EP4585704A1

EP4585704A1 - 6000-series aluminum alloy sheet manufacturing method and aluminum alloy sheet

Info

Publication number: EP4585704A1
Application number: EP23862444.9A
Authority: EP
Inventors: Lingyong CAO; Gaohui CAO; Xini YUAN; Xiaokun Yang; Wen Zhang; Bing Yang
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-09-06
Filing date: 2023-09-06
Publication date: 2025-07-16
Also published as: US20260071304A1; WO2024051750A1; CN117701847A; KR20250053201A; CN117701847B; JP2025528955A

Abstract

Disclosed are a 6000-series aluminum alloy sheet having high formability, high flangability and few roping line defects, and a manufacturing method therefor. The sheet has an average grain size of 20-32 µm, a recrystallization texture density of 6.5-10.0, a cubic texture component content of less than or equal to 8%, and a Gaussian texture component content of less than or equal to 7%. The method comprises: (1) homogenizing a cast ingot, the temperature of homogenization being 530-580°C; (2) directly performing hot rough rolling, hot finish rolling, and hot final rolling and coiling on the homogenized cast ingot, controlling the initial rolling temperature of the hot finish rolling to be 400-480°C, and controlling the temperature of the hot final rolling and coiling to be above 250°C; (3) cold rolling: controlling the total deformation of the cold rolling to be 50-85%; (4) solution treatment; and (5) performing pre-aging treatment, and then performing air cooling, so as to obtain the 6000-series aluminum alloy sheet.

Description

Technical field

The present disclosure relates to an aluminum alloy sheet and a manufacturing method therefor, in particular to a 6000-series aluminum alloy sheet and a manufacturing method therefor.

Background Art

The 6000 series aluminum alloy has the advantages of high strength, good corrosion resistance, good surface quality after baking and improved strength after baking, and the 6000 series alloy is increasingly used in the manufacture of body exterior coverings.
As a body cover, the surface quality of 6000 series aluminum alloy sheet for automobile is as important as its mechanical properties, which is related to whether the appearance of the automobile after painting is ideal. The roping defect is one of the factors affecting the surface quality of aluminum alloy sheet for automobile.
In addition, in the process of flanging of aluminum alloy sheets, the interface between coarse intermetallic compounds and the substrate of aluminum plate often causes serious stress concentrations and induces the initiation of microcracks, which will reduce the flanging performance of the alloy sheet, so it is also of great significance to improve the flanging performance of aluminum alloy sheets.
The Chinese patent document with a publication number of CN101935785B and a title of "An aluminum alloy for automobile body panels with high formability" 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 this patent only focuses on yield strength, plasticity and work hardening rate, and does not pay attention to the r-value, flanging performance and roping defects, which are closely related to the forming of automobile body coverings.
The Chinese patent document with a publication number of CN105074028B, a publication date of June 6, 2017 , and a title of "An aluminum alloy sheet with excellent characteristics after aging at room temperature" discloses an aluminum alloy sheet that still has excellent performance after aging at room temperature by adding an appropriate amount of Sn element into the chemical composition and the manufacturing method therefor, and the material prepared therefrom has excellent formability. This patent achieves a good technical effect by adding the alloying element Sn, but the patent does not focus on how to improve the flanging performance of the sheet.
Therefore, in the prior art, the 6000 series aluminum alloy plate more or less has problems of poor flanging performance and obvious roping defects on the surface after stamping, which affects the large-scale promotion and application of the 6000 series sheet for automobile.
Based on the above, it is expected to obtain a manufacturing method that makes the 6000 series aluminum alloy sheet have high formability, high flanging performance and low roping defects.

Summary

One of the objectives of the present disclosure is to provide a manufacturing method of a 6000 series aluminum alloy sheet having high formability, high flanging performance and low roping defects at the same time. The manufacturing method of the 6000 series aluminum alloy sheet adopts a reasonable process design, which can provide an alloy sheet with a certain number and proportion of the second phase and a certain grain size through soaking, hot rolling, coiling, optional intermediate annealing and cold rolling process, then stimulate the recrystallization nucleation (PSN) effect in the subsequent solution pre-aging treatment, which weakens the recrystallization texture content, especially the content of cubic texture components and Gaussian texture components, thereby significantly improving the formability and flanging performance of the final aluminum alloy sheet and improving the roping defects of the aluminum alloy sheet.
In order to achieve the above object, the present disclosure provides a manufacturing method of a 6000 series aluminum alloy sheet having high formability, high flanging performance and low roping defects at the same time, which comprises the following steps:

(1) subjecting an ingot to a homogenization treatment, wherein the temperature of the homogenization treatment is 530~580 °C;
(2) subjecting the homogenized ingot to hot rough rolling, hot finish rolling and hot final rolling and coiling directly, wherein the rolling-start temperature of hot finish rolling is controlled to be 400~480 °C, and the temperature of hot final rolling and coiling is controlled to be 250 °C or higher;
(3) cold rolling: wherein the total deformation rate of cold rolling is controlled to be 50~85%, the average size of Mg₂Si precipitate phase in the obtained cold-rolled sheet is 1.3~1.7µm, and the areal density of Mg₂Si precipitate phase is ≥ 55000 pieces/mm²;
(4) solid solution treatment;
(5) pre-aging treatment, followed by air cooling, to obtain a 6000 series aluminum alloy sheet.

