Homogenizing heat treatment process for regenerated aluminum alloy

Abstract

The invention relates to a secondary aluminum alloy homogenizing heat treatment process which comprises the following steps: putting a secondary aluminum alloy ingot into a heat treatment furnace, and heating to the homogenizing temperature of 550-590 DEG C; after the regenerated aluminum alloy cast ingot is heated to the homogenization temperature, homogenization heat preservation is conducted, and the homogenization heat preservation time is 6-10 h; and after homogenization and heat preservation, the regenerated aluminum alloy cast ingot is taken out of the heat treatment furnace for water quenching, and the homogenized regenerated aluminum cast ingot is obtained. By means of the homogenizing process, inclusions, air holes and shrinkage porosity are effectively eliminated, the morphology of an iron-rich phase is improved, the MgSi phase is promoted to be redissolved into a matrix, the plasticity of the aluminum alloy is remarkably improved, an optimal structure is provided for subsequent extrusion forming production of a high-performance regenerated wrought aluminum alloy profile, and important industrial application value is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy heat treatment, in particular to a homogenization heat treatment process for recycled aluminum alloy. Background Art

[0002] In order to reduce environmental pollution and achieve energy conservation and emission reduction, the recycling of aluminum has become an inevitable choice for sustainable development. Aluminum is an infinitely recyclable material, which provides a theoretical basis for the recycling of aluminum. Recycling involves the remelting of metals, which consumes only 5% of the energy used to produce the original aluminum. This means that recycling aluminum can greatly reduce energy consumption and make the continuous recycling of aluminum possible.

[0003] Deformed aluminum alloys represented by the 6000 series are widely used in automobiles. Therefore, the recycling of 6000 series deformed aluminum alloy scrap is expected to become the main part of aluminum alloy scrap recycling in the future. However, a large number of waste 6000 series aluminum alloys are often downgraded and recycled into impurity-resistant cast aluminum alloys, which makes it difficult to achieve the same level of recycled deformed aluminum alloys. After remelting and regeneration, they can no longer return to the 6000 series deformed aluminum alloy sequence. This is because deformed aluminum alloys have strict requirements on alloy composition specifications.

[0004] During the recycling process, 6000 series aluminum alloys will introduce a variety of impurity elements, forming defects such as inclusions, pores, shrinkage and iron-rich phases, resulting in a decrease in the plastic forming ability of the recycled aluminum alloy. In order to reduce the adverse effects of these defects, homogenization treatment can effectively eliminate inclusions, pores and shrinkage, improve the morphology of the iron-rich phase, inhibit the formation of needle-shaped or lamellar β-iron-rich phases, and promote their transformation into Chinese characters or other α-iron-rich phases that are less harmful to the performance of aluminum alloys. At the same time, it promotes the dissolution of MgSi phases back into the matrix, significantly improving the plastic properties of recycled aluminum. At present, there are many studies on the homogenization process of primary 6000 series aluminum alloys. The homogenization temperature of primary aluminum is low and the homogenization time is long, which is to avoid the growth of grains and the reduction of mechanical properties. Therefore, the homogenization heat treatment efficiency of primary aluminum is low, the time cost is high, and the low homogenization temperature cannot meet the elimination of recycled aluminum defects and the homogenization of the organization.

[0005] Therefore, the existing homogenization technology obviously has inconveniences and defects in practical use, so it is necessary to explore a homogenization heat treatment process for recycled aluminum alloy. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a homogenization heat treatment process for recycled aluminum alloy, which can save processing time and obtain better mechanical properties.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: A homogenization heat treatment process for recycled aluminum alloy, comprising the following steps, Put the recycled aluminum alloy ingot into a heat treatment furnace and heat it to the homogenization temperature of 550 - 590 °C; After the recycled aluminum alloy ingot is heated to the homogenization temperature, carry out homogenization heat preservation, and the homogenization heat preservation time is 6 - 10 h; After homogenization heat preservation, take out the recycled aluminum alloy ingot from the heat treatment furnace for water quenching to obtain a homogenized recycled aluminum ingot.

