A production process for 7xxx aluminum alloy coils with high cold upsetting formability

Abstract

The present invention relates to a production process of a 7xxx aluminum alloy coil bar with high cold upsetting formability, comprising: rapidly cooling and continuously casting an aluminum alloy melt into an aluminum alloy rod, peeling the aluminum alloy rod to remove an oxide layer after homogenization, continuously extruding the aluminum alloy coil bar, drawing the aluminum alloy coil bar, and after drawing, adopting a two-stage low-temperature annealing treatment to obtain a 7xxx aluminum alloy coil bar with high cold upsetting formability; the drawing deformation is ≥20%; the two-stage low-temperature annealing treatment conditions are: firstly heat preservation at 200-260℃ for 2-4h, then heating to 320-360℃ for 2-6h, after the heat preservation is finished, cooling to 240-280℃ at a cooling rate of ≤30℃ / h, and air cooling out of the furnace. The present invention can produce 7xxx aluminum alloy coil bars with uniform performance and excellent cold upsetting formability, and is particularly suitable for the production of large coil weight (>200Kg) aluminum alloy coil bars.

Description

Technical Field

[0001] The invention belongs to the technical field of metal plastic processing and relates to a production process of 7xxx aluminum alloy coil bar with high cold upsetting formability. Background Art

[0002] With the rapid development of lightweight and connection technologies in automobiles, especially new energy vehicles, aerospace, high-speed rail, etc., 7xxx series Al-Zn-Mg-Cu alloy is a heat-treatable and strengthened aluminum alloy with excellent properties such as high specific strength, high specific stiffness, good processing performance, high fracture toughness and riveting performance. It is widely used in the fields of advanced equipment such as aerospace, automobiles, and rail transportation to manufacture cold heading parts and fasteners. At the same time, the cold heading industry is developing in the direction of high speed, intelligence, and automation, and urgently needs aluminum alloy coils and bars with large coils, uniform performance, and excellent forming performance. Although 7xxx aluminum alloy has high strength and good mechanical properties, its cold working forming performance is relatively low. Specifically, when it is used in the cold heading process, it still has the problem of relatively low plasticity and strong tendency to work hardening, which makes it difficult to form by cold working deformation at room temperature without cracks or other defects. In addition, as the amount of cold deformation increases, the hardness of the material increases rapidly, making cold deformation difficult, which may affect the dimensional accuracy and surface quality of the final product.

[0003] At present, the production methods of aluminum alloy bars are mainly semi-continuous ingot casting-extrusion method and semi-continuous ingot casting-hot rolling method. The production process of semi-continuous ingot casting-extrusion method mainly includes: semi-continuous casting → ingot homogenization → ingot heating → hot extrusion → aluminum alloy bar. Due to the length limitation of extruded ingots, usually fixed-length extruded bars have to be frequently stopped for material replacement during downstream applications, which cannot meet the development needs of the modern cold heading industry in the direction of high speed, intelligence and automation.

[0004] In order to increase the length of aluminum alloy bars to improve production efficiency, the semi-continuous casting-hot rolling method has been developed in China in recent years. Its production process mainly includes: semi-continuous casting → homogenization of long cast bars → heating of long cast bars → hot rolling of long cast bars → coiling → hot finishing rolling → aluminum alloy coil bars. Compared with the fixed length of the semi-continuous ingot casting-extrusion method, the semi-continuous casting-hot rolling method can produce bars with larger coil weight (about 250Kg). However, for larger diameter bars, in addition to solving the problem of bar length, more importantly, the current production process is prone to coarse grains and microcracks due to the small deformation of the center of the bar when producing large diameter bars, which will directly affect its cold heading formability.

[0005] In view of the shortcomings of the above-mentioned large-volume high-performance aluminum alloy coil bar production process and the low cold working performance of 7xxx aluminum alloy, the cold heading industry urgently needs to develop a method that can produce

[0006] Production process for 7xxx aluminum alloy bars with large coil weight (single coil greater than 200Kg) and excellent cold heading formability. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a production process for 7xxx aluminum alloy coil bars with high cold heading formability, which can produce 7xxx aluminum alloy coil bars with uniform performance and excellent cold heading formability, and is particularly suitable for the production of large coil weight (>200Kg) aluminum alloy coil bars. It solves the technical problem that the prior art is difficult to produce 7xxx aluminum alloy coil bars with large coil weight and high cold heading formability and cannot meet the high-speed, intelligent and automated processing requirements of the cold heading industry.

