Production process of wide 7075 aluminum alloy plate

Abstract

The invention discloses a production process of a wide 7075 aluminum alloy plate. The production process comprises the following steps that S1, an extrusion die is designed and manufactured; s2, the extrusion die is installed on an extrusion machine; and S3, the wide 7075 aluminum alloy plate is prepared through extrusion. By the adoption of the production process of the wide 7075 aluminum alloy plate, through temperature control of all links, the problems that crystalline grains are coarse and large and the surface of the plate is prone to cracking can be avoided, it can be guaranteed that deformation resistance is not too large, a large-tonnage extruder does not need to be adopted, the production cost is reduced, and meanwhile, the production efficiency is improved. By improving the adaptability of the extrusion die, the service life of the extrusion die is greatly prolonged, the die repairing frequency is reduced, in cooperation with temperature improvement of the process, extrusion forming of the wide 7075 aluminum alloy plate can be achieved, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy extrusion processes, and specifically relates to a production process for wide-width 7075 aluminum alloy plates. Background Art

[0002] 7075 aluminum alloy is a high-strength, heat-treatable Al-Zn-Mg-Cu series alloy, having excellent mechanical properties and lightweight effects. Among 7000 series aluminum alloys, 7075 aluminum alloy has the highest strength, and its extruded products are generally used as high-strength components, and are commonly used in fields such as aerospace, high-end equipment, and sports equipment, and are one of the core materials in high-end manufacturing.

[0003] However, due to its high zinc and magnesium content (Zn 5.1 - 6.1%, Mg 2.1 - 2.9%), 7075 aluminum alloy has low plasticity, and cracks are likely to occur during extrusion, and the temperature and deformation rate need to be strictly controlled. In particular, 7075 aluminum alloy has extremely high temperature sensitivity during the extrusion process. If the extrusion temperature is too high, the grains will become coarse, and the surface of the product is likely to crack; if the extrusion temperature is too low, the deformation resistance will increase, increasing the extrusion difficulty (it cannot be extruded and a larger-tonnage extruder needs to be used), resulting in a very large load on the extrusion die and extremely likely to crack. Also, compared with common 6063 aluminum alloy, the extrudability index of 7075 aluminum alloy is only about one-tenth of that of 6063 aluminum alloy. Therefore, currently, 7075 aluminum alloy is basically only formed into large-sized round bars or square bars through the extrusion process, and there are no cases of wide-width plates being formed by extrusion. The super-wide-width plates on the market are all rolled, and the production efficiency is low, correspondingly resulting in high production costs. Summary of the Invention

[0004] In view of this, the present invention provides a production process for wide-width 7075 aluminum alloy plates.

[0005] The technical solution is as follows:

[0006] The first aspect of the present application relates to a production process for wide-width 7075 aluminum alloy plates, including the following steps:

[0007] S1. Design and manufacture an extrusion die, which is carried out according to the following steps:

[0008] S11. Conduct a structural design of the extrusion die;

[0009] S12. According to the structural design of the extrusion die, manufacture the extrusion die;

[0010] S2. Install the extrusion die on an extruder, which is carried out according to the following steps:

[0011] S21. Conduct nitriding treatment on the extrusion die;

[0012] S22. Install the extrusion die into the die sleeve.

[0013] S23. Heat the extrusion die and the die sleeve.

[0014] S24. Install the extrusion die and the die sleeve onto the die holder of the extruder, making the outlet end face of the extrusion cylinder closely fit with the inlet end face of the extrusion die.

[0015] S3. Produce a wide-width 7075 aluminum alloy plate by extrusion, following the steps below:

[0016] S31. Prepare the ingredients according to the composition and weight percentage of 7075 aluminum alloy.

[0017] S32. Casting: Add the prepared 7075 aluminum alloy raw materials into the melting furnace, uniformly mix them and melt them into liquid aluminum alloy, and then melt-cast the liquid aluminum alloy into 7075 aluminum alloy cast rods.

[0018] S33. Homogenization: Perform homogenization treatment on the 7075 aluminum alloy cast rods in a homogenizing furnace, and cool the 7075 aluminum alloy cast rods after they are taken out of the furnace.

[0019] S34. Heating: Heat all the 7075 aluminum alloy cast rods to 370°C - 390°C, and heat the extrusion cylinder to 380°C - 420°C.

[0020] S35. Extrusion: Place the heated 7075 aluminum alloy cast rods into the extrusion cylinder of the extruder for extrusion to obtain a wide-width 7075 aluminum alloy plate. Among them, the outlet temperature of the extruder is controlled at 420°C - 450°C.

