6061 aluminum alloy for large hollow thin-wall profile and high-speed extrusion forming process

Abstract

The invention discloses a 6061 aluminum alloy for a large hollow thin-wall profile and a high-speed extrusion forming process. The high-speed extrusion forming process comprises the steps of burdening, casting, soaking, heating, extruding, online quenching, stretching and straightening, finished product sawing and aging strengthening. By the adoption of the technical scheme, through deformation energy in the extrusion process of the 6061 aluminum alloy material, the material is nucleated again and crystal nucleus grows up, the grain refining effect is achieved, and therefore the strength and toughness of the aluminum alloy profile are improved, and the aluminum alloy profile is suitable for preparing large hollow thin-wall profiles; by reducing the contents of Mg, Si, Cu, Mn and Cr in the 6061 aluminum alloy, reducing the alloying degree of an aluminum bar and reducing the extrusion resistance of a material in the extrusion process, the service life of a die is prolonged, the extrusion speed of the material can be greatly increased by 3-6 times due to the fact that surface coarse grain structures cannot be formed in the extrusion process, and the extrusion resistance of the material is reduced by 3-6 times due to the low precious metal content. And the production cost is further reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy profile preparation, and in particular to a 6061 aluminum alloy for large hollow thin-walled profiles and a high-speed extrusion molding process. Background Art

[0002] Please refer to Chinese patents CN116815028A and CN116815028A. In order to reduce the surface coarse grain thickness and obtain higher mechanical properties, traditional 6061 aluminum alloy generally uses aluminum bars with high Mg, Si, Cu, Mn, and Cr content, especially the Mn content is generally around 1%. The required profiles are then formed by high-temperature and low-speed extrusion.

[0003] The applicant has found in production practice that there is no problem in using the existing 6061 aluminum alloy to prepare small profiles. However, if the existing 6061 aluminum alloy is used to prepare large hollow thin-walled profiles, the following three problems will arise:

[0004] 1. Due to the high alloying degree of the existing 6061 aluminum alloy, the aluminum alloy has high deformation resistance. The extrusion resistance increases during the aluminum bar extrusion process, which has an adverse effect on the mold life and the mold cost remains high.

[0005] 2. Since the wall thickness of large hollow thin-walled aluminum alloy profiles is very thin (within 5mm), surface coarse grain problems are more likely to occur during the extrusion process. Therefore, the extrusion speed must be controlled below 5m / min, usually around 3m / min, and the extrusion efficiency is very low.

[0006] 3. The existing 6061 aluminum alloy has high contents of Mg, Si, Cu, Mn and Cr, especially Mn and Cr, which leads to high production costs.

[0007] Solving the above problems has become a top priority. Summary of the Invention

[0008] In order to solve the technical problems of short die life, low extrusion efficiency and high production cost when using existing 6061 aluminum alloy to prepare large hollow thin-walled profiles, the present invention provides a 6061 aluminum alloy for large hollow thin-walled profiles and a high-speed extrusion forming process.

[0009] The technical solution is as follows:

[0010] The invention discloses a 6061 aluminum alloy for large hollow thin-walled profiles. The main features of the 6061 aluminum alloy are as follows: Si: 0.56-0.65%, Fe: 0.17-0.22%, Cu: 0.16-0.25%, Mn: 0.02-0.04%, Mg: 0.83-0.93%, Cr: 0.06-0.10%, Zn≤0.03%, Ti≤0.15%, impurities≤0.12%, and the balance is Al.