[0009] (II) Technical solution

[0010] The present invention provides a production process for a 7xxx aluminum alloy coil bar with high cold upsetting formability, comprising: rapidly cooling and continuously casting an aluminum alloy melt into an aluminum alloy rod, peeling the aluminum alloy rod to remove an oxide layer after homogenization, continuously extruding the aluminum alloy coil bar, drawing the aluminum alloy coil bar, and after drawing, performing a two-stage low-temperature annealing treatment to obtain a 7xxx aluminum alloy coil bar with high cold upsetting formability;

[0011] Wherein, the drawing deformation is ≥20%;

[0012] The double-stage low-temperature annealing treatment conditions are: first keep at 200-260°C for 2-4h, then heat to 320-360°C and keep for 2-6h, after the insulation is completed, cool to 240-280°C (preferably 260°C) at a cooling rate of ≤30°C / h, and then air-cool out of the furnace.

[0013] According to a preferred embodiment of the present invention, the aluminum alloy melt is rapidly cooled and continuously cast into bars with a diameter of 22-25 mm, and the casting speed is 500-700 mm / min, preferably 550-600 mm / min.

[0014] According to a preferred embodiment of the present invention, the rapid cooling continuous casting is horizontal continuous casting or upward continuous casting, the cooling rate of the rapid cooling continuous casting is >200°C / S; and the continuous casting temperature is controlled at 680-690°C.

[0015] According to a preferred embodiment of the present invention, the homogenization treatment conditions are: keep at 460-480°C for 8-16h, cool to 240-280°C (preferably 260°C) at a cooling rate of ≤30°C / h, and air cool out of the furnace.

[0016] According to a preferred embodiment of the present invention, during the peeling process, the peeling amount is 2-5 mm.

[0017] According to a preferred embodiment of the present invention, during the continuous extrusion process, the temperature at the outlet of the extrusion die cavity is 420-460°C, and the speed of the extrusion wheel is 2-6 rpm. In particular, when forming an aluminum alloy bar with a diameter of more than 16 mm, an extended continuous extrusion method is used; when forming an aluminum alloy bar with a diameter of less than 16 mm, a conventional continuous extrusion method is used.

[0018] According to a preferred embodiment of the present invention, a disc pulling machine is used for drawing, for example, the disc pulling machine is an 1800 disc pulling machine or a 1200 disc pulling machine.

[0019] In a second aspect, the present invention provides a 7xxx aluminum alloy coil bar with high cold upsetting formability, which is prepared by the production process of any of the above embodiments.

[0020] Preferably, the microstructure of the high cold upsetting formability 7xxx aluminum alloy coil bar is characterized by no coarse grains in the transverse section, fibrous grains in the longitudinal direction, a forging ratio of the cold upsetting test of less than 1 / 3, and very good cold upsetting formability.

[0021] Preferably, the weight of a single coil of the high cold upsetting formability 7xxx aluminum alloy coil bar is greater than 200Kg, more preferably greater than 500Kg. The 7xxx series high-strength aluminum alloys include but are not limited to 7A03, 7075, 7475, 7050, 7A04, 7A31 and other aluminum alloys.

[0022] In the present application, the forging ratio refers to the ratio of the sample height after cold forging to the sample height before cold forging. The smaller the ratio is, the better the cold working performance of the aluminum alloy material is.

