Aluminum product with eliminated color difference of anodic oxide film and method for producing the same

Abstract

The present application relates to the technical field of metal surface treatment, and particularly relates to an aluminum product for eliminating color difference of an anodic oxidation film and a preparation method thereof. The present application discloses an aluminum product for eliminating color difference of an anodic oxidation film, comprising: an aluminum alloy base body, a first cladding layer cladded on at least part of the surface of the aluminum alloy base body, a second cladding layer cladded on at least part of the surface of the first cladding layer, and a third cladding layer cladded on at least part of the surface of the second cladding layer; wherein the first cladding layer is an AlMn alloy layer; the second cladding layer is an Al metal layer; and the third cladding layer is an anodic oxidation film layer. The present application sets the three-layer composite structure of the AlMn alloy layer, the pure Al layer and the anodic oxidation film layer on the aluminum alloy base body in sequence, solves the technical problems of the existing technology that the aluminum alloy is prone to crystal flowers, the color difference of the anodic oxidation film is obvious, and the appearance is uneven, and simultaneously improves the coating adhesion, the surface flatness and the corrosion resistance, so as to meet the use requirements of high-end appearance parts.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to an aluminum product for eliminating color difference in anodized films and its preparation method. Background Technology

[0002] Aluminum alloys, due to their low density, high specific strength, and excellent machinability, are widely used in consumer electronics, automobiles, aerospace, and decorative building materials. To improve the wear resistance, corrosion resistance, and decorative effect of aluminum alloy surfaces, anodizing is typically required. However, the aluminum alloy matrix contains alloying elements such as Mg, Si, Zn, Cu, and Fe, which form intermetallic compound second phases such as CuAl2, FeAl3, and Mg2Si. These second phases undergo selective dissolution during anodizing, leading to increased oxide film porosity, decreased corrosion resistance, and color variations such as graying, reddish tinge, blackening, streaks, and dark gray, resulting in poor appearance consistency and failing to meet the requirements of high-end exterior components.

[0003] To address the aforementioned issues, the industry typically employs a method of plating a pure aluminum layer onto the aluminum alloy surface followed by anodizing. The pure aluminum layer lacks a second alloy phase, resulting in a uniformly colored and dense anodized film. However, when directly electroplating pure aluminum onto the aluminum alloy surface, the deposition behavior of aluminum atoms is strongly influenced by the grain orientation of the aluminum alloy matrix, easily forming crystalline spots on the plating surface, leading to uneven appearance. These crystalline defects are retained in the subsequent anodized film, resulting in noticeable color differences and poor appearance even after oxidation, severely limiting the application of aluminum plating anodizing processes on exterior parts. Therefore, developing an aluminum alloy surface treatment technology that can fundamentally shield against the influence of matrix grains, completely eliminate crystalline appearance, and achieve highly uniform color in the anodized film has become a pressing technical problem to be solved in this field. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing an aluminum product and its preparation method that eliminates color differences in anodized films. By sequentially setting an AlMn alloy layer, a pure Al layer, and an anodized film layer on an aluminum alloy substrate, the invention solves the technical problems of easy crystal growth, obvious color differences in anodized films, and uneven appearance caused by direct aluminum plating of aluminum alloys in existing technologies. At the same time, it improves the adhesion of the coating, surface smoothness, and corrosion resistance, meeting the usage requirements of high-end appearance parts.

[0005] Therefore, the first objective of this invention is to provide an aluminum product that eliminates color difference in anodized films.

[0006] The second objective of this invention is to provide a method for preparing aluminum products that eliminates color differences in anodized films.

[0007] To achieve the first objective of this invention, the technical solution of this invention provides an aluminum product for eliminating color difference in anodized film, comprising: an aluminum alloy substrate, a first coating layer covering at least a portion of the surface of the aluminum alloy substrate, a second coating layer covering at least a portion of the surface of the first coating layer, and a third coating layer covering at least a portion of the surface of the second coating layer; wherein, the first coating layer is an AlMn alloy layer; the second coating layer is an Al metal layer; and the third coating layer is an anodized film layer.

[0008] Compared with existing technologies, the technical effects achieved by this solution are as follows: The AlMn alloy layer can completely cover the aluminum alloy substrate with an amorphous or microcrystalline structure and block the induction effect of substrate grain orientation and grain boundaries on surface aluminum deposition. From the nucleation mechanism, it avoids the preferential growth of aluminum atoms along the substrate to form a flower-like morphology. The Al metal layer is a single-phase high-purity aluminum structure without second-phase particles, which can eliminate the color difference of the oxide film caused by the selective dissolution of the alloy phase. The anodic oxide film layer has a regular porous alumina structure, which improves the surface wear resistance, corrosion resistance and decoration. The three-layer structure matches layer by layer, has stable bonding force and works synergistically to achieve no color difference and uniform appearance of the aluminum alloy anodic oxide film throughout the process.