[0021] S36. Cooling and quenching: First, perform on-line cooling on the wide-width 7075 aluminum alloy plate, and then transfer it to a quenching furnace for off-line quenching.

[0022] S37. Stretch straightening: Stretch the wide-width 7075 aluminum alloy plate after the quenching treatment is completed.

[0023] S38. Finish sawing: Saw the wide-width 7075 aluminum alloy plate after stretching is completed.

[0024] S39. Age hardening: Perform age hardening on the wide-width 7075 aluminum alloy plate after sawing is completed.

[0025] Adopt the above production process of wide-width 7075 aluminum alloy plates. Through the temperature control of each link, it can not only avoid the problems of coarse grains and easy cracking on the surface of the plates, but also ensure that the deformation resistance is not too large, without the need to use large-tonnage extrusion presses, reducing production costs. At the same time, through the adaptive improvement of the extrusion die, not only the service life of the extrusion die is greatly increased, the die repair frequency is reduced, but also combined with the temperature improvement of the process, the extrusion forming of wide-width 7075 aluminum alloy plates can be realized, improving production efficiency and reducing production costs.

[0026] In some embodiments, in step S11, the extrusion die includes a die body. Two die holes are provided on the die body and penetrate along its axis direction. The cross-sections of the two die holes are both slit-shaped structures extending in the horizontal direction and are arranged parallel to each other on the upper and lower sides of the central axis of the die body. One end of each die hole close to the inlet is a working belt, and one end close to the outlet is expanded in diameter to form an outlet belt. The working belt is sequentially divided into an inlet section and a sizing section towards the outlet belt. The sizing section is a cylindrical structure, and the inlet section is a conical surface structure that gradually increases in the direction away from the sizing section. Both ends in the length direction of the inlet section are surrounded by sunken pits formed on the adjacent end faces of the die body. Each sunken pit includes a flat section that surrounds the corresponding end of the inlet section in a U shape and a slope section that extends from both ends of the flat section to the corresponding end face of the die body in an inclined plane. The flat sections are parallel to the adjacent end faces of the die body, and the slope sections at both ends of the flat section are symmetrically arranged on both sides in the width direction of the inlet section in parallel.

[0027] In some embodiments, the part of the working belt located between two corresponding sunken pits is the middle working belt, and the part of the working belt located in the corresponding sunken pit is the end working belt. The lengths of all positions of the sizing section are equal. The lengths of all positions of the inlet section located in the middle working belt are equal. The inlet section located in the end working belt includes a thin-wall section inside the flat section and tapered sections respectively located at both ends of the thin-wall section. The lengths of all positions of the thin-wall section are equal and are less than the length of the inlet section located in the middle working belt. The length of the tapered section gradually extends from the end connected to the thin-wall section to the end connected to the middle working belt.

[0028] In some embodiments, step S12 is carried out according to the following steps:

[0029] S121. Rough machine the outer shape of the forged die blank using a lathe;

[0030] S122. Machine threaded holes, pin holes and reliefs for the outlet belt on the die blank by milling and / or drilling;

[0031] S123. Heat-treat the die blank;

[0032] S124. Grind both end faces of the die blank;

[0033] S125. Finish machining the outer shape of the die blank using a lathe;

[0034] S126. Machine various sink holes on the feed end face of the die blank by milling;

[0035] S127. Machine two die holes on the die blank by wire cutting to obtain an extrusion die;

[0036] S128. Grind and polish the die holes of the extrusion die;

[0037] S129. Treat the extrusion die by first heating, then holding, then quenching by rapid cooling, and finally stress relieving by multiple tempering.

[0038] In some embodiments, the step S21 is carried out according to the following steps:

[0039] S211. Judge whether the extrusion die has been used: if no, go to step S213; if yes, go to step S212;

[0040] S212. Carry out sandblasting or shot peening on the extrusion die, and after completion, go to step S213;

[0041] S213. Transfer the extrusion die to a nitriding furnace;

[0042] S214. Set the temperature in the nitriding furnace to 515°C - 530°C, set the ammonia decomposition rate to 20% - 35%, and hold for 10h - 12h;

[0043] S215. Set the temperature in the nitriding furnace to 535°C - 550°C, set the ammonia decomposition rate to 35% - 45%, and hold for 5h - 6h;

[0044] S216. Stop holding, and take out the extrusion die after it naturally cools to 180°C in the nitriding furnace.