[0023] (III) Beneficial effects

[0024] Aiming at the technical problem that the existing technology is difficult to produce 7xxx aluminum alloy coils and bars with large coil weight and high cold upsetting performance, the present invention provides a production process of 7xxx aluminum alloy coils and bars with high cold upsetting formability, which mainly includes the processes of rapid cooling and continuous casting, homogenization treatment, peeling, continuous extrusion, drawing and double-stage low-temperature annealing of aluminum alloy bars. The present invention mainly controls the drawing deformation amount to be not less than 20% during the drawing process, adopts double-stage low-temperature annealing treatment, so that its organizational characteristics are that there is no coarse grain in the transverse section and the longitudinal grains are fibrous; the forging ratio of the cold upsetting test of the aluminum alloy coils and bars is less than 1 / 3, and the cold upsetting formability is higher than the standard of 1 / 2 specified in the national standard "GBT233-2000 Metal Material Upsetting Test Method", and its high cold upsetting formability can meet the performance requirements of cold upsetting forming of complex cold upsetting parts and fasteners of 7xxx series high-strength aluminum alloys.

[0025] On the one hand, the present invention solves the problem that the prior art is difficult to produce large-weight aluminum alloy coils and bars. There is no upper limit to the weight of a single coil, which can reach hundreds or even thousands of kilograms. On the other hand, the 7xxx series high-strength aluminum alloy prepared by the present invention has very high cold processing performance, uniform product performance, and a cold forging test forging ratio of less than 1 / 3, and has very good cold heading formability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the actual cold forging test of 7075 and 7A03 aluminum alloy coils and bars. The left side is 7075 aluminum alloy and the right side is 7A03 aluminum alloy. DETAILED DESCRIPTION

[0027] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods.

[0028] Aiming at the technical problem that it is difficult to produce 7xxx aluminum alloy coils and bars with large coil weight and high cold upsetting formability in the prior art, the present invention provides a production process for 7xxx aluminum alloy coils and bars with high cold upsetting formability, which mainly comprises: rapidly cooling and continuously casting an aluminum alloy melt into an aluminum alloy bar, peeling the aluminum alloy bar to remove the oxide layer after homogenization, continuously extruding the aluminum alloy coils and bars, drawing the aluminum alloy coils and bars, and after drawing, performing a two-stage low-temperature annealing treatment to obtain 7xxx aluminum alloy coils and bars with high cold upsetting formability;

[0029] Among them, the drawing deformation is ≥20%, and the maximum drawing deformation should ensure that the aluminum alloy bar will not be broken. Experiments have shown that if the drawing deformation is less than 20%, uneven deformation will occur, which will ultimately affect the uniformity of product performance.

[0030] The two-stage low-temperature annealing treatment conditions are: first keep at 200-260℃ for 2-4h, then heat to 320-360℃ for 2-6h, and after the end of the heat preservation, cool to 240-280℃ (preferably 260℃) at a cooling rate of ≤30℃ / h, and air-cool out of the furnace. During the period from the end of the heat preservation to the furnace cooling to 240-280℃, the heat preservation effect of the furnace body can be used to prevent the quenching effect caused by excessive cooling speed, which will reduce the extrusion processing performance of the aluminum alloy; if the furnace temperature is higher than 280℃, the quenching effect still exists, which reduces the extrusion processing performance of the aluminum alloy, and if the furnace temperature is less than 240℃, it is not conducive to saving energy consumption and the high heat preservation requirements of the furnace body will also increase costs.

[0031] The first stage of the two-stage low-temperature annealing is pre-annealing, the temperature is 200-260°C, and the pre-annealing temperature is relatively low; the second stage is main annealing, the temperature is 320-360°C, and the temperature is higher than the first stage. Through the treatment of two different temperature stages, the mechanical properties, ductility and processing properties are improved, stress is released, the tendency of stress corrosion cracking during subsequent processing is prevented, the grain structure is refined, and the cold heading forming properties of 7xxx aluminum alloy coils and bars are improved. Under the two-stage low-temperature annealing and its temperature setting conditions, the work hardening caused by cold drawing can be eliminated, and the recrystallization and precipitation strengthening phase coarsening can be avoided.

[0032] Preferably, the aluminum alloy melt is rapidly cooled and continuously cast into a bar with a diameter of 22-25 mm, with a casting speed of 500-700 mm / min, preferably 550-600 mm / min; the continuous casting temperature is controlled at 680-690° C. For 7xxx aluminum alloys, if the casting temperature exceeds this range, the cooling speed will be too slow and the casting will not form, and if the casting temperature is lower than this range, it is easy to cause fracture.

