A method for manufacturing a 6000 series aluminum alloy sheet and an aluminum alloy sheet

Abstract

The present invention discloses a method for manufacturing a 6000 series aluminum alloy plate having high forming performance, high flanging performance and low ribbing defects, comprising the following steps: (1) homogenizing an ingot, wherein the homogenizing temperature is 530-580°C; (2) directly performing hot rough rolling, hot finishing rolling and hot final rolling coiling on the homogenized ingot, wherein the hot finishing rolling start temperature is controlled to be 400-480°C, and the hot final rolling coiling temperature is controlled to be above 250°C; (3) cold rolling: wherein the total cold rolling deformation is controlled to be 50-85%, and the average size of the Mg2Si precipitate phase in the obtained cold rolled plate is 1.3-1.7 μm, and the surface density of the Mg2Si precipitate phase is ≥55000 / mm 2 ; (4) solution treatment; (5) pre-aging treatment, followed by air cooling, to obtain a 6000 series aluminum alloy plate. Accordingly, the present invention also discloses a 6000 series aluminum alloy plate obtained by the method.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy plate and a manufacturing method thereof, and in particular to a 6000 series aluminum alloy plate and a manufacturing method thereof. Background Art

[0002] 6000 series aluminum alloys have the advantages of high strength, good corrosion resistance, good surface quality after baking and increased strength after baking. This series of alloys are increasingly used in the manufacture of vehicle body exterior coverings.

[0003] As a body covering, the surface quality of 6000 series aluminum alloy automobile sheets is as important as its mechanical properties, which is related to whether the appearance of the car after painting is ideal. The ribbed grain defect is one of the factors affecting the surface quality of aluminum alloy automobile sheets.

[0004] In addition, during the flanging process of aluminum alloy plates, the interface between coarse intermetallic compounds and the aluminum plate matrix often causes severe stress concentration, inducing the initiation of microcracks, thereby reducing the flanging performance of the alloy plate. Therefore, improving the flanging performance of aluminum alloy plates is also of great significance.

[0005] The Chinese patent document with publication number CN101935785B and titled "A High Formability Aluminum Alloy for Automobile Body Panels" discloses a 6000 series aluminum alloy for automobile body panels with excellent formability obtained by adjusting the content and ratio of the main elements Si, Mg, and Cu. The excellent formability described in the patent only focuses on yield strength, plasticity, and work hardening rate, and does not focus on the r-value, flanging performance, and ribbing performance that are closely related to the forming of automobile body panels.

[0006] The Chinese patent document with publication number CN105074028B and publication date June 6, 2017, entitled "Aluminum alloy plate with excellent properties after room temperature aging", discloses an aluminum alloy and a plate manufacturing method thereof, which has excellent properties after room temperature aging by adding an appropriate amount of Sn element to the chemical composition, and the prepared material has excellent forming properties. The patent achieves good technical effects by adding the alloy element Sn, but the patent does not focus on how to improve the flanging performance of the plate.

[0007] Therefore, in the prior art, 6000 series aluminum alloy sheets have more or less problems such as poor flanging performance and obvious ribbing defects on the surface after stamping, which affects the large-scale promotion and application of 6000 series automotive sheets.

[0008] Based on this, it is desired to obtain a manufacturing method that enables 6000 series aluminum alloy sheets to have high formability, high flanging performance and low ribbing defects. Summary of the invention

[0009] One of the purposes of the present invention is to provide a method for manufacturing a 6000 series aluminum alloy plate having high formability, high flanging performance and low ribbing defects. The method for manufacturing the 6000 series aluminum alloy plate adopts a reasonable process design. Through soaking, hot rolling, coiling, optional intermediate annealing and cold rolling processes, an alloy plate with a certain amount and proportion of second phases and a grain size can be obtained, and then in the subsequent solid solution pre-aging treatment process, a recrystallization nucleation (PSN) effect is stimulated to weaken the recrystallization texture content, especially the content of cubic texture components and Gossian texture components, thereby significantly improving the formability and flanging performance of the final aluminum alloy plate, and improving the ribbing defects of the aluminum alloy plate.

[0010] In order to achieve the above object, the present invention proposes a method for manufacturing a 6000 series aluminum alloy sheet having high forming performance, high flanging performance and low ribbing defects, which comprises the steps of:

[0011] (1) homogenizing the ingot at a temperature of 530 to 580° C.