After a lot of research, the inventors have found that the second phase particles will have a great impact on the recrystallization texture of the 6000 series aluminum alloy, and when there are coarse second phase particles precipitated in the alloy, the coarse second phase will stimulate the recrystallization nucleation (PSN, Particle Stimulated Nucleation), thereby promoting the recrystallization and making the recrystallized texture components mainly random texture, reducing the texture strength and the content of cubic texture component and Gaussian texture component of typical recrystallization textures, so as to reduce the aggregation degree of the two components and reduce the degree of roping defects. In addition, the inventors have also found that the grain size decreases as the cold rolling reduction rate increases.
Based on the above, in order to overcome the technical problems of insufficient formability, poor flanging performance and easily appeared roping defects of the existing 6000 series aluminum alloy sheet, under the premise of ensuring the rationality of the process, the manufacturing method of the present disclosure regulates the size and quantity of the coarse Mg₂Si phase in the 6000 series aluminum alloy sheet by regulating process parameters of soaking, hot rolling, coiling, and optional intermediate annealing in the processing, and gives full play to the PSN (Particle Stimulated Nucleation) effect of the coarse Mg₂Si phase in the subsequent solid solution process, which regulates the texture. Secondly, the texture and grain size can be further regulated by adjusting the cold rolling reduction rate in the subsequent cold rolling process, in order to achieve the purpose of weakening and regulating the type, proportion and spatial distribution of the recrystallization texture, and refining the grain size, so as to obtain the 6000 series aluminum alloy sheet for automobile body with high formability, high flanging performance and low roping defects.
In particular, the non-equilibrium eutectic phase in the as-cast 6000 series aluminum alloy is easy to lead to uneven composition or structure, which causes problems such as poor plasticity due to subsequent thermal deformation, which restricts the formability of the 6000 series aluminum alloy to a certain extent. Therefore, in the present technical solution, the soaking temperature is controlled to exceed 530°C during homogenization to ensure the dissolution of most of the overly coarse Mg₂Si, and it also aims to improve the hot processability of the 6000 series aluminum alloy and eliminate the influence of non-equilibrium eutectic phases in the alloy.
In addition, the inventors have found that in the present technical solution, if the rolling-start temperature of hot finish rolling is controlled to be 400~480 °C, the size of the second phase (i.e., Mg₂Si precipitate phase) in the cold-rolled sheet can be controlled to be 1.3~1.7µm and the areal density of the second phase is 55,000 pieces/mm or more. If the rolling-start temperature of hot finish rolling is too high, the precipitated second phase will have too large size and low quantity. If the rolling-start temperature of hot finish rolling is too low, the size of the precipitated second phase is too small.
In addition, the inventors have found that in the present technical solution, if the cold rolling reduction rate is less than 50%, it will cause the grain in the finished sheet to be coarse, on the one hand, it will cause defects such as microcracks or continuous necking on the outer sheet surface of the alloy sheet after flanging, and reduce the flanging performance. On the other hand, it will make the sheet form an orange peel-like rough surface after punch forming, which reduces 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 formability. Therefore, in the present disclosure, the cold rolling reduction rate is controlled to be 50%~85%.
Thus, in the above-mentioned technical solution of the present disclosure, through the soaking treatment with reasonable temperature and time of the ingot, the non-equilibrium eutectic phase in the ingot is dissolved. Then the homogenized ingot is directly subjected to hot rough rolling to eliminate or reduce the casting defects and processed into an intermediate billet that satisfies the requirement of hot finish rolling. The hot-finish rolling, intermediate annealing and cold-rolling process are then controlled to obtain a cold-rolled sheet with a large number of coarse second phases and fine grains. In the solid solution pre-aging process before subsequent delivery, on the one hand, the PSN mechanism excited by the coarse second phase weakens the recrystallization texture content; on the other hand, by adjusting the cold rolling reduction rate, the finished sheet with fine grains is obtained, thereby providing the 6000 aluminum alloy sheet with high formability, high flanging performance and low roping defects.
In other words, the manufacturing method of the present disclosure effectively regulates the number, distribution and grain size of the coarse second phase inside the aluminum alloy through specific process matching, and then regulates the texture and structure of the 6000 series aluminum alloy sheet in the final T4P state, and significantly improves the formability, flanging performance and roping defect of the 6000 series aluminum alloy sheet.
Further, in step (2) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the coiling temperature of hot final rolling is controlled to be 250~350 °C. Further, when the coiling temperature of hot final rolling is 250~340 °C, intermediate annealing is carried out before cold rolling in step (3): the temperature of intermediate annealing is controlled to be 350~430 °C, and the holding time is 1~4h, and then the sheet is cooled to room temperature in the furnace. When the coiling temperature of hot final rolling is higher than 340 °C, step (3) is carried out directly without intermediate annealing.
In order to facilitate the subsequent cold working, intermediate annealing can be added between the hot rolling and cold rolling processes. In the present technical solution, intermediate annealing can reduce the deformation resistance and is conductive to the realization of easy deformation. According to the research of the inventors, when the temperature of hot final rolling and coiling is 250~340 °C, intermediate annealing is required to control the second phase, so that the average size of the Mg₂Si precipitate phase is 1.3~1.7µm, and its areal density is ≥ 55000 pieces/mm². When the intermediate annealing temperature is 350°C or higher, the precipitation rate of the second phase is relatively fast, and the size of the second phase is relatively large. When the intermediate annealing temperature is 350°C or lower, the precipitation rate of the second phase is relatively slow, and the particle size of the second phase is relatively small, which is not conducive to the occurrence of PSN mechanism. However, when the intermediate annealing temperature is higher than 430°C, the size of the precipitated second-phase particle is too large, which will become the initiation point of micro-cracks during processing and is not conducive to the subsequent sheet forming. At the same time, it will tend to reduce the number of second-phase particles at high temperature, which is not conducive to the formation of subsequent PSN textures.
In addition, in other embodiments, if the coiling temperature of hot final rolling is higher than 340 °C, the second phase comprising Mg₂Si precipitate phase with an average size of 1.3~1.7 µm and an areal density of ≥55000 pieces/mm² can also be obtained without intermediate annealing at this time.
Further, in step (2), the hot rough rolling is carried out at a temperature of 530~570 °C, preferably at a temperature of 540~560 °C.
Further, in step (2), when intermediate annealing is carried out, the heating rate of intermediate annealing is 13~17 °C/h, and the cooling rate of intermediate annealing is 12~15 °C/h.
Further, in step (1) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the holding time of the homogenization treatment is 6~16h, preferably 8~12h.
Further, in step (1) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the heating rate of the homogenization treatment is 20-50 °C/h.
Further, in step (1) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the temperature of the homogenization treatment is 550~570 °C.
Further, in step (2) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the total deformation rate of hot rough rolling is controlled to be greater than 70%, such as 70~95%; and/or the total deformation rate of hot finish rolling is greater than 80%, such as 85~90%.
Further, in step (2) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the rolling-start temperature of hot finish rolling is 440~480°C.
Further, in step (3) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the total deformation rate of cold rolling is 60~85%.
Further, in step (4) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the solid solution treatment temperature is 550~570 °C, the heating rate of the solid solution is 15~30 °C/s, the holding time of the solid solution treatment is 1~5min, and the quenching method is water cooling.
Further, in step (5) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the pre-aging treatment is carried out within 3 minutes after the end of step (4).
Further, in step (5) of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure, the pre-aging treatment is performed by raising the temperature to 80∼100°C and then slowly reducing the temperature from 80∼100°C to room temperature, and the cooling rate is 1~4°C/h.
Correspondingly, another objective of the present disclosure is to provide a 6000 series aluminum alloy sheet with high formability, high flanging performance and low roping defects at the same time. The 6000 series aluminum alloy sheet is easy to produce, and the production cost is not high, and it has quite high formability, high flanging performance and low roping defects, so that it can be effectively applied in the vehicle manufacturing industry, and satisfies the requirements of vehicle lightweight.
In order to achieve the above purpose, the present disclosure proposes a 6000 series aluminum alloy sheet with high formability, high flanging performance and low roping defects at the same time, which is prepared by adopting the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure.
Further, the 6000 series aluminum alloy sheet described in the present disclosure has an average grain size of 20~32µm, a recrystallization texture density of 6.5~10.0, a cubic texture component content of ≤8%, and a Gaussian texture component content of ≤7%.
Further, the 6000 series aluminum alloy sheet described in the present disclosure satisfies: a tensile strength of ≥ 210MPa, preferably ≥ 215MPa, a yield strength of ≥ 104MPa, preferably ≥ 110MPa, an elongation of ≥24%, preferably ≥24.5%.
Further, the 6000 series aluminum alloy sheet described in the present disclosure also satisfies: a plastic strain ratio r of ≥0.68, preferably r ≥0.70, preferably r ≥0.72, and more preferably ≥0.74, a plane anisotropy index Δr of ≤0.10, preferably ≤0.08, more preferably ≤0.06, and more preferably ≤0.04; a flanging grade (flanging factor of 0.6) rated as 1; a roping grade rated as 1.
In this context, the 6000 series aluminum alloy is a series of aluminum alloys containing elements such as silicon and magnesium, and its composition meets the GB/T33227-2016 standard. Common 6000 series aluminum alloy grades include 6A16, 6111, 6013, 6014, 6016, 6022, 6061, 6063, 6181, 6082, etc. In this context, by mass percentage, the 6000 series aluminum alloy can contain: Si: 0.3~1.5%, Fe: 0.05~0.5%, Cu: 0.02~1.1%, Mg: 0.35~1.2%, Zn: ≤0.8%, Mn: ≤0.8%, Cr: ≤0.35%, Ti: ≤0.15%, V: ≤0.20%, with a balance of Al and unavoidable impurities, such as P, S and O, etc.
In some embodiments, the element composition of the aluminum alloy sheet described in the present disclosure is as follows: Mg: 0.4~0.7%, Si: 0.5~0.8%, Fe: 0.1~0.3%, Mn: 0.05~0.15%, Cu: 0.05~0.3%, Zn: ≤0.05%, V: ≤0.05%, Cr: ≤0.05%, with a balance of Al and unavoidable impurities.
In some embodiments, the present disclosure provides a 6000 series aluminum alloy sheet, which has an average grain size of 20~32µm, a recrystallization texture density of 6.5~10.0, a cubic texture component content of ≤8%, and a Gaussian texture component content of ≤7%. Preferably, the 6000 series aluminum alloy sheet has a tensile strength of ≥ 210MPa, a yield strength of ≥ 104MPa, an elongation of ≥24%. Further preferably, the 6000 series aluminum alloy sheet has a plastic strain ratio r of ≥0.68, preferably r ≥0.70, preferably r ≥0.72, and more preferably ≥0.74. Further preferably, the 6000 series aluminum alloy sheet has a plane anisotropy index Δr of ≤0.10, preferably ≤0.08, more preferably ≤0.06, and more preferably ≤0.04. Further preferably, the 6000 series aluminum alloy sheet has a flanging grade rated as 1 and a roping grade rated as 1. Preferably, by mass percentage, the 6000 series aluminum alloy may contain: Si: 0.3~1.5%, Fe: 0.05~0.5%, Cu: 0.02~1.1%, Mg: 0.35~1.2%, Zn: ≤0.8%, Mn: ≤0.8%, Cr: ≤0.35%, Ti: ≤0.15%, V: ≤0.20%, with a balance of Al and unavoidable impurities; further preferably, the element composition of the aluminum alloy sheet is as follows: Mg: 0.4~0.7%, Si: 0.5~0.8%, Fe: 0.1~0.3%, Mn: 0.05~0.15%, Cu: 0.05~0.3%, Zn: ≤0.05%, V: ≤0.05%, Cr: ≤0.05%, with a balance of Al and unavoidable impurities.
Compared with the prior art, the manufacturing method of the 6000 series aluminum alloy sheet of the present disclosure have the following advantages and beneficial effects:

(1) The manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure can provide a large number of large second phases through homogenization, hot rolling, coiling, optional intermediate annealing, cold rolling process, thereby inducing the recrystallization nucleation of PSN mechanism in the subsequent solid solution treatment and pre-aging process, reducing the density of the recrystallization texture, especially the content of the soft texture, i.e. cubic texture, and the hard texture, i.e. Gaussian texture, and thereby improving the formability of the sheet (wherein the plastic strain ratio r is ≥0.68, the plane anisotropy index Δr is ≤0.10) and reduce the roping defects of the sheet.
(2) The manufacturing method of 6000 series aluminum alloy sheet described in the present disclosure can make the grain of the aluminum alloy sheet fine by regulating the cold rolling process in the processing, thereby improving the flanging performance of aluminum alloy sheet.
(3) The process of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure is simple, and it can be optimized by adjusting the parameters on the basis of the existing aluminum alloy heat treatment production line, and its applicability is quite extensive, and can meet the needs of industrial production.
(4) The manufacturing method of the present disclosure can quantify the structure and texture of the 6000 aluminum alloy sheet, and the prepared 6000 series aluminum alloy sheet has high formability, high flanging performance, and low roping defects. It can be effectively applied in the vehicle manufacturing industry to meet the requirements of vehicle lightweight and has a very broad application prospect.