[0033] Preferably, the rapid cooling continuous casting is horizontal continuous casting or upward continuous casting, and the cooling rate of the rapid cooling continuous casting is >200°C / S.

[0034] Preferably, the homogenization treatment conditions are: keeping at 460-480°C for 8-16h, cooling to 240-280°C (preferably 260°C) at a cooling rate of ≤30°C / h, and air cooling out of the furnace.

[0035] Generally speaking, the homogenization time of large plate ingots needs more than 24 hours, but for the rods of the present invention, due to the small diameter and high cooling rate, the uniformity of the structure is good. Therefore, if the homogenization time is controlled within 8-16 hours, a good homogenization effect can be achieved, thereby saving energy. During the period from the end of insulation to the furnace cooling to 240-280℃, the insulation effect of the furnace body can be used to prevent the quenching effect caused by excessive cooling, which will reduce the extrusion processing performance of the aluminum alloy; if the furnace temperature is higher than 280℃, the quenching effect still exists, which reduces the extrusion processing performance of the aluminum alloy. If the furnace temperature is less than 240℃, it is not conducive to saving energy and the high insulation requirements of the furnace body will also increase costs.

[0036] Preferably, during the peeling process, the peeling amount is 2-5 mm.

[0037] Preferably, during the continuous extrusion process, the extrusion die outlet temperature is 420-460°C, and the extrusion wheel speed is 2-6 rpm. If the continuous extrusion speed is too low, the continuous extruder may shut down due to excessive load, while if the continuous extrusion speed is too high, the product may easily crack.

[0038] In particular, when forming an aluminum alloy bar with a diameter of more than 16 mm, an extended continuous extrusion method is used; when forming an aluminum alloy bar with a diameter of less than 16 mm, a conventional continuous extrusion method is used.

[0039] Preferably, a disc drawing machine is used for drawing, for example, the disc drawing machine is an 1800 disc drawing machine or a 1200 disc drawing machine. The maximum diameter of the wire drawing disc of the 1800 disc drawing machine is 1800 mm (or larger), which can process thicker wires and achieve a larger tensile deformation. The maximum diameter of the wire drawing disc of the 1200 disc drawing machine is 1200 mm, which is suitable for processing wires with medium diameters.

[0040] The 7xxx aluminum alloy coils and bars produced by the process of the present invention have high cold heading formability, and their organizational characteristics are that there is no coarse grain in the transverse section, the longitudinal grains are fibrous, and the forging ratio of the cold heading test is less than 1 / 3, and the process of the present invention is particularly suitable for producing aluminum alloy coils and bars with large coil weights. Preferably, the aluminum alloy coils and bars that can be produced by the present invention have a single coil weight of several hundred to several thousand, and there is no upper limit in theory, and are suitable for producing 7xxx aluminum alloy coils and bars for cold heading of aluminum alloys including but not limited to 7A03, 7075, 7475, 7050, 7A04, 7A31, etc.

[0041] The scheme and technical effects of the present invention are described below in conjunction with specific embodiments.

[0042] Example 1

[0043] This embodiment provides a production process for 7A03 aluminum alloy coil bar for manufacturing cold heading automobile parts, with a target diameter of 26 mm and a single coil weight of more than 1000 kg.

[0044] The production process of the aluminum alloy coil bar is as follows:

[0045] (1) Rapid cooling continuous casting: 99.7% aluminum ingots, zinc ingots and magnesium ingots as well as Al-10Cu, Al-5Mn, Al-5Ti and Al-5Cr master alloys were used. The weight ratio of each alloy was calculated according to the chemical composition range of 7A03 aluminum alloy. The ingredients were mixed according to this ratio. After melting, refining, heat preservation and online filtration in a double 1000Kg gas melting furnace, samples were taken for alloy chemical composition testing, as shown in Table 1. Horizontal continuous casting was used to continuously cast bars with a diameter of 25 mm. The continuous casting temperature was controlled at 680-690℃, the cooling rate was greater than 200℃ / s, and the casting speed was set to 550mm / min.

