the focal length of the field lens by moving the laser optical path bearing bracket up and down to ensure that the defocus of the marking experiment does not exceed ±0.1mm, and the focal length is 254mm;

[0035] S4: Turn on the red light indicator positioning, determine the required marking position on the aluminum plate surface, edit a 12×12mm square in the marking software, and input the following laser parameters for marking white: pulse width 9ns, pulse frequency 850KHz, scanning speed 700mm / s, fill spacing 0.04mm, and average power 12W. Edit a 10×10mm QR code in the marking software, input the laser parameters for marking the QR code, conduct a single-factor marking experiment, and explore the optimal parameter combination. Place the QR code layer on the top layer, ensuring that the white bottom layer is marked first and then the QR code.

[0036] S5: Click the Start Marking button to laser mark the QR code. The marked QR code is captured by a CCD industrial camera, and a grayscale image is taken for contrast measurement. The optimal marking process parameters are selected through grayscale image comparison and analysis.

[0037] In the present invention, the aluminum plate used is Al 1060 aluminum plate with a thickness of 1 mm, a size of 100×100 mm, a metallic bright white color, and no surface coating. After the laser marking is completed, a grayscale image of the QR code image is captured, and a picture of the marked area taken by the industrial camera is captured in the software corresponding to the camera, and the grayscale value of the image is obtained through the software.

[0038] For the recognition process of QR codes, when other conditions are met for recognition, the contrast of the QR code image is the most critical factor. The higher the contrast of the QR code, the higher the index parameter level, and the faster it can be recognized. The contrast of a QR code is the difference between the average pixel value of the 10% pixels with the smallest pixel value (i.e., the marked area) and the average pixel value of the 10% pixels with the largest pixel value (i.e., the unmarked area) in the grayscale image of the barcode obtained by the image acquisition system. This experiment selected the process of marking a layer of white base layer first and then marking the QR code, which can identify the QR code more quickly. The formula for calculating the contrast is: C = 1-A / B, where the grayscale value of the white base layer is B and the grayscale value of the marked area is A.

[0039] Experimental plan:

[0040] (1) Mark the white bottom layer to increase contrast

[0041] Since the aluminum plate has a high reflectivity after brushing and polishing, the contrast is low after the QR code is directly marked on the aluminum plate surface. When verifying the readability of the QR code, it was found that the reading time of the directly marked QR code is too long or even impossible to read. Therefore, before marking the QR code, a process method is adopted to laser mark a white bottom layer on the aluminum plate surface and then mark the QR code. Verification of its readability found that the QR code recognition and reading time is significantly reduced and the QR code contrast is significantly increased after marking the white bottom layer. Figure 2 As shown in the figure, the contrast ratio increased from 0.56 to 0.88, which greatly improved the stability and application range of high-quality QR code marking technology, and provided a greater guarantee for the readability of QR codes in practical engineering applications. The parameters of the white bottom layer of the laser marking in this experiment were selected after a large number of experiments. Figure 3 shown.

[0042] (2) QR code laser marking experiment

[0043] Draw a 10mm×10mm square QR code in the laser marking software. Set different marking control parameters for each QR code. To avoid the influence of uneven lighting or other human factors, use a scanner CCD to collect the grayscale image of all QR codes on the aluminum plate surface after marking.

[0044] The contrast of the QR code marked under different parameters is quite different. Use image processing software to collect the gray value of the marked QR code. Select the positioning block of the QR code in the collection area, such as Figure 15 The contrast ratio is calculated by calculating the collected grayscale value, and the curve of the relationship between different laser parameters and the contrast ratio of the marking area is obtained with the help of Origin software. Figure 1 shown.

[0045] The influence of pulse waveform on the marking effect of QR code

[0046] (1) Impact of pulse waveform on contrast of QR code

[0047] Based on the selected MOPA structure fiber laser, there are 16 waveforms. As shown in Chapter 2, the pulse width of each waveform has a corresponding power reduction frequency. 16 pulse widths and corresponding power reduction frequencies are selected. Other laser parameters remain unchanged. A QR code is marked on a white substrate that has been scanned at high speed. A CCD camera is used to capture the contrast image. The resulting QR code is as follows: Figure 4 shown. Figure 4 Waveforms 1 to 16 correspond to Figure 1 The pulse width is 1ns~200ns, and the corresponding frequency is 1000KHz~45KHz.

