Preparation method of high-strength corrosion-resistant 7-series aluminum alloy strip

Abstract

The application discloses a preparation method of high-strength corrosion-resistant 7-series aluminum alloy sheet strip, which comprises the steps of semi-continuous casting, homogenization heat treatment, sawing and milling, preheating, hot rolling, cold rolling, solid solution quenching, aging treatment and the like. The application improves the purity of the melt through the casting process, controls the hot rolling reduction, adopts a reasonable heat treatment system matched with each pass, and combines with the component design, so that the generation of coarse second phase particles is effectively reduced, the precipitation of nanoscale phases is promoted, and the high-strength corrosion-resistant performance of the aluminum alloy is improved. The application utilizes the conventional means, does not need to add special trace elements and processes, and is suitable for industrialized mass production.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy strip preparation, specifically relating to a method for preparing high-strength and corrosion-resistant 7-series aluminum alloy thin plates and strips. Background Technology

[0002] 7-series aluminum alloys have advantages such as high strength, low density, and non-magnetic properties, and are widely used in aerospace and automotive fields. However, due to their poor plasticity and toughness and poor corrosion resistance, their application is greatly limited in forming conditions such as bending and stamping, as well as in harsh acid and alkali environments. In fact, there are no precedents for their use in harsh environments, both domestically and internationally.

[0003] Current research on improving the high strength and corrosion resistance of 7-series aluminum alloys mainly focuses on two aspects: Firstly, by using aging (T7x), regressive aging (RRA), or even multi-stage artificial aging (T7xxx) to disrupt the continuity of grain boundary precipitates, increase the spacing between grain boundary precipitates, and maintain a fine and dispersed distribution of intragranular precipitates, the overall strength and corrosion resistance of the alloy are improved. Secondly, by adding trace amounts of rare earth elements and reducing impurity elements such as Fe and Si, the high damage tolerance of the material is enhanced.

[0004] Patent application number 202110668036.7 discloses a high-damage-tolerance 7-series aluminum alloy thick plate for aerospace applications and its preparation method. This method improves the damage tolerance of the aluminum alloy thick plate by controlling elements such as Fe≤0.08%, Si≤0.07%, and Mn≤0.06% through ultra-high purification, employing multi-stage homogenization to eliminate segregation and residual second-phase content in large-size ingots, and further improving the substructural microstructure by using a multi-stage hot rolling process with large reduction pressure. However, its ultra-high purification technology limits the source of raw materials and increases production costs to some extent. Furthermore, the hot rolling finishing temperature ≥350℃ easily causes the precipitation of coarse second-phase after cooling. Additionally, this method is limited to aluminum alloy thick plates.

[0005] Patent application number 202011322585.0 discloses a production process for 7-series aluminum alloy thick plates with high damage tolerance and low quenching sensitivity. It also uses ultra-high purity to control harmful elements such as Fe≤0.08%, Si≤0.05%, and Mn≤0.06%, and adopts two-stage solid solution and two-stage aging to improve the strength, fracture toughness and corrosion resistance of the finished product. However, it requires a hot rolling temperature of 430±20℃, which can easily cause the phase to fall into the sensitive zone after hot rolling and cooling, resulting in the precipitation of a large amount of coarse second phase. This method is also limited to aluminum alloy thick plates.

[0006] Patent application number 202110592066.4 discloses a method for preparing high-strength, high-toughness, and corrosion-resistant 7055 aluminum alloy medium-thick plates. It achieves good comprehensive performance by limiting Si≤0.06%, Fe≤0.08%, Zn / Mg=3.7~3.9, and performing a two-stage homogeneous heat treatment at 465℃ / (10-15h) + 475℃ / (20-25)h, while simultaneously employing a three-stage aging process at (100~110)℃ / 24h + (175~185)℃ / (30-120)min + 121℃ / 24h. This method is also limited to medium-thick plates.