[0046] (2) Homogenization treatment: Place the rod material with a single coil weight of 1462 kg in a homogenization furnace and heat it to 465°C for 12 hours. After the furnace cools to 260°C, take it out of the furnace and air cool it.

[0047] (3) The homogenized bar material is peeled with a peeling amount of 5 mm.

[0048] (4) The peeled bar material was extruded into a 30 mm diameter coiled bar material on a 400-type aluminum continuous extruder by an extended continuous extrusion method. The extrusion outlet temperature was set to 430°C and the extrusion wheel speed was 5.5 rpm.

[0049] (5) The coiled bar with a diameter of 30 mm is drawn on an 1800 plate drawing machine into a finished coiled bar with a diameter of 26 mm, and the drawing deformation is 24.89%.

[0050] (6) The drawn coil with a diameter of 26 mm is subjected to a double-stage low-temperature annealing treatment. The double-stage low-temperature annealing treatment conditions are: keeping at 230°C for 2 hours, then keeping at 340°C for 4 hours, cooling the furnace to 260°C, and then air cooling.

[0051] Example 2

[0052] This embodiment provides a production process for 7075 aluminum alloy coil bar material for manufacturing cold heading fasteners, which is required to have a diameter of 13.5 mm and a single coil weight of more than 500 kg.

[0053] The production process of the aluminum alloy coil bar is as follows:

[0054] (1) Rapid cooling continuous casting: 99.7% aluminum ingots, zinc ingots and magnesium ingots as well as Al-10Cu, Al-5Mn, Al-5Ti and Al-5Cr master alloys were used. The weight ratio of each alloy was calculated according to the chemical composition range of 7075 aluminum alloy. The ingredients were mixed according to this ratio. After melting, refining, heat preservation and online filtration in a double 1000Kg gas melting furnace, samples were taken for alloy chemical composition testing, as shown in Table 1. Horizontal continuous casting was used to continuously cast bars with a diameter of 25mm. The continuous casting temperature was controlled at 680-690℃, the cooling rate was greater than 200℃ / s, and the casting speed was set to 600mm / min.

[0055] (2) Homogenization treatment: Place the rod material with a single coil weight of 1522 kg in a homogenization furnace, heat it to 465°C, keep it at this temperature for 12 hours, cool it to 260°C, and then take it out of the furnace and air cool it.

[0056] (3) The homogenized bar material is peeled with a peeling amount of 5 mm.

[0057] (4) The peeled rods were extruded into coils with a diameter of 15.5 mm by conventional continuous extrusion. The extrusion outlet temperature was set to 450 °C and the extrusion wheel speed was 3.2 rpm.

[0058] (5) The coiled bar with a diameter of 15.5 mm is drawn on a 1200 plate drawing machine to a finished coiled bar with a diameter of 13.5 mm, and the drawing deformation is 24.14%.

[0059] (6) The drawn coil with a diameter of 13.5 mm is subjected to a double-stage low-temperature annealing treatment. The double-stage low-temperature annealing treatment conditions are: first, keep it at 230°C for 2 hours, then keep it at 320°C for 4 hours, cool it to 260°C in the furnace, and then take it out of the furnace and air cool it.

[0060] Finally, samples were taken from the head and tail of 7075 and 7A03 aluminum alloy coils and bars, and mechanical properties were tested using a universal material testing machine (CMT-5105GL) (see Table 1) and cold forging tests were performed using a four-column hydraulic press (YW32-100T). The results are shown in Tables 2 and Figure 1 .

[0061] Table 1: Main chemical composition of 7A03 (6.0-6.7) and 7075 aluminum alloys (weight percentage, %)

[0062]

[0063] Table 2: Mechanical properties and cold forging test results of 7A03 and 7075 aluminum alloy coils and bars

[0064]

[0065] From Table 2 and Figure 1 From the mechanical properties and cold forging test results, it can be seen that the 7A03 and 7075 aluminum alloy coils and bars prepared by the production process of the present invention have excellent mechanical properties. The forging ratios of the cold forging test are 32.6% and 29.1% respectively, both less than 1 / 3, and the cold forging formability is higher than the standard of the national standard "GBT233-2000 Metal Material Upsetting Test Method".