[0009] In one embodiment of the present invention, the thickness of the first coating layer is 2μm-10μm; the thickness of the second coating layer is 3μm-10μm; and the thickness of the third coating layer is 3μm-12μm.

[0010] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: an AlMn alloy layer thickness of more than 2μm can ensure complete shielding of the substrate grain boundaries and grain orientation, preventing the recurrence of grain flowers; a thickness control of less than 10μm can reduce internal stress, improve interlayer bonding, and prevent coating warping and peeling; an Al metal layer of 3μm-10μm or more can provide a sufficiently pure and uniform oxide substrate to ensure the continuity and defect-free anodic oxide film; and an anodic oxide film thickness of 3μm to 12μm can balance protective performance and appearance flatness, avoiding cracking or color difference caused by excessive film thickness.

[0011] In one embodiment of the present invention, the Mn content in the first coating layer is 6 at.% to 20 at.%.

[0012] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: when the Mn content is above 6 at.%, it can effectively inhibit the crystallization of aluminum lattice and promote the formation of amorphous or nanocrystalline structures in AlMn alloys, thereby completely eliminating the grain boundary conduction effect. When the Mn content is below 20 at.%, it can avoid alloy hardening and embrittlement and deposition defects, ensuring that the coating is dense and flat and firmly bonded to the substrate and the surface aluminum layer. This composition range enables the AlMn alloy layer to simultaneously possess excellent shielding effect, structural stability, and interface compatibility.

[0013] In one technical solution of the present invention, the material type of the aluminum alloy substrate includes at least one of 6061, 7075, 2024 and 5052.

[0014] Furthermore, the aluminum alloy matrix can be selected from aluminum alloys produced from recycled aluminum.

[0015] Furthermore, the forming methods of the aluminum alloy substrate include extrusion forming of aluminum alloy and surface polishing of aluminum alloy.

[0016] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: The above-mentioned aluminum alloys contain alloying elements such as magnesium, silicon, copper, zinc, and iron, which easily generate second phases such as CuAl2, FeAl3, and Mg2Si, resulting in graying, blackening, reddish-graying, and striped color differences during conventional anodizing. The multi-layer structure of this invention can specifically solve the appearance defects of such mainstream industrial aluminum alloys, and improve the versatility and industrial applicability of the solution.

[0017] To achieve the second objective of this invention, the technical solution of this invention provides a method for preparing aluminum products that eliminates color difference in anodized films, used to prepare aluminum products as described in any of the above technical solutions, comprising the following steps: S100, placing an aluminum alloy substrate in a first ionic liquid and performing a first electroplating treatment to obtain a first intermediate; S200, placing the first intermediate in a second ionic liquid and performing a second electroplating treatment to obtain a second intermediate; S300, placing the second intermediate in an anodizing solution and performing anodizing treatment to obtain an aluminum product.

[0018] Furthermore, before step S100, the method further includes: performing surface treatment on the aluminum alloy substrate to remove the oxide film on the surface of the aluminum alloy substrate.

[0019] Further surface treatment of the aluminum alloy substrate includes steps such as degreasing, chemical polishing, and stripping of the black film.

[0020] Furthermore, step S100, after the first electroplating treatment, also includes: ionic liquid rinsing.

[0021] Furthermore, step S200, after the second electroplating process, also includes cleaning and drying.

[0022] Compared with existing technologies, the technical effects achieved by this solution are as follows: by first electroplating an AlMn alloy layer in a first ionic liquid, then electroplating an Al metal layer in a second ionic liquid, and finally performing anodizing, the ionic liquid electroplating process avoids interference from aqueous solutions and can achieve low-defect, high-uniformity alloy and pure aluminum deposition on the aluminum alloy surface. The step-by-step electroplating follows the mechanism of first shielding and then pure plating to sequentially build transition layers and functional layers, avoiding the crystallization problem of direct aluminum plating. The overall process flow conforms to the interface growth law of electrodeposition and anodizing, and can stably achieve the batch preparation of color-difference-free oxide films.

[0023] In one embodiment of the present invention, the first ionic liquid is an AlCl3-EMIC ionic liquid containing MnCl2, wherein the molar ratio of AlCl3-EMIC is (1.5~2.0):1, and the concentration of MnCl2 is 0.1mol / L-0.3mol / L.