[0048] Reference Figure 4 The contrast of the QR codes was found to be best for waveforms 1 to 5, corresponding to pulse widths of 1ns, 2ns, 4ns, 6ns, and 9ns, with a smooth surface and an overall color closer to black. The QR codes corresponding to waveforms 6 to 9 had a rougher surface, with the color gradually shifting from gray-black to gray-white, with the gray-white color being more pronounced in waveforms 7 to 9. From waveforms 10 to 16, the surface was rougher, but the color gradually shifted to gray-black. A contrast comparison of the QR code images detected using a CCD camera revealed that the contrast changes were consistent with actual results. The QR codes corresponding to waveforms 1 to 5 had higher contrast and darker colors, with the contrast reaching as high as 0.901 for waveform 2. The QR codes corresponding to waveforms 6 to 9 had lower contrast, reaching the lowest contrast of 0.426 for waveform 7, consistent with actual results, with a gray-white appearance at this point. The contrast of the QR codes corresponding to waveforms 10 to 16 began to gradually increase.

[0049] (2) Laser marking process under different pulse waveforms

[0050] In order to analyze the interaction process between laser and aluminum alloy under each waveform, the ultra-depth-of-field microscope was used to observe the microscopic morphology of the QR code positioning block, such as Figure 5 The figure shows the microscopic morphology of the laser marked QR code positioning under different waveforms. Figure 5 (a) to (p) correspond one-to-one to the QR codes of the 16 waveform marks mentioned above.

[0051] It was observed that as the pulse waveform changes, the pulse width gradually increases and the pulse frequency gradually decreases, and the corresponding microscopic morphology of the QR code changes significantly. Figure 5 (a), (b), (c), (d) and (e) in the figure. When the pulse width is low, the molten aluminum alloy particles are very small and appear relatively flat. When the pulse width is 2ns, the corresponding pulse frequency is 850KHz. This is because the contrast is the highest at this time. Figure 5 In (b), a relatively flat irregular network structure can be seen. This is because at low pulse widths, the laser emits a pulse wave for a very short time, resulting in an extremely high pulse frequency. For a given power, the energy of a single spot is low, while the peak power of each waveform in the MOPA structure is high. This allows the aluminum alloy surface to be cratered even at low pulse widths. However, the heat-affected zone formed by the spot is smaller, and less aluminum alloy melts around the crater, resulting in a relatively flat surface.

[0052] When the pulse width gradually increases and the pulse frequency decreases, it means that the action time of each light spot increases. When the power is constant, this indicates that the energy of a single light spot increases. Figure 5 As can be seen from (f) to (k), after the aluminum alloy surface is impacted by the laser, the overall microstructure presents larger aluminum alloy particles.

[0053] As the pulse width continues to increase, when the increase is large, the degree of pulse frequency reduction decreases, and the pulse energy density of the laser decreases, corresponding to Figure 5 (k) to (p). The microscopic morphology shows that the aluminum alloy particles on the surface gradually become smaller after laser marking. Due to the large pulse width and the longer dwell time of the laser spot, the laser impact craters on the aluminum alloy are larger than those at lower pulse widths, resulting in larger particles.

[0054] The influence of average power on the marking effect of QR code

[0055] (1) Impact of average power on QR code contrast

[0056] In the previous section, it was concluded that the effect of laser marking QR codes is better at low pulse widths, so when the pulse widths are 1ns, 2ns, and 4ns, different powers are used to laser mark the aluminum alloy surface. Figure 6 The grayscale image and contrast change pattern of the QR code under different powers.

[0057] Through the QR code contrast image, it is observed that the pulse energy density increases during the marking process due to the increase in pulse width and the corresponding decrease in pulse frequency. This can be seen in Figure 6 As can be seen in the figure, when the pulse width is 1ns and the laser power is 4W, the QR code marked with 1ns is completely invisible, the code marked with 2ns is extremely light in color, and the QR code marked with 4ns begins to become gradually clear. During the marking process, as the laser power increases, the grayscale value of the QR code gradually decreases, the contrast gradually increases, and the marking effect gradually approaches black.