[0045] In some embodiments, the step S23 is carried out according to the following steps:

[0046] S231. Transfer the extrusion die and the die sleeve to a die furnace together;

[0047] S232. Set the temperature in the die furnace to 450°C - 470°C, and hold for more than 5 hours;

[0048] S233. Detect whether the surface temperature of the extrusion die reaches 400°C - 430°C: if yes, go to step S24; if no, go to step S234;

[0049] S234. Keep the extrusion die and the die sleeve in the die furnace for the set time and then return to step S233.

[0050] In some embodiments, in step S32, the length of the 7075 aluminum alloy cast rod is less than or equal to 1200 mm, and in step S35, the extrusion speed is 0.8 - 1.2 m / min.

[0051] In some embodiments, in step S36, first transfer the wide-width 7075 aluminum alloy plate to a quenching furnace and heat it up to 465°C - 475°C, then immerse the wide-width 7075 aluminum alloy plate in water for quenching within 30 s, and control the water temperature before and after quenching within 40°C.

[0052] In some embodiments, in step S37, the elongation rate of the wide-width 7075 aluminum alloy plate is 1.5% - 2.5%.

[0053] In some embodiments, in step S39, the aging temperature is 115°C - 120°C and the holding time is 22 h - 24 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flowchart of the production process of the wide-width 7075 aluminum alloy plate;

[0055] Figure 2 It is a cross-sectional view of the extrusion die;

[0056] Figure 3 It is a schematic plan view of the extrusion die;

[0057] Figure 4 It is a schematic three-dimensional view of the extrusion die from one perspective;

[0058] Figure 5 It is a schematic three-dimensional view of the extrusion die from another perspective;

[0059] Figure 6 It is a schematic view of the structure of two die holes. DETAILED DESCRIPTION OF THE INVENTION

[0060] The present invention will be further described below in conjunction with the embodiments and the drawings.

[0061] As Figure 1 shown, a production process of a wide-width 7075 aluminum alloy plate includes the following steps:

[0062] S1. Design and manufacture an extrusion die.

[0063] S2. Install the extrusion die on an extruder.

[0064] S3. Obtain a wide-width 7075 aluminum alloy plate by extrusion.

[0065] Step S1 is carried out according to the following steps:

[0066] S11. Carry out structural design on the extrusion die.

[0067] Specifically, please refer to Figures 2 - 6 , in step S11, the extrusion die includes a die body 1, and the die body 1 is of a cylindrical structure.

[0068] Two die holes 110 are provided on the die body 1 and both penetrate along its axis direction. In this embodiment, the length of the cross-section of the die hole 110 is 353 mm, the width is 22 mm, and the length-width ratio is greater than 15. The cross-sections of the two die holes 110 are both slit-like structures extending in the horizontal direction, and the two die holes 110 are arranged in parallel on the upper and lower sides of the central axis of the die body 1. By setting the two die holes 110, the extrusion efficiency of the 7075 aluminum alloy plate is doubled.

[0069] Further, the distance between the upper die hole 110 and the central axis of the die body 1 is 2 mm - 3 mm larger than the distance between the lower die hole 110 and the central axis of the die body 1, so as to achieve an asymmetric design, which can compensate for the problem that the center of the die shifts downward due to the natural sinking of the die after it is installed in the die sleeve, ensuring that the metal fluidity of the two die holes 110 is consistent and there is no phenomenon that the metal flow rate of the upper die hole 110 is faster than that of the lower die hole 110. If no offset design is made, the upper hole will be fast and the lower hole will be slow, resulting in the two simultaneously extruded plates overlapping but the head and tail being misaligned after being unloaded by the traction machine at the end of extrusion, thus causing the problem that it is not convenient to perform pre-stretching on the two plates.

[0070] In this embodiment, one end of the die hole 110 close to the inlet is a working zone 111, and one end close to the outlet is expanded to form an outlet zone 112. The working zone 111 is successively divided into an inlet section 111a and a sizing section 111b towards the outlet zone 112. The sizing section 111b is of a cylindrical structure, and the inlet section 111a is a conical surface structure that gradually increases in the direction away from the sizing section 111b. By designing the inlet section 111a as a conical surface structure that gradually increases in the direction away from the sizing section 111b, an obstruction angle is formed, which can not only achieve a good pressure-increasing design, balance the flow velocity at each position in the die hole 110, but also compensate for the dimensional changes caused by die deformation, and at the same time is beneficial to improving the surface quality of the extruded product.

[0071] Further, the included angle between the inlet section 111a and the central axis of the lower die 1 is preferably 2° - 3°. The design of the small angle of the inlet section 111a is beneficial to ensuring the surface quality of the extruded profile during extrusion.