[0008] Furthermore, the recycled aluminum alloy ingot is heated to the homogenization temperature of 550 - 590 °C in the heat treatment furnace at a temperature rise rate of 10 °C / s.

[0009] Furthermore, the water quenching temperature is 20 - 25 °C, and the quenching transfer time is less than 20 s.

[0010] Furthermore, during water quenching, the ingot rotates in the cooling water to make the cooling of different positions of the ingot uniform.

[0011] Furthermore, the weight percentages of the recycled aluminum alloy ingot are as follows: Mg is 0.761 wt%, Si is 0.711 wt%, Fe is 0.255 wt%, Mn is 0.284 wt%, Cu is 0.130 wt%, Cr is 0.104 wt%, V is 0.058 wt%, and the balance is Al and impurity elements.

[0012] Furthermore, the raw materials of the recycled aluminum alloy ingot are automotive 6000 series aluminum alloy scraps, processing leftovers, pure aluminum ingots and master alloys. Among them, the scrap ratio is 40%. The recycled 6008 aluminum alloy ingot is produced by a semi - continuous casting process. During this process, through on - line composition detection and composition adjustment, the composition of the aluminum melt meets the requirements of the target recycled aluminum composition.

[0013] Furthermore, the preparation method of the recycled aluminum alloy ingot comprises the following steps, Sort, crush, remove paint and wash the recycled automotive 6000 series aluminum alloy scraps and processing leftovers in sequence; Charge and melt the automotive 6000 series aluminum alloy scraps. During the melting process, add pure aluminum ingots, master alloys, modifiers and refining agents in sequence, remove slag multiple times, and finally carry out casting.

[0014] Furthermore, for as - cast detection, samples are taken from the recycled 6008 aluminum alloy ingot to detect its microstructure and mechanical properties. Specifically, samples are taken by wire - cutting at a position of R / 2 from the center of the cross - section radius of the ingot. Then, they are ground, polished and corroded, and the microstructure of the ingot is observed under an optical microscope, an electron microscope and electron backscatter diffraction to detect the grain size of the ingot, the phases and phase distribution of the ingot. Emphasis is placed on analyzing defects such as inclusions, pores, shrinkage porosity and iron - rich phases.

[0015] Furthermore, the modifier composition consists of Al, Sr and Re elements, and the refining agent is cryolite.

[0016] Furthermore, the refining temperature is 780 °C.

[0017] Furthermore, the microstructure of the homogenized ingot is observed under an optical microscope, an electron microscope and electron backscatter diffraction, and its grain size, phase and phase distribution are detected. Emphasis is placed on analyzing the percentage of the second phase and whether overburning occurs.

[0018] Generally speaking, the present invention has the following advantages: The present invention provides a homogenization heat treatment process for recycled aluminum alloy, which can meet the elimination of defects such as inclusions, pores and shrinkage porosity in recycled aluminum and the homogenization of the structure, shorten the homogenization holding time, improve production efficiency, and at the same time improve the morphology of the iron-rich phase, greatly improve the plastic forming ability of the recycled aluminum alloy, obtain better mechanical properties, and provide the optimal structure for the subsequent extrusion processing of the recycled aluminum profile. Brief Description of the Drawings

[0019] Figs. 1(a) and 1(b) are OM metallographic diagrams of the ingot in Example 2; Figure 2 is the SEM scanning electron micrograph of Example 2; Figure 3 is the OM metallographic diagram after the homogenization treatment in Example 3; Figure 4 is the SEM scanning electron micrograph after the homogenization treatment in Example 3; Figure 5 is the OM metallographic diagram after the homogenization treatment in Comparative Example 1; Figure 6 is the SEM scanning electron micrograph after the homogenization treatment in Comparative Example 1; Figure 7 is the OM metallographic diagram after the homogenization treatment in Comparative Example 2; Figure 8 is the SEM scanning electron micrograph after the homogenization treatment in Comparative Example 2; Figure 9 is the OM metallographic diagram after the homogenization treatment in Comparative Example 3; Figure 10 is the SEM scanning electron micrograph after the homogenization treatment in Comparative Example 3; Figure 11 is the OM metallographic diagram after the homogenization treatment in Comparative Example 4; Figure 12 is the SEM scanning electron micrograph after the homogenization treatment in Comparative Example 4; Figure 13 is the tensile curve diagram of Example 2 and Example 3. Specific Embodiments