[0007] Patent application number 201810533142.2 discloses a 7xxx series aluminum alloy sheet and its preparation process, which restricts trace elements such as Fe≤0.1%, Si≤0.06%, and Mn≤0.01%, and adopts high-temperature homogenization at 450-500℃ and high-temperature preheating at 420-500℃, with the aim of obtaining good anodized surface quality.

[0008] Patent application number 202111284311.1 discloses a stress corrosion resistant Al-Zn-Mg-Cu alloy and its preparation method. By controlling the content and ratio of Zn, Mg and Cu elements, adding an appropriate amount of rare earth element Y and reinforcing particles, and performing a long-term complex three-stage homogenization treatment at 380~430℃ / 6~10 hours + 450~468℃ / 5~8 hours + 470~480℃ / 20~40 hours, the aluminum alloy is guaranteed to have both high strength and good corrosion resistance.

[0009] Patents with application numbers 201610810550.9 and 201811002836.X disclose a 7-series aluminum alloy and its preparation method. By controlling the strengthening elements Cu and Mg to a low level, the strength is sacrificed to a certain extent, and the tensile strength is only about 410-460 MPa and 450 MPa, respectively. These two methods are only used for aluminum profile preparation processes and do not involve the manufacturing method of rolled thin plates.

[0010] This invention improves the casting process, enhances melt purity, regulates hot rolling reduction, employs appropriate heat treatment regimes for each pass, and combines composition design to effectively reduce the formation of coarse second-phase particles, promote the precipitation of nanoscale phases, and thus improve the high strength and corrosion resistance of aluminum alloys. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing high-strength, corrosion-resistant 7-series aluminum alloy thin plates and strips.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for preparing high-strength, corrosion-resistant 7-series aluminum alloy thin plates and strips includes the following steps: semi-continuous casting, homogenization heat treatment, sawing and milling, preheating, hot rolling, cold rolling, solution quenching, aging treatment, and tension bending and straightening; the specific operations of each step are as follows:

[0014] (1) Semi-continuous casting: Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloys or additives to adjust the composition, then transfer the resulting melt to a holding furnace, let it stand at 720-740℃ for 1-4 hours, then degas it online through SNIF, remove slag through 40ppi+60ppi double-stage plate filter, and then cast it to obtain ingots.

[0015] (2) Heat treatment: The obtained ingots are subjected to homogenization heat treatment at 470-485℃ / 10-32h, and then cooled naturally after being taken out of the furnace;

[0016] (3) Sawing and milling: Sawing and milling the ingot after homogenization and heat treatment;

[0017] (4) Preheating: Heat the milled flat ingot to 400-418℃ at a rate of ≥30℃ / h and keep it at that temperature for 4~12 hours;

[0018] (5) Hot rolling: The preheated flat ingot is hot rolled continuously, including 11-17 passes of hot roughing, with a single pass reduction of ≥50mm, a speed of >2.0m / s for the last 2 passes of hot roughing, and a final rolling temperature of ≤300℃ for hot finishing; after rolling, it is air-cooled to ≤180℃.

[0019] (6) Cold rolling: The hot-rolled coil is cold-rolled to a thickness of 0.30~1.0mm;

[0020] (7) Solution quenching: The cold-rolled coil obtained in step (6) is subjected to a two-stage solution quenching treatment of 460℃~464℃ / 100~200sec+472℃~475℃ / 100~200sec in an air cushion continuous annealing furnace.

[0021] (8) Aging treatment: The quenched coil obtained in step (7) is subjected to artificial aging treatment at 120℃ for 16-32h;

[0022] (9) Stretch bending and straightening: The artificially aged coil obtained in step (8) is stretched and straightened to finally obtain the high-strength corrosion-resistant 7-series aluminum alloy thin sheet and strip.

[0023] Furthermore, based on a total mass percentage of 100%, the composition ratio of the ingot obtained in step (1) is as follows: Si≤0.30%, Fe≤0.20%, Cu≤0.19%, Mn≤0.16%, Mg 2.55%-3.55%, Zn 6.8%-7.4%, with the remainder being Al and other impurities.