[0072] In this embodiment, sunken pits 120 formed with depressions are surrounded at both ends in the length direction of the inlet section 111a on the adjacent end faces of the die body 1. The sunken pits 120 each include a flat section 121 that surrounds the corresponding end of the inlet section 111a in a U shape and ramp sections 122 that extend obliquely from both ends of the flat section 121 to the corresponding end face of the die body 1. The flat sections 121 are all parallel to the adjacent end faces of the die body 1. The ramp sections 122 at both ends of the flat section 121 are symmetrically arranged on both sides in the width direction of the inlet section 111a in parallel, and the flat section 121 and the ramp sections 122 at both of its ends also jointly surround the corresponding end of the inlet section 111a in a U shape.

[0073] By providing the sunken pits 120 and cooperating with the working belt 111, it is possible to ensure sufficient metal supply at both ends of the cross-section of the die hole 110 while also ensuring that the metal in the sunken pits 120 is extruded by the next ingot without causing adhesion between products (i.e., avoiding product connection caused by welding and joining of the head and tail of the ingot), preparing for the separation of the plates extruded by the front and rear two ingots, ensuring that the plates are independent individuals before pre-stretching, thus avoiding the need for a cutting process before pre-stretching the plates and improving production efficiency. Moreover, through the design of the cooperation between the working belt 111 and the sunken pits 120, the outlet end of the die hole 110 is flush, while the inlet end is not flush. Such a design is beneficial for the processing of the extrusion die, especially reducing the electric discharge machining process and lowering the processing difficulty of the extrusion die. Among them, due to the design of the ramp sections 122, it is not a sudden straight drop, so that a ramp drop is formed between the working belts at both ends of the die hole 110 and the working belt at the central position, which can avoid surface quality problems caused by a vertical drop.

[0074] Further, the part of the working belt 111 located between two corresponding sunken pits 120 is the middle working belt, and the part of the working belt 111 located in the corresponding sunken pit 120 is the end working belt, that is, one end working belt is provided at each end of the middle working belt. The lengths of all positions of the sizing section 111b are equal, the lengths of all positions of the inlet section 111a located in the middle working belt are equal, and the inlet section 111a located in the end working belt includes a thin-wall section 111a1 located inside the flat section 121 and gradually changing sections 111a2 located at both ends of the thin-wall section 111a1 respectively. The lengths of all positions of the thin-wall section 111a1 are equal and are less than the length of the inlet section 111a located in the middle working belt. The length of the gradually changing section 111a2 gradually extends from the end connected to the thin-wall section 111a1 to the end connected to the middle working belt. Such a design can further compensate for the problem of poor metal flow caused by the two ends of the die hole 110 being far from the extrusion center, making the metal flow at all positions of the die hole 110 tend to be consistent.

[0075] Furthermore, the length of the middle working zone is preferably 45%-50% of the cross-sectional width of the die hole 110. Meanwhile, the length of the inlet section 111a of the middle working zone is preferably 50%-70% of the length of the middle working zone. Thus, the inlet section 111a is as long as possible, and the effect of balancing the metal flow rate is better.

[0076] In this embodiment, the distance between the flat section 121 and the adjacent end face of the die body 1 is preferably 50%-60% of the length of the middle working zone, and the length of the end working zone located inside the flat section 121 is preferably 40%-50% of the length of the middle working zone. Through such a design, the consistency of the metal flow velocity at each position of the die hole 110 can be further improved.

[0077] Furthermore, the projected area of the sink 120 on the adjacent end face of the die body 1 is 2-3 times the projected area of the partial die hole 110 located inside the sink 120 on the adjacent end face of the die body 1, so as to further ensure sufficient metal supply at both ends of the die hole 110.

[0078] In this embodiment, the widths of the cross-section of the die hole 110 at each position corresponding to the middle working zone are equal, the widths of the cross-section of the die hole 110 at the corresponding end working zone gradually increase in the direction away from the middle working zone, and the maximum width of the cross-section of the die hole 110 is 0.4 mm - 0.6 mm larger than its minimum width. Through the pre-deformation design, the wall thickness thinning effect of the extruded sheet at both ends of the die hole 110 can be offset, so that the wall thicknesses at each position of the extruded sheet tend to be consistent.

[0079] In this embodiment, the end of the exit zone 112 away from the working zone 111 is expanded to form an exit zone relief 112a, which increases the metal supply, thereby effectively reducing the risk of surface quality problems.