[0024] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the ionic liquid with this molar ratio can provide stable aluminum coordination ions and electrodeposition potential to ensure controllable coating composition; the MnCl2 of 0.1 mol / L to 0.3 mol / L can precisely control the amount of manganese co-deposition, so that the AlMn layer is stably within the effective range of 6 at.% to 20 at.%.

[0025] In one embodiment of the present invention, in step S100, the temperature of the first electroplating treatment is 25°C to 80°C; the current density of the first electroplating treatment is 6 mA / cm². 2 ~15mA / cm 2 .

[0026] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: suitable temperature can improve the conductivity and ion diffusion rate of ionic liquids to ensure uniform deposition, and reasonable current density can control the nucleation rate and growth speed of AlMn alloys to avoid coarse or loose grains.

[0027] In one embodiment of the present invention, the second ionic liquid is an AlCl3-EMIC ionic liquid, wherein the molar ratio of AlCl3-EMIC is (1.5~2.0):1.

[0028] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: This system can achieve stable electrodeposition of high-purity aluminum, avoid the introduction of impurities and alloy phases, ensure uniform single-phase aluminum structure on the surface, provide a defect-free substrate for anodizing, and eliminate the source of color difference from the essence of the coating.

[0029] In one embodiment of the present invention, in step S200, the temperature of the second electroplating treatment is 25°C to 80°C; the current density of the second electroplating treatment is 5 mA / cm². 2~60mA / cm 2 .

[0030] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the process window can be adapted to the preparation requirements of pure aluminum layers of different thicknesses, the appropriate temperature reduces internal stress and improves density, and the reasonable current density can control the uniform spread of aluminum atoms along the surface rather than preferential orientation growth, further suppressing the formation of crystal flowers and improving surface gloss and smoothness.

[0031] In one technical solution of the present invention, in step S300, the temperature of the anodizing treatment is 25°C to 80°C; the voltage of the anodizing treatment is 12V to 14V.

[0032] Furthermore, the anodizing solution includes at least one of sulfuric acid solution and oxalic acid solution.

[0033] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: stable voltage can control the electric field strength and film growth rate of anodizing, ensuring uniform pore size and thickness of porous alumina structure; suitable temperature can avoid local overheating of the oxidation reaction, which may lead to uneven film dissolution or color difference, ultimately forming an anodized film with consistent color, uniform appearance, and stable protective performance.

[0034] The technical solution provided by this invention can achieve at least one of the following effects: (1) The present invention adopts a composite structure in which an AlMn alloy layer, an Al metal layer and an anodic oxide film layer are sequentially arranged on the outside of an aluminum alloy substrate. The AlMn alloy layer can block the conduction of the substrate grain boundary and grain orientation from the deposition mechanism, completely eliminate the flower-like defects caused by direct aluminum plating, provide a uniform and flat substrate for surface anodizing, and significantly improve the appearance consistency of aluminum products. (2) By limiting the manganese content and thickness range of each layer of the AlMn alloy layer, the present invention can ensure that the coating forms a stable amorphous or nanocrystalline structure, while optimizing the interlayer bonding state, so as to achieve complete shielding of the second phase and grain boundary defects of the matrix, and avoid excessive internal stress or loose structure of the coating, thereby improving the structural stability and service life of aluminum products. (3) The present invention adopts a preparation process of stepwise electroplating with ionic liquid combined with conventional anodizing. The ionic liquid system can achieve uniform and controllable deposition of high-purity aluminum and aluminum-manganese alloy. With optimized electrical and oxidation parameters, it can stably prepare a uniform anodized film without impurities, second phase, or local dissolution, thus solving the color difference problem of traditional aluminum alloy anodizing from the root. (4) The present invention is applicable to a variety of mainstream industrial aluminum alloys, with strong process compatibility and can be implemented in industrial batches. While eliminating color difference and improving appearance quality, it simultaneously enhances the corrosion resistance and wear resistance of aluminum products, greatly expanding the application range of aluminum alloys in consumer electronics, decorative parts and other high appearance requirements. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be discussed below. Obviously, the technical solutions described in conjunction with the accompanying drawings are only some embodiments of the present invention. For those skilled in the art, other embodiments and their accompanying drawings can be obtained based on the embodiments shown in these drawings without creative effort.