[0024] Further, the casting in step (1) is carried out at 692-699°C after adding 60-100ppm of 5Ti1B titanium wire online and in an environment with a water temperature of 20-30°C and a water flow rate of 1000-1200L / min.

[0025] Furthermore, the ingot obtained in step (1) has the following dimensions: thickness 400-600 mm, width 1200-1800 mm, and length 5000-6000 mm; its hydrogen content ≤0.14 ml / 100 g and slag content ≤0.012 mm. 2 / kg.

[0026] Furthermore, the air cooling in step (5) is controlled within 5 hours.

[0027] Furthermore, the resulting aluminum alloy sheet / strip has a thickness of 0.30~1.0mm, a tensile strength ≥510MPa, and a maximum depth of grain boundary corrosion ≤0.07mm.

[0028] The casting process is closely related to the original internal structure, microsegregation, and slag inclusion content of the melt. By matching a reasonable casting temperature, the safety of subsequent processing and the service life of the end product can be ensured.

[0029] If the temperature is too low or the holding time is too short during the heat treatment process, it will not be able to effectively improve the segregation of the ingot; if the temperature is too high or the holding time is too long, it will easily cause the internal structure to overheat or waste energy.

[0030] Preheating treatment should avoid being too long and falling into the precipitation-sensitive zone, while a reasonable preheating temperature should avoid the problem of low-temperature hot rolling cracking.

[0031] Hot rolling process can avoid the precipitation of a large amount of coarse MgZn2.

[0032] Two-stage solution quenching can achieve sufficient resolution and avoid the risk of overheating at high temperatures.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention improves melt purity through casting processes, controls hot rolling reduction, employs appropriate heat treatment regimes for each pass, and combines composition design to effectively reduce the formation of coarse second-phase particles and promote the precipitation of nanoscale phases, thereby enhancing the high strength and corrosion resistance of aluminum alloys. The resulting aluminum sheet / strip has a thickness of 0.30~1.0mm, a tensile strength ≥510MPa, and a maximum grain boundary corrosion depth ≤0.07mm. Attached Figure Description

[0035] Figure 1 This is a comparison diagram of inclusions in the ingot melt obtained by different casting processes in Example 1 (A) and Comparative Example 1 (B).

[0036] Figure 2 The images show a comparison of bending cracking of aluminum sheet strips obtained by different casting processes in Example 1 and Comparative Example 1.

[0037] Figure 3 This is a comparison diagram of the second phase microstructure of aluminum sheet and strip obtained by different hot rolling processes in Example 2 (A) and Comparative Example 2 (B).

[0038] Figure 4 The images show a comparison of the surface corrosion morphology of aluminum sheet and strip obtained by different hot rolling processes in Example 2 and Comparative Example 2 after alkaline washing at 50°C for 120 seconds in a 0.08% sodium hydroxide + 92% aqueous solution environment.

[0039] Figure 5 This is a comparison diagram of the intergranular corrosion performance of aluminum sheet and strip obtained by different hot rolling processes in Example 3 (A) and Comparative Example 3 (B). Detailed Implementation

[0040] A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip, comprising the following steps:

[0041] (1) Semi-continuous casting: Prepare raw materials according to the alloy composition ratio, heat the raw materials until completely melted, add intermediate alloys or additives to adjust the composition, then transfer the resulting melt to a holding furnace, let it stand at 720-740℃ for 1-4 hours, then degas it online via SNIF, remove slag by 40ppi+60ppi double-stage plate filtration, and then add 60-100ppm of 5Ti1B titanium wire online. Casting is carried out at 692-699℃ in an environment with a water temperature of 20-30℃ and a water flow rate of 1000-1200L / min to obtain large-size ingots (thickness 400-600mm × width 1200-1800mm × length 5000-6000mm), with a hydrogen content ≤0.14ml / 100g and a slag content ≤0.012mm. 2 / kg;

[0042] (2) Heat treatment: The obtained ingots are subjected to homogenization heat treatment at 470-485℃ / 10-32h, and then cooled naturally after being taken out of the furnace;

[0043] (3) Sawing and milling: Sawing and milling the ingot after homogenization and heat treatment;

[0044] (4) Preheating: Heat the milled flat ingot to 400-418℃ at a rate of ≥30℃ / h and keep it at that temperature for 4~12 hours;

[0045] (5) Hot rolling: The preheated flat ingot is hot rolled continuously, including 11-17 passes of hot roughing, with a single pass reduction of ≥50mm, a speed of >2.0m / s for the last 2 passes of hot roughing, and a final rolling temperature of ≤300℃ for hot finishing; after rolling, it is air-cooled to ≤180℃ within 5 hours.