[0012] (2) directly performing hot rough rolling, hot finishing rolling and hot final rolling coiling on the ingot after homogenization treatment, controlling the starting rolling temperature of hot finishing rolling to be 400-480°C, and controlling the hot final rolling coiling temperature to be above 250°C;

[0013] (3) Cold rolling: The total cold rolling deformation is controlled to be 50-85%, and the average size of the Mg2Si precipitate phase in the obtained cold-rolled sheet is 1.3-1.7 μm, and the surface density of the Mg2Si precipitate phase is ≥55,000 / mm 2 ;

[0014] (4) Solution treatment;

[0015] (5) Pre-aging treatment, followed by air cooling, to obtain 6000 series aluminum alloy plates.

[0016] After extensive research, the inventors found that the second phase particles have a great influence on the recrystallization texture of the 6000 series aluminum alloy. When coarse second phase particles are precipitated in the alloy, the coarse second phase will stimulate recrystallization nucleation (PSN, Particle Stimulated Nucleation), thereby promoting recrystallization and making the texture components after recrystallization mainly random texture, reducing the texture strength, as well as the content of cubic texture components and Gaussian texture components in the typical recrystallization texture, thereby reducing the aggregation degree of the two and reducing the degree of ribbed grain defects. In addition, the inventors also found through research that the grain size decreases with the increase of cold rolling reduction rate.

[0017] Based on this, in order to overcome the technical problems of insufficient forming performance, poor flanging performance and easy occurrence of rib-line defects in the existing 6000 series aluminum alloy plates, under the premise of ensuring the rationality of the process, the manufacturing method described in the present invention adjusts the size and amount of coarse Mg2Si phases in the 6000 series aluminum alloy plates by adjusting the soaking, hot rolling, coiling, and optional intermediate annealing process parameters during the processing, and gives full play to the particle induced recrystallization nucleation (PSN, Particle Stimulated Nucleation) effect of the coarse Mg2Si phase in the subsequent solid solution process, thereby adjusting the texture; secondly, the texture and grain size can be further adjusted by adjusting the cold rolling reduction rate and in the subsequent cold rolling process, so as to achieve the purpose of weakening and adjusting the type, proportion, spatial distribution of the recrystallization texture, and refining the grain size, thereby obtaining a 6000 series aluminum alloy plate for automobile body with high forming performance, high flanging performance and low rib-line defects.

[0018] Specifically, the non-equilibrium eutectic phase in the cast 6000 series aluminum alloy easily leads to uneven composition or structure, which causes problems such as poor plasticity of subsequent hot deformation, which to a certain extent restricts the forming and processing performance of the 6000 series aluminum alloy. Therefore, the technical solution controls the soaking temperature during the homogenization process to exceed 530°C to ensure that most of the overly coarse Mg2Si is dissolved, and also aims to improve the hot processing performance of the 6000 series aluminum alloy and eliminate the influence of the non-equilibrium eutectic phase in the alloy.

[0019] In addition, the inventors have found that in the present technical solution, if the hot finishing rolling start temperature is controlled to be 400-480°C, the size of the second phase in the cold-rolled plate can be controlled to be 1.3-1.7 μm, and the surface density of the second phase is above 55,000 / mm; if the hot finishing rolling start temperature is too high, the size of the precipitated second phase is too large and the number is small; if the hot finishing rolling start temperature is too low, the size of the precipitated second phase is too small.

[0020] In addition, the inventor has found that in this technical solution, if the cold rolling reduction rate is lower than 50%, the grains in the finished plate will be coarse, which will cause defects such as microcracks or continuous necking on the outer plate surface after flanging of the alloy plate, reducing the flanging performance. On the other hand, the plate will form an orange peel-like rough surface after punching, reducing the surface quality; if the cold rolling reduction rate is higher than 85%, the local deformation zone around the coarse second phase particles is too large, and this area will become the initiation area of ​​microcracks during the forming process, which is not conducive to the forming performance. Therefore, the present invention controls the cold rolling reduction rate to 50% to 85%.