[0066] The aluminum alloy coil bar product prepared by the production process of the present invention is further processed into automobile parts and fasteners by cold heading, and the parts and fasteners are crack-free, and the dimensional accuracy and surface quality are good. It is thus explained that the production process of the present invention, by controlling the key process drawing deformation amount to be not less than 20% and adopting a two-stage low-temperature annealing treatment, makes the cold forging test forging ratio of the produced aluminum alloy coil bar product less than 1 / 3, which shows that the 7xxx aluminum alloy bar prepared by the present invention has good cold heading deformation performance, and can fully meet the requirements of 7xxx series high-strength aluminum alloy complex cold heading parts and fastener cold heading forming. In addition, the mechanical properties of the head and tail of the bar product prepared by the present invention are consistent.

[0067] In summary, the production process of the present invention solves the problem that the prior art is difficult to produce large-volume aluminum alloy coils and bars. There is no upper limit to the weight of a single coil, which can reach hundreds or even thousands of kg. At the same time, the 7xxx series high-strength aluminum alloy prepared by the present invention has very high cold processing performance, uniform product performance, and excellent cold heading forming performance, which solves the technical problem that the current cold heading industry urgently needs to produce high-strength aluminum alloy coils and bars with heavy coils and excellent forming performance in order to adapt to the development of high speed, intelligence and automation.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production process for 7xxx aluminum alloy coils and bars with high cold upsetting formability, characterized in that: include: The aluminum alloy melt is rapidly cooled and continuously cast into an aluminum alloy bar, the aluminum alloy bar is subjected to a peeling treatment to remove an oxide layer after a homogenization treatment, and the aluminum alloy coil bar is continuously extruded, and the aluminum alloy coil bar is drawn. After the drawing is completed, a two-stage low-temperature annealing treatment is performed to obtain a 7xxx aluminum alloy coil bar with high cold upsetting formability; The homogenization treatment conditions are as follows: keep at 460-480℃ for 8-16h, cool to 240-280℃ at a cooling rate of ≤30℃ / h, and air cool out of the furnace; Wherein, the drawing deformation is ≥20%; The double-stage low-temperature annealing treatment conditions are: first keep at 200-260°C for 2-4h, then heat to 320-360°C and keep for 2-6h, after the insulation is completed, cool to 240-280°C at a cooling rate of ≤30°C / h, and then air-cool out of the furnace.

2. The production process according to claim 1, characterized in that: The aluminum alloy melt is rapidly cooled and continuously cast into bars with a diameter of 22-25 mm at a casting speed of 500-700 mm / min.

3. The production process according to claim 1, characterized in that: The rapid cooling continuous casting is horizontal continuous casting or upward continuous casting, and the cooling rate of the rapid cooling continuous casting is greater than 200°C / S.

4. The production process according to claim 1, characterized in that: During the peeling process, the peeling amount is 2-5 mm.

5. The production process according to claim 1, characterized in that: During the continuous extrusion process, the outlet temperature of the extrusion die cavity is 420-460°C, and the extrusion wheel speed is 2-6rpm; if an aluminum alloy bar with a diameter of more than 16 mm is formed, an extended continuous extrusion method is adopted; when an aluminum alloy bar with a diameter of less than 16 mm is formed, a conventional continuous extrusion method is adopted.

6. The production process according to claim 1, characterized in that: The drawing is done using a disc drawing machine.

7. A 7xxx aluminum alloy coil bar with high cold upsetting formability, characterized in that: The product is prepared by the production process described in any one of claims 1 to 6.

8. The high cold upsetting formability 7xxx aluminum alloy coil and bar according to claim 7, characterized in that: The microstructure characteristics of the high cold upsetting formability 7xxx aluminum alloy coil bar are that there is no coarse grain in the transverse section and the longitudinal grains are fibrous.

9. The high cold upsetting formability 7xxx aluminum alloy coil and bar according to claim 7, characterized in that: The single coil weight of the high cold upsetting formability 7xxx aluminum alloy coil bar is greater than 200Kg.

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