[0011] A high-speed extrusion molding process, the key points of which are to follow the following steps:

[0012] A. Ingredients: Prepare the ingredients according to the composition and weight percentage of the above-mentioned 6061 aluminum alloy;

[0013] B. Casting: Add the prepared 6061 aluminum alloy raw materials into a melting furnace, mix them evenly, and then melt them into liquid aluminum alloy, and then cast the liquid aluminum alloy into 6061 aluminum alloy casting bars;

[0014] C. Soaking: The 6061 aluminum alloy casting rod is subjected to a heat treatment in a homogenizing furnace, and the 6061 aluminum alloy casting rod is cooled after being taken out of the furnace;

[0015] D. Heating: heating the 6061 aluminum alloy casting rod;

[0016] E. Extrusion: The heated 6061 aluminum alloy cast rod is placed in the extrusion barrel of the extruder for extrusion to obtain a large hollow thin-walled profile;

[0017] F. Online quenching: Online quenching of large hollow thin-walled profiles;

[0018] G. Stretching and straightening: stretching the large hollow thin-walled profiles after quenching;

[0019] H. Finished product sawing: sawing of large hollow thin-walled profiles that have been stretched;

[0020] I. Aging Strengthening: Aging strengthening is performed on large hollow thin-walled profiles that have been sawn.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. In view of the problem that large hollow thin-walled profiles are prone to surface coarse grains, reverse thinking is adopted. The deformation energy of 6061 aluminum alloy during the extrusion process is used to make the material re-nucleate and grow the crystal nucleus, thereby achieving the effect of grain refinement, thereby improving the strength and toughness of the aluminum alloy profile, making it suitable for the preparation of large hollow thin-walled profiles;

[0023] 2. By reducing the Mg, Si, Cu, Mn, and Cr contents in the 6061 aluminum alloy, the alloying degree of the aluminum rod is reduced, and the extrusion resistance of the material during the extrusion process is reduced. This not only extends the life of the mold and reduces the investment cost of the mold, but also, since no surface coarse-grained structure is formed during the extrusion process, the extrusion speed of the material can be greatly increased, and the extrusion speed can reach 12 m / min to 20 m / min. Especially for large hollow thin-walled profiles, compared with the existing 6061 aluminum alloy, the extrusion efficiency of the 6061 aluminum alloy of the present invention can be increased by 3-6 times, and due to the low content of precious metals, the production cost is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flowchart of high-speed extrusion process. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0026] Example 1:

[0027] The invention discloses a 6061 aluminum alloy for large hollow thin-walled profiles. The composition and weight percentage of the 6061 aluminum alloy are as follows: Si: 0.56-0.65%, Fe: 0.17-0.22%, Cu: 0.16-0.25%, Mn: 0.02-0.04%, Mg: 0.83-0.93%, Cr: 0.06-0.10%, Zn≤0.03%, Ti≤0.15%, impurities≤0.12%, and the balance is Al.

[0028] Compared to the existing 6061 aluminum alloy, the Mg, Si, Cu, Mn, and Cr contents in this embodiment are all reduced to varying degrees, thereby reducing the alloying degree of the aluminum bar and, in turn, the extrusion resistance of the material during extrusion. Specifically, by reducing the Mn and Cr contents, the recrystallization resistance during aluminum alloy extrusion is reduced, thereby achieving grain refinement and improving the material's strength and toughness.

[0029] Example 2:

[0030] A high-speed extrusion molding process is carried out according to the following steps:

[0031] A. Ingredients: Calculate the amount of 6061 aluminum alloy raw materials and prepare the aluminum alloy raw materials according to the proportions. The mass percentages of each element in the 6061 aluminum alloy raw materials are as follows:

[0032]

[0033] B. Casting: Add the prepared 6061 aluminum alloy raw materials into the melting furnace and mix them evenly before melting them into liquid aluminum alloy. After standing, refining, slagging, online degassing and filtering processes, the liquid aluminum alloy is cast into 6061 aluminum alloy rods by semi-continuous water-cooling casting. The rod length of the 6061 aluminum alloy rods is 6000 mm.

[0034] C. Soaking: 6061 aluminum alloy cast bars undergo a soaking treatment in a homogenizing furnace at a temperature of 560-580°C for 8-10 hours. After exiting the furnace, the bars are cooled to room temperature using a forced air stream. Compared to existing soaking treatments for 6061 aluminum alloy cast bars, this soaking treatment temperature is lowered, resulting in energy savings.