[0058] (2) Laser marking process analysis

[0059] A QR code marked with a pulse waveform with a pulse width of 2ns was selected to perform microscopic morphology analysis on its location, and then the interaction process between the laser and the aluminum alloy was analyzed. Figure 7 (a)~(h) It can be found that with the increase of laser power, at low power, Figure 7 The laser scanning traces can be seen relatively clearly in (a) to (c), but due to the low energy density of aluminum alloy, the amount of molten aluminum alloy is relatively small. As the laser power increases, the energy of the laser acting on the aluminum alloy surface increases, the mark depth increases, the molten aluminum alloy begins to contact and fuse, the molten part becomes larger, and an irregular network structure gradually forms. As the laser power continues to increase, the molten part begins to grow. This is because the laser is a continuous spot moving regularly. When the energy acting on the aluminum alloy surface surges, the pit formed by the impact of a laser spot is further deepened than before, and the surrounding re-melted and solidified aluminum alloy increases. The molten aluminum alloy between the two spots begins to fuse, the molten part increases, and the uneven network structure begins to grow.

[0060] The impact of scanning speed on the effect of marking QR codes

[0061] (1) The impact of scanning speed on QR code contrast

[0062] In order to explore the effect of scanning speed on the marking effect of QR code, different scanning speeds were used to mark the QR code when the pulse width was 1ns, 2ns and 4ns. Figure 8The grayscale image of a QR code is shown. Observations show that the contrast of the QR code increases gradually with increasing scanning speed, starting at a scanning speed of 30 mm / s, and the marking quality also becomes clearer. At a scanning speed of 100 mm / s, the color reaches its darkest. As the scanning speed continues to increase, the contrast of the marked QR code begins to decrease, and the marking quality gradually deteriorates. Measurements of the QR code image contrast reveal that the effect of scanning speed on contrast is generally consistent at 1 ns, 2 ns, and 4 ns. With increasing scanning speed, the contrast of the QR code image first increases and then decreases, reaching a maximum value of 0.872 at a scanning speed of 100 mm / s. Before the scanning speed reaches 100 mm / s, the increase is small, and the change in QR code image contrast is minimal. After 100 mm / s, the contrast decreases significantly with increasing scanning speed.

[0063] (2) Laser marking process analysis

[0064] Using a single-factor experimental method, a QR code marked with a pulse waveform with a pulse width of 1ns was selected for microscopic morphology analysis at the location, further analyzing the interaction between the laser and the aluminum alloy. While other laser parameters remained constant, the contrast value initially increased with increasing scanning speed, reaching a maximum at a scanning speed of 100 mm / s, after which the contrast value began to decrease.

[0065] Figure 9 It is the interaction process between laser and aluminum alloy during the process of laser marking QR code at different scanning speeds. Figure 9 (a) to (h) correspond to the scanning speed increasing from 30 mm / s to 100 mm / s in units of 10 mm / s. Figure 9 The corresponding scanning speeds of (i) to (l) are 120 mm / s, 150 mm / s, 180 mm / s, and 200 mm / s, respectively.

[0066] It can be seen that when the scanning speed is 30mm / s, the surface of the aluminum alloy is almost completely melted into one piece. As the speed increases, the morphology changes from sheet to mass to spherical. Figure 9 (e) to (h) it gradually turns into an irregular mesh. This is because when the scanning speed is low, the laser interacts with the aluminum alloy surface for a longer time, and the overlap between the light spots on the same scanning line is also tighter. When marking the second line, the overlapping part of the first line continues to melt. After the final marking is completed, the aluminum alloy melts and solidifies into almost a single piece. When the scanning speed continues to increase, such as Figure 9(c) to (h), the scanning speed increases. The marking time becomes shorter, but the energy is still very large. After laser marking, the surface of the aluminum alloy changes from almost completely melted to partially melted, and solidified to form a spherical structure. The speed continues to increase. It can be seen that when the speed reaches 100mm / s, Figure 9 As shown in (h), the overall action time is reduced, the overlap rate between adjacent spots is reduced, the marking depth is reduced, the spherical particles become smaller, and the spherical particles begin to merge with each other to form an irregular network structure. When the speed continues to increase to 150mm / s, as shown in Figure 9 (k) to (l), the laser acts on the aluminum alloy surface for a short time, and the fusion between the spherules begins to become less and less obvious.

