A 7020 aluminum alloy profile and its extrusion process

Abstract

The invention belongs to the field of aluminum processing and manufacturing, and relates to a 7020 aluminum alloy profile and an extrusion process thereof. The aluminum alloy profile has the following component contents in percentage: Si≤0.15, Mg1.15-1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80-5.00, Zr: 0.10-0.16, Pb: —, Cr: —, a single impurity is ≤0.05, a total of ≤0.15, and the rest is Al. The extrusion process comprises material inspection, heating treatment, extrusion profile, stretching and straightening, finished product sawing and artificial aging, wherein the artificial aging method is to first heat the sawed 7020 aluminum alloy profile to 105±3°C in an aging furnace, and keep the temperature for 7-8h, and then heat it to 135±3°C, and keep the temperature for 6-8h. The 7020 aluminum alloy profile prepared by the 7020 aluminum alloy profile extrusion process provided by the present invention has an elongation of 70-80 MPa higher than the standard value, and a tensile strength of 40-50 MPa higher than the standard value, has excellent product performance, and a yield rate of more than 75%.

Description

Technical Field

[0001] The invention belongs to the field of aluminum processing and manufacturing, and relates to a 7020 aluminum alloy profile and an extrusion process thereof. Background Art

[0002] 7020 aluminum alloy is a medium- and high-strength Al-Zn-Mg alloy with high performance strength, good welding performance and processing technology performance. It is the main welding structural material for aerospace, high-end vehicles and high-end equipment. 7020 aluminum alloy material is also widely used in the processing and manufacturing of EMU and high-speed train body materials.

[0003] The production process of aluminum profiles mainly includes three processes: melting, extrusion and surface treatment. Among them, extrusion is the means of profile forming. Extrusion is to first design and manufacture the mold according to the cross-section of the profile product, use the extruder to extrude the heated round cast rod from the mold, and then go through the air-cooling quenching process and the subsequent artificial aging process to complete the heat treatment strengthening. The extruded 7020 aluminum alloy has good comprehensive properties after heat treatment. Therefore, the 7020 aluminum alloy has a greater range of use strength than the 6082 aluminum alloy, but its disadvantage is that the extrusion processing ability is low, that is, the yield is low. It is an aluminum alloy that has difficulties in the field of extrusion processing.

[0004] Therefore, it is necessary to propose a new 7020 aluminum alloy profile extrusion process. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a 7020 aluminum alloy profile and an extrusion process thereof, by adjusting the element content ratio of the 7020 aluminum alloy and optimizing the process parameters, and adopting double-stage artificial aging, under the premise of ensuring the comprehensive performance of the 7020 aluminum alloy profile, overcome the disadvantage of low extrusion processing and forming ability of the 7020 aluminum alloy and improve the yield of the 7020 aluminum alloy profile.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In one aspect, the present invention provides a 7020 aluminum alloy profile extrusion process, comprising the following steps:

[0008] a. Material inspection: The material is a homogenized 7020 aluminum bar, the composition percentage of which is as follows: Si≤0.15, Mg1.15~1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80~5.00, Zr: 0.10~0.16, Pb: —, Cr: —, single impurity ≤0.05, total ≤0.15, the rest is Al;

[0009] b. Heating treatment: heat the aluminum bar to 480℃~500℃ and the mold to 500℃~520℃

[0010] c. Extrusion profile: Assemble the heated aluminum rod and the die to the extruder and perform extrusion processing to obtain a 7020 aluminum alloy profile, and perform online quenching on the 7020 aluminum alloy profile;

[0011] d. Stretching and straightening: After the quenched 7020 aluminum alloy profile is cooled to room temperature, stretching and straightening are performed;

[0012] e. Finished product sawing: saw the stretched and straightened 7020 aluminum alloy profiles according to the agreed size;

[0013] f. Artificial aging: First, heat the sawn 7020 aluminum alloy profile to 105±3℃ in the aging furnace and keep it warm for 7~8h, then heat it to 135±3℃ and keep it warm for 6~8h. After the insulation, remove the 7020 aluminum alloy profile from the aging furnace and cool it naturally to room temperature.

[0014] In some embodiments of the present disclosure, in step b, a resistance speed heating industrial frequency furnace is used as the heating equipment, which has the characteristics of being able to increase the temperature in a short time and improve production efficiency.

[0015] In some embodiments of the present disclosure, the model of the extruder in step c is 75MN / 7500T.