Description of the drawings

Fig. 1 schematically shows the process flow diagram of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure.

Detailed Description

The 6000-series aluminum alloy sheet and the manufacturing method thereof of the present disclosure will be further explained and interpreted below in conjunction with the specific examples and the drawings of the description, but the explanation and interpretation do not constitute an undue limitation to the technical solution of the present disclosure.

Examples 1-8 and Comparative Examples 1-4

Table 1 lists the chemical composition of the 6000-series aluminum alloy sheets of Examples 1-8 and the aluminum alloy sheets of Comparative Examples 1-4. Table 1. (wt.%, the balance of Al and other impurities)

Chemical elements

Mg Si Fe Mn Cu Zn V Cr

0.56 0.65 0.15 0.083 0.13 0.0047 0.0083 0.0023
It should be noted that because the present disclosure does not limit the ratio of the components of the aluminum alloy sheet, the above Table 1 is only used to sufficiently disclose the manufacturing method of the present disclosure, and not to limit the manufacturing method and the aluminum alloy sheet described in the present disclosure.
Fig. 1 schematically shows the process flow diagram of the manufacturing method of the 6000 series aluminum alloy sheet described in the present disclosure.
As shown in Fig.1, the 6000-series aluminum alloy sheet of Examples 1-8 in the present disclosure was prepared by the following steps:

(1) Smelting and casting: according to the chemical composition shown in Table 1, the ingredients were batched and casted after melting in a melting furnace to prepare an aluminum alloy cast ingot;
(2) Homogenization treatment: the aluminum alloy cast ingot was heated in a homogenization heat treatment furnace, wherein the temperature was raised to 530~580°C at a heating rate of 20-50 °C/h; and preferably, the holding time of the homogenization treatment was controlled to be 6~16 hours;
(3) Hot rough rolling: the cast ingot was subjected to hot rough rolling at 530-570°C and the total deformation rate of hot rough rolling was more than 70%;
(4) Hot finish rolling: the hot rough rolled sheet was subjected to hot finish rolling, the rolling-start temperature of hot finish rolling was controlled to be 400~480°C; the temperature of hot final rolling and coiling was controlled to be 250°C or higher, and the total deformation rate of hot finish rolling was controlled to be more than 80%;
(5) Intermediate annealing: when the temperature of hot final rolling and coiling was 250~340 °C, intermediate annealing was carried out, wherein the temperature of intermediate annealing was controlled to be 350~430 °C, the holding time was 1~4h, the heating rate of intermediate annealing was 13~17 °C/h, and the cooling rate of intermediate annealing was 12~15 °C/h; when the temperature of hot final rolling and coiling was higher than 340°C, cold rolling was directly performed without intermediate annealing;
(6) Cold rolling: wherein the total deformation rate of cold rolling was controlled to be 50~85%;
(7) Solid solution treatment: wherein the solid solution treatment temperature was controlled to be 550~570°C, the heating rate of the solid solution was controlled to be 15~30°C/s, the solid solution treatment time was controlled to be 1 ~5min, and then water cooling was carried out;
(8) Pre-aging treatment: the pre-aging treatment was carried out immediately within 3 min after the end of step (7), wherein the temperature was raised to 80∼100°C and slowly reduced from 80∼100°C to room temperature, and the cooling rate was 1~4°C/h, thereby obtaining an aluminum alloy sheet in T4P state.