[0021] Therefore, in the above technical scheme of the present invention, the non-equilibrium eutectic phase in the ingot is dissolved by subjecting the ingot to a heat treatment at a reasonable temperature and time, and then the homogenized ingot is directly subjected to hot rough rolling to eliminate or reduce casting defects and to be processed into an intermediate billet that meets the hot finishing rolling conditions, and then the hot finishing rolling, intermediate annealing and cold rolling processes are controlled to obtain a cold-rolled sheet with a large amount of coarse second phase and fine grains. In the subsequent solution pre-aging process before delivery, on the one hand, the recrystallization texture content is weakened through the PSN mechanism stimulated by the coarse second phase; on the other hand, a finished sheet with fine grains is obtained by adjusting the cold rolling reduction rate, thereby obtaining a 6000 aluminum alloy sheet with high formability, high flanging performance and low ribbing defects.

[0022] In other words, the manufacturing method described in the present invention effectively regulates the amount and distribution of coarse second phases and grain size inside the aluminum alloy through specific process coordination, thereby regulating the texture and organization of the final finished T4P state 6000 series aluminum alloy plate, and significantly improving the forming performance, flanging performance and ribbing defects of the 6000 series aluminum alloy plate.

[0023] Furthermore, in step (2) of the method for manufacturing a 6000 series aluminum alloy sheet material of the present invention, when the hot finish rolling coiling temperature is 250-340°C, intermediate annealing is performed before cold rolling in step (3): the intermediate annealing temperature is controlled to be 350-430°C, the holding time is 1-4 hours, and then the sheet is cooled to room temperature in the furnace; when the hot finish rolling coiling temperature is higher than 340°C, intermediate annealing is not performed and step (3) is performed directly.

[0024] In order to facilitate further cold processing, intermediate annealing can be added between the hot rolling and cold rolling processes. In this technical solution, the deformation resistance and the ease of deformation can be reduced after intermediate annealing. The inventors have found that when the hot final rolling coiling temperature is 250-340°C, intermediate annealing is required to control the second phase so that the average size of the Mg2Si precipitation phase is 1.3-1.7μm, and its surface density is ≥55000 / mm 2 When the intermediate annealing temperature is above 350℃, the second phase precipitation rate is relatively fast and the second phase size is also relatively large; when the intermediate annealing temperature is below 350℃, the second phase precipitation rate is relatively slow and the second phase particle size is relatively small, which is not conducive to the occurrence of PSN mechanism; but when the intermediate annealing temperature is higher than 430℃, the size of the precipitated second phase particles is too large, which will become the initiation point of microcracks during the processing process, which is not conducive to the subsequent sheet forming. At the same time, high temperature often leads to a small number of second phase particles, which is not conducive to the subsequent formation of PSN texture.

[0025] In addition, in another embodiment, if the hot rolling coiling temperature is higher than 340°C, without intermediate annealing, the surface density of Mg2Si precipitates with an average size of 1.3 to 1.7 μm can be obtained to be ≥ 55,000 / mm 2 The second phase.

[0026] Furthermore, in step (2), when intermediate annealing is performed, the heating rate of the intermediate annealing is 13-17° C. / h, and the cooling rate of the intermediate annealing is 12-15° C. / h.

[0027] Furthermore, in step (1) of the method for manufacturing a 6000 series aluminum alloy sheet material of the present invention, the holding time of the homogenization treatment is 6 to 16 hours.

[0028] Furthermore, in step (1) of the method for manufacturing a 6000 series aluminum alloy sheet material of the present invention, the temperature of the homogenization treatment is 550-570°C.

[0029] Furthermore, in step (2) of the method for manufacturing 6000 series aluminum alloy sheet of the present invention, the total deformation of hot rough rolling is controlled to be greater than 70%; and / or the total deformation of hot finish rolling is controlled to be greater than 80%.

[0030] Furthermore, in step (2) of the method for manufacturing a 6000 series aluminum alloy sheet of the present invention, the starting temperature of hot finishing rolling is 440-480°C.

[0031] Furthermore, in step (3) of the method for manufacturing a 6000 series aluminum alloy sheet of the present invention, the total cold rolling deformation is controlled to be 60-85%.

[0032] Furthermore, in step (4) of the method for manufacturing 6000 series aluminum alloy plates described in the present invention, the solution treatment temperature is 550-570°C, the solution heating rate is 15-30°C / s, the solution treatment holding time is 1-5 min, and the quenching method is water cooling.

