A 6000-series aluminum alloy sheet for exterior covering with optimized paint brush lines

Abstract

The application discloses a kind of paint brush line optimized 6 series outer covering aluminum alloy sheet, belong to non-ferrous metal processing technical field.The application is by using three different processing rate requirement cold rolling process to be matched with twice intermediate annealing process, change aluminum alloy strip inside grain size proportion and texture proportion, wherein two intermediate annealing time are 5s~20s, three cold rolling processing rates are 30%~60%, 15%~30%, 40%~70% in turn respectively, effectively improve the paint brush line problem of sheet, improve the comprehensive performance of sheet.The grain average size of aluminum alloy sheet product provided by the application is less than 30 μm, the number of second phase equivalent circle with diameter greater than or equal to 2 μm accounts for less than 10%, and the Goss texture accounts for less than or equal to 5%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of non-ferrous metal processing, and relates to an aluminum alloy, in particular to a 6-series outer covering part aluminum alloy plate with optimized paint brush lines. BACKGROUND

[0002] With the development of the automobile industry, people have higher requirements for the safety and light weight of automobiles. The light weight of automobiles refers to reducing the overall weight of automobiles as much as possible under the premise of ensuring the strength and safety performance of automobiles, so as to improve the power of automobiles, reduce fuel consumption and reduce exhaust pollution. Aluminum alloy has become the most ideal material for automobile light weight due to its high strength and rigidity, good impact resistance, excellent forming performance and extremely high recycling rate. The paint brush line problem has always been one of the important factors affecting the appearance quality of 6-series aluminum alloy plates, which seriously restricts its application in the field of high-end automobile outer covering parts.

[0003] As a commonly used automobile body outer plate, the 6-series aluminum alloy has high requirements for the paint brush line performance in addition to having good excellent mechanical properties and high bake hardening performance, so as to obtain excellent appearance quality. In the forming process of automobile covering parts, good paint brush line performance can ensure the overall aesthetic degree of automobile appearance parts, improve the assembly precision and structural strength of automobiles, and thus improve the safety and reliability of automobiles.

[0004] In recent years, a large amount of research has been conducted on how to improve the paint brush line performance of 6-series body plates. However, there are still some problems, for example, insufficient texture control, traditional process (such as single long-time intermediate annealing) is easy to form strong Goss texture, which leads to uneven stripes (paint brush lines) on the surface after painting, affecting the appearance consistency; the randomness of grain orientation during recrystallization is insufficient, and it is difficult to balance formability and surface quality. The contradiction between mechanical properties and surface quality can be improved in strength by single annealing or adjusting the cold rolling rate, but the grain size uniformity may be sacrificed, and the paint brush line defect is aggravated; high strain hardening rate leads to significant anisotropy during subsequent stamping forming, which aggravates the appearance of paint brush lines. The process window is narrow, and the temperature-time parameters of single intermediate annealing are difficult to optimize recrystallization and texture evolution at the same time, which is easy to cause partial recrystallization or excessive growth, affecting the surface uniformity.

[0005] The present application balances the microstructure (grain size, texture component) and macroscopic performance (formability, surface quality) through the synergistic design of two intermediate annealings, especially provides a mass production process path for the paint brush line problem of 6-series aluminum alloy body plates. The core innovation lies in the phased regulation of recrystallization kinetics, rather than relying on single annealing or alloy composition adjustment. SUMMARY

[0006] The purpose of the present application is to provide a 6-series aluminum alloy sheet with excellent mechanical properties, bake hardening properties and excellent paint brush line performance. Through unique process design, especially the introduction of two intermediate annealing processes, the proportion of grain size and texture in the aluminum alloy sheet is changed. The two intermediate annealing times are 5s~20s, and the three cold rolling processing rates are 30%~60%, 15%~30% and 40%~70% respectively. The paint brush line problem of the sheet is effectively improved, and the comprehensive performance of the sheet is improved. The present application is realized by adopting the following technical scheme:

[0007] A 6-series outer cover aluminum alloy sheet with optimized paint brush line, the aluminum alloy sheet comprises the following components by mass percentage: Mg: 0.1%~1.4%; Cu: ≤0.35%; Mn: ≤0.3%; Cr: ≤0.3%; Si: 0.3%~1.8%; Fe: ≤0.45%, and the balance of Al, the average grain size of the finished aluminum alloy sheet is <30μm, the number of second phase equivalent circles with a diameter of ≥2μm accounts for <10%, and the Goss texture accounts for ≤5%.