It should be noted that the manufacturing step flow of Comparative Examples 1-4 was similar to that of the Examples of the present disclosure, but its process parameters did not conform to the design scope of the present disclosure.

Table 2-1 and Table 2-2 list the specific process parameters in the above process steps for the 6000-series aluminum alloy sheets of Examples 1-8 and the aluminum alloy sheets of Comparative Examples 1-4.

Table 2-1.

No.	Homogenization treatment temperature (°C)	Holding time of the homogenization treatment (h)	Hot rough rolling temperature (°C)	Total deformation rate of hot rough rolling (%)	Rolling-start temperature of hot finish rolling (°C)	Temperature of final rolling and coiling in hot finish rolling (°C)	Total deformation rate of hot finish rolling (%)
Ex. 1	530	15	530	70.8	400	260	90
Ex. 2	545	12	535	75.1	440	300	89.5
Ex. 3	555	10	540	77.4	470	330	88.8
Ex. 4	560	10	550	80.5	400	260	88.5
Ex. 5	565	8	540	85.8	400	260	88.3
Ex. 6	570	6	570	87.4	470	330	88.0
Ex. 7	570	6	560	89.2	470	330	89.5
Ex. 8	580	6	555	94.8	480	350	88.8
CEx. 1	560	10	530	71.0	400	260	89.6
CEx. 2	565	10	540	77.5	400	260	89.5
CEx. 3	555	12	560	87.2	470	330	89.9
CEx. 4	570	6	550	95.8	470	330	88.9

Table 2-2.

No.	Intermediate annealing				Total deformation rate of cold rolling (%)	Solid solution treatment			Pre-aging treatment
No.	Heating rate (°C/h)	Intermediate annealing temperature (°C)	Holding time (h)	Cooling rate (°C/h)	Total deformation rate of cold rolling (%)	Solid solution temperature (°C)	Heating rate (°C/s)	Solid solution time (min)	Start cooling temperature (°C)	Cooling rate (°C/h)
Ex. 1	17.0	350	4.0	12.0	50	550	30.0	5	90	2.2
Ex. 2	16.3	360	3.4	12.3	65	555	25.5	4	90	2.2
Ex. 3	16.3	360	2.4	12.3	75	560	22.2	3	100	2.2
Ex. 4	14.1	390	1.9	13.8	75	565	20.5	2	90	2.2
Ex. 5	13.1	420	1.8	14.4	75	570	15.0	1	80	4.0
Ex. 6	13.1	420	1.7	14.4	65	555	26.5	4	85	3.0
Ex. 7	13.1	430	1.0	15.0	85	560	21.2	3	90	2.2
Ex. 8	14.1	--	--	--	75	570	15.5	1	90	1.0
CEx. 1	--	--	--	--	75	565	22.3	2	95	1.8
CEx. 2	12.5	*480*	2	14.9	75	570	15.0	1	100	1.5
CEx. 3	13.1	420	1.8	14.4	45	560	22.2	3	90	2.2
CEx. 4	13.1	420	1.8	14.4	90	560	22.5	3	90	2.2

It should be noted that in the present disclosure, the dimensions and distribution of the second phase (Mg₂Si precipitated phase) of the longitudinal section of the aluminum alloy sheet in each Example and comparative example were observed on the cold-rolled sheet, not the final finished sheet. This is because the recrystallization process occurs in the process of solid solution treatment of the cold-rolled plate, so it is necessary to observe the second phase of the cold-rolled plate to evaluate the effect of the second phase on the recrystallization process and the microstructure and texture.
In the present disclosure, a square of 12mm (rolling direction) × 10mm (transverse direction) was intercepted from the corresponding cold-rolled sheet sample of each Example and Comparative Example. The longitudinal section of the sheet was grinded, and 320 mesh, 800 mesh and 1500 mesh waterproof sandpaper were used sequentially for coarse grinding; then, 800 mesh metallographic sandpaper was used for fine grinding, and a polishing cloth was used finally for polishing the longitudinal section of the sheet. After that, the size and distribution of the second phase (i.e., Mg₂Si precipitated phase) in the longitudinal section of the aluminum alloy sheet were observed and analyzed by Sirion 200 field emission scanning electron microscope, and the relevant observation and analysis results were listed in Table 3 below.

Table 3 lists the average size and areal density of Mg₂Si precipitated phase of the cold rolled sheets of Examples 1-8 and Comparative Examples 1-4.

Table 3.