[0033] Furthermore, in step (5) of the method for manufacturing a 6000 series aluminum alloy sheet material of the present invention, a pre-aging treatment is performed within 3 minutes.

[0034] Furthermore, in step (5) of the method for manufacturing a 6000 series aluminum alloy sheet material of the present invention, the pre-aging treatment is to slowly reduce the temperature from 80 to 100° C. to room temperature, and the cooling rate is 1 to 4° C. / h.

[0035] Correspondingly, another object of the present invention is to provide a 6000 series aluminum alloy sheet having high formability, high flanging performance and low ribbing defects. The 6000 series aluminum alloy sheet is easy to produce and has low production cost. It has relatively high formability, high flanging performance and low ribbing defects, so that it can be effectively used in the vehicle manufacturing industry to meet the requirements of vehicle lightweighting.

[0036] In order to achieve the above objectives, the present invention proposes a 6000 series aluminum alloy plate having high forming performance, high flanging performance and low ribbing defects, which is manufactured by the manufacturing method of the 6000 series aluminum alloy plate of the present invention.

[0037] Furthermore, the average grain size of the 6000 series aluminum alloy plate of the present invention is 20-32 μm, the recrystallization texture density is 6.5-10.0, the cubic texture component content is ≤8%, and the Gossian texture component content is ≤7%.

[0038] Furthermore, the performance of the 6000 series aluminum alloy plate described in the present invention meets the following requirements: tensile strength ≥ 210 MPa, yield strength ≥ 104 MPa, elongation ≥ 24%; plastic strain ratio r ≥ 0.68, plane anisotropy index Δr ≤ 0.10, flanging grade (flanging factor is 0.6) is rated as 1, and ribbed grade is rated as 1.

[0039] Compared with the prior art, the 6000 series aluminum alloy sheet manufacturing method of the present invention has the following advantages and beneficial effects:

[0040] (1) The manufacturing method of the 6000 series aluminum alloy plate of the present invention can obtain a large number of large second phases through homogenization, hot rolling, coiling, optional intermediate annealing, and cold rolling processes, thereby inducing PSN mechanism recrystallization nucleation during subsequent solution treatment and pre-aging, thereby reducing the density of recrystallization texture, especially the content of soft texture cubic texture and hard texture Goss texture, thereby improving the formability of the plate and reducing the ribbed grain defects of the plate.

[0041] (2) The manufacturing method of the 6000 series aluminum alloy sheet described in the present invention can make the grain size of the aluminum alloy sheet fine by regulating the cold rolling process during the processing, thereby improving the flanging performance of the aluminum alloy sheet.

[0042] (3) The manufacturing method of the 6000 series aluminum alloy plate described in the present invention has a simple process. The process can be optimized by adjusting parameters on the basis of the existing aluminum alloy heat treatment production line. It has a wide range of applicability and can meet the needs of industrial production.

[0043] (4) The manufacturing method of the present invention can be used to quantify the organization and texture of 6000 aluminum alloy plates. The prepared 6000 series aluminum alloy plates have high formability, high flanging performance, and low ribbing defects. They can be effectively used in the vehicle manufacturing industry to meet the requirements of vehicle lightweighting and have very broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The process flow chart of the method for manufacturing the 6000 series aluminum alloy sheet material of the present invention is schematically shown. DETAILED DESCRIPTION

[0045] The 6000 series aluminum alloy sheet and the manufacturing method thereof described in the present invention will be further explained and illustrated below in conjunction with specific embodiments and the accompanying drawings of the specification. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0046] Examples 1-8 and Comparative Examples 1-4

[0047] Table 1 lists the chemical compositions of the 6000 series aluminum alloy plates of Examples 1-8 and the aluminum alloy plates of Comparative Examples 1-4.

[0048] Table 1. (wt.%, the balance is Al and other unavoidable impurities)

[0049]

[0050] It should be noted that, since the present invention does not limit the composition ratio of the aluminum alloy plate, the above Table 1 is only used to fully explain the manufacturing method described in the present invention, but not to limit the manufacturing method and aluminum alloy plate described in the present invention.

[0051] Figure 1 The process flow chart of the method for manufacturing the 6000 series aluminum alloy sheet material of the present invention is schematically shown.