[0008] The preparation method of the 6-series outer cover aluminum alloy sheet with optimized paint brush line comprises the following steps:

[0009] (1) preparing an aluminum alloy ingot;

[0010] (2) homogenization: after milling the surface of the ingot, heating to 490℃~560℃ and keeping for 1h~10h;

[0011] (3) hot rolling: the homogenized ingot is hot rolled to a thickness of 6.0mm~8.0mm, and the final rolling temperature is 260℃~300℃;

[0012] (4) first cold rolling: the hot rolled sheet is first cold rolled, the thickness of the first cold rolled sheet is 2.5mm~4.0mm, the first cold rolling processing rate is 30%~60%, and the rolling speed is 100m / min~300m / min;

[0013] (5) first intermediate annealing: first intermediate annealing treatment is carried out in a gas cushion continuous annealing furnace, the annealing temperature is 400℃~500℃, and the annealing time is 5s~20s;

[0014] (6) second cold rolling: the sheet after the first intermediate annealing is second cold rolled, the thickness of the second cold rolled sheet is 2.0mm~3.0mm, the second cold rolling processing rate is 15%~30%, and the rolling speed is 300m / min~500m / min;

[0015] (7) second intermediate annealing: second intermediate annealing treatment is carried out again in a gas cushion continuous annealing furnace, the annealing temperature is 400℃~500℃, and the annealing time is 5s~20s;

[0016] (8) Third cold rolling: the plate after the second intermediate annealing is cold rolled to the finished product thickness, the thickness of the third cold rolled plate is 0.8mm~1.5mm, the rolling speed is 500m / min~800m / min, and the third cold rolling processing rate is 40%~70%;

[0017] (9) Solid solution treatment: the third cold rolled plate is subjected to solid solution treatment in a gas cushion type continuous annealing furnace, the solid solution temperature is 510℃~560℃, and the solid solution time is 30s~150s.

[0018] The 6-series outer covering aluminum alloy plate obtained by the above preparation method has a significantly optimized paint brush line, good surface quality, and excellent mechanical properties and forming properties.

[0019] Compared with the closest prior art, the technical scheme provided by the present application has the following excellent effects:

[0020] (1) The 6-series aluminum alloy plate with high paint brush line performance provided by the present application is prepared by adopting a third cold rolling process with different processing rates and two intermediate annealings, the proportion of coarse second phase and fine second phase in the plate structure after the intermediate annealing is adjusted, the double effects of the coarse second phase promoting recrystallization nucleation (PSN mechanism) and the fine second phase hindering recrystallization grain growth are fully played, so that the grain size of the final plate is improved, and the proportion of the second phase with a diameter of ≥2μm in the final product plate is adjusted to be <10%, and the proportion of Goss texture is ≤5%. When the Cube texture and Goss texture in the plate after the solid solution treatment appear regular distribution in the RD and TD directions, the deformation process is easy to form local deformation unevenness caused by the "soft" and "hard" differences of the Cube texture and Goss texture during loading, and the Cube texture which is easier to deform (softer) is more likely to be thinned during deformation, and the Goss texture which is not easy to deform (harder) is not easy to be thinned during deformation, so the surface morphology with concave-convex characteristics is formed. That is, the paint brush line is a strip-shaped feature parallel to the RD direction after the solid solution treatment, and is alternately distributed along the TD direction.

[0021] (2) The two intermediate annealings consume a large number of dislocations in the cold rolled plate, and at the same time, the intermediate annealing reduces the cold rolling rate of the finished product plate, thereby reducing the shear band. The reduction of the shear band and the dislocation density will limit the formation of Goss texture from the aspects of nucleation and growth, thereby significantly reducing the proportion of Goss texture in the T4P finished product plate, and further improving the paint brush line performance of the finished product plate.

[0022] (3) The high paint brush line performance 6 series aluminum alloy plate provided by the present application adjusts the second phase distribution and grain size in the aluminum alloy by strictly controlling the intermediate annealing and solid solution heat treatment, especially introduces twice intermediate annealing process, effectively improves the paint brush line problem of the plate, thereby greatly improves the paint brush line performance of the plate, is easy to realize in industry, and can be widely used for automobile 6 series aluminum alloy outer panel; compared with the traditional once long time intermediate annealing, the twice short time intermediate annealing is adopted in the present application, and the twice annealing time in the present application is not higher than the total time of the traditional once annealing, and the final adjustment effect is better; and the twice can meet the requirements, but the three times or more have low production efficiency and high cost.