[0080] Meanwhile, rounded corners 112b are provided at the corners of the exit zone relief 112a. The radius of the rounded corner 112b is preferably 5 mm, which can effectively reduce the risk of die cracking, improve the service life of the die, and reduce the maintenance frequency.

[0081] S12. According to the structural design of the extrusion die, the extrusion die is manufactured.

[0082] Specifically, step S12 is carried out according to the following steps:

[0083] S121. Rough-process the outer shape of the forged die blank using a lathe. The forging die blank is made of H13 steel (US brand: AISIH13, Chinese brand: 4Cr5MoSiV1), which is a hot working die steel widely used in molds working in high temperature and high pressure environments, such as die-casting molds, hot forging molds, extrusion molds, etc. It is known for its excellent thermal strength, thermal fatigue resistance and wear resistance, and is one of the most commonly used materials in hot working die steel.

[0084] S122: Processing threaded holes, pin holes and outlet strip blanks 112a on the mold blank by milling and / or drilling.

[0085] S123, heat treating the die blank can effectively improve the service life, deformation resistance and extrusion precision of the extrusion die. In this embodiment, a quenching process is first performed, followed by multiple tempering processes, so that the overall hardness reaches HRC48-50.

[0086] S124. Grind the two end faces of the mold blank to ensure sealing performance when connected to the extrusion cylinder.

[0087] S125. Use a lathe to fine-process the shape of the mold blank.

[0088] S126 , processing each sinkhole 120 on the feed end face of the mold blank by milling.

[0089] S127 , using wire cutting to machine two die holes 110 on the die blank to obtain an extrusion die.

[0090] S128. Grind and polish the die hole of the extrusion die.

[0091] S129, the extrusion die is treated by first heating, then keeping warm, then rapidly cooling and quenching, and finally tempering multiple times to relieve stress.

[0092] In step S12, the die's structural design eliminates the need for the electrical discharge (ED) process, a common process used in conventional die manufacturing (the undulating exit end of the die's working band requires EDM processing). This improves die production efficiency. Furthermore, after wire cutting and polishing, a tempering step is performed to eliminate die stress after wire cutting, reduce die deformation, and stabilize product dimensions.

[0093] S2. Install the extrusion die on the extruder and follow the steps below:

[0094] S21. Perform nitriding treatment on the extrusion die.

[0095] Specifically, step S21 is carried out according to the following steps:

[0096] S211. Determine whether the extrusion die has been used: If not, the entire die hole is very clean, so directly enter step S213; if yes, the die hole needs to be cleaned, especially the working belt needs to be polished, so enter step S212.

[0097] S212. Carry out sandblasting or shot peening on the extrusion die, and then enter step S213 after completion.

[0098] S213. Transfer the extrusion die to the nitriding furnace.

[0099] S214. Set the temperature in the nitriding furnace to 515°C - 530°C, set the ammonia decomposition rate to 20% - 35%, and keep warm for 10h - 12h.

[0100] S215. Set the temperature in the nitriding furnace to 535°C - 550°C, set the ammonia decomposition rate to 35% - 45%, and keep warm for 5h - 6h.

[0101] S216. Stop keeping warm, and take out the extrusion die after it cools naturally in the nitriding furnace to 180°C.

[0102] After step S21 is completed, the depth of the nitrided layer on the working belt of the extrusion die is 0.12mm - 0.15mm; the hardness of the nitrided layer is 830HV - 900HV, which improves the hardness and wear resistance of the surface of the working belt of the extrusion die and can ensure the stable progress of the extrusion forming of the 7075 wide-width plate.

[0103] S22. Install the extrusion die into the die sleeve, and the two form a working die.

[0104] Specifically, the extrusion press in this embodiment adopts a horizontal press, and the normal-temperature extrusion die is installed into the die sleeve. The extrusion die and the die sleeve are in clearance fit, and the difference between the inner diameter of the die sleeve and the diameter of the extrusion die is 2mm - 3mm. The extrusion die is positioned by the cooperation of the pin on its outer circle and the keyway of the inner hole of the die sleeve.

[0105] S23. Heat the working die (extrusion die and die sleeve).

[0106] Specifically, step S23 is carried out according to the following steps:

[0107] S231. Transfer the extrusion die and the die sleeve together to the die furnace;

[0108] S232. Set the temperature in the die furnace to 450°C - 470°C and keep warm for more than 5 hours;

[0109] S233. Detect whether the surface temperature of the extrusion die reaches 400°C - 430°C: If yes, go to step S24; if no, go to step S234;

[0110] S234. Keep the extrusion die and the die sleeve in the die furnace for a set time and then return to step S233.