[0052] like Figure 1 As shown, the 6000 series aluminum alloy plates of Examples 1-8 of the present invention are prepared by the following steps:

[0053] (1) Melting and casting: The ingredients are prepared according to the chemical composition shown in Table 1, melted in a smelting furnace and then cast to prepare an aluminum alloy ingot;

[0054] (2) Homogenization treatment: The aluminum alloy ingot is heated in a homogenization heat treatment furnace and heated to 530-580° C. at a heating rate of 20-50° C. / h, preferably to 550-570° C. for homogenization heat treatment; and the holding time of the homogenization treatment is preferably controlled to be 6-16 hours, and more preferably controlled to be 8-12 hours;

[0055] (3) Hot rough rolling: The ingot is subjected to hot rough rolling, and the total deformation of the hot rough rolling is controlled to be greater than 70%;

[0056] (4) hot finishing rolling: hot finishing rolling is performed on the hot rough rolled plate, the hot finishing rolling start temperature is controlled to be 400-480°C, preferably between 440-480°C; the hot final rolling coiling temperature is controlled to be above 250°C, and the total deformation of hot finishing rolling is controlled to be greater than 80%;

[0057] (5) Intermediate annealing: When the hot final rolling coiling temperature is 250-340°C, intermediate annealing is carried out, the intermediate annealing temperature is controlled to be 350-430°C, the holding time is 1-4h, the intermediate annealing heating rate is 13-17°C / h, and the intermediate annealing cooling rate is 12-15°C / h; when the hot final rolling coiling temperature is higher than 340°C, intermediate annealing is not carried out and cold rolling is directly performed;

[0058] (6) Cold rolling: the total deformation of cold rolling is controlled to be 50-85%, preferably the total deformation of cold rolling can be controlled to be 60-85%;

[0059] (7) Solution treatment: The solution treatment temperature is controlled at 550-570°C, the solution heating rate is 15-30°C / s, the solution treatment time is 1-5 min, and then water cooling is used.

[0060] (8) Pre-aging treatment: The pre-aging treatment is immediately carried out within 3 minutes, and the temperature is slowly reduced from 80-100°C to room temperature at a cooling rate of 1-4°C / h to obtain a T4P aluminum alloy plate.

[0061] It should be noted that the manufacturing process of comparative examples 1-4 is similar to that of the present embodiment, but the process parameters thereof do not conform to the design range of the present invention.

[0062] Table 2-1 and Table 2-2 list the specific process parameters of the 6000 series aluminum alloy plates of Examples 1-8 and the aluminum alloy plates of Comparative Examples 1-4 in the above process steps.

[0063] Table 2-1.

[0064]

[0065]

[0066] Table 2-2.

[0067]

[0068] It should be noted that in the present invention, the size and distribution of the second phase (Mg2Si precipitation phase) in the longitudinal section of the aluminum alloy plate of each embodiment and comparative example are sampled on the cold-rolled plate, rather than the final finished plate. This is because: the recrystallization process occurs during the solution treatment of the cold-rolled plate, so in order to observe the influence of the second phase on the recrystallization process and its microstructure, it is necessary to observe the second phase of the cold-rolled plate.

[0069] In the present invention, a 12 mm (rolling direction) × 10 mm (transverse) block is cut from the cold-rolled plate sample corresponding to each embodiment and comparative example, and the longitudinal section of the plate is ground, and 320 mesh, 800 mesh and 1500 mesh water-abrasive sandpaper are used for coarse grinding in sequence; then 800 mesh metallographic sandpaper is used for fine grinding, and finally the longitudinal section of the plate is polished with a polishing cloth, and then the size and distribution of the second phase (i.e., Mg2Si precipitation phase) in the longitudinal section of the aluminum alloy plate are observed and analyzed using a Sirion 200 field emission scanning electron microscope. The relevant observation and analysis results are listed in the following Table 3.

[0070] Table 3 lists the average size and surface density of the Mg2Si precipitate phase in the cold-rolled plates of Examples 1-8 and Comparative Examples 1-4.

[0071] Table 3.

