Heat treatment method for hot extrusion aluminum alloy profile

Abstract

The invention discloses a heat treatment method for a hot extrusion aluminum alloy profile. The heat treatment process for the hot extrusion aluminum alloy profile comprises solid solution and two-stage aging. By the adoption of the heat treatment process, residual stress generated by hot extrusion deformation of the hot extrusion aluminum alloy profile is eliminated, a non-equilibrium second phase is dissolved into a matrix, the structure is more uniform, and grains are isotropic. During solution treatment, the aluminum alloy profile is heated to a certain proper temperature above a solubility curve and below a solidus, and heat preservation is conducted for a certain time, so that a second phase in the structure is dissolved into a solid solution; then rapidly cooling in water or other media to inhibit re-precipitation of the second phase so as to obtain a supersaturated solid solution at room temperature; and through aging treatment with low-temperature heat preservation, solid solution elements in the solid solution form some stable precipitation phases, the precipitation strengthening effect on the aluminum alloy is achieved, and therefore the hardness and strength of the aluminum alloy profile are improved. Solid solution and two-stage aging are adopted in the process, so that the structure performance of the hot-extruded aluminum alloy profile is uniform and consistent, the residual stress is effectively reduced, and the strength and hardness of the profile are improved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloys, and in particular to a heat treatment method for hot extruded aluminum alloy profiles. Background Art

[0002] Among the 6XXX series alloys, 6082 aluminum alloy has the highest strength, good overall corrosion resistance, and good performance; 6082 is a medium-strength aluminum alloy in the Al-Mg-Si series with good corrosion resistance and processing properties. It is widely used in large welded structures, marine parts, and blanks for mold processing.

[0003] The performance optimization of this alloy often depends on the appropriate heat treatment process. Heat treatment has good characteristics in homogenizing and refining the eutectic structure and improving the alloy properties, and has low processing cost and convenience. Among them, solid solution aging treatment (T6 treatment) is one of the most commonly used methods. Therefore, in order to improve the mechanical properties of 6082 aluminum alloy profiles produced by hot extrusion, 6082 hot extruded aluminum alloy profiles need to be heat treated.

[0004] At present, the research on aluminum alloy heat treatment process mostly adopts quenching or single-stage solid solution and single-stage aging treatment. This process easily causes the coarsening of grain size and forms a continuous intracrystalline precipitation reinforcement phase. Although it is beneficial to improve the strength performance of aluminum alloy, it also has an adverse effect on corrosion resistance. Summary of the invention

[0005] The object of the present invention is to provide a method for heat treatment of hot extruded aluminum alloy profiles, the method for heat treatment of hot extruded aluminum alloy profiles comprising a solution heat treatment and a two-stage aging step, specifically comprising:

[0006] (1) Solution heat treatment: The hot extruded aluminum alloy profile is heated to 520-560°C. The heating rate is divided into two stages. When the temperature is below 500°C, the heating rate is 10°C / min. After the temperature reaches 500°C, the heating rate is 5°C / min. The temperature is kept for 30-50 minutes. After the insulation is completed, it is placed in water for water cooling. The transfer time does not exceed 3 seconds.

[0007] (2) Double-stage aging: After solution heat treatment, the hot extruded aluminum alloy profiles are significantly improved in strength after double-stage aging of pre-aging and final aging. The pre-aging temperature is 110-120℃, and the holding time is 2-3h. The final aging temperature is 160-170℃, and the holding time is 4-5h. After the holding is completed, it is air-cooled to room temperature.

[0008] After the heat treatment process of the present invention, the residual stress caused by hot extrusion deformation of the 6082 aluminum alloy profile is eliminated, and the precipitated non-equilibrium second phase is mostly dissolved into the matrix after heat treatment, and the organization also shows a trend of uniform distribution, and the anisotropy of the grains is improved. In terms of alloy properties, although the plasticity of the alloy is slightly reduced after heat treatment, the strength is significantly improved.

[0009] Beneficial effects of the present invention:

[0010] (1) After the heat treatment process of the present invention, the plasticity of the 6082 aluminum alloy profile is slightly reduced, but the strength is significantly improved, and the disordered structure caused by hot extrusion deformation is sorted out, the residual stress is eliminated, the non-equilibrium second phase in the matrix structure is almost completely dissolved into the matrix, and the structure also shows a trend of uniform distribution.

[0011] (2) In the double-stage aging process of the present invention, after the pre-aging holding time is up, no transfer is performed, and the temperature is directly raised from the pre-aging temperature to the final aging temperature, thereby reducing the number of heat treatments. Compared with the single-stage aging, after the double-stage aging treatment, the electrical conductivity of the sample is better, the corrosion morphology changes from intergranular corrosion to pitting corrosion, the corrosion depth is significantly shallowed, and the corrosion resistance of the sample is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the temperature curve of the heat treatment process of the hot extruded profile of the present invention.