[0020] Currently, there is a common phenomenon of downgrading in the recycling process of waste 6000 series wrought aluminum alloys. The main restrictive factors lie in the various impurities introduced during the recycling process and the resulting microstructural defects. These defects mainly include inclusions, pores, shrinkage porosity, and iron-rich phases, etc. Among them, the iron-rich phase has the most significant impact on the alloy properties. At high temperatures, the solubility of iron element in the aluminum matrix is relatively high, resulting in the easy dissolution of Fe element into the melt during the recycling of waste aluminum and the difficulty in effectively removing it. However, when the temperature drops to 660 °C, the solubility of Fe in the alloy drops sharply to 0.05%. This significant change in solubility leads to almost all of the dissolved Fe elements precipitating in the form of iron-containing intermetallic compounds (IMCs) during the solidification process of the alloy. These hard and brittle iron-rich phases precipitate in complex morphologies such as needle-like, massive, and Chinese character-like shapes, and aggregate and distribute along the grain boundaries, seriously damaging the continuity of the matrix, thereby significantly reducing the mechanical properties of the alloy, especially the plastic forming ability. To eliminate the adverse effects of these defects on the material properties, homogenization treatment processes are usually adopted for improvement. The present invention proposes a homogenization heat treatment method for improving the extrudability of recycled 6008 aluminum alloy. By setting the homogenization temperature and homogenization time, and quantitatively detecting the inclusion content, grain size, and phase distribution, comprehensively considering overburning, grain size, the morphology of the second phase, and the percentage of the second phase, under the condition of achieving the same homogenization effect, the homogenization holding time is shortened, and the production efficiency is improved. At the same time, the plastic deformation ability of the recycled 6008 aluminum alloy is improved, providing the optimal microstructure for the subsequent extrusion processing of this recycled aluminum profile. The present invention also provides a preparation method for recycled aluminum alloy. By adding a rare earth modifier during the melting process, heterogeneous nucleation sites are provided for the growth of the iron-rich phase, converting the flaky and coarse β iron-rich phase into spherical and dispersed α iron-rich phase. At the same time, a judgment link for the defects of the as-cast recycled aluminum is also introduced.

[0021] The following will further elaborate on the present invention.

[0022] A homogenization heat treatment method for improving the plasticity of recycled 6008 aluminum alloy, including a detection method for the microstructure of recycled aluminum ingots and a determination method for the homogenization process: S1. Prepare a recycled 6008 aluminum alloy ingot. The weight percentages of the ingot are: Mg 0.761 wt%, Si 0.711 wt%, Fe 0.255 wt%, Mn 0.284 wt%, Cu 0.130 wt%, Cr 0.104 wt%, V 0.058 wt%, and the balance is Al and impurity elements; Further, step S1 also includes the following steps: S11. Pretreatment, successively perform sorting, crushing, paint removal, and water washing and other pretreatments on the recycled automotive 6000 series aluminum alloy waste and processing leftovers; S12. Batching: Batch the automotive 6000 series aluminum alloy waste, processing leftovers, aluminum ingots, Al-Cu master alloy, Al-Si master alloy, Al-Mn master alloy, and Al-Cr master alloy according to a certain weight ratio. S13. Add the prepared aluminum alloy raw materials into the melting furnace, uniformly mix them, and melt them into liquid recycled aluminum alloy. After alloying, standing, refining, slag skimming, online degassing, and filtering processes, cast the liquid recycled aluminum alloy into recycled aluminum alloy ingots. S14. Let the molten recycled aluminum alloy stand for 30 min to obtain ingots.