No.	Average size of Mg₂Si precipitate phase (µm)	Areal density of Mg₂Si precipitate phase (pieces/mm²)
Ex. 1	1.37	55310
Ex. 2	1.42	56322
Ex. 3	1.45	57032
Ex. 4	1.56	57321
Ex. 5	1.64	58239
Ex. 6	1.51	57653
Ex. 7	1.37	57877
Ex. 8	1.41	56743
CEx. 1	*0.84*	*3032*
CEx. 2	*2.02*	*31230*
CEx. 3	1.67	56783
CEx. 4	*1.21*	63432

In the present disclosure, the finished aluminum alloy sheets in T4P state of each Example and Comparative Example were also sampled and tested for the grain size. The specific methods were as follows:
A rectangular specimen of 15mm (rolling direction) × 10mm (transverse direction) was cut from the corresponding finished aluminum alloy sheet in T4P state of each Example and Comparative Example, and the statistical surface was based on a longitudinal section. The specimen was sanded sequentially with a waterproof sandpaper with a particle size of 320, 800, 1000 and 1500 on the water mill and a metallographic sandpaper with a particle size of 800 and 1000, and then mechanically polished by a woolen cloth applied with a diamond abrasive paste having a particle size of 0.5 µm. The polished specimen was anodized by DC power supply. Then, a metallographic microscope was used to take metallographic photographs at 100 times magnification, and the grain size of the aluminum alloy sheet was detected by ImageJ software with an intercept method. The test results are listed in Table 4.
In addition, in order to illustrate the relationship between the structure and texture and the properties, the finished 6000 series aluminum alloy sheets of Examples 1-8 and the aluminum alloy sheets of Comparative Examples 1-4 were also sampled respectively in the present disclosure to test the macroscopic texture. The preparation and test methods of XRD macroscopic texture samples for testing were as follows:
A square of 15mm (rolling direction) × 10mm (transverse direction) was cut from the corresponding finished aluminum alloy sheet sample in T4P state having a thickness of 1mm of each Example 1-8 and Comparative Example 1-4, and the test surface was the plane of the sheet. The sample was required to be sanded with the waterproof sandpaper and the metallographic sandpaper until the test surface was close to the center of the sheet thickness. Then it was soaked in 30% NaOH aqueous solution for 8~15min, taken out, placed in 10% HNO₃ aqueous solution and soaked for 5s. The sample was washed with water and blow-dried after being taken out. The macroscopic texture test was performed on a Bruker D8 Discover X-ray diffractometer with a tube voltage of 40 kV, a tube current of 40 mA, CuKα radiation, and Ni filter. According to the Shulz reflection method, the three incomplete pole diagrams {111}, {200} and {220} and the corresponding background with peak center deviation Δθ=±1.4° of pure aluminum powder and each sample were determined respectively (α=0°~75°; β=0°~360°); Mtex-4.1.4 was used to correct the background and defocus, and the orientation distribution function (ODF) was calculated. The test results are listed in Table 4.
In addition, in order to further illustrate the mechanical properties, flanging performance and surface quality of the finished 6000 series aluminum alloy sheet described in the present disclosure, the finished 6000 series aluminum alloy sheets of Examples 1-8 and the finished aluminum alloy sheets of Comparative Examples 1-4 were sampled again in the present disclosure, and the mechanical properties, flanging performance and roping defects of the finished aluminum alloy sheet of each Example and Comparative Example were tested and evaluated.
The testing method for the relevant mechanical properties was as follows:
The tensile performance at room temperature of the corresponding finished aluminum alloy sheet sample in T4P state of each Example and Comparative Example was tested after 7 days of natural aging at room temperature. The tensile test at room temperature was carried out according to the requirement of ASTM E8/E8M-16a, and the tensile specimens at room temperature were intercepted from the finished aluminum alloy sheet sample in T4P state in three directions with angles of 0°, 45° and 90° to the rolling direction of the sheet. The tensile test at room temperature was carried out on MTS810 tensile testing machine, and the tensile rate was controlled to be 2mm/min. Correspondingly, the value of the plastic strain ratio r and the value of the plane anisotropy index Δr were determined according to the standard of GB/T 5027-2007.
The evaluation method for the relevant flanging performance was as follows:
A rectangular sample of 250mm (rolling direction) × 30mm (transverse direction) was cut from the corresponding finished aluminum alloy sheet sample in T4P state of each Example and Comparative Example for the evaluation of flanging performance. The evaluation of flanging performance was carried out according to the requirement of GMW 15421-2018. After the sample was pre-stretched by 10% along the rolling direction, a rectangular sample of 50mm (rolling direction) × 30mm (transverse) was cut, and then a 180° bending test was carried out by using an indenter with a radius of 0.6mm, and the spacing of the back-up rollers was guaranteed to be 3.0~3.1 mm during the experiment. After bending, the outer surface was graded according to the standard as follows: Grade 1: Smooth surface; Grade 2:
Discontinuous local contractions; Grade 3: Microcrack morphology; Grade 4: Obvious crack morphology, where Grade 1 and 2 are acceptable and Grade 3 and 4 are unacceptable.
The evaluation method for the relevant roping defects was as follows:
A rectangular specimen of 250mm (rolling direction) × 35mm (transverse direction) was intercepted from the corresponding finished aluminum alloy sheet sample in T4P state of each Example 1-8 and Comparative Example 1-4 for roping defect evaluation. The polishing of the specimen for roping defect evaluation was required to be carried out on a flat working surface. First, an oil paper was placed under the sample for the convenience of cleaning after the test. The black ink was evenly applied to the surface of the sample. After a volatilization time of 10~15s, the surface of the specimen was polished by using a sponge pad with a sandpaper on the surface, and a slight pressure needed to be applied to the surface of the specimen during polishing. Generally, it was polished 2~3 times in one direction along the rolling direction, and then the grade evaluation of the roping defects was carried out manually: Level 1: it is required to have no vertical stripes parallel to the rolling direction on the surface; Grade 2: it is allowed to have 1~5 vertical stripes parallel to the rolling direction on the surface; 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 of the vertical stripes is less than 3mm, where Grade 1 and 2 are acceptable, and Grade 3 and 4 are unacceptable.