[0013] Figure 2 This is the metallographic structure diagram of the 6082 aluminum alloy profile in Example 1 of the present invention.

[0014] Figure 3 This is the metallographic structure diagram of the 6082 aluminum alloy profile in Comparative Example 1 of the present invention.

[0015] Figure 4 This is the metallographic structure diagram of the 6082 aluminum alloy profile in Comparative Example 2 of the present invention.

[0016] Figure 5 This is the metallographic structure diagram of the 6082 aluminum alloy profile in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] The heat treatment method for hot extruded aluminum alloy profiles described in the present invention includes solution heat treatment and two-stage aging steps, specifically including:

[0019] (1) Solution heat treatment: Heat the 6082 hot extruded aluminum alloy profile to 520-560°C and keep it at this temperature for 30-50 min.

[0020] (2) Double-stage aging: After solution heat treatment, the 6082 hot-extruded aluminum alloy profile is subjected to double-stage aging of pre-aging and final aging to obtain a 6082 hot-extruded aluminum alloy profile with significantly improved strength.

[0021] The heating described in step (1) is to control the heating time of the 6082 hot-extruded aluminum alloy profile from room temperature to the solution heat treatment temperature of 520-560° C. to be 0.8-1.2 h.

[0022] The heating rate can affect the grain size, hardness, strength and other properties of the material. After solution heat treatment at a heating rate greater than 10°C / min, Mg 2 The non-equilibrium eutectic phase of Si phase breaks at the grain boundary, and some Mg 2 Si phase dissolves and the elements in it are dissolved into the matrix, but relative to the heat treatment at a heating rate of 2℃ / min, Mg 2 The amount of Si phase changes at the grain boundary, and its amount decreases significantly with the decrease of heating rate, and its size decreases slightly. More elements are dissolved into the matrix, so the solid solubility is higher.

[0023] The 6082 hot extruded aluminum alloy profile after solution heat treatment also includes a water quenching step.

[0024] Water quenching is a common process for heat treatment of aluminum alloys. Its principle is to use the strong cooling effect of water to force the material to cool rapidly, thereby changing the structure and properties of the material. After the aluminum alloy is solution treated at high temperature, it needs to be quickly cooled to room temperature through water quenching to form a uniform and fine structure. During the water quenching process, due to the rapid cooling of the aluminum alloy, on the one hand, the chemical composition of the aluminum alloy is made more uniform, and on the other hand, the crystals inside the aluminum alloy material are arranged in an orderly manner to form high-density and high-strength grain boundaries; it contains more subgrain boundaries and fine grains; thereby improving the tensile strength and plasticity of the aluminum alloy.

[0025] The quenching transfer time in the water quenching step does not exceed 3s.

[0026] The pre-aging temperature in step (2) is 110-120°C, and the holding time is 2-3h. After the solution treatment, the 6082 hot extruded aluminum alloy profile forms a supersaturated solid solution, and also generates a large number of supersaturated vacancies. The supersaturated vacancies can significantly improve the diffusion of solute atoms in the supersaturated solid solution. In the pre-aging stage, at the aging temperature, the supersaturated solid solution undergoes dissolution and decomposition, and the intracrystalline precipitate phase and the grain boundary precipitate phase in the organization begin to precipitate, which plays a pinning role on the organization. As the aging time increases, the size and number of the precipitate phase increase with the increase of the aging time, forming a local coherent relationship with the matrix, so that the alloy is strengthened.

[0027] The heating time of the 6082 hot extruded aluminum alloy profile after the solution heat treatment from room temperature to the pre-aging temperature is controlled within 0.5 to 0.8 hours.

[0028] The final aging temperature in step (2) is 160-170°C and the holding time is 4-5h. The increase in temperature is conducive to the growth and increase in the number of precipitated phases, thus having a stronger inhibitory effect on dislocation movement, and having the best effect at a certain temperature and time; the reason for this may be the precipitation of a metastable precipitate phase, and the hardness reaches the highest value.

[0029] After the pre-aging holding time in step (2) is over, no transfer is performed, and the heating time from the pre-aging temperature to the final aging temperature is controlled to be 0.1 to 0.2 hours. For different heat treatment processes, it is necessary to select a suitable heating rate to achieve the best heat treatment effect; a slower heating rate is conducive to the low-angle grain boundaries having enough time to migrate during the heating process, and it is easy to form an area that is conducive to recrystallization nucleation.