[0111] Furthermore, heat the support tool (such as the support ring) of the die. In this embodiment, it is preferably to heat the support tool to 300°C to reduce the temperature difference between the die and the support tool, thereby reducing the dimensional change of the die holes of the extrusion die and improving the forming quality of the sheet.

[0112] S24. Install the extrusion die and the die sleeve on the die holder of the extruder, and make the outlet end face of the extrusion cylinder closely fit with the inlet end face of the extrusion die.

[0113] It should be noted that the time requirement for transporting the tooling to the die holder does not exceed 10 minutes to reduce heat loss and avoid dimensional changes in the die holes of the extrusion die.

[0114] In step S24, the end face of the extrusion cylinder is in direct contact and sealed with the end face of the extrusion die. The locking pressure is preferably about 22 MPa, and the locking method is to make the extrusion cylinder closely lean against the end face of the extrusion die during the extrusion process to prevent the leakage of aluminum alloy from the sealing surface.

[0115] S3. Produce a wide-width 7075 aluminum alloy sheet by extrusion, which is carried out according to the following steps:

[0116] S31. Prepare the ingredients according to the composition and weight percentage of 7075 aluminum alloy.

[0117] Specifically, the composition and weight percentage of 7075 aluminum alloy are as follows:

[0118]

[0119] S32. Casting: Add the prepared 7075 aluminum alloy raw materials into the melting furnace, mix them evenly and melt them into liquid aluminum alloy, and then melt-cast the liquid aluminum alloy into 7075 aluminum alloy ingots.

[0120] Specifically, add the prepared 7075 aluminum alloy raw materials into the melting furnace, mix them evenly and melt them into liquid aluminum alloy. After standing, refining, slag skimming, online degassing, and filtering processes, melt-cast the liquid aluminum alloy into 7075 aluminum alloy ingots by semi-continuous water-cooled casting method.

[0121] Since an overly long ingot can cause "jamming", that is, a problem where the head end cannot be pushed, in this embodiment, the length of the 7075 aluminum alloy ingot is preferably less than or equal to 1200 mm. At the same time, the length of the butt is controlled to be greater than or equal to 35 mm. Before extrusion, the residue in the extrusion cylinder needs to be cleaned to ensure that the inner wall of the extrusion cylinder is clean without metal residue from the previous extrusion.

[0122] S33. Soaking: The 7075 aluminum alloy ingot is subjected to soaking heat treatment in a homogenizing furnace, and the 7075 aluminum alloy ingot after being taken out of the furnace is cooled. Through this step, the tissue uniformity of the 7075 aluminum alloy ingot can be improved, internal stress can be eliminated, and the extrusion performance and the forming quality of the sheet can be enhanced.

[0123] S34. Heating: All the 7075 aluminum alloy ingots are heated to 370°C - 390°C, and the extrusion cylinder is heated to 380°C - 420°C.

[0124] By designing the temperatures of the extrusion cylinder, the extrusion die, and the 7075 aluminum alloy ingot to be lower than those of conventional 6XXX series aluminum alloys, the problem of cracks on the surface of the extruded sheet can be avoided, and the forming quality is improved.

[0125] S35. Extrusion: The heated 7075 aluminum alloy ingot is placed in the extrusion cylinder of an extruder for extrusion to obtain a wide-width 7075 aluminum alloy sheet. Among them, the outlet temperature of the extruder is controlled at 420°C - 450°C.

[0126] In this embodiment, the extrusion speed is preferably 0.8 - 1.2 m / min. Through the coordinated cooperation of the extrusion speed and the outlet temperature, the occurrence of a coarse grain ring is further ensured to be avoided, and the problem of cracks on the surface of the sheet is avoided.

[0127] S36. Cooling and quenching: First, the wide-width 7075 aluminum alloy sheet is cooled online, and then transferred to a quenching furnace for offline quenching.

[0128] Specifically, the online cooling adopts a method of weak air flow combined with natural cooling. First, the sheet is cooled by weak air flow to avoid damage to the felt by the hot sheet, and then the sheet is moved to the cooling bed by a tractor for natural cooling.

[0129] Usually, the sheet is quenched within 6 hours after cooling. First, the wide-width 7075 aluminum alloy sheet is transferred to the quenching furnace and heated to 465°C - 475°C, and then the wide-width 7075 aluminum alloy sheet is immersed in water for quenching within 30 s until there is no boiling on the liquid surface, and the water temperature before and after quenching is controlled within 40°C.