[0023] (4) In the preparation process of the present application, three cold rolling processes are introduced, different cold rolling processing rates are adopted in the cold rolling process, for the F state hot rolled blank with a thickness of 6.0mm~8.0mm, the first cold rolling processing rate is 30%~60%, and the relatively slow speed of 100m / min~300m / min is adopted, which is beneficial to the biting of the material and the control of the plate shape, and at the same time, the pass reduction amount in this range can effectively break the grain size, and provide the deformation energy storage of the once intermediate annealing material recrystallization; the second cold rolling processing rate is 15%~30%, which adjusts the texture distribution of the material after the first intermediate annealing, and the smaller processing rate can effectively reduce the proportion of Goss texture, and the medium rolling speed of 300m / min~500m / min can further improve the material plate shape and improve the rolling efficiency; the third cold rolling processing rate is 40%~70%, a larger processing rate is adopted to fully break the material grain structure without additional increase of Goss texture proportion, to provide sufficient deformation energy storage for the finished product solid solution, refine the finished product grain and phase size, and the high speed rolling speed of 500m / min~800m / min can further improve the material plate shape and improve the rolling efficiency.

[0024] (5) The preparation of the 6 series outer cover aluminum alloy plate provided by the present application adopts air cushion type continuous annealing, which can shorten the production time, speed up the output cycle, shorten the metal turnover cycle, and is easy to realize in industrial production without increasing equipment, and the total time is consistent with the single annealing time, which can realize better adjustment of the texture than the single long time intermediate annealing, uniform distribution, and the negative influence of the slight decrease in efficiency can be almost ignored. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The 6 series aluminum alloy plate preparation process flow chart provided by the present application;

[0026] Figure 2 The paint brush line result schematic diagram of the 6 series aluminum alloy plate prepared by the present application example 1 and the comparative example 1, wherein (a) is the first level paint brush line appearance of the plate obtained by the example 1, and (b) is the third level paint brush line appearance of the plate obtained by the comparative example 1.

[0027] Figure 3 ODF images of finished plate material prepared for Example 1 and Comparative Example 1 of the present application; wherein (a) is the finished plate material of Example 1, and (b) is the finished plate material of Comparative Example 1. DETAILED DESCRIPTION

[0028] The present application provides a 6-series outer covering aluminum alloy plate material with optimized paint brush lines, wherein the relevant terms are explained as follows:

[0029] Weight percentage: the percentage of the mass (weight) of a certain alloy component in the total mass.

[0030] Yield strength: the yield limit of aluminum alloy when the yield phenomenon occurs, which is defined as the stress value that produces 0.2% residual deformation. The yield strength data is obtained by obtaining the stress-strain curve through uniaxial tensile test.

[0031] T4P state yield strength: the finished plate material obtained after casting, homogenization, hot rolling, cold rolling, solid solution, pre-aging, and slicing. The yield strength is obtained by testing the mechanical properties of the finished plate material after 7 days of room temperature storage through uniaxial tensile test.

[0032] Paint brush line performance: a long strip-shaped sample with a length of 250 mm and a width of 35 mm is cut from the finished plate material, the length direction of the sample is perpendicular to the rolling direction, and the width direction is parallel to the rolling direction. After pre-stretching the sample by 10% along the length direction, polishing the sample with 320 mesh oil stone, and evaluating the surface morphology of the polished sample, the evaluation levels are as follows: Grade 1: no obvious paint brush lines along the width direction; Grade 2: intermittent paint brush lines along the width direction, no through paint brush lines; Grade 3: sparse through paint brush lines along the width direction; Grade 4: dense through paint brush lines along the width direction. Grades 1 and 2 are acceptable, and grades 3 and 4 are unacceptable.

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0034] Examples 1-6:

[0035] The present application provides a preparation method of a 6-series outer covering aluminum alloy plate material with optimized paint brush lines, and the process flow is as shown in Figure 1 The preparation method comprises the following steps:

[0036] (1) Melting pure aluminum and various intermediate alloys with different component proportions, and casting aluminum alloy ingots using semi-continuous casting equipment after refining the melt, and sequentially numbering 1#-6#; the alloy ingot composition is shown in Table 1.

[0037] (2) homogenization: each ingot is heated to 490-560 DEG C after milling the surface and kept for 1-10 hours.

[0038] (3) hot rolling: the homogenized ingot is hot rolled to a thickness of 6.0-8.0 mm, and the final rolling temperature is 260-300 DEG C.