[0072]

[0073] The present invention also samples and tests the grain size of the finished T4P aluminum alloy sheet in each embodiment and comparative example. The specific method is as follows:

[0074] A rectangular sample of 15 mm (rolling direction) × 10 mm (transverse direction) was cut from the finished T4P aluminum alloy sheet corresponding to each embodiment and comparative example, and the statistical surface was the longitudinal section. The sample was polished on a water mill with water-abrasive sandpaper with a particle size of 320, 800, 1000, and 1500 and metallographic sandpaper with a particle size of 800 and 1000, and then a diamond grinding paste with a particle size of 0.5 μm was applied to the woolen cloth for mechanical polishing. The polished sample was anodic coated using a DC power supply. After that, a metallographic microscope was used to take metallographic photos under a magnification of 100 times, and the grain size of the aluminum alloy sheet was detected using the intercept method using ImageJ software. The test results are listed in Table 4.

[0075] In addition, in order to describe the relationship between organization and texture and performance, the present invention also samples the finished 6000 series aluminum alloy plates of Examples 1-8 and the aluminum alloy plates of Comparative Examples 1-4 to test the macro texture. The preparation of XRD macro texture test samples and the detection method are as follows:

[0076] Cut a 15mm (rolling direction) × 10mm (transverse) block from the 1mm thick finished T4P aluminum alloy plate sample corresponding to each embodiment 1-8 and comparative example 1-4, and the test surface is the plate plane. The sample needs to be polished with water-abrasive sandpaper and metallographic sandpaper, and the test surface is ground to near the center of the plate thickness, and then soaked in a 30% NaOH aqueous solution for 8 to 15 minutes, taken out and soaked in a 10% HNO3 aqueous solution for 5 seconds, and washed with water and blown dry after the sample is taken out. The macro texture test was carried out on a Bruker D8Discover X-ray diffractometer, and the test conditions were 40kV tube voltage, 40mA tube current, CuKα radiation, and Ni filtering. The three incomplete pole figures (α = 0° to 75°; β = 0° to 360°) of {111}, {200}, and {220} of pure aluminum powder and each sample were measured by the Shulz reflection method, and the corresponding background with the peak center deviation of Δθ = ±1.4° was measured; Mtex-4.1.4 was used to perform background correction and defocus correction, and the orientation distribution function (ODF) was calculated. The test results are listed in Table 4.

[0077] In addition, in order to further illustrate the mechanical properties, flanging performance and surface quality of the finished 6000 series aluminum alloy plates described in the present invention, the present invention also samples the finished 6000 series aluminum alloy plates of Examples 1-8 and the finished comparative aluminum alloy plates of Comparative Examples 1-4 again, and tests and evaluates the mechanical properties, flanging performance and ribbing defects of the finished aluminum alloy plates of each embodiment and comparative example.

[0078] The relevant mechanical properties testing methods are as follows:

[0079] The finished T4P aluminum alloy sheet samples corresponding to each embodiment and comparative example were subjected to room temperature tensile performance test after 7 days of natural aging at room temperature. The room temperature tensile test was carried out according to the requirements of ASTM E8 / E8M-16a, and the room temperature tensile specimens were respectively taken from the finished T4P aluminum alloy sheet samples at three directions with an angle of 0°, 45° and 90° to the sheet rolling direction. The room temperature tensile test was carried out on an MTS810 tensile testing machine, and the tensile rate was controlled to be 2mm / min. Accordingly, the plastic strain ratio r value and the plane anisotropy index Δr value were measured according to the GB / T 5027-2007 standard.

[0080] The relevant flanging performance evaluation methods are as follows:

[0081] Rectangular specimens of 250mm (rolling direction) × 30mm (transverse) were cut from the finished T4P aluminum alloy sheet samples corresponding to each embodiment and comparative example for flanging performance evaluation. The flanging performance evaluation was carried out according to the requirements of GMW15421-2018. After the sample was pre-stretched 10% along the rolling direction, a rectangular specimen of 50mm (rolling direction) × 30mm (transverse) was cut, and then a 180° bending test was performed using a pressure head with a radius of 0.6mm. During the experiment, the spacing between the support rollers was ensured to be 3.0-3.1mm. After bending, the outer surface was graded according to the standards in the figure: Grade 1: smooth surface; Grade 2: discontinuous local shrinkage; Grade 3: microcrack morphology; Grade 4: obvious crack morphology, of which grades 1 and 2 are acceptable, and grades 3 and 4 are unacceptable.

