Extrusion production process for improving the anodizing effect of 7075 aluminum alloy profiles

Abstract

This invention discloses a profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy, relating to the field of aluminum alloy pressure processing technology. By adjusting the extrusion temperature and extrusion ratio, this invention breaks down the insoluble second phase, reduces the size of coarse second phases, and uniformly disperses them within the soft Al matrix. This avoids the distribution of coarse Mg2Si and Fe-containing phases along the extrusion direction, eliminating the defect of black lines after anodizing. It avoids the existing method of refining and filtering the melt by reducing the Fe and Si element content, significantly reducing raw material prices and production costs, and improving production efficiency. Simultaneously, the resulting 7075 aluminum alloy extruded profiles also possess excellent mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy pressure processing, and particularly relates to a profile extrusion production process that improves the anodizing effect of 7075 aluminum alloy. Background Technology

[0002] 7075 aluminum alloy is a high-strength hard aluminum alloy with advantages such as light weight, easy processing, good corrosion resistance and strong impact resistance. It can be processed by milling, stamping, stretching, forging and welding, and is therefore widely used in high-strength parts in aerospace, automotive, electronics and machinery fields.

[0003] Anodizing 7075 aluminum alloy can generate an artificial oxide film, which is more uniform, dense, and corrosion-resistant, further protecting the metal surface from oxidation corrosion, improving surface wear resistance and aesthetics, and increasing the service life of parts. However, the anodized surface of 7055 aluminum alloy also has oxidation defects such as surface roughness, black lines, scratches, and burrs. According to literature research, the "black line" defect is mainly caused by the continuous distribution of the second phase on the alloy surface. Scratches, oil stains, and other surface defects during subsequent processing can also produce black lines. By controlling the amount of iron and silicon additives added during the smelting process and strengthening the control of refining, filtration, and impurity removal methods, the occurrence of black lines can be effectively reduced. However, reducing the Fe and Si content in large-scale smelting processes will greatly increase production costs. Therefore, research on the anodizing performance of aluminum alloys is extremely important. It is necessary to further improve the extrusion temperature and extrusion ratio of aluminum alloys and optimize the extrusion process to meet market application requirements. Researching a production process for 7055 aluminum alloy profiles with good anodizing effect is of great significance for expanding the application fields of high-strength aluminum alloys.

[0004] With the deepening research on aluminum alloy surface treatment processes, existing studies have developed various methods to prepare aluminum alloys with excellent anodizing properties, including optimizing the casting process and increasing the solution treatment time. Gradually, some improved anodizing processes for aluminum alloys have been developed. Existing patents impose strict requirements on raw material composition, mostly controlling the content of elements such as Fe, Si, and Cu in the melt. They utilize large amounts of remelted aluminum ingots and high-temperature aluminum liquid, with a relatively small proportion of waste material used, increasing raw material costs. The casting process also requires multiple refining and degassing operations, making the production process overly complex. This increases the technical difficulty and production cost of element control during production. The resulting ingot core inevitably exhibits second-phase segregation, and segregation nodules may also appear on the surface during casting. Controlling melt purity cannot directly control the second phase and grain size. Summary of the Invention

[0005] This invention effectively reduces the black line defects caused by anodizing of 7075 aluminum alloy by adjusting the extrusion temperature and extrusion ratio, avoids the increase in production costs caused by reducing the Fe and Si content in raw materials and melt refining and filtration, and improves production efficiency.

[0006] The purpose of this invention is to provide an extrusion process for 7075 aluminum alloy profiles that reduces the proportion of anodized black lines while maintaining good mechanical properties.

[0007] The specific technical solution adopted in this invention is as follows:

[0008] A profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy includes the following steps:

[0009] (1) Prepare raw materials according to the alloy element composition of 7075 aluminum alloy, and smelt to obtain melt;

[0010] (2) The melt is cast into 7075 aluminum alloy ingots using a semi-continuous casting method;

[0011] (3) The ingot is homogenized;

[0012] (4) The homogenized ingot is extruded to obtain the profile;

[0013] (5) The profile is subjected to solution quenching treatment;

[0014] (6) Straighten the profiles after solution quenching;

[0015] (7) The straightened profiles are subjected to aging treatment;

[0016] (8) Perform surface treatment on the aging-treated profiles.

[0017] As a preferred option, the 7075 aluminum alloy composition by mass percentage is as follows: Zn 5.1-6.1wt%, Mg 2.1-2.9wt%, Cu 1.2-2.0wt%, Mn<0.3wt%, Cr 0.18-0.28wt%, Ti<0.2wt%, Fe<0.5wt%, Si<0.4wt%, alloy impurities<0.15wt%, and the remainder is Al.