[0016] In some embodiments of the present disclosure, a bellows-type cooling device is used as a quenching device in the step c. The bellows-type cooling device is characterized in that the cooling intensity is more stable and the degree of deformation caused by the cooling rate on the size is easy to adjust. The temperature of the 7020 aluminum alloy profile before quenching is controlled to be 500-560°C, and the temperature after quenching is ≤150°C, which can effectively prevent the drastic temperature change caused by the aluminum rod flowing out through extrusion and prevent the 7020 aluminum alloy profile from overburning.

[0017] In some embodiments of the present disclosure, the stretching rate in step d is 1% to 1.2%. While ensuring that the profile size allows, the stretching rate is controlled at 1% to 1.2%, so that a certain proportion of residual stress inside the profile after deformation and cooling is fully released, the deformation and stress distribution are uniform, the extrusion and twisting deformation effects are reduced, and an auxiliary effect is provided for the double-stage artificial aging of the heat treatment.

[0018] In some embodiments of the present disclosure, the tolerance length of the sawing in step e is controlled to be 0 to 20 mm.

[0019] In some embodiments of the present disclosure, in step e, 1.5 to 2 m is cut off at the head end of the process geometric waste, and 3.5 to 4 m is cut off at the tail end to ensure that there are no shrinkage cracks in the profile structure.

[0020] In some embodiments of the present disclosure, in step e, a length of 350 mm is reserved at both ends of the head and tail of the portion of the 7020 aluminum alloy profile as a sample for physical and chemical testing.

[0021] In some embodiments of the present disclosure, the aging furnace in step f is an electrically heated floor-standing aging furnace.

[0022] On the other hand, the present invention also provides a 7020 aluminum alloy profile, the component content percentage of the aluminum alloy profile is: Si≤0.15, Mg1.15~1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80~5.00, Zr: 0.10~0.16, Pb: —, Cr: —, single impurity ≤0.05, total ≤0.15, and the rest is Al.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention provides a 7020 aluminum alloy profile extrusion process. By adjusting the element content ratio of the 7020 aluminum alloy and optimizing the process parameters, and adopting double-stage artificial aging, the elongation of the prepared 7020 aluminum alloy profile is increased by 70Mpa to 80Mpa compared with the standard value, the tensile strength is increased by 40Mpa to 50Mpa compared with the standard value, and the elongation is increased by 6% to 7.5% compared with the standard. The product has excellent product performance and the yield rate can reach more than 75%, which greatly improves the yield rate of the 7020 aluminum alloy profile.

[0025] 2. The present invention reduces the content of Si element, limits the content of Mg element, and optimizes and adjusts other elements by adjusting the element content in the aluminum rod, thereby improving the material's own performance to prevent the generation of various extrusion cracks and extrusion surface granular matter, and further improves the material's forming performance by reorganizing and refining the tissue particles during the extrusion process. It also plays a synergistic role with the subsequent online quenching and artificial aging treatment processes to reduce the occurrence of material brittleness, thereby improving the mechanical property requirements of the required aluminum alloy profiles.

[0026] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 It is a structural schematic diagram of a 7020 aluminum alloy profile;

[0029] Figure 2 A schematic diagram of the high-magnification structure of a 7020 aluminum alloy profile Figure 1 ;

[0030] Figure 3 A schematic diagram of the high-magnification structure of a 7020 aluminum alloy profile Figure 2 .

[0031] Figure numerals: 1-connecting buckle groove. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0033] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0034] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] See also Figure 1 to Figure 3, is a 7020 aluminum alloy profile, which is the connecting buckle groove 1 in the rail product. Its performance requirements are extension strength Rp0.2≥350Mpa, tensile strength Rm≥410Mpa, elongation after fracture A50mm%≥10, hardness≥120HB, good corrosion resistance, and cannot contain Cr and Pb elements, and has high environmental protection requirements.

[0036] The component content percentages of the aluminum alloy profile are: Si≤0.15, Mg1.15~1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80~5.00, Zr: 0.10~0.16, Pb: —, Cr: —, single impurity ≤0.05, total ≤0.15, and the rest is Al.