[0046] (6) Cold rolling: The hot-rolled coil is cold-rolled to a thickness of 0.30~1.0mm;

[0047] (7) Solution quenching: The cold-rolled coil obtained in step (6) is subjected to a two-stage solution quenching treatment of 460℃~464℃ / 100~200sec+472℃~475℃ / 100~200sec in an air cushion continuous annealing furnace.

[0048] (8) Aging treatment: The quenched coil obtained in step (7) is subjected to artificial aging treatment at 120℃ for 16-32h;

[0049] (9) Stretch bending and straightening: The artificially aged coil obtained in step (8) is stretched and straightened to finally obtain the high-strength corrosion-resistant 7-series aluminum alloy thin sheet and strip.

[0050] The composition of the ingot obtained in step (1) is as follows, based on the sum of mass percentages of 100%: Si≤0.30%, Fe≤0.20%, Cu≤0.19%, Mn≤0.16%, Mg 2.55%-3.55%, Zn 6.8%-7.4%, with the remainder being Al and other impurities.

[0051] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto. Example 1

[0052] A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip includes the following specific steps:

[0053] (1) Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloy or additives to adjust the composition, then transfer the resulting melt to a holding furnace and let it stand at 720°C for 3 hours. Then, after online degassing by SNIF and slag removal by 40ppi+60ppi double-stage plate filtration, 80ppm of 5Ti1B titanium wire is added online. Casting is carried out at 692°C in an environment with a water temperature of 23°C and a water flow rate of 1050L / min to obtain an ingot with a thickness of 450mm × width of 1500mm × length of 6000mm. Its composition is Si 0.274%, Fe 0.161%, Cu 0.184%, Mn 0.158%, Mg 3.02%, Zn 7.2%, and the remainder is Al and other impurities. Its hydrogen content is 0.13ml / 100g and the slag content is 0.011mm. 2 / kg;

[0054] (2) The obtained ingots were subjected to homogenization heat treatment at 470℃ for 32h, and then cooled naturally after being taken out of the furnace;

[0055] (3) The homogenized heat-treated ingot is sawed and milled;

[0056] (4) Heat the milled flat ingot to 418°C at a rate of 32°C / h and hold for 4 hours;

[0057] (5) The preheated flat ingot is subjected to hot continuous rolling, including 11 passes of hot roughing, a single pass reduction of 53 mm, a speed of 2.2 m / s for the last two passes of hot roughing, a final rolling temperature of 270℃ for hot finishing, and air cooling to ≤180℃ for 3.5 h after rolling.

[0058] (6) Cold roll the hot-rolled coil to a thickness of 1.0 mm;

[0059] (7) The cold-rolled coil is subjected to a two-stage solution quenching treatment of 460℃ / 200sec+472℃ / 150sec in an air-cushion continuous annealing furnace;

[0060] (8) The obtained quenched coil is subjected to artificial aging treatment at 120℃ / 24h;

[0061] (9) The obtained artificially aged coil is straightened by bending to obtain a high-strength and corrosion-resistant 7-series aluminum alloy sheet and strip.