Table 4 lists the structure, texture and performance test result of the finished 6000 series aluminum alloy sheets of Examples 1-8 and the finished aluminum alloy sheets of Comparative Examples 1-4.

Table 4.

No.	Recrystallization texture density	Cubic texture component content (%)	Gaussian texture component content (%)	Grain size (µm)	Tensile strength (MP))	Yield strength (MPa)	Elongation (%)	Plastic strain ratio r	Plane anisotropy index Δr	Flanging grade (flanging factor of 0.6)	Roping defect grade
Ex. 1	6.7	5	4	28	221	110	24.5	0.73	0.10	1	1
Ex. 2	7.2	7	5	26	221	110	24.8	0.72	0..09	1	1
Ex. 3	7.8	6	4	25	220	109	25.0	0.72	0.08	1	1
Ex. 4	8.2	8	7	30	226	113	24.0	0.71	0.06	1	1
Ex. 5	9.4	7	7	31	224	115	25.8	0.76	0.09	1	1
Ex. 6	8.5	4	5	28	217	108	25.2	0.75	0.02	1	1
Ex. 7	8.8	6	5	23	222	112	24.7	0.68	0.06	1	1
Ex. 8	8.4	4	6	27	223	114	24,5	0.74	0.09	1	1
CEx. 1	*16.2*	12	10	30	211	106	25.6	*0.65*	*0.22*	1	3
CEx. 2	*6.3*	6	7	37	215	104	24.7	0.82	0.06	4	2
CEx. 3	9.0	6	5	40	212	106	25.6	0.78	-0.05	4	1
CEx. 4	*14.4*	12	14	21	220	109	24.5	*0.60*	*0.25*	1	3

As shown in Table 3 and Table 4, the 6xxx sheet prepared according to the process of Example 1-8 satisfies the requirements of the present disclosure. The areal density of Mg₂Si precipitated phase with an average size of 1.3~1.7 µm of the cold-rolled sheet is ≥ 55,000 pieces/mm². The average grain size of the finished sheet is 20~32µm, 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 properties of the finished sheet satisfy: the tensile strength is ≥210Mpa, the yield strength is ≥ 104MPa, the elongation is ≥ 24%, the value of plastic strain ratio r is ≥ 0.68, Δr is ≤ 0.10, the flanging grade (flanging factor is 0.6) is rated as 1, and the roping defect grade is rated as 1. But in the comparative examples, the 6xxx series sheet prepared according to the process of Comparative Example 1-4 does not meet the process scope of the present disclosure, resulting in the following result:
For Comparative Example 1, because the temperature of final rolling and coiling in hot finish rolling is below 340 °C but no intermediate annealing is carried out, too many fine second phases are precipitated, and the number of coarse second phases is too low, which inhibits the PSN effect excited by the coarse second phase in the subsequent solid solution process, resulting in overly high recrystallization texture density, so that the formability of the finished sheet is poor (low r value, high Δ r value). In particular, the contents of soft orientation component of the cubic texture and hard orientation component of the Gaussian texture are higher, and the aggregation of the two texture components is alternately distributed along the rolling direction, resulting in the grains with hard orientation of the Gaussian texture are not easy to deform and show ridges when it is pre-stretched at 10% perpendicular to the rolling direction, while the grains with soft orientation of the cubic texture are easy to deform and become thin, showing valleys, resulting in undulating roping defects along the rolling direction.
For Comparative Example 2, due to the overly high intermediate annealing temperature, the second phase is overgrown, which makes the size of the coarse second phase too large, and left in the final finished sheet since it is difficult to be fully re-melt in the subsequent solid solution process, resulting in an increase in crack sources in the flanging process, which in turn leads to poor flanging performance (flanging grade is 4).
For Comparative Example 3, due to the low reduction rate of cold rolling, the grain size in the finished sheet is too large, and the coarse grains will promote the generation and propagation of shear bands in the flanging process, and thus the flanging performance is poor (flanging grade is 4).
For Comparative Example 4, due to the overly high reduction rate of cold rolling, the deformation texture density in the cold-rolled sheet is too high. Due to the genetic effect of the texture, the recrystallization texture density in the finished sheet is also high, especially the content of soft orientation component of the cubic texture and hard orientation component of the Gaussian texture is high, which leads to serious roping defects (roping defect grade is 3).
It can be seen that, with respect to the manufacturing method of the 6000 series aluminum alloy sheet having high formability, high flanging performance and low roping defects at the same time described in the present disclosure, on the one hand, the size and quantity of the coarse Mg₂Si precipitate phase in the 6000 series aluminum alloy sheet are regulated by reasonably regulating the process parameters of soaking, hot rolling, coiling and intermediate annealing in the processing, and the PSN effect of the coarse Mg₂Si phase in the subsequent solid solution process is fully exerted, thereby adjusting the texture; on the other hand, the texture and grain size of the finished sheet are further controlled by adjusting 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 realized, thereby providing the 6000 series aluminum alloy sheet with high formability, high flanging performance and low roping defects for automobile body.
It should be noted that combinations of the various technical features in this case are not limited to the combinations disclosed in the claims of this case or the combinations disclosed in the specific Examples. All technical features disclosed in this case can be combined freely or associated in any way unless a contradiction occurs.
It should also be noted that the Examples listed above are only specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above Examples, and changes or modifications made thereto can be directly derived from the present disclosure or easily conceived of by those skilled in the art, all of which fall within the protection scope of the present disclosure.