[0035] D. Heating: The 6061 aluminum alloy cast rods are heated at a temperature of 440-500°C with a temperature gradient of 20-50°C / m. Compared to existing 6061 aluminum alloy profile preparation processes, the cast rod heating temperature in this embodiment is significantly lowered, saving energy and reducing production costs while also shortening heating time and improving production efficiency.

[0036] E. Extrusion: The heated 6061 aluminum alloy cast rod is placed in the extrusion barrel of a 40MN extruder for extrusion to obtain a large hollow thin-walled profile; wherein, the extrusion speed is 12 to 25 m / min, and the outlet temperature of the extrusion barrel is controlled at 510 to 560°C. Compared with the existing 6061 aluminum alloy profile preparation process, the extrusion speed of this embodiment is greatly improved (the existing 6061 aluminum alloy profile preparation process is generally 0.5 to 5 m / min), greatly improving the extrusion production efficiency.

[0037] Since the greater the temperature difference between the extrusion barrel and the 6061 aluminum alloy cast rod, the greater the friction, a reasonable amount of friction can prevent impurities on the surface of the cast rod from flowing into the interior of the profile, but excessive friction will reduce the profile production efficiency. Therefore, in this embodiment, the extrusion barrel and the mold are also heated. The extrusion barrel temperature is preferably 30℃±10℃ lower than the 6061 aluminum alloy cast rod temperature, and the mold temperature is preferably 520℃±5℃.

[0038] F. Online Quenching: Online quenching is performed on large hollow thin-walled profiles. Since the wall thickness of large hollow thin-walled profiles is less than 5mm, they are prone to solid solution. Therefore, to reduce deformation during the quenching process, the quenching method adopts air cooling, with a cooling rate of ≥0.5℃ / s and a wind speed of 30-50m / s. The higher the wind speed, the more stable the material's final mechanical properties (tensile strength and specified non-proportional elongation strength).

[0039] G. Stretching and straightening: stretch the large hollow thin-walled profiles that have been quenched. The internal stress of the material produced by air-cooling quenching is not high, and the stretching rate is preferably 0.1-0.3%.

[0040] H. Sawing of finished products: Sawing of large hollow thin-walled profiles that have completed stretching, removing the deformed area at the head and the unquenched area at the tail.

[0041] I. Aging strengthening: Large hollow thin-walled profiles are artificially aged at a temperature of 175-185°C for 4-8 hours.

[0042] Comparative Example 1:

[0043] The difference between Comparative Example 1 and Example 2 is that the mass percentage ratio of each element in the 6061 aluminum alloy raw material in step A is as follows:

[0044]

[0045] Comparative Example 2:

[0046] The difference between Comparative Example 2 and Example 2 is that in step E, the profile extrusion speed is adjusted to a low speed, and the extrusion speed is 1 to 3 m / min.

[0047] Comparative Example 3:

[0048] The difference between Comparative Example 3 and Example 2 is that in step E, in step F, the quenching method is changed from ordinary air cooling to weak air cooling, and the wind speed is 3 to 5 m / s.

[0049] Comparative Example 4:

[0050] The difference between Comparative Example 4 and Example 2 is that in step I, the finished large hollow thin-walled profile is artificially aged at a temperature of 190° C. for 4 h.

[0051] Table 1 Process parameter record table of Examples and Comparative Examples

[0052]

[0053] Table 2 Performance standards of 6061 aluminum alloy profiles and mechanical properties of examples and comparative examples

[0054]

[0055] From Table 1 and Table 2, we can see that:

[0056] In Comparative Example 1, the Mn and Cr contents are increased compared to Example 2. Therefore, the mechanical properties (tensile strength and specified non-proportional elongation strength) are increased, but the elongation is significantly decreased (lower than the national standard). It can be seen that the 6061 aluminum alloy with high Mn and Cr contents is not suitable for high-speed extrusion of large hollow thin-walled profiles.