[0023] S2. Observe the microstructure of the recycled aluminum. Grind, polish, and corrode the recycled aluminum ingots sampled at specific positions, and observe the microstructure under an optical microscope, an electron microscope, and electron backscatter diffraction. Detect the grain size, phase, and phase distribution of the ingots. Focus on analyzing defects such as inclusions, pores, shrinkage porosity, and iron-rich phases.

[0024] S3. Rapid heating: Place the recycled aluminum ingots in a heat treatment furnace and perform rapid heating. Further, step S3 also includes the following steps: S31. Put the recycled aluminum ingots into the heat treatment furnace and heat them to the homogenization temperature of 550 - 590 °C at a rate of 10 °C / s. S32. Load the recycled aluminum ingots into the heat treatment furnace, and keep an equal distance interval of 20 - 80 mm between adjacent ingots. S4. After the recycled aluminum ingots are heated to the homogenization temperature, perform homogenization holding, and the homogenization holding time is 6 - 10 h. S5. Take out the ingots and cool them in room temperature water to 20 - 25 °C to obtain homogenized recycled aluminum ingots.

[0025] Further, step S5 also includes the following steps: S51. Take out the recycled aluminum ingots from the heat treatment furnace for water quenching, where the quenching transfer time is less than 20 s. S52. During water quenching, the ingots rotate clockwise in the cooling water to ensure uniform cooling of different positions of the ingots.

[0026] Example 1 Add the prepared aluminum alloy raw materials into the melting furnace, uniformly mix them, and melt them into liquid recycled aluminum alloy. After alloying, standing, refining, slag skimming, online degassing, and filtering processes, cast the liquid recycled aluminum alloy into recycled aluminum alloy ingots. Example 2 In the embodiment, in step S2, the recycled aluminum ingot is detected. The present invention uses an optical microscope (OM), a scanning electron microscope (SEM) and / or electron backscatter diffraction (EBSD) to detect the grain size of the ingot, the phases of the ingot and the phase distribution. Those skilled in the art can make a reasonable configuration for each detection item according to the actual detection resources.

[0027] Example 3 In this embodiment, in step S31, the aluminum alloy ingot is heated to 570 °C at a rate of 10 °C / min in a heat treatment furnace; in step S3, the recycled aluminum ingot is kept warm in the heat treatment furnace for 8 h.

[0028] Comparative Example 1 In this comparative example, in step S31, the aluminum alloy ingot is heated to 550 °C at a rate of 10 °C / min in a heat treatment furnace; in step S3, the recycled aluminum ingot is kept warm in the heat treatment furnace for 8 h.

[0029] Comparative Example 2 In this comparative example, in step S31, the aluminum alloy ingot is heated to 590 °C at a rate of 10 °C / min in a heat treatment furnace; in step S3, the recycled aluminum ingot is kept warm in the heat treatment furnace for 8 h.

[0030] Comparative Example 3 In this comparative example, in step S31, the aluminum alloy ingot is heated to 570 °C at a rate of 10 °C / min in a heat treatment furnace; in step S3, the recycled aluminum ingot is kept warm in the heat treatment furnace for 6 h.

[0031] Comparative Example 4 In this comparative example, in step S31, the aluminum alloy ingot is heated to 570 °C at a rate of 10 °C / min in a heat treatment furnace; in step S3, the recycled aluminum ingot is kept warm in the heat treatment furnace for 10 h.

[0032] In Example 1, the refining temperature of the present invention is 780 °C, which can melt the high-melting-point inclusions such as iron and copper in the recycled aluminum alloy melt, reduce the nucleation points of the high-temperature precipitation phases, and prevent the growth of high-melting-point precipitation phases such as iron-rich phases with them as the matrix. At the same time, it can also promote the full and uniform diffusion of inclusions in the melt. Adding a rare earth modifier refined the iron-rich phase.

[0033] In Example 2, there are inclusions, pores, shrinkage porosity, and the morphologies of β and α iron-rich phases in the recycled aluminum ingot of the present invention.

[0034] Table 1 is obtained from the homogenization time statistics of the above examples and comparative examples.