[0018] As a preferred option, in step (3), the aluminum alloy ingot is subjected to two homogenization processes. The homogenization process is as follows: the first homogenization process is to hold at 440-460℃ for 12-36 hours, and the second homogenization process is to raise the temperature to 460-475℃ and hold for 12-36 hours, then cool down to 100-150℃ by furnace cooling, and then air cool to room temperature.

[0019] Preferably, in step (4), the mold, extrusion cylinder and ingot are preheated before extrusion: the mold is preheated to 320-370℃ for 6-12 hours, the extrusion cylinder is preheated to 300-350℃ for 0.5-1 hours, and the extrusion bar is preheated to 300-350℃ for 0.5-1 hours.

[0020] Preferably, in step (4), extrusion is performed using a die with an extrusion ratio within the selected range: the extrusion ratio is 25-35.

[0021] As a preferred option, in step (5), the solution quenching process is as follows: keep at 460-475℃ for 2-12 hours and cool with warm water at 25℃.

[0022] Preferably, in step (6), the stretching amount of the straightening treatment is 1%-2%.

[0023] As a preferred option, in step (7), the aging process is as follows: the aging temperature is 110-150℃, the heat preservation time is 12-24h, and the air cooling is brought to room temperature.

[0024] Preferably, in step (8), the surface treatment process includes: polishing, degreasing, alkaline etching, neutralization, chemical polishing, and anodizing.

[0025] The present invention proposes a profile extrusion production process to improve the anodizing effect of 7075 aluminum alloy, the design principle of which is as follows:

[0026] The black oxide lines on 7075 aluminum alloy profiles are mainly caused by the continuous distribution of coarse second phases along the extrusion direction. These coarse second phases are mainly Mg2Si and Fe-containing phases. During the extrusion process, these coarse second phases deform and are distributed in strips along the extrusion direction. During the anodizing process, a dense oxide film is formed in the parts where the second phase is evenly distributed, while the oxide film in the areas where the second phase is rich has pores, forming black oxide lines.

[0027] Studies have shown that large plastic deformation or lowering the deformation temperature can break down the insoluble second phase, reduce the size of the coarse second phase, and distribute it uniformly in the soft Al matrix. This effectively reduces surface corrosion during the anodizing process, alleviates stress concentration, and improves the anodizing effect and mechanical properties of the profile surface. This invention mainly adjusts the extrusion temperature and extrusion ratio to break down and distribute the coarse second phase in the extruded profile, thereby avoiding the formation of black lines after anodizing.

[0028] The Mg2Si and Fe-containing phases in 7075 aluminum alloy are high-temperature phases that are difficult to remove through homogenization and solution treatment. Therefore, controlling the extrusion temperature at 300-350℃, the die temperature at 320-370℃, and the extrusion ratio at 25-35 can increase the degree of extrusion deformation and the extrusion pressure to break up the Mg2Si and Fe-containing phases uniformly, thereby reducing the size of the Mg2Si and Fe-containing phases.

[0029] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0030] 1. This invention does not require reducing the content of Mg2Si and Fe-containing phases in the ingot, and does not place excessive demands on smelting cleanliness and refining processes. Therefore, compared with existing technologies, the technical solution contained in this invention reduces raw material prices and production costs. On this basis, this invention can also effectively reduce the proportion of anodized black lines.

[0031] 2. The present invention also provides an extrusion process for 7075 aluminum alloy profiles, the products of which have good mechanical properties. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments and comparative examples will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a metallographic photograph of the extruded profile from Example 1 magnified 200 times.

[0034] Figure 2 This is a scanning electron microscope image of Example 1 after anodizing, magnified 500 times;

[0035] Figure 3 This is a metallographic photograph of the extruded profile from Example 2 magnified 200 times;

[0036] Figure 4 This is a scanning electron microscope image of Example 2 after anodizing, magnified 500 times;

[0037] Figure 5 This is a metallographic photograph of the extruded profile from Example 3 magnified 200 times.

[0038] Figure 6 This is a scanning electron microscope image of Example 3 after anodizing, magnified 500 times;

[0039] Figure 7 This is a metallographic photograph of the extruded profile from Example 4, magnified 200 times.

[0040] Figure 8 This is a scanning electron microscope image of Example 4 after anodizing, magnified 500 times;

[0041] Figure 9 This is a metallographic photograph of the extruded profile of Comparative Example 1 magnified 200 times;

[0042] Figure 10 This is a scanning electron microscope image of Comparative Example 1 after anodizing, magnified 500 times;

[0043] Figure 11 The image shows a metallographic photograph of the extruded profile from Comparative Example 2, magnified 200 times.