[0039] (4) primary cold rolling: the hot-rolled plate is subjected to primary cold rolling, the thickness of the primary cold-rolled plate is 2.5-4.0 mm, the primary cold rolling reduction is 30-60%, and the rolling speed is 100-300 m / min.

[0040] (5) primary intermediate annealing: the primary intermediate annealing treatment is carried out in a gas cushion continuous annealing furnace, the annealing temperature is 400-500 DEG C, and the annealing time is 5-20 s.

[0041] (6) secondary cold rolling: the plate after the primary annealing is subjected to secondary cold rolling, the thickness of the secondary cold-rolled plate is 2.0-3.0 mm, the secondary cold rolling reduction is 15-30%, and the rolling speed is 300-500 m / min.

[0042] (7) secondary intermediate annealing: the secondary intermediate annealing treatment is carried out again in a gas cushion continuous annealing furnace, the annealing temperature is 400-500 DEG C, and the annealing time is 5-20 s.

[0043] (8) tertiary cold rolling: the plate after the secondary intermediate annealing is cold rolled to the finished product thickness, the thickness of the tertiary cold-rolled plate is 0.8-1.5 mm, the tertiary cold rolling reduction is 40-70%, and the rolling speed is 500-800 m / min.

[0044] (9) solid solution treatment: the tertiary cold-rolled plate is subjected to solid solution treatment in a gas cushion continuous annealing furnace, the solid solution temperature is 510-560 DEG C, and the solid solution time is 30-150 s, thereby obtaining 6-series outer covering aluminum alloy plate with different brush line optimization.

[0045] In the examples 1-6, the process flow is the same as that in the comparative examples 1-14, and the difference lies in different process parameters, and the specific process parameters are shown in Tables 1 and 2.

[0046] Comparative examples 1-14:

[0047] In the comparative examples 1-14 of the present application, the process flow is the same as that in the examples 1-6, and the difference lies in different process parameters, and the specific process parameters are shown in Tables 1 and 2.

[0048] Table 1. Composition of different alloy ingots (wt%);

[0049]

[0050] ;​

[0051] The yield strength, paint brush line performance, average grain size <30 μm, equivalent circle number ratio of diameter ≥2 μm and Goss texture ratio of different aluminum alloy plates prepared by the examples and comparative examples of the present application are characterized, and the results are shown in Table 3.

[0052] Table 3. Performance list of different aluminum alloy plates;

[0053] ;

[0054] From the data in Table 3, it can be seen that the performance of the finished plates obtained by examples 1-6 of the present application is qualified, and the paint brush line is excellent, which can reach level 1, while comparative examples 1-14 are not qualified.

[0055] The total deformation rate of example 1 and comparative example 1 of the present application is consistent, but only one pass is fired, the rolling texture is not uniform, and the paint brush line performance is not good, which is specifically embodied in:

[0056] 1. The paint brush line results of the finished plates are different. The paint brush line results of different aluminum alloy plates prepared by example 1 and comparative example 1 of the present application are shown in Figure 2 From Figure 2 (a), it can be seen that the paint brush line of example 1 is level 1, there are intermittent paint brush lines along the width direction, and there is no through paint brush line; Figure 2 (b), the paint brush line of comparative example 1 is level 3, there are sparse through paint brush lines along the width direction.

[0057] 2. The crystal texture of the finished plates is different. The ODF diagrams of the finished plates prepared by example 1 and comparative example 1 of the present application are shown in Figure 3 From the figure, it can be seen that example 1 is mainly Cube texture, and Goss texture is not obvious, and comparative example 1 is mainly Goss texture. The Cube and Goss texture percentages of the two finished plates are shown in Table 4. The data in Table 4 further shows that under the premise that the Cube texture ratio has no obvious change, the linearly distributed Goss texture ratio is significantly reduced in the finished plate prepared according to the scheme provided by the present application.