[0037] The extrusion process of the above 7020 aluminum alloy profile comprises the following steps:

[0038] a. Material inspection: The material is a homogenized 7020 aluminum bar, the composition percentage of which is: Si≤0.15, Mg1.15~1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80~5.00, Zr: 0.10~0.16, Pb: —, Cr: —, single impurity ≤0.05, total ≤0.15, the rest is Al, and the original aluminum bar with a diameter of φ446 is turned to remove 10mm of the outer skin, leaving the φ436×1600mm aluminum bar for production and use to prevent surface defects from flowing into subsequent steps;

[0039] b. Heating treatment: Use a resistance speed heating power frequency furnace as the heating equipment to heat the aluminum bar to 480℃~500℃ and the mold to 500℃~520℃;

[0040] c. Extruded profile: A 75MN / 7500T extruder is used to manufacture this product. The heated aluminum rod and the die are assembled on the extruder and extruded. The extrusion speed is controlled to be 1.2-1.8 m / min to obtain a 7020 aluminum alloy profile. The 7020 aluminum alloy profile is quenched online. A bellows-type cooling device is used as a quenching device. The temperature of the 7020 aluminum alloy profile before quenching is controlled to be 500-560°C, and the temperature after quenching is ≤150°C.

[0041] d. Stretching and straightening: After the quenched 7020 aluminum alloy profile is cooled to room temperature, stretching and straightening are performed. Under the condition that the profile size allows, the stretching rate is controlled at 1% to 1.2%, so that a certain proportion of residual stress inside the 7020 aluminum alloy profile after deformation and cooling is fully released, so that the deformation and stress distribution are uniform, the extrusion and twisting deformation effect is reduced, and the subsequent heat treatment double-stage artificial aging is provided to help;

[0042] e. Sawing of finished products: saw the stretched and straightened 7020 aluminum alloy profiles according to the agreed size, that is, cut the material according to the length specified by the customer, with a tolerance length of 0 to 20 mm, cut off 1.5 to 2 m at the head end of the process geometric waste, and cut off 3.5 to 4 m at the tail end to ensure that there are no defects such as shrinkage cracks in the profile structure. After sawing at both ends, use a deburring auxiliary tool to remove the burrs at both ends of the cut material, and wipe off the excess residual material on the surface of the profile with a cleaning cloth. In addition, during the sawing and cutting process, some 7020 aluminum alloy profiles need to reserve samples for physical and chemical testing. Generally, 350 mm in length is cut from both ends as physical and chemical test samples. The number of 7020 aluminum alloy profiles that need to reserve physical and chemical test samples can refer to the 28 principle;

[0043] f. Artificial aging: An electrically heated floor-standing aging furnace is preferably used as the aging furnace. The sawn 7020 aluminum alloy profile is first heated to 105±3°C in the aging furnace and kept warm for 7-8 hours, and then heated to 135±3°C and kept warm for 6-8 hours. After the insulation is completed, the 7020 aluminum alloy profile is removed from the aging furnace and naturally cooled to room temperature. The double-stage aging method is used to ensure that the alloy recrystallization obtains better performance toughness and uniform grain structure;

[0044] g. Physical and chemical testing: The 7020 aluminum alloy profiles after artificial aging are tested and sent for inspection according to the test items.

[0045] Key References Figure 2-Figure 3 , respectively, are high-magnification microstructure diagrams of 1# and 2# 7020 aluminum alloy profiles prepared by this process. The AXIO universal research-grade inverted material microscope is used as the testing equipment. The testing standard is GB / T6892-2015, and the testing method is GB / T3246.1-2012. Figure 2-Figure 3 It can be seen that both 1# and 2# samples are qualified, indicating that the 7020 aluminum alloy profiles prepared by this process have good corrosion resistance.

[0046] Table 1

[0047]

[0048] Table 1 is a composition inspection table of 1#~4#7020 aluminum alloy profiles prepared by this process. The test equipment is ARL-3460 direct reading spectrometer, the test standard is the internal control standard, and the test method is GB / T7999-2015. The test results show that the composition of the 7020 aluminum alloy profiles prepared by this process does not contain Cr and Pb elements, which meets the requirements.

[0049] Table 2

[0050]

[0051] Table 2 is a tensile performance test table of 1#~8#7020 aluminum alloy profiles prepared by this process. The testing equipment is AG-X100KN electronic universal testing machine. The testing standards are elongation strength Rp0.2≥350Mpa, tensile strength Rm≥410Mpa, and elongation after fracture A50mm%≥10. The testing method is EN ISO 6892-1:2016. The test results show that the elongation of the 7020 aluminum alloy profile prepared by this process is 70Mpa~80Mpa higher than the standard value, the tensile strength is 40Mpa~50Mpa higher than the standard value, and the elongation is 6%~7.5% higher than the standard, which has excellent product performance.

[0052] Table 3 is a hardness test table of 1#~8#7020 aluminum alloy profiles prepared by this process. The test equipment is an OMNITEST multifunctional hardness tester, the test standard is hardness ≥120HB, and the test method is ISO 6506-1:2014. The test results show that the hardness of the 7020 aluminum alloy profile prepared by this process is at least greater than the standard value of 9HB, which meets the hardness requirements.