[0130] Furthermore, after the sheet in the quenching furnace is heated up, it needs to be transferred to water for quenching within 30 s to ensure the quenching effect.

[0131] S37. Stretch straightening: Stretch the wide-width 7075 aluminum alloy plate after quenching treatment.

[0132] Specifically, the stretching rate of the wide-width 7075 aluminum alloy plate is preferably 1.5%-2.5% to eliminate the residual stress of the plate after solution heat treatment.

[0133] S38. Finish sawing: Saw the stretched wide-width 7075 aluminum alloy plate.

[0134] S39. Aging strengthening: Perform aging strengthening on the sawn wide-width 7075 aluminum alloy plate.

[0135] Specifically, the aging temperature is 115°C - 120°C and the holding time is 22h - 24h, so as to effectively strengthen the wide-width 7075 aluminum alloy plate.

[0136] According to the above heat treatment process, the performance of the wide-width 7075 aluminum alloy plate can meet the requirements of tensile strength Rm≥530 Mpa and yield strength Rp0.2≥460 Mpa. Therefore, through the temperature control of each link, it is possible to avoid the problems of coarse grains and easy cracking of the plate surface, and at the same time ensure that the deformation resistance is not too large, without the need to use a large-tonnage extruder, reducing the production cost. At the same time, through the adaptive improvement of the extrusion die, not only the service life of the extrusion die is greatly increased and the die repair frequency is reduced, but also combined with the temperature improvement of the process, the extrusion forming of the wide-width 7075 aluminum alloy plate can be realized, improving the production efficiency and reducing the production cost.

[0137] Finally, it should be noted that the above description is only the preferred embodiment of the present invention. Under the inspiration of the present invention, those of ordinary skill in the art can make various similar representations without violating the purpose and claims of the present invention, and such transformations all fall within the protection scope of the present invention.

Claims

1. A production process for a wide-width 7075 aluminum alloy sheet, characterized in that, It includes the following steps: S1. Design and manufacture an extrusion die according to the following steps: S11. Conduct a structural design of the extrusion die; S12. Manufacture the extrusion die according to the structural design of the extrusion die; S2. Install the extrusion die on the extruder according to the following steps: S21. Conduct nitriding treatment on the extrusion die; S22. Install the extrusion die into the die sleeve; S23. Heat the extrusion die and the die sleeve; S24. Install the extrusion die and the die sleeve on the die holder of the extruder, and make the outlet end face of the extrusion cylinder closely fit with the inlet end face of the extrusion die; S3. Extrude a wide-width 7075 aluminum alloy plate according to the following steps: S31. Prepare materials according to the composition and weight percentage of 7075 aluminum alloy; S32. Casting: Add the prepared 7075 aluminum alloy raw materials into the melting furnace, uniformly mix them and melt them into liquid aluminum alloy, and then melt-cast the liquid aluminum alloy into 7075 aluminum alloy casting rods; S33. Homogenizing: Conduct homogenizing treatment on the 7075 aluminum alloy casting rods in the homogenizing furnace, and cool the 7075 aluminum alloy casting rods after they are taken out of the furnace; S34. Heating: Heat all the 7075 aluminum alloy casting rods to 370°C - 390°C, and heat the extrusion cylinder to 380°C - 420°C; S35. Extrusion: Place the heated 7075 aluminum alloy casting rods into the extrusion cylinder of the extruder for extrusion to obtain a wide-width 7075 aluminum alloy plate. Among them, the outlet temperature of the extruder is controlled at 420°C - 450°C; S36. Cooling and quenching: First, conduct on-line cooling on the wide-width 7075 aluminum alloy plate, and then transfer it to the quenching furnace for off-line quenching; S37. Stretch straightening: Stretch the wide-width 7075 aluminum alloy plate after the quenching treatment is completed; S38. Finished product sawing: Saw the wide-width 7075 aluminum alloy plate after stretching is completed; S39. Age hardening: Conduct age hardening on the wide-width 7075 aluminum alloy plate after sawing is completed.