[0058] Table 4. Comparison of texture components of finished plates;

[0059] ;

[0060] From the data in Table 2 and Table 3, it can be seen that the hot rolling final rolling temperature of Comparative Example 2 is too high, the grain size is too large, and the paint brush performance is poor; the open rolling temperature of Comparative Example 3 is too low, a large amount of Mg2Si precipitates, resulting in insufficient strength of the final product plate; the one-time cold rolling processing rate of Comparative Example 4 is too large, the grain size and texture cannot meet the requirements, and the paint brush line performance is poor; the two-time cold rolling processing rate of Comparative Example 5 is too large, the grain size and texture cannot meet the requirements, and the paint brush line performance is poor; the three-time cold rolling processing rate of Comparative Example 6 is too large, the rolling texture proportion is too much, and the paint brush line performance is poor; the one-time intermediate temperature of Comparative Example 7 is too high, the grain is coarse, and the requirements are not met, and the paint brush performance is poor; the one-time intermediate time of Comparative Example 8 is too long, the grain is coarse, and the requirements are not met, and the paint brush performance is poor; the two-time intermediate temperature of Comparative Example 9 is too high, the grain size and texture do not meet the requirements, and the paint brush performance is poor; the two-time intermediate time of Comparative Example 10 is too long, the grain size and texture do not meet the requirements, and the paint brush performance is poor; the solid solution temperature of Comparative Example 11 is low, the phase resolubilization is not uniform, and the paint brush performance is poor; the solid solution temperature of Comparative Example 12 is high, the grain size is coarse and uneven, and the paint brush performance is poor; the solid solution time of Comparative Example 13 is short, the phase resolubilization is not uniform, and the paint brush performance is poor; the solid solution time of Comparative Example 14 is long, the grain size is coarse and uneven, and the paint brush performance is poor.

[0061] The above description is only the preferred embodiment of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A 6000-series aluminum alloy sheet for an outer panel with a paintbrush line optimized, characterized in that, The aluminum alloy plate comprises the following components in percentage by mass: Mg: 0.1%-1.4%; Cu: ≤0.35%; Mn: ≤0.3%; Cr: ≤0.3%; Si: 0.3%-1.8%; Fe: ≤0.45%, and the balance of Al; The grain average size of the finished aluminum alloy plate is <30 μm, the number ratio of second phase equivalent circles with a diameter ≥2 μm is <10%, and the Goss texture ratio is ≤5%; The preparation method of the aluminum alloy plate comprises the following steps: Step 1. Preparation of alloy ingot: an aluminum alloy ingot is prepared according to the component composition of the target alloy plate; Step 2. Homogenization: the ingot is heated and kept after surface milling; Step 3. Hot rolling: the homogenized ingot is hot rolled to obtain a hot-rolled plate; Step 4. First cold rolling: the hot-rolled plate is first cold rolled; Step 5. First intermediate annealing: the first cold-rolled plate is first intermediate annealed in a gas cushion continuous annealing furnace; Step 6. Second cold rolling: the first intermediate annealed plate is second cold rolled; Step 7. Second intermediate annealing: the second cold-rolled plate is second intermediate annealed in a gas cushion continuous annealing furnace; during the second intermediate annealing, the annealing temperature is 400-500 ℃, and the annealing time is 5-20 s; Step 8. Third cold rolling: the second intermediate annealed plate is cold rolled to the finished thickness; Step 9. Solution treatment: the third cold-rolled plate is solution treated in a gas cushion continuous annealing furnace to obtain a 6-series outer covering aluminum alloy plate with optimized brush lines; In step 5, the annealing temperature during the first intermediate annealing is 400-500 ℃, and the annealing time is 5-20 s; In step 6, the thickness of the second cold-rolled plate is 2.0-3.0 mm; In step 8, the thickness of the third cold-rolled plate is 0.8-1.5 mm, and the third cold rolling reduction is 40-70%.

2. A paint brush line optimized 6000-series over plating sheet aluminum alloy according to claim 1, characterized in that, In step 2, the heating temperature is 490-560 ℃, and the holding time is 1-10 h; In step 3, the hot rolling is performed to a plate thickness of 6.0-8.0 mm, and the final rolling temperature is 260-300 ℃.

3. A paint brush line optimized 6000-series over plating sheet aluminum alloy according to claim 1, characterized in that, In step 4, the thickness of the first cold-rolled plate is 2.5-4.0 mm, the first cold rolling reduction is 30-60%, and the rolling speed is 100-300 m / min.

4. A paint brush line optimized 6000-series over plating sheet aluminum alloy according to claim 1, characterized in that, In step 6, the second cold rolling reduction is 15-30%, and the rolling speed is 300-500 m / min.

5. A paint brush line optimized 6000-series over plating sheet aluminum alloy as defined in claim 1 wherein, In step 8, the rolling speed is 500-800 m / min.

6. A paint brush line optimized 6000-series over plating sheet aluminum alloy as defined in claim 1 wherein, In step 9, the solution temperature is 510-560 ℃, and the solution time is 30-150 s.

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