[0036] Figure 1 This is an appearance diagram of the aluminum product sample obtained in Example 1 of the present invention; Figure 2 This is an appearance diagram of the aluminum product sample prepared in Comparative Example 1 of the present invention. Figure 3 This is an appearance diagram of the second intermediate obtained in Embodiment 1 of the present invention; Figure 4 This is an appearance diagram of the aluminum alloy substrate after direct aluminum plating in Comparative Example 1 of the present invention; Figure 5 This is a stripe reflection pattern of the aluminum product sample obtained in Example 1 of the present invention; Figure 6 This is a stripe reflection pattern of the aluminum product sample prepared in Comparative Example 1 of the present invention. Figure 7 This is a SEM (500x) image of the aluminum product sample obtained in Example 1 of this invention; Figure 8 This is a SEM (500x) image of the aluminum product sample prepared in Comparative Example 1 of this invention. Figure 9 These are the XRD patterns of the aluminum alloy substrate of the present invention, the aluminum alloy substrate of Comparative Example 1 after direct aluminum plating, and the second intermediate obtained in Example 1. Detailed Implementation

[0037] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The following reference Figures 1 to 9 The technical solutions of some embodiments of the present invention are described below.

[0039]

Example 1

[0040]

Example 2

[0041]

Example 3

[0042]

Example 4

[0043]

Example 5

[0044]

Example 6

[0045]

Example 7

[0046]

Example 8

[0047]

Example 9

[0048] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that the AlMn alloy layer is not deposited by S100 ionic liquid.

[0049] Comparative Example 2 The preparation method of this comparative example is the same as that in Example 1, except that the concentration of MnCl2 in the plating solution in S200 is 0.05 mol / L, so that the Mn content in the AlMn alloy layer is 4 at.%.

[0050] Comparative Example 3 The preparation method of this comparative example is the same as that in Example 1, except that the thickness of the AlMn alloy layer in S200 is 1 μm.

[0051] Comparative Example 4 The preparation method of this comparative example is the same as that in Example 1, except that the aluminum alloy substrate is directly anodized without plating an AlMn alloy layer or a pure aluminum layer.

[0052] Table 1

[0053] Based on the test results in Table 1 above and Figures 1 to 9 It can be seen that the composite coating samples prepared in Examples 1 to 9 all have a gloss of 20° above 22 GU and a gloss of 60° above 218 GU after coating. The surface is smooth and bright without crystalline defects, and the appearance uniformity is excellent. The appearance images of the second intermediate and aluminum product samples obtained in Example 1 are as follows. Figure 3 , 1 As shown, the appearance is uniform, with no crystalline color difference; the composite-plated sample was photographed aligned with stripe number 30 (0.13mm wide, 0.13mm spacing) on ​​the ISO12233 resolution test chart (enhanced type). Figure 5 As shown, the clearly visible reflective stripes indicate that the coating surface has excellent specular reflection properties; the SEM (scanning electron microscope) image of the composite coating surface is shown below. Figure 7As shown, the coating is uniform and smooth; the samples prepared in Comparative Examples 1 to 4 have a maximum gloss of only 9.3 GU at 20° and only 141 GU at 60° after plating, with obvious crystal blooms and color differences on the surface, resulting in poor appearance consistency. The examples show a significant improvement in appearance performance compared to the comparative examples; the appearance images of the aluminum alloy substrate directly plated with aluminum and the aluminum product samples prepared in Comparative Example 1 are shown below. Figure 4 , 2 As shown, the sample exhibits uneven appearance and crystal blooms after plating. The composite-plated sample was photographed aligned with stripe number 30 (0.13mm wide, 0.13mm spacing) on ​​an ISO 12233 resolution test chart (enhanced type). [Image showing...] Figure 6 As shown, the reflective stripes are not clearly visible; the SEM (scanning electron microscope) image of the composite coating surface is as follows. Figure 8 As shown, the morphology of different areas of the coating varies, and there are obvious grain boundaries. The grain boundary size is close to that of the substrate after NaOH etching, indicating that direct aluminum plating is greatly affected by the substrate, resulting in the appearance of grain patterns; for example... Figure 9 As shown, compared with the aluminum alloy substrate and the aluminum alloy substrate of Comparative Example 1 after direct aluminum plating, the second intermediate (i.e., composite plating) prepared in Example 1 shows a significantly preferred orientation. Examples 1, 4, and 5 show that when the Mn content in the AlMn alloy layer is in the range of 6 at.% to 20 at.%, the gloss after plating remains at a high level, and the plating layer is free of crystal defects. This indicates that this Mn content range can ensure the formation of a stable amorphous structure in the AlMn layer, achieving a good shielding effect. Examples 1, 6, and 7 show that changing the electroplating temperature or current density of the AlMn layer has little effect on the gloss of the plating layer, indicating that the process parameter window of this invention is wide, the process stability is strong, and it is suitable for industrial production. Examples 1 and 8 show that reducing the thickness of the pure aluminum plating layer slightly decreases the gloss, but it still remains at a high level, indicating that the pure aluminum layer needs to reach a certain thickness to provide a sufficiently smooth surface. Examples 1 and 9 show that changing the aluminum alloy substrate from 6061 to 7075 increases the gloss of the plating layer. The gloss levels remain high, indicating that this invention is applicable to various grades of aluminum alloys and has strong versatility. In Comparative Example 1, no AlMn alloy layer was set, and a pure aluminum layer was directly plated, resulting in a significant decrease in gloss and obvious crystal blooms on the surface. This shows that the AlMn layer is the key structure for eliminating crystal blooms and improving gloss. In Comparative Example 2, the Mn content was less than 6 at.%, and in Comparative Example 3, the AlMn layer thickness was less than 2 μm. Neither of these could completely shield the influence of the substrate, resulting in a significant decrease in gloss and obvious crystal bloom defects. This indicates that an Mn content of 6 at.% to 20 at.% and an AlMn layer thickness of 2 μm to 10 μm are the necessary parameter ranges for achieving a good appearance. In Comparative Example 4, the aluminum alloy substrate was directly anodized, resulting in the lowest gloss and the most obvious color difference. This further proves that the composite coating structure of this invention can eliminate the color difference of the anodized film from the root and improve the appearance quality and consistency of the aluminum alloy surface.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims, not by the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0055] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An aluminum product for eliminating color difference in anodized films, characterized in that, include: An aluminum alloy substrate, a first coating layer covering at least a portion of the surface of the aluminum alloy substrate, a second coating layer covering at least a portion of the surface of the first coating layer, and a third coating layer covering at least a portion of the surface of the second coating layer; The first coating layer is an AlMn alloy layer; The second coating layer is an Al metal layer; The third coating layer is an anodic oxide film layer.