Claims

A 6000 series aluminum alloy sheet, wherein the 6000 series aluminum alloy sheet has an average grain size of 20~32µm, a recrystallization texture density of 6.5~10.0, a cubic texture component content of ≤8%, and a Gaussian texture component content of ≤7%.
The 6000 series aluminum alloy sheet of claim 1, wherein the 6000 series aluminum alloy sheet has a tensile strength of ≥ 210MPa, a yield strength of ≥ 104MPa, and an elongation of ≥24%.
The 6000 series aluminum alloy sheet of claim 1 or 2, wherein the 6000 series aluminum alloy sheet has a plastic strain ratio r of ≥0.68, a plane anisotropy index Δr of ≤0.10, a flanging grade rated as 1 and a roping grade rated as 1.
The 6000 series aluminum alloy sheet of claim 3, wherein the 6000 series aluminum alloy sheet has a plastic strain ratio r of ≥0.70, preferably r ≥0.72, more preferably r ≥0.74.
The 6000 series aluminum alloy sheet of claim 3 or 4, wherein the 6000 series aluminum alloy sheet has a plane anisotropy index Δr of ≤0.08, preferably ≤0.06, more preferably ≤0.04.
The 6000 series aluminum alloy sheet of any one of claims 1-5, wherein, by mass percentage, the 6000 series aluminum alloy sheet may contain: Si: 0.3~1.5%, Fe: 0.05~0.5%, Cu: 0.02~1.1%, Mg: 0.35~1.2%, Zn: 0.8%, Mn: 0.8%, Cr: ≤0.35%, Ti: ≤0.15%, V: ≤0.20%, with a balance of Al and unavoidable impurities; preferably, the element composition of the aluminum alloy sheet is as follows: Mg: 0.4~0.7%, Si: 0.5~0.8%, Fe: 0.1~0.3%, Mn: 0.05~0.15%, Cu: 0.05~0.3%, Zn: ≤0.05%, V: ≤0.05%, Cr: ≤0.05%, with a balance of Al and unavoidable impurities.
A manufacturing method of the 6000 series aluminum alloy sheet having high formability, high flanging performance and low roping defects at the same time, wherein it comprises the following steps:
(1) subjecting a cast ingot to a homogenization treatment, wherein the temperature of the homogenization treatment is 530~580 °C, preferably 550~570 °C;

(2) subjecting the homogenized ingot to hot rough rolling, hot finish rolling and hot final rolling and coiling directly, wherein the rolling-start temperature of hot finish rolling is controlled to be 400~480 °C, preferably 440~480 °C, and the temperature of hot final rolling and coiling is controlled to be 250 °C or higher;

(3) cold rolling: the total deformation rate of cold rolling is controlled to be 50~85%, so as to obtain a cold rolled plate having an average size of Mg₂Si precipitate phase of 1.3~1.7µm, and an areal density of Mg₂Si precipitate phase of ≥ 55000 pieces/mm²;

(4) solid solution treatment;

(5) pre-aging treatment, followed by air cooling, to obtain a 6000 series aluminum alloy sheet.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (2), the temperature of hot final rolling and coiling is 250~340°C; in step (3), intermediate annealing is carried out before cold rolling: the temperature of intermediate annealing is controlled to be 350~430 °C, and the holding time is 1~4h, and then the sheet is cooled to room temperature in furnace, preferably, the heating rate of intermediate annealing is 13~17°C/h, the cooling rate of intermediate annealing is 12~15°C/h; or if the temperature of hot final rolling and coiling is higher than 340°C, the step (3) is directly carried out without intermediate annealing.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (1), the holding time of the homogenization treatment is 6~16h.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (2), the hot rough rolling temperature is controlled to be 530~570°C; and/or the total deformation rate of hot rough rolling is greater than 70%; and/or the total deformation rate of hot finish rolling is greater than 80%.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (3), the total deformation rate of cold rolling is 60~85%.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (4), the solid solution treatment temperature is 550~570°C, the heating rate of solid solution is 15~30°C/s, the holding time of solid solution treatment is 1~5min, and the quenching method is water cooling.
The manufacturing method of the 6000 series aluminum alloy sheet of claim 7, wherein in step (5), the pre-aging treatment is carried out immediately within 3 min after the end of step (4); and/or the pre-aging treatment is carried out by raising the temperature to 80∼100°C and then slowly reducing from 80∼100°C to room temperature with a cooling rate of 1 ~4°C/h.
The manufacturing method of the 6000 series aluminum alloy sheet of any one of claims 7-13, wherein the 6000 series aluminum alloy sheet is the 6000 series aluminum alloy sheet according to any one of claims 1-6.
A 6000 series aluminum alloy sheet prepared by the manufacturing method of any one of claims 8-13; preferably, the 6000 series aluminum alloy sheet has an average grain size of 20~32µm, a recrystallization texture density of 6.5~10.0, a cubic texture component content of ≤8%, and a Gaussian texture component content of ≤7%; more preferably, the 6000 series aluminum alloy sheet also satisfies the following performances:
a tensile strength of ≥ 210MPa, a yield strength of ≥ 104MPa, an elongation of ≥24%;

a plastic strain ratio r of ≥0.68, a plane anisotropy index Δr of ≤0.10, a flanging grade rated as 1; a roping grade rated as 1.