[0035] Table 1 Homogenization Time Statistics of Each Example and Comparative Example

[0036] The homogenized and annealed recycled aluminum ingots obtained from the above process were respectively sanded, polished and corroded, and then metallographic inspection was carried out.

[0037] Please refer to Figures 3 - 12 The metallographic diagrams and SEM scanning diagrams of the aluminum alloy ingots after homogenization treatment in each example and comparative example were obtained, and the statistical data in Table 2 were obtained.

[0038] Table 2 Comparison table of homogenization effects of each example and comparative example

[0039] Please refer to Figure 13 The mechanical property comparison diagrams of as-cast aluminum alloy and homogenized aluminum alloy in the examples were obtained, and the statistical data in Table 3 were obtained.

[0040] Table 3 Comparison table of tensile properties of as-cast and homogenized states in Example 1

[0041] Analysis of the above experimental data found that there are some defects in the recycled 6008 aluminum alloy ingots, which affect the mechanical properties of the as-cast state. By using the homogenization heat treatment method provided by the present invention, defects such as inclusions, pores and shrinkage porosity are eliminated, the morphology of the iron phase is improved, the plastic forming ability of the recycled 6008 aluminum alloy is greatly improved, and the same-level recycling of the recycled aluminum alloy becomes possible.

[0042] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A homogenizing heat treatment process for recycled aluminum alloy, characterized in that: Including the following steps, Put the recycled aluminum alloy ingot into a heat treatment furnace and heat it to the homogenization temperature of 550 - 590 °C; After the recycled aluminum alloy ingot is heated to the homogenization temperature, carry out homogenization heat preservation, and the homogenization heat preservation time is 6 - 10 h; After homogenization heat preservation, take out the recycled aluminum alloy ingot from the heat treatment furnace for water quenching to obtain a homogenized recycled aluminum ingot.

2. The homogenization heat treatment process of recycled aluminum alloy according to claim 1, characterized in that: The recycled aluminum alloy ingot is heated to the homogenization temperature of 550 - 590 °C in the heat treatment furnace at a temperature rise rate of 10 °C / s.

3. A homogenization heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: The water quenching temperature is 20 - 25 °C, and the quenching transfer time is less than 20 s.

4. A homogenization heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: During water quenching, the ingot rotates in the cooling water to make the cooling of different positions of the ingot uniform.

5. A homogenization heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: The weight percentages of the recycled aluminum alloy ingot are as follows: Mg is 0.761 wt%, Si is 0.711 wt%, Fe is 0.255 wt%, Mn is 0.284 wt%, Cu is 0.130 wt%, Cr is 0.104 wt%, V is 0.058 wt%, and the balance is Al and impurity elements.

6. A homogenizing heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: The raw materials of the recycled aluminum alloy ingot are automotive 6000 series aluminum alloy scraps, processing leftovers, pure aluminum ingots and master alloys. Among them, the scrap ratio is 40%. The recycled 6008 aluminum alloy ingot is produced by a semi - continuous casting process. During this process, through on - line composition detection and composition adjustment, the composition of the aluminum melt meets the requirements of the target recycled aluminum composition.

7. A homogenizing heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: The preparation method of the recycled aluminum alloy ingot includes the following steps, Sort, crush, remove paint and wash the recycled automotive 6000 series aluminum alloy scraps and processing leftovers in sequence for pretreatment; Charge the automotive 6000 series aluminum alloy scraps, load them into the furnace and carry out melting; during the melting process, add pure aluminum ingots, master alloys, modifiers and refining agents in sequence, remove slag multiple times, and finally carry out casting.

8. A homogenization heat treatment process for recycled aluminum alloy according to claim 7, characterized in that: The modifier consists of Al, Sr and Re elements, and the refining agent is cryolite.

9. A homogenization heat treatment process for recycled aluminum alloy according to claim 7, characterized in that: The refining temperature is 780 °C.

10. A homogenizing heat treatment process for recycled aluminum alloy according to claim 1, characterized in that: Observe the microstructure of the homogenized ingot under an optical microscope, an electron microscope and electron backscatter diffraction, and detect its grain size, phases and phase distribution.

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