[0030] The temperature mentioned in the present invention refers to the temperature of the plate.

[0031] Example 1

[0032] (1) Take 6082 hot-extruded aluminum alloy profiles and use solid solution heat treatment: heat from room temperature to solid solution heat treatment temperature 530℃, the heating time is controlled within 1h, and after reaching the solid solution heat treatment temperature, keep it warm for 50min, quench in water, and the quenching transfer time does not exceed 3s, until it cools to room temperature, takes it out of water, and wipes off the surface moisture with a dry cotton cloth.

[0033] (2) Then, double-stage aging is carried out, which is divided into pre-aging and final aging: the room temperature is raised to the pre-aging temperature of 120°C, the heating time is controlled at 0.6h, and the temperature is kept at 120°C for 2h; after the pre-aging holding time is up, no transfer is carried out, and the pre-aging temperature is raised from 120°C to the final aging temperature of 170°C, the heating time is controlled at 0.1h, and the temperature is kept at 170°C for 4h. After the final aging temperature is kept, air cool to room temperature.

[0034] The tensile strength of the 6 series hot extruded aluminum alloy profile treated in this embodiment is 305.1MPa. Figure 2 For its metallographic structure, statistics on grain size showed that its average grain size was 54.53μm and the grain distribution was relatively uniform.

[0035] Comparative Example 1

[0036] Take 6082 hot extruded aluminum alloy profiles and only use pre-aging treatment:

[0037] Heat the mixture from room temperature to the solution heat treatment temperature of 530°C, with the heating time controlled within 1h. Keep the mixture at the solution heat treatment temperature for 50min, quench in water, with the quenching transfer time not exceeding 3s, until it cools to room temperature, is taken out of the water, and the surface moisture is wiped off with a dry cotton cloth; heat the mixture from room temperature to the pre-aging temperature of 120°C, with the heating time controlled within 0.6h. Keep the mixture at the pre-aging temperature of 120°C for 2h; air cool to room temperature after the insulation is completed.

[0038] The tensile strength of the 6 series hot extruded aluminum alloy profile treated in this embodiment is 152.1MPa. Figure 3 The metallographic structure of the grain size was statistically analyzed and the average grain size was found to be 210.53 μm.

[0039] By comparison with Example 1, it can be seen that the grains in the profile structure treated only with pre-aging are coarse, which will have a certain impact on the mechanical properties, but the tensile strength of the sample only subjected to pre-aging is greatly reduced. This is mainly because the pre-aging temperature is relatively low and the time is relatively short. The supersaturated solid solution formed by solid solution cannot be precipitated to precipitate more dispersion strengthening phases, and the dispersion strengthening effect is not obvious.

[0040] Comparative Example 2

[0041] Take 6082 hot extruded aluminum alloy profiles and only use final aging treatment:

[0042] Heat the mixture from room temperature to the solution heat treatment temperature of 530°C, with the heating time controlled within 1h. Keep the mixture at this temperature for 50min, quench in water, with the quenching transfer time not exceeding 3s, until it cools to room temperature, is taken out of the water, and the surface moisture is wiped off with a dry cotton cloth. Heat the mixture from room temperature to the final aging temperature of 170°C, with the heating time controlled within 0.8h. Keep the mixture at this temperature for 4h after reaching the final aging temperature of 170°C. Air cool the mixture to room temperature after the insulation is completed.

[0043] The tensile strength of the 6 series hot extruded aluminum alloy profile treated in this embodiment is 250.8MPa. Figure 4 For its metallographic structure, statistics on grain size revealed that its average grain size is 101.27μm.

[0044] By comparing with Example 1, it can be seen from the metallographic diagram that the average grain size of the profile treated only with final aging is also larger than that of Example 1. This is because the final aging temperature is higher and the time is longer than that of the pre-aging, and more dispersion strengthening phases are precipitated from the supersaturated solid solution formed by solid solution, and the dispersion strengthening effect is improved, but its dispersion strengthening effect is still not as good as that of Example 1.

[0045] Comparative Example 3

[0046] Take 6082 hot extruded aluminum alloy profiles and use conventional solution aging treatment:

[0047] Heat the mixture from room temperature to the solution heat treatment temperature of 530°C, with the heating time controlled within 1h. Keep the mixture at this temperature for 50min, quench in water, with the quenching transfer time not exceeding 3s, until it cools to room temperature, is taken out of the water, and the surface moisture is wiped off with a dry cotton cloth. Heat the mixture from room temperature to the aging temperature of 160°C, with the heating time controlled within 0.8h. Keep the mixture at this temperature for 6h after reaching the aging temperature of 160°C. Air cool the mixture to room temperature after the insulation is completed.