[0044] Figure 12 This is a scanning electron microscope image of Comparative Example 2 after anodizing, magnified 500 times. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of 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.

[0046] Example 1, such as Figure 1 , Figure 2 As shown, a profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy includes the following specific steps:

[0047] (1) Prepare raw materials according to the alloy element composition of 7075 aluminum alloy, and smelt to obtain melt;

[0048] (2) The melt is cast into 7075 aluminum alloy ingots using a semi-continuous casting method; the mass percentage of each component of the 7075 aluminum alloy ingot obtained according to the above steps is: Zn 5.5wt%, Mg 2.5wt%, Cu 1.5wt%, Mn 0.1wt%, Cr 0.2wt%, Ti 0.1wt%, Fe 0.35wt%, Si 0.25wt%, and the remaining components are Al and impurity elements.

[0049] (3) The ingot is subjected to two homogenization processes: the first homogenization process is to hold at 450°C for 24 hours, and the second homogenization process is to raise the temperature to 470°C and hold for 12 hours, then cool it to 100°C with the furnace and then air cool it to room temperature.

[0050] (4) The ingot after homogenization is subjected to extrusion treatment: the die is preheated at 350℃ for 6 hours before extrusion, the extrusion cylinder and the ingot are preheated at 320℃ for 0.5 hours, the extrusion speed is 1m / min, the extrusion ratio is 25, the thickness of the extrusion residue is 50mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0051] (5) Solution hardening treatment of profiles: keep at 470℃ for 6 hours and then quench with warm water at 25℃.

[0052] (6) Straightening treatment of profiles after solution quenching: Straighten profiles after pre-stretching by 1%.

[0053] (7) Aging treatment of the straightened profile: The profile is kept at 120℃ for 12 hours and then air-cooled to room temperature.

[0054] (8) The produced profiles are subjected to surface treatment processes such as polishing, degreasing, alkaline etching, neutralization, chemical polishing, and anodizing.

[0055] Example 2, as Figure 3 , Figure 4 As shown, its 7075 aluminum alloy ingot is consistent with that of Example 1.

[0056] The difference from Example 1 lies in the preparation method:

[0057] In step (3), the ingot is subjected to two homogenization processes: the first homogenization process is to hold at 430°C for 36 hours, and the second homogenization process is to raise the temperature to 465°C and hold for 24 hours, then cool it to 120°C with the furnace and then air cool it to room temperature.

[0058] In step (4), the homogenized ingot is subjected to extrusion treatment: the die is preheated at 365℃ for 10h before extrusion, the extrusion cylinder and ingot are preheated at 320℃ for 0.5h, the extrusion speed is 1.5m / min, the extrusion ratio is 30, the thickness of the extrusion residue is 50mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0059] In step (5), the profile is subjected to solution quenching treatment: it is kept at 470℃ for 12 hours and then quenched with warm water at 25℃.

[0060] In step (7), the straightened profile is subjected to aging treatment: the profile is kept at 150℃ for 12 hours and then air-cooled to room temperature.

[0061] Example 3, as Figure 5 , Figure 6 As shown, its 7075 aluminum alloy ingot is consistent with that of Example 1.

[0062] The difference from Example 1 lies in the preparation method:

[0063] In step (3), the ingot is subjected to two homogenization processes: the first homogenization process is to hold at 450°C for 36 hours, and the second homogenization process is to raise the temperature to 470°C and hold for 24 hours, then cool it down to 150°C with the furnace and then air cool it to room temperature.

[0064] In step (4), the homogenized ingot is subjected to extrusion treatment: the die is preheated at 350℃ for 12 hours before extrusion, the extrusion cylinder and the ingot are preheated at 350℃ for 0.5 hours, the extrusion speed is 2m / min, the extrusion ratio is 35, the thickness of the extrusion residue is 50mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0065] In step (5), the profile is subjected to solution quenching treatment: it is kept at 470℃ for 12 hours and then quenched with warm water at 25℃.

[0066] In step (7), the straightened profile is subjected to aging treatment: the profile is kept at 150℃ for 12 hours and then air-cooled to room temperature.

[0067] Example 4, as Figure 7 , Figure 8 As shown, its 7075 aluminum alloy ingot is consistent with that of Example 1.

[0068] The difference from Example 1 lies in the preparation method:

[0069] In step (4), the homogenized ingot is subjected to extrusion treatment: the die is preheated at 320℃ for 6 hours before extrusion, the extrusion cylinder and ingot are preheated at 300℃ for 0.5 hours, the extrusion speed is 0.5 m / min, the extrusion ratio is 35, the thickness of the extrusion residue is 50 mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0070] Comparative Example 1, such as Figure 9 , Figure 10 As shown, its 7075 aluminum alloy ingot is consistent with that of Example 1.