[0053] Table 3

[0054]

[0055] In this application, the content of Si element is reduced, the content of Mg element is limited, and other elements are optimized and adjusted by adjusting the element content in the aluminum rod, so as to improve the material's own performance, so as to prevent the generation of various extrusion cracks and extrusion surface granular materials, and further improve the material's forming performance by reorganizing and refining the tissue particles during the extrusion process, and synergize with the subsequent online quenching and artificial aging treatment process to reduce the occurrence of material brittleness, thereby improving the mechanical properties requirements of the required aluminum alloy profiles; by optimizing the process parameters in the extrusion process, the extrusion The parameters of the aluminum alloy profile stretching and straightening are optimized to pave the way for the subsequent double-stage artificial aging. Through double-stage artificial aging, the heating temperature and holding time are strictly controlled, and the heating temperature is gradually increased. Under the condition of preventing the aluminum alloy profile from being overburned, it is ensured that the 7020 aluminum alloy profile has sufficient temperature and holding time for recrystallization, thereby obtaining better toughness and uniform microstructure grains, improving the comprehensive performance of the 7020 aluminum alloy profile, and avoiding the product performance being unqualified and becoming waste, thereby achieving the purpose of improving the yield rate of 7020 aluminum alloy profiles. It is calculated that the yield rate can reach more than 70% to 80%.

[0056] The present invention provides a 7020 aluminum alloy profile extrusion process. By adjusting the element content ratio of the 7020 aluminum alloy and optimizing the process parameters, and adopting double-stage artificial aging, the prepared 7020 aluminum alloy profile has not only an elongation of 70Mpa-80Mpa increased by 40Mpa-50Mpa compared with the standard value, but also an elongation of 6%-7.5% increased compared with the standard, and has excellent product performance. Moreover, on the basis of adopting positive extrusion equipment for production and performing a surplus process to cut the head and tail residues, after calculating the yield rate of the extrusion process, the extrusion process yield rate of the present application can reach more than 70%-80%, which greatly improves the yield rate of the 7020 aluminum alloy profile.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A 7020 aluminum alloy profile extrusion process, characterized in that: The following steps are involved: a. Material inspection: The material is a homogenized 7020 aluminum bar, the composition percentage of which is as follows: Si≤0.15, Mg1.15~1.25, Fe≤0.25, Cu≤0.15, Mn≤0.25, Ti≤0.05, Zn: 4.80~5.00, Zr: 0.10~0.16, Pb: —, Cr: —, single impurity ≤0.05, total ≤0.15, the rest is Al; b. Heating treatment: heat the aluminum bar to 480℃~500℃ and the mold to 500℃~520℃ c. Extruded profile: Assemble the heated aluminum rod and the die to the extruder and perform extrusion processing to obtain a 7020 aluminum alloy profile, and perform online quenching on the 7020 aluminum alloy profile, using a bellows cooling device as a quenching device, and control the temperature of the 7020 aluminum alloy profile before quenching to 500-560°C, and the temperature after quenching to ≤150°C; d. Stretching and straightening: After cooling the quenched 7020 aluminum alloy profile to room temperature, stretch and straighten it with a stretching rate of 1% to 1.2%; e. Finished product sawing: saw the stretched and straightened 7020 aluminum alloy profiles according to the agreed size; f. Artificial aging: First, heat the sawn 7020 aluminum alloy profile to 105±3℃ in the aging furnace and keep it warm for 7~8h, then heat it to 135±3℃ and keep it warm for 6~8h. After the insulation, remove the 7020 aluminum alloy profile from the aging furnace and cool it naturally to room temperature.

2. A 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: In the step b, a resistance rapid heating industrial frequency furnace is used as the heating equipment.

3. A 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: The model of the extruder in step c is 75MN / 7500T.

4. The 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: In the step e, the tolerance length of the sawing is controlled to be 0-20 mm.

5. The 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: In the step e, 1.5 to 2 m is cut off from the head end of the process geometric waste, and 3.5 to 4 m is cut off from the tail end to ensure that there are no shrinkage cracks in the profile structure.

6. The 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: In the step e, a length of 350 mm is reserved at both ends of the head and tail of the 7020 aluminum alloy profile as a sample for physical and chemical testing.

7. The 7020 aluminum alloy profile extrusion process according to claim 1, characterized in that: The aging furnace in step f is an electrically heated floor-standing aging furnace.

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