[0048] The tensile strength of the 6 series hot extruded aluminum alloy profile treated in this embodiment is 286.9MPa. Figure 4 For its metallographic structure, statistics on grain size revealed that its average grain size is 115.94μm.

[0049] By comparison with Example 1, it can be seen that the grain size after conventional solution aging treatment is larger than that of Example 1, which will have an adverse effect on the mechanical properties of the profile to a certain extent. The tensile strength of the sample using conventional heat treatment is still lower than that of Example 1. This is mainly because the pre-aging treatment of Example 1 can suppress the negative effects of natural aging to a certain extent, and has a certain promoting effect on the precipitation of the dispersed phase during the final aging process. Therefore, the mechanical properties of Example 1 are better.

[0050] Example 2

[0051] (1) Take 6082 hot extruded aluminum alloy profiles and use solid solution heat treatment: heat from room temperature to solid solution heat treatment temperature 520℃, the heating time is controlled at 0.8h, and after reaching the solid solution heat treatment temperature, keep it warm for 40min, quench in water, and the quenching transfer time does not exceed 3s, until it cools to room temperature, takes it out of water, and wipes the surface moisture with a dry cotton cloth.

[0052] (2) Then, double-stage aging is carried out, which is divided into pre-aging and final aging: the room temperature is raised to the pre-aging temperature of 110°C, the heating time is controlled at 0.5h, and the temperature is kept at 110°C for 3h; after the pre-aging holding time is up, no transfer is carried out, and the pre-aging temperature is raised from 110°C to the final aging temperature of 160°C, the heating time is controlled at 0.1h, and the temperature is kept at 160°C for 4.5h. After the final aging temperature is kept, air cool to room temperature.

[0053] The tensile strength of the 6 series hot extruded aluminum alloy profile after treatment in this embodiment is 311.33 MPa.

[0054] Example 3

[0055] (1) Take 6082 hot extruded aluminum alloy profiles and use solid solution heat treatment: heat from room temperature to solid solution heat treatment temperature 560℃, the heating time is controlled at 0.9h, and after reaching the solid solution heat treatment temperature, keep it warm for 30min, quench in water, and the quenching transfer time does not exceed 3s, until it cools to room temperature, takes it out of water, and wipes off the surface moisture with a dry cotton cloth.

[0056] (2) Then, double-stage aging is carried out, which is divided into pre-aging and final aging: the room temperature is raised to the pre-aging temperature of 115°C, the heating time is controlled at 0.8h, and the temperature is kept at 115°C for 1.5h; after the pre-aging holding time is up, no transfer is carried out, and the pre-aging temperature is raised from 115°C to the final aging temperature of 165°C, the heating time is controlled at 0.2h, and the temperature is kept at 165°C for 4h; after the final aging temperature is kept, air cool to room temperature.

[0057] The tensile strength of the 6 series hot extruded aluminum alloy profile after treatment in this embodiment is 323.28 MPa.

Claims

1. A method for heat treatment of hot extruded aluminum alloy profiles, characterized in that: The heat treatment method for hot extruded aluminum alloy profiles includes solution heat treatment and two-stage aging steps, specifically including: (1) Solution heat treatment: The hot extruded aluminum alloy profile is heated to 520-560°C, and the heating rate is divided into two stages. When the temperature is below 500°C, the heating rate is 10°C / min, and when the temperature reaches 500°C, the heating rate is 5°C / min, and the temperature is kept for 30-50 minutes; after the end of the heat preservation, water quenching is performed, and the transfer time does not exceed 3s; (2) Double-stage aging: After solution heat treatment, the hot extruded aluminum alloy profiles are significantly improved in strength after double-stage aging of pre-aging and final aging. The pre-aging temperature is 110-120°C and the holding time is 2-3h; the final aging temperature is 160-170°C and the holding time is 4-5h. After the holding period, the profiles are air-cooled to room temperature.

2. The heat treatment method for hot extruded aluminum alloy profiles according to claim 1, characterized in that: The heating described in step (1) is to control the heating time of the hot extruded aluminum alloy profile from room temperature to the solution heat treatment temperature of 520-560° C. to be 0.8-1 h.

3. The heat treatment method for hot extruded aluminum alloy profiles according to claim 1, characterized in that: The quenching transfer time in step (1) does not exceed 3s.

4. The heat treatment method for hot extruded aluminum alloy profiles according to claim 1, characterized in that: In step (2), the heating time from room temperature to the pre-aging temperature of the hot-extruded aluminum alloy profile after solution heat treatment is controlled to be 0.5 to 0.8 h; and the heating time from the pre-aging temperature to the final aging temperature is controlled to be 0.1 to 0.2 h.

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