[0062] The resulting aluminum sheet and strip finished product has a thickness of 1.0 mm, a tensile strength of 585 MPa, and a maximum depth of grain boundary corrosion of 0.032 mm as tested according to GB / T 7889-2005 standard. Example 2

[0063] A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip includes the following specific steps:

[0064] (1) Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloy or additives to adjust the composition, then transfer the resulting melt to a holding furnace and let it stand at 730℃ for 2 hours. Then, after online degassing by SNIF and slag removal by 40ppi+60ppi double-stage plate filtration, 60ppm of 5Ti1B titanium wire is added online. Casting is carried out at 695℃ in an environment with a water temperature of 20℃ and a water flow rate of 1000L / min to obtain an ingot with a thickness of 500mm × width of 1300mm × length of 5000mm. Its composition is Si 0.154%, Fe 0.123%, Cu 0.121%, Mn 0.131%, Mg 3.23%, Zn 6.92%, and the remainder is Al and other impurities. Its hydrogen content is 0.10ml / 100g and the slag content is 0.010mm. 2 / kg;

[0065] (2) The obtained ingots were subjected to homogenization heat treatment at 475℃ for 15h and then cooled naturally after being taken out of the furnace;

[0066] (3) The homogenized heat-treated ingot is sawed and milled;

[0067] (4) Heat the milled flat ingot to 410℃ at a rate of 40℃ / h and keep it at that temperature for 7 hours;

[0068] (5) The preheated flat ingot is subjected to hot continuous rolling, including 13 passes of hot roughing, a single pass reduction of 65mm, a speed of 3.2m / s for the last two passes of hot roughing, a final rolling temperature of 300℃ for hot finishing, and air cooling to ≤180℃ for 4 hours after rolling.

[0069] (6) Cold roll the hot-rolled coil to a thickness of 0.50 mm;

[0070] (7) The cold-rolled coil is subjected to a two-stage solution quenching treatment of 462℃ / 120sec+475℃ / 100sec in an air cushion continuous annealing furnace;

[0071] (8) The obtained quenched coil is subjected to artificial aging treatment at 120℃ for 16h;

[0072] (9) The obtained artificially aged coil is straightened by bending to obtain a high-strength and corrosion-resistant 7-series aluminum alloy sheet and strip.

[0073] The resulting aluminum sheet and strip finished product has a thickness of 0.50 mm, a tensile strength of 548 MPa, and a maximum depth of grain boundary corrosion of 0.042 mm as tested according to GB / T 7889-2005 standard. Example 3

[0074] A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip includes the following specific steps:

[0075] (1) Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloy or additives to adjust the composition, then transfer the resulting melt to a holding furnace and let it stand at 725°C for 2 hours. Then, after online degassing by SNIF and slag removal by 40ppi+60ppi double-stage plate filtration, 70ppm of 5Ti1B titanium wire is added online. Casting is carried out at 696°C in an environment with a water temperature of 23°C and a water flow rate of 1100L / min to obtain an ingot with a thickness of 550mm × width of 1650mm × length of 5500mm. Its composition is Si 0.162%, Fe 0.153%, Cu 0.134%, Mn 0.153%, Mg 3.12%, Zn 7.03%, and the remainder is Al and other impurities. Its hydrogen content is 0.124ml / 100g and the slag content is 0.009mm. 2 / kg;

[0076] (2) The obtained ingots were subjected to homogenization heat treatment at 478℃ for 30h, and then cooled naturally after being taken out of the furnace;

[0077] (3) The homogenized heat-treated ingot is sawed and milled;

[0078] (4) Heat the milled flat ingot to 413°C at a rate of 34°C / h and hold for 5 hours;

[0079] (5) The preheated flat ingot is subjected to hot continuous rolling, including 15 passes of hot roughing, a single pass reduction of 57 mm, a speed of 2.8 m / s for the last two passes of hot roughing, a final rolling temperature of 290℃ for hot finishing, and air cooling to ≤180℃ for 3.8 h after rolling.

[0080] (6) Cold roll the hot-rolled coil to a thickness of 0.35 mm;

[0081] (7) The cold-rolled coil is subjected to a two-stage solution quenching treatment of 463℃ / 125sec + 474℃ / 150sec in an air-cushion continuous annealing furnace;

[0082] (8) The obtained quenched coil is subjected to artificial aging treatment at 120℃ for 32h;

[0083] (9) The obtained artificially aged coil is straightened by bending to obtain a high-strength and corrosion-resistant 7-series aluminum alloy sheet and strip.