2. The aluminum product for eliminating color difference in anodized film according to claim 1, characterized in that, The thickness of the first coating layer is 2μm-10μm; The thickness of the second coating layer is 3μm-10μm; The thickness of the third coating layer is 3μm-12μm.

3. The aluminum product for eliminating color difference in anodized film according to claim 1, characterized in that, The Mn content in the first coating layer is 6 at.% to 20 at.%.

4. The aluminum product for eliminating color difference in anodized film according to claim 1, characterized in that, The material type of the aluminum alloy substrate includes at least one of 6061, 7075, 2024 and 5052.

5. A method for preparing aluminum products with color difference elimination of anodized film, used to prepare aluminum products with color difference elimination of anodized film as described in any one of claims 1-3, characterized in that, Includes the following steps: S100. The aluminum alloy substrate is placed in a first ionic liquid and subjected to a first electroplating treatment to obtain a first intermediate. S200: The first intermediate is placed in the second ionic liquid and subjected to a second electroplating process to obtain the second intermediate; S300. The second intermediate is placed in an anodizing solution and subjected to anodizing treatment to obtain the aluminum product.

6. The method for preparing aluminum products with color difference in anodized film according to claim 5, characterized in that, The first ionic liquid is an AlCl3-EMIC ionic liquid containing MnCl2, wherein the molar ratio of AlCl3-EMIC is (1.5~2.0):1, and the concentration of MnCl2 is 0.1mol / L-0.3mol / L.

7. The method for preparing aluminum products with color difference in anodized film according to claim 5, characterized in that, In step S100, The temperature for the first electroplating treatment is 25℃~80℃; The current density for the first electroplating treatment is 6 mA / cm². 2 ~15mA / cm 2 .

8. The method for preparing aluminum products with color difference in anodized film according to claim 5, characterized in that, The second ionic liquid is an AlCl3-EMIC ionic liquid, wherein the molar ratio of AlCl3-EMIC is (1.5~2.0):

1.

9. The method for preparing aluminum products with color difference in anodized film according to claim 5, characterized in that, In step S200, The temperature for the second electroplating treatment is 25℃~80℃; The current density for the second electroplating process is 5 mA / cm². 2 ~60mA / cm 2 .

10. The method for preparing aluminum products with color difference of anodic oxide film according to claim 5, characterized in that, In step S300, The anodizing temperature is 25℃~80℃; The voltage for anodizing is 12V~14V.

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