[0067] The impact of padding spacing on the effect of marking QR codes

[0068] (1) The impact of padding spacing on QR code contrast

[0069] In order to explore the effect of filling spacing on the marking effect of QR code, different filling spacings were used for QR code marking when the pulse width was 1ns, 2ns and 4ns, and the following results were obtained: Figure 10 The grayscale image of the QR code and the pattern of contrast changes are shown. Observation revealed that the contrast of the QR code gradually increases starting with a fill spacing of 0.001mm. When the fill spacing increases to 0.003mm, the color reaches its darkest, and the contrast reaches its maximum, reaching 0.804. As the fill spacing increases further, the contrast of the marked QR code begins to decrease, and the effect of the marked QR code gradually deteriorates. At 1ns, 2ns, and 4ns, the effect of the fill spacing on contrast is generally consistent. As the fill spacing increases, the contrast of the QR code image first increases and then decreases. The minimum contrast corresponding to different pulse widths varies, but all reach their maximum value at 0.003mm.

[0070] (2) Laser marking process analysis

[0071] A QR code marked with a pulse waveform with a pulse width of 1ns was selected, and the low-light morphology analysis was performed on its positioning position, and then the interaction process between the laser and the aluminum alloy was analyzed. Figure 11 The effect of filling spacing on micromorphology is shown in Figure 2. Figure 11 (a) to (j) correspond to the filling spacing starting from 0.001mm and increasing to 0.01mm in units of 0.001mm. Figure 11 (k) to (l) correspond to filling spacings of 0.012mm and 0.015mm respectively. Figure 11The microscopic morphology corresponding to the filling spacing can be seen in the figure. Similar to the microscopic morphology corresponding to the scanning speed, when the filling spacing is 0.001mm and 0.002mm, the aluminum alloy surface is impacted by dense laser spots, and the impact craters formed have a high repetition rate. After the laser scanning, the molten aluminum alloy is almost completely solidified and fused into one piece. As the filling spacing increases, the overlap between adjacent scanning lines decreases, and the molten aluminum alloy forms a discontinuous network structure. The molten aluminum alloy part of the network structure gradually becomes smaller and thinner, as shown in the figure. Figure 11 (c)~(i). After 0.01mm, if Figure 11 (j) to (l), the traces of light spot etching can be clearly seen, and the morphology between adjacent scanning lines gradually emerges.

[0072] In summary, the laser has the best marking effect on QR codes when the pulse width is 1ns, 2ns, or 4ns. Based on the low pulse widths of 1ns, 2ns, and 4ns, the effects of laser average power, scanning speed, and fill spacing on the contrast of QR codes were explored, and it was found that the contrast change trend was consistent under the three pulse widths. As the average laser power gradually increased, the contrast gradually increased, and the marking effect was good. The best effect was achieved when the average power was 18W. As the scanning speed increased, the contrast showed an effect of first rising and then falling, with the highest contrast at 100mm / s. The exploration of the fill spacing found that as the fill spacing increased, the contrast showed an effect of first rising and then falling, with the best effect when the fill spacing was 0.003mm. Therefore, the laser parameters for the best marking effect are a pulse width of 2ns, a pulse frequency of 850KHz, an average power of 18W, a scanning speed of 100mm / s, and a fill spacing of 0.003mm.

[0073] Applicability of processing parameters

[0074] Through the previous experimental research, it was found that the use of low pulse width pulse waveform laser can mark high contrast QR code on the surface of 1060 aluminum alloy. In order to explore whether the laser parameters used at low pulse width can mark high contrast QR code on the surface of other brands of aluminum alloy, three types of brushed aluminum plates, namely 5052, 6061 and 7075, were selected for laser marking QR code test. It was proved that the combination of laser parameters used at low pulse width can still mark high contrast QR code, such as Figure 12 As shown, the contrast of the markings on the 7075 aluminum alloy surface is even higher, such as Figure 13 As shown, the contrast ratio is as high as 0.912, and the color is closer to black.