[0084] The resulting aluminum sheet and strip finished product has a thickness of 0.35 mm, a tensile strength of 571 MPa, and a maximum depth of grain boundary corrosion of 0.069 mm as tested according to GB / T 7889-2005 standard. Example 4

[0085] A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip includes the following specific steps:

[0086] (1) Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloy or additives to adjust the composition, then transfer the resulting melt to a holding furnace and let it stand at 740℃ for 1 hour. Then, after online degassing by SNIF and slag removal by 40ppi+60ppi double-stage plate filtration, 100ppm of 5Ti1B titanium wire is added online. Casting is carried out at 692℃ in an environment with a water temperature of 28℃ and a water flow rate of 1200L / min to obtain an ingot with a thickness of 600mm × width of 1800mm × length of 5500mm. Its composition is Si 0.213%, Fe 0.189%, Cu 0.172%, Mn 0.155%, Mg 2.99%, Zn 6.97%, and the remainder is Al and other impurities. Its hydrogen content is 0.09ml / 100g and the slag content is 0.010mm. 2 / kg;

[0087] (2) The obtained ingots were subjected to homogenization heat treatment at 478℃ for 25h, and then cooled naturally after being taken out of the furnace;

[0088] (3) The homogenized heat-treated ingot is sawed and milled;

[0089] (4) Heat the milled flat ingot to 405℃ at a rate of 50℃ / h and keep it at that temperature for 8 hours;

[0090] (5) The preheated flat ingot is subjected to hot continuous rolling, including 17 passes of hot roughing, a single pass reduction of 65mm, a speed of 2.8m / s for the last two passes of hot roughing, a final rolling temperature of 265℃, and air cooling to ≤180℃ for 2 hours after rolling.

[0091] (6) Cold roll the hot-rolled coil to a thickness of 0.45 mm;

[0092] (7) The cold-rolled coil is subjected to a two-stage solution quenching treatment of 462℃ / 120sec + 474℃ / 120sec in an air-cushion continuous annealing furnace;

[0093] (8) The obtained quenched coil is subjected to artificial aging treatment at 120℃ / 18h;

[0094] (9) The obtained artificially aged coil is straightened by bending to obtain a high-strength and corrosion-resistant 7-series aluminum alloy sheet and strip.

[0095] The resulting aluminum sheet and strip finished product has a thickness of 0.45 mm, a tensile strength of 565 MPa, and a maximum depth of grain boundary corrosion of 0.053 mm as tested according to GB / T 7889-2005 standard.

[0096] Comparative Example 1

[0097] The heat preservation and standing time in step (1) is adjusted to 6 hours, and the rest of the operation is the same as in Example 1.

[0098] The results showed that the excessively long holding time resulted in a high slag content in the resulting ingots (e.g., Figure 1 ), which is 0.015mm 2 / kg, ultimately causing cracking and corrosive deterioration at the product application stage (such as... Figure 2 ).

[0099] Comparative Example 2

[0100] In step (4), the heating rate is adjusted to 25℃ / h, and the rest of the operation is the same as in Example 2.

[0101] The results showed that due to the slow preheating rate and excessively long heating time, a large amount of MgZn2 precipitated and coarsened in the finished product (e.g., Figure 3 The material has poor bending properties, and after alkaline corrosion, many black corrosion spots will form on the surface (such as...). Figure 4 ).

[0102] Comparative Example 3

[0103] In step (5), the reduction of a single pass in hot roughing is adjusted to 40 mm, and the rest of the operation is the same as in Example 3.

[0104] The results showed that insufficient reduction in a single pass of hot roughing, i.e., an unsuitable hot rolling process, resulted in a large amount of MgZn2 precipitation and coarsening in the finished product, with a tensile strength of only 537 MPa and a maximum intergranular corrosion depth of 0.075 mm (e.g., Figure 5 ).