[0071] The difference from Example 1 lies in the preparation method:

[0072] In step (4), the homogenized ingot is subjected to extrusion treatment: the die is preheated at 400℃ for 6 hours before extrusion, the extrusion cylinder and ingot are preheated at 370℃ for 0.5 hours, the extrusion speed is 1m / min, the extrusion ratio is 15, the thickness of the extrusion residue is 50mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0073] Comparative Example 2, such as Figure 11 , Figure 12 As shown, its 7075 aluminum alloy ingot is consistent with that of Example 1.

[0074] The difference from Example 1 lies in the preparation method:

[0075] In step (4), the homogenized ingot is subjected to extrusion treatment: the die is preheated at 415℃ for 12 hours before extrusion, the extrusion cylinder and the ingot are preheated at 380℃ for 1 hour, the extrusion speed is 1m / min, the extrusion ratio is 20, the thickness of the extrusion residue is 50mm, and the extruded profile is air-cooled to room temperature to obtain the profile.

[0076] The mechanical properties of the 7075 aluminum alloy profiles obtained in the embodiments and comparative examples of this invention were tested according to GB / T228.1-2010 "Metallic materials, tensile testing - Part 1: Test method at room temperature". The test results are shown in Table 1. Table 1 shows the mechanical properties of the alloys in Examples 1-4 and Comparative Examples 1-2.

[0077] Table 1. Mechanical property test results and black oxide line test results for each sample.

[0078]

[0079] As shown in Table 1, the present invention improves the anodizing effect of 7075 aluminum alloy by adjusting the extrusion temperature and extrusion ratio. The surface oxide film is evenly distributed with no obvious black line areas, which better meets the requirements for product appearance.

[0080] like Figures 1-8 As shown, the profiles produced according to the processes of Examples 1-4 have a uniform second phase distribution, no coarse second phase inside the grains, and a uniform oxide film distribution on the surface after anodizing.

[0081] like Figures 9-12 As shown, the second phase of the profile produced according to the process of Comparative Example 1-2 is obviously coarse, the distribution of the oxide film on the surface after anodizing is obviously uneven, there are pores on the surface of the oxide film and obvious oxide stripes along the extrusion direction.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy, characterized in that, Includes the following steps: (1) Prepare raw materials according to the alloy element composition of 7075 aluminum alloy and smelt to obtain melt; The 7075 aluminum alloy composition by mass percentage is as follows: Zn 5.1-6.1wt%, Mg 2.1-2.9wt%, Cu 1.2-2.0wt%, Mn<0.3wt%, Cr 0.18-0.28wt%, Ti<0.2wt%, Fe<0.5wt%, Si<0.4wt%, alloy impurities<0.15wt%, and the remainder is Al; (2) The melt is cast into 7075 aluminum alloy ingots using a semi-continuous casting method; (3) The ingot is homogenized; (4) The homogenized ingot is extruded to obtain the profile; Before extrusion, preheat the mold, extrusion cylinder and ingot: preheat the mold to 320-370℃ for 6-12 hours, preheat the extrusion cylinder to 300-350℃ for 0.5-1 hour, and preheat the ingot to 300-350℃ for 0.5-1 hour. Extrusion is performed using a die with an extrusion ratio within the selected range: extrusion ratio is 25-35; (5) The profile is subjected to solution quenching treatment; (6) Straighten the profiles after solution quenching; (7) The straightened profiles are subjected to aging treatment; (8) Perform surface treatment on the aged profile.

2. The profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy according to claim 1, characterized in that, In step (3), the aluminum alloy ingot is subjected to two homogenization processes: the first homogenization process is to hold at 440-460℃ for 12-36 hours, and the second homogenization process is to raise the temperature to 460-475℃ and hold for 12-36 hours, then cool it down to 100-150℃ by furnace cooling, and then air cool it to room temperature.

3. The profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy according to claim 1, characterized in that, In step (5), the solution quenching process is as follows: keep at 460-475℃ for 2-12 hours and cool with warm water at 25℃.

4. The profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy according to claim 1, characterized in that, In step (6), the stretching amount of the straightening treatment is 1%-2%.

5. The profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy according to claim 1, characterized in that, In step (7), the aging process is as follows: the aging temperature is 110-150℃, the heat preservation time is 12-24h, and the air cooling is brought to room temperature.

6. The profile extrusion production process for improving the anodizing effect of 7075 aluminum alloy according to claim 1, characterized in that, In step (8), the surface treatment process includes: polishing, degreasing, alkaline etching, neutralization, chemical polishing, and anodizing.

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