[0075] The principle of using this process to mark ultra-black QR codes:

[0076] Observe the microscopic area of ​​the black QR code and find that Figure 14(a) The process of laser marking a "black" QR code on the surface of aluminum alloy is a laser remelting and condensation process. When the power density F = 6.1W / cm2, a characteristic structure of randomly distributed micron holes is formed on the surface of the aluminum alloy, and the hole diameter is about 2 to 5μm. Figure 14 As shown in (b), it can be observed that during the marking process, due to the slow scanning speed and small spacing between filling lines, the aluminum alloy melted and resolidified to form micron holes and pits. When observing the micron hole and pit structure under high magnification, as shown in Figure 14 As shown in (c), it is found that there are also hole structures nested in the pits, and some pits are multi-hole structures with 2 to 3 holes, and there are clusters of micron-protrusions around these pits and holes. Figure 14 (d) It can be observed that the sidewall surface of the micron hole and the area around the hole also have micron protrusions and micron particles. The micron cluster structure and the seemingly smooth area around the hole are observed at 10,000 times and 20,000 times respectively. Figure 14 As shown in (e), it is found that these cluster structures are covered with well-developed subscale particle structures with sizes in the hundreds of nanometers. Figure 14 As can be seen in (f), when the seemingly smoother area is magnified, it is also a "cracked" and porous structure composed of hundreds of nanometer-scale cluster structures and smaller microcracks.

[0077] Principle: The laser wavelength used in this study is 1064nm, and most of the holes formed in the microscopic morphology are about 1 to 5μm in diameter. This shows that the absorption effect of micron holes is mainly the "light trapping" effect of light and the multiple reflections of incident light entering the micron holes. Figure 14 A multi-hole nested structure is formed, whereby large pits are nested with small holes, creating a more complex light "trap." Once light enters the nested porous structure, it is difficult to escape, and multiple internal reflections occur within the nested holes, significantly reducing the surface reflectivity. Furthermore, in addition to the light-trapping effect of the micron structure, the surface is covered with multi-scale, randomly distributed aluminum alloy submicron particle clusters, microcracks, and microporous structures. For submicron structures, this anti-reflection effect is achieved primarily by exciting surface plasmons and forming localized surface plasmon resonances, further enhancing the light absorption effect of "black aluminum."

[0078] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A process for laser marking high-contrast two-dimensional codes on aluminum alloy surfaces, characterized in that: The following steps are involved: S1: Uncoated aluminum sheets need to be cleaned with alcohol to remove surface contaminants before use; S2: The laser uses MOPA structure fiber laser, and the field lens size is 100×100-140×140mm; S3: Place the aluminum plate to be marked flat on the marking platform, and adjust the focal length of the field lens by moving the laser optical path support up and down to ensure that the defocus of the marking experiment does not exceed ±0.1mm, and the focal length is 185-254mm; S4: Turn on the red light indication positioning, determine the required marking position on the aluminum plate surface, edit a 12×12mm square in the marking software, and enter the optimized laser parameter combination for printing the white background color block: pulse width of 9ns, pulse frequency of 850KHz, scanning speed of 700mm / s, filling spacing of 0.04mm, and average power of 12W. Then edit a 10×10mm QR code in the operating software, enter the laser parameters for printing the QR code, and conduct a single-factor marking test experiment to test the laser parameter combination for printing the best dark QR code on the white marking block: pulse width, frequency, speed, and power, obtain the best grayscale value of the QR code, and do not damage the white background film. Place the QR code layer on the top of the white background, ensuring that the white bottom layer is printed first and then the black QR code is printed; S5: Click the Start Print button to print the white background with the laser and then print the QR code. The printed QR code is captured by a CCD industrial camera, and its grayscale or dark image is taken for contrast measurement. The optimal marking process parameters are selected through grayscale image optimization and comparative analysis. The laser parameters for the best marking effect are: pulse width 2ns, pulse frequency 850KHz, average power 18W, scanning speed 100mm / s, and fill spacing 0.003mm. The aluminum plate used is Al 1060 aluminum plate with a thickness of 1 mm, a size of 100×100 mm, a metallic bright silver color, and an uncoated surface. The industrial camera model is Hikvision MV-CA003-50GM. After the laser marking is completed, a grayscale image of the QR code image is captured, and a picture of the printing area taken by the industrial camera is captured in the software corresponding to the camera, and the grayscale value of the image is obtained through the Visionmaster software.

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