[0105] Comparative Example 4

[0106] In step (5), the final rolling temperature of the hot finishing mill is adjusted to 340℃, and the remaining operations are the same as in Example 4.

[0107] The results showed that due to the excessively high final rolling temperature and the rapid temperature change after rolling, a large amount of MgZn2 precipitated and coarsened in the finished product, resulting in a tensile strength of only 543 MPa and a maximum intergranular corrosion depth of 0.089 mm.

[0108] As can be seen from the above embodiments and comparative examples, high-strength corrosion-resistant 7-series aluminum alloy thin sheets and strips with a thickness of 0.3~1.0 mm can be successfully prepared and produced according to the present invention.

[0109] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a high-strength, corrosion-resistant 7-series aluminum alloy thin sheet / strip, characterized in that: Includes the following steps: (1) Semi-continuous casting: Prepare raw materials according to the alloy composition ratio, heat the raw materials until they are completely melted, add intermediate alloys or additives to adjust the composition, then transfer the resulting melt to a holding furnace, let it stand at 720-740℃ for 1-4 hours, then degas it online through SNIF, remove slag through 40ppi+60ppi double-stage plate filter, and then cast it to obtain ingots. (2) Heat treatment: The obtained ingots are subjected to homogenization heat treatment and then cooled naturally after being taken out of the furnace; (3) Sawing and milling: Sawing and milling the ingot after homogenization and heat treatment; (4) Preheating: Heat the milled flat ingot to 400-418℃ at a rate of ≥30℃ / h and keep it at that temperature for 4~12 hours; (5) Hot rolling: The preheated flat ingot is hot rolled continuously and then air-cooled to ≤180℃; (6) Cold rolling: The hot-rolled coil is cold-rolled to a thickness of 0.30~1.0mm; (7) Solution quenching: The cold-rolled coil obtained in step (6) is subjected to two-stage solution quenching in an air cushion continuous annealing furnace. (8) Aging treatment: The quenched coil obtained in step (7) is subjected to artificial aging treatment; (9) Stretch bending and straightening: The artificially aged coil obtained in step (8) is stretched and straightened to finally obtain the high-strength corrosion-resistant 7-series aluminum alloy thin sheet and strip; In step (5), the hot roughing in the hot continuous rolling process consists of 10-17 passes, wherein the reduction per pass is ≥50mm, the speed of the last two passes of the hot roughing is >2.0m / s, and the final rolling temperature of the hot finishing is ≤300℃. The resulting aluminum alloy sheet and strip have a thickness of 0.30~1.0mm, a tensile strength ≥510MPa, and a maximum depth of grain boundary corrosion ≤0.07mm.

2. The preparation method according to claim 1, characterized in that: Based on a total mass percentage of 100%, the composition of the ingot obtained in step (1) is as follows: Si≤0.30%, Fe≤0.20%, Cu≤0.19%, Mn≤0.16%, Mg 2.55%-3.55%, Zn 6.8%-7.4%, with the remainder being Al and other impurities.

3. The preparation method according to claim 1, characterized in that: The casting in step (1) is carried out at 692-699℃ after adding 60-100ppm of 5Ti1B titanium wire online and in an environment with a water temperature of 20-30℃ and a water flow rate of 1000-1200L / min.

4. The preparation method according to claim 1, characterized in that: The ingot obtained in step (1) has the following dimensions: thickness 400-600mm, width 1200-1800mm, and length 5000-6000mm; its hydrogen content ≤0.14ml / 100g and slag content ≤0.012mm. 2 / kg.

5. The preparation method according to claim 1, characterized in that: The parameters for the homogenization heat treatment in step (2) are 470-485℃ / 10-32h.

6. The preparation method according to claim 1, characterized in that: The air cooling in step (5) is controlled within 5 hours.

7. The preparation method according to claim 1, characterized in that: The parameters for the two-stage solution quenching process in step (7) are 460℃~464℃ / 100~200sec + 472℃~475℃ / 100~200sec.

8. The preparation method according to claim 1, characterized in that: The parameters for the artificial aging process in step (8) are 120℃ / 16-32h.

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