[0057] In Comparative Example 2, compared with Example 2, the extrusion speed is greatly reduced, and the surface coarse-grained structure of the large hollow thin-walled profile is greatly increased. Therefore, the tensile strength does not change much, the specified non-proportional elongation strength is improved, and the elongation is significantly reduced (lower than the national standard). It can be seen that the 6061 alloy of Example 2 is suitable for high-speed extrusion molding of large hollow thin-walled profiles, but not suitable for low-speed extrusion molding.

[0058] Compared with Example 2, Comparative Example 3 has a slower quenching cooling rate due to the lower wind speed; however, the mechanical properties (tensile strength and specified non-proportional elongation strength) of the material in Comparative Example 3 are greatly reduced at a lower quenching cooling rate. This shows that the performance of 6061 aluminum alloy material is relatively sensitive to quenching.

[0059] Compared with Example 2, Comparative Example 4 has a higher aging temperature and a shorter holding time, but the strength of the large hollow thin-walled profile finally obtained does not decrease significantly and is still in the peak aging range, indicating that the aging temperature and aging time selected in Example 2 can achieve the same aging effect while consuming less energy.

[0060] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Under the guidance of the present invention, ordinary technicians in this field can make various similar expressions without violating the purpose and claims of the present invention. Such changes fall within the scope of protection of the present invention.

Claims

1. A 6061 aluminum alloy for large hollow thin-walled profiles, characterized in that: The composition and weight percentage of 6061 aluminum alloy are: Si: 0.56~0.65%, Fe: 0.17~0.22%, Cu: 0.16~0.25%, Mn: 0.02~0.04%, Mg: 0.83~0.93%, Cr: 0.06~0.10%, Zn≤0.03%, Ti≤0.15%, impurities≤0.12%, and the balance is Al.

2. The 6061 aluminum alloy for large hollow thin-walled profiles according to claim 1, characterized in that: The composition and weight percentage of 6061 aluminum alloy are: Si: 0.60%, Fe: 0.19%, Cu: 0.20%, Mn: 0.03%, Mg: 0.88%, Cr: 0.08%, Ti: 0.05%, impurities ≤ 0.12%, and the balance is Al.

3. A high-speed extrusion molding process, characterized in that: Follow these steps: A. Ingredients: Ingredients are prepared according to the composition and weight percentage of the 6061 aluminum alloy described in claim 1 or 2; B. Casting: Add the prepared 6061 aluminum alloy raw material into a melting furnace, mix evenly, and then melt it into liquid aluminum alloy, and then cast the liquid aluminum alloy into 6061 aluminum alloy casting rods; C. Heat-saturation: The 6061 aluminum alloy casting rod is heat-saturated in a homogenizing furnace, and the 6061 aluminum alloy casting rod is cooled after being taken out of the furnace; D. Heating: heating the 6061 aluminum alloy casting rod; E. Extrusion: The heated 6061 aluminum alloy cast rod is placed in the extrusion barrel of the extruder for extrusion to obtain a large hollow thin-walled profile; F. Online quenching: Online quenching of large hollow thin-walled profiles; G. Stretching and straightening: stretching the large hollow thin-walled profiles after quenching; H. Finished product sawing: sawing of large hollow thin-walled profiles that have been stretched; I. Aging strengthening: Aging strengthening is carried out on large hollow thin-walled profiles that have been sawn.

4. The high-speed extrusion molding process according to claim 3, characterized in that: In the step C, the temperature of the heat treatment is 560-580° C., and the heat preservation time is 8-10 hours.

5. The high-speed extrusion molding process according to claim 3, characterized in that: In the step D, the 6061 aluminum alloy cast rod is heated in a heating furnace, the heating temperature is controlled at 440-500° C., and the temperature gradient is 20-50° C. / m.

6. The high-speed extrusion molding process according to claim 3, characterized in that: In the step E, the outlet temperature of the profile is controlled at 510-560° C., and the extrusion speed is 12-25 m / min.

7. The high-speed extrusion molding process according to claim 6, characterized in that: In the step E, the extrusion barrel is heated to a temperature 30°C±10°C lower than the 6061 aluminum alloy casting rod, and the mold temperature is heated to 520°C±5°C.

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