[0082] The relevant evaluation methods for ribbed defects are as follows:

[0083] A rectangular sample of 250 mm (rolling direction) × 35 mm (transverse direction) was cut from the finished T4P aluminum alloy sheet samples corresponding to each of Examples 1-8 and Comparative Examples 1-4 for evaluation of ribbed grain defects. The polishing of the sample for evaluation of ribbed grain defects needs to be carried out on a flat work surface. First, oil paper is placed under the sample to facilitate cleaning after the test. Black ink is evenly applied to the surface of the sample and waited for 10 to 15 seconds for volatilization. Then use a sponge pad with sandpaper on the surface to grind the surface of the sample. Apply slight pressure on the surface of the sample during grinding. Generally, grind unidirectionally along the rolling direction 2 to 3 times. Then manually evaluate the grade of the ribbed grain defects: Grade 1: The surface requires no vertical stripes parallel to the rolling direction; Grade 2: The surface is allowed to have 1 to 5 vertical stripes parallel to the rolling direction; Grade 3: The number of vertical stripes parallel to the rolling direction on the surface exceeds 5; Grade 4: The number of vertical stripes parallel to the rolling direction on the surface exceeds 5 and the spacing between the vertical stripes is less than 3mm. Grades 1 and 2 are acceptable, and grades 3 and 4 are unacceptable.

[0084] Table 4 lists the microstructure, texture and performance test results of the finished 6000 series aluminum alloy plates of Examples 1-8 and the finished aluminum alloy plates of Comparative Examples 1-4.

[0085] Table 4.

[0086]

[0087]

[0088] As shown in Table 3 and Table 4, the 6xxx plates prepared according to the process of Examples 1-8 meet the requirements of the present invention, and the surface density of the Mg2Si precipitate phase with an average size of 1.3 to 1.7 μm in the cold-rolled plate is ≥55,000 / mm 2The average grain size of the finished plate is 20-32 μm, the recrystallization texture density is 6.5-10.0, the cubic texture component content is ≤8%, and the Gaussian texture component content is ≤7%; the performance of the finished plate meets the requirements of tensile strength ≥210 MPa, yield strength ≥104 MPa, elongation ≥24%, plastic strain ratio r value ≥0.68, Δr ≤0.10, and the flanging grade (flanging factor is 0.6) is rated as 1, and the ribbed grade is rated as 1. In the comparative examples, the 6xxx series plates prepared by the process of comparative examples 1-4 do not meet the process range of the present invention, resulting in the following results:

[0089] In Comparative Example 1, because the final rolling coiling temperature of hot finishing rolling is below 340°C but no intermediate annealing is performed, too many fine second phases are precipitated, while the amount of coarse second phases is too low, thereby inhibiting the PSN effect stimulated by the coarse second phases in the subsequent solid solution process, resulting in too high recrystallization texture density, and thus poor forming performance of the finished plate (low r value, high Δr value); in particular, the content of cubic texture soft orientation components and Gossian texture hard orientation components is high, and the two texture components are clustered and distributed alternately along the rolling direction, resulting in that when 10% pre-stretching is performed perpendicular to the rolling direction, the grains with Gossian texture hard orientation are not easy to deform and present ridges, while the grains with cubic texture soft orientation are easy to deform and thin, presenting valleys, resulting in undulating rib-grain defects along the rolling direction.

[0090] In Comparative Example 2, the intermediate annealing temperature is too high, the second phase grows excessively, and the size of the coarse second phase is too large. It is difficult to fully melt back in the subsequent solid solution process and remains in the final finished plate, resulting in an increase in crack sources during the flanging process, which in turn leads to poor flanging performance (flanging grade is 4).

[0091] In Comparative Example 3, the cold rolling reduction rate is too low, resulting in excessively large grain size in the finished plate. The coarse grains promote the generation and propagation of shear bands during the flanging process, resulting in poor flanging performance (flanging grade 4).

[0092] In Comparative Example 4, the cold rolling reduction rate is too high, resulting in a too high deformation texture density in the cold-rolled plate. Due to the genetic effect of the texture, the recrystallization texture density in the finished plate is also high, especially the content of the soft-oriented component of the cubic texture and the hard-oriented component of the Gossian texture is high, which leads to serious rib-grain defects (rib-grain defect rating is 3).