2. The production process of a wide-width 7075 aluminum alloy sheet according to claim 1, characterized in that, In the step S11, the extrusion die includes a die body. There are two die holes that penetrate along its axis direction on the die body. The cross-sections of the two die holes are both slit-like structures extending in the horizontal direction, and are arranged parallel to each other on the upper and lower sides of the central axis of the die body. One end of each die hole close to the inlet is a working belt, and one end close to the outlet is expanded to form an outlet belt. The working belt is successively divided into an inlet section and a sizing section towards the outlet belt. The sizing section is a cylindrical structure, and the inlet section is a conical surface structure that gradually increases in the direction away from the sizing section. Both ends in the length direction of the inlet section are surrounded by sinkholes formed by depressions on the adjacent end faces of the die body. Each sinkhole includes a flat section that surrounds the corresponding end of the inlet section in a U shape and a slope section that extends from both ends of the flat section to the corresponding end face of the die body in an inclined plane. The flat sections are parallel to the adjacent end faces of the die body, and the slope sections at both ends of the flat section are symmetrically arranged parallel to each other on both sides of the width direction of the inlet section.

3. The production process of a wide-width 7075 aluminum alloy plate according to claim 2, characterized in that, The part of the working belt located between two corresponding sunken pits is the middle working belt, and the part of the working belt located in the corresponding sunken pit is the end working belt. The lengths of all positions of the sizing section are equal. The lengths of all positions of the inlet section located in the middle working belt are equal. The inlet section located in the end working belt includes a thin-walled section inside the plane section and tapered sections respectively located at both ends of the thin-walled section. The lengths of all positions of the thin-walled section are equal and are less than the length of the inlet section located in the middle working belt. The length of the tapered section gradually extends from the end connected to the thin-walled section to the end connected to the middle working belt.

4. The production process of a wide-width 7075 aluminum alloy sheet according to claim 2 or 3, characterized in that, The step S12 is carried out according to the following steps: S121. Rough machine the outer shape of the die blank obtained by forging using a lathe; S122. Machine threaded holes, pin holes and an exit belt relief on the die blank by milling and / or drilling; S123. Heat-treat the die blank; S124. Grind the two end faces of the die blank; S125. Finish machine the outer shape of the die blank using a lathe; S126. Machine each sunken pit on the feed end face of the die blank by milling; S127. Machine two die holes on the die blank by wire cutting to obtain an extrusion die; S128. Grind and polish the die holes of the extrusion die; S129. Treat the extrusion die by first heating, then heat preserving, then rapidly cooling and quenching, and finally tempering multiple times to remove stress.

5. The production process of a wide-width 7075 aluminum alloy sheet according to claim 1, characterized in that, The step S21 is carried out according to the following steps: S211. Judge whether the extrusion die has been used: If no, go to step S213; if yes, go to step S212; S212. Carry out sandblasting or shot peening on the extrusion die, and after completion, go to step S213; S213. Transfer the extrusion die to a nitriding furnace; S214. Set the temperature in the nitriding furnace to 515°C - 530°C, set the ammonia decomposition rate to 20% - 35%, and heat preserve for 10h - 12h; S215. Set the temperature in the nitriding furnace to 535°C - 550°C, set the ammonia decomposition rate to 35% - 45%, and heat preserve for 5h - 6h; S216. Stop heat preservation, and take out the extrusion die after it naturally cools to 180°C in the nitriding furnace.

6. The production process of a wide-width 7075 aluminum alloy sheet according to claim 5, characterized in that, The step S23 is carried out according to the following steps: S231. Transfer the extrusion die and the die sleeve to a die furnace together; S232. Set the temperature in the die furnace to 450°C - 470°C and heat preserve for more than 5 hours; S233. Detect whether the surface temperature of the extrusion die reaches 400°C - 430°C: If yes, go to step S24; if no, go to step S234; S234. Heat preserve the extrusion die and the die sleeve in the die furnace for a set time and then return to step S233.

7. The production process of a wide-width 7075 aluminum alloy sheet according to claim 1, characterized in that, In the step S32, the lengths of the 7075 aluminum alloy casting rods are all less than or equal to 1200 mm. In the step S35, the extrusion speed is 0.8 - 1.2 m / min.

8. The production process of a wide-width 7075 aluminum alloy sheet according to claim 7, characterized in that, In the step S36, first transfer the wide-width 7075 aluminum alloy sheet into a quenching furnace, heat it up to 465°C - 475°C, then immerse the wide-width 7075 aluminum alloy sheet in water for quenching within 30 s, and control the water temperature before and after quenching within 40°C.

9. The production process of a wide-width 7075 aluminum alloy sheet according to claim 8, characterized in that, In the step S37, the elongation rate of the wide-width 7075 aluminum alloy sheet is 1.5% - 2.5%.

10. The production process of a wide-width 7075 aluminum alloy plate according to claim 9, characterized in that, In the step S39, the aging temperature is 115°C - 120°C, and the holding time is 22 h - 24 h.

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