[0093] It can be seen from this that the method for manufacturing a 6000 series aluminum alloy sheet with high formability, high flanging resistance and low ribbing defects described in the present invention, on the one hand, regulates the size and amount of the coarse Mg2Si precipitated phase in the 6000 series aluminum alloy sheet by reasonably regulating the soaking, hot rolling, coiling and intermediate annealing process parameters during the processing, and gives full play to the PSN effect of the coarse Mg2Si phase in the subsequent solid solution process, thereby adjusting the texture; on the other hand, the texture and grain size of the finished sheet are further regulated by regulating the cold rolling reduction rate, and finally the purpose of weakening the recrystallization texture density of the finished sheet and refining the grain size of the finished sheet is achieved, thereby obtaining a 6000 series aluminum alloy sheet for automobile body with high formability, high flanging resistance and low ribbing defects.

[0094] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0095] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A method for manufacturing a 6000 series aluminum alloy sheet having high forming performance, high flanging performance and low ribbing defects, characterized in that: Includes steps: (1) homogenizing the ingot at a temperature of 530 to 580° C. (2) directly performing hot rough rolling, hot finishing rolling and hot final rolling coiling on the ingot after homogenization treatment, controlling the start rolling temperature of hot finishing rolling to be 400-480°C, and controlling the hot final rolling coiling temperature to be above 250°C; wherein when the hot final rolling coiling temperature is 250-340°C, performing intermediate annealing before cold rolling in step (3): controlling the intermediate annealing temperature to be 350-430°C, holding time to be 1-4h, and then cooling to room temperature with the furnace, wherein the intermediate annealing heating rate is 13-17°C / h, and the intermediate annealing cooling rate is 12-15°C / h; when the hot final rolling coiling temperature is higher than 340°C, performing step (3) directly without performing intermediate annealing; (3) Cold rolling: The total cold rolling deformation is controlled to be 50-85%, and the average size of the Mg2Si precipitate phase in the obtained cold-rolled sheet is 1.3-1.7 μm, and the surface density of the Mg2Si precipitate phase is ≥55,000 / mm 2 ; (4) Solution treatment: The solution treatment temperature is 550-570°C, the solution heating rate is 15-30°C / s, the solution treatment holding time is 1-5 min, and the quenching method is water cooling; (5) Pre-aging treatment is performed within 3 minutes, followed by air cooling to obtain a 6000 series aluminum alloy plate; wherein the pre-aging treatment is performed by slowly cooling the temperature from 80 to 100°C to room temperature at a cooling rate of 1 to 4°C / h.

2. The method for manufacturing a 6000 series aluminum alloy sheet material according to claim 1, characterized in that: In step (1), the holding time of the homogenization treatment is 6 to 16 hours.

3. The method for manufacturing a 6000 series aluminum alloy sheet material according to claim 1, characterized in that: In step (1), the temperature of the homogenization treatment is 550-570°C.

4. The method for manufacturing a 6000 series aluminum alloy sheet material according to claim 1, wherein: In step (2), the total deformation of the hot rough rolling is controlled to be greater than 70%; and / or the total deformation of the hot finish rolling is controlled to be greater than 80%.

5. The method for manufacturing a 6000 series aluminum alloy sheet material according to claim 1, characterized in that: In step (2), the start rolling temperature of hot finish rolling is 440-480°C.

6. The method for manufacturing a 6000 series aluminum alloy sheet material according to claim 1, wherein: In step (3), the total cold rolling deformation is controlled to be 60-85%.

7. A 6000 series aluminum alloy plate, produced by the manufacturing method according to any one of claims 1 to 6.

8. The 6000 series aluminum alloy sheet according to claim 7, characterized in that: The average grain size is 20-32 μm, the recrystallization texture density is 6.5-10.0, the cubic texture component content is ≤8%, and the Goss texture component content is ≤7%.

9. The 6000 series aluminum alloy sheet according to claim 7, characterized in that: Its performance meets: Tensile strength ≥ 210MPa, yield strength ≥ 104MPa, elongation ≥ 24%; The plastic strain ratio r≥0.68, the plane anisotropy index Δr≤0.10, the flanging grade is rated as 1, and the rib weave grade is rated as 1.

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