5-series aluminum alloy plate with low-temperature baking hardening response and preparation method of 5-series aluminum alloy plate

Abstract

The invention relates to the technical field of metal materials, in particular to a 5-series aluminum alloy plate with low-temperature baking hardening response and a preparation method of the 5-series aluminum alloy plate. The content of Zn is 1.5%-3.5%; the content of Cu is 0.3%-1.2%; the content of Mn is 0.1 to 0.3 percent; the content of Cr is 0.03 to 0.15 percent; the content of Zr is 0.05 to 0.15 percent; the content of Ti is 0.01 to 0.10 percent; si content is less than or equal to 0.2%; fe content is less than or equal to 0.25%; the La content is less than or equal to 0.2%; the Ce content is less than or equal to 0.2%; the content of Yb is less than or equal to 0.2%; the balance is Al; the bake hardening response efficiency function phi BH of the 5-series aluminum alloy plate is 0.15-1.2; the steel plate has low yield strength, high elongation, high formability and high sinking resistance, and baking varnish hardening is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically to a 5-series aluminum alloy sheet with low-temperature baking hardening response and its preparation method. Background Technology

[0002] In recent years, the global automotive industry has been undergoing a profound transformation towards lightweighting and new energy. In order to reduce vehicle energy consumption, extend the range of electric vehicles, and reduce carbon emissions, aluminum alloys, due to their excellent specific strength, corrosion resistance, and recyclability, have gradually replaced traditional steel and become the mainstream lightweight material in automobile body manufacturing.

[0003] In the aluminum alloy system for automotive sheet metal, two main categories are currently used: 5xxx series Al-Mg alloys, represented by AA5182 and AA5052, are widely used in body panels, reinforcements, and structural components due to their good elongation, formability, and corrosion resistance. However, this series is a non-heat-treatable strengthening alloy, relying mainly on cold work hardening. During automotive painting, they not only lack strengthening effects but may also soften due to annealing, limiting their application in high-dip-resistance areas such as exterior panels. 6xxx series Al-Mg-Si alloys, represented by AA6016 and AA6111, possess excellent bake-hardening (BH) capabilities. These materials maintain a low yield strength (T4) in the delivery state, facilitating stamping. During the painting process, strength is significantly improved through precipitation phase hardening, meeting the requirements for dip resistance and structural stiffness. However, these alloys have low inherent elongation and insufficient formability, making them difficult to meet the manufacturing requirements of complex deep-drawn parts.

[0004] Therefore, the existing automotive aluminum sheet system exhibits a clear performance complementarity pattern: the 5xxx series has excellent formability but lacks paint hardening; the 6xxx series has paint hardening but insufficient formability. To bridge this performance gap, recent studies have attempted to impart paint hardening capabilities by introducing elements such as Cu and Zn into the 5 series. However, these modification schemes often lack systematic design, resulting in limited performance improvements, and a versatile aluminum alloy that can simultaneously satisfy high formability and strong paint hardening has not yet been formed.

[0005] Existing technologies for improving 5-series aluminum alloys for automobiles involve introducing 0.5–1.0% Cu or 1–2% Zn into traditional Al-Mg alloys (such as 5182 and 5052) to achieve aging or paint-curing effects similar to those of 6xxx series alloys. However, due to the lack of complete microstructure control processes, these approaches often only achieve limited strength improvements and significantly reduce formability. Alternatively, research has been conducted on combining the advantages of 5-series and 6-series alloys through laminates and composite materials. However, these approaches are costly to manufacture, have complex processes, and are difficult to recycle, making them unsuitable for large-scale applications.

[0006] In summary, existing modification techniques mostly focus on adjusting single components, lacking systematic utilization of microstructure-controlling elements such as Mn / Cr / Zr. Therefore, it is difficult to simultaneously achieve: high elongation and high n value to ensure formability, high ΔYS to ensure paint hardening, and excellent corrosion resistance and weldability.

[0007] In summary, there is an urgent need to address the problem that existing technologies for 5-series aluminum alloys cannot simultaneously achieve low yield strength, high elongation, guaranteed paint hardening, high formability, and high dent resistance. Summary of the Invention

[0008] The present invention aims to solve the technical problem of how to provide a 5-series aluminum alloy that combines low yield strength, high elongation, guaranteed paint hardening, high formability, and high dent resistance.

[0009] To achieve the above objectives, a first aspect of the present invention provides a 5-series aluminum alloy sheet with a low-temperature bake-hardening response, wherein the components and their weight percentages in the 5-series aluminum alloy sheet are as follows:

[0010] The Mg content is 2.5-5.0%;

[0011] The Zn content is 1.5-3.5%;

[0012] The Cu content is 0.3-1.2%;

[0013] The Mn content is 0.1-0.3%;

[0014] The Cr content is 0.03-0.15%;

[0015] The Zr content is 0.05-0.15%;

[0016] The Ti content is 0.01-0.10%;

[0017] Si content ≤ 0.2%;

[0018] Fe content ≤ 0.25%;

[0019] La content ≤ 0.2%;

[0020] Ce content ≤0.2%;

[0021] Yb content ≤ 0.2%;

[0022] The content of a single impurity is ≤0.03%;

[0023] The total content of other impurity elements is ≤0.1%;

[0024] The balance is Al;

[0025] Among them, the bake hardening response efficiency function Φ of 5-series aluminum alloy sheets BH The value is 0.15-1.2;

[0026] Formula I,

[0027] In Formula I, ω(Zn), ω(Cu), ω(Mg), and ω(Zn / 6) represent the weight fractions of Zn, Cu, Mg, and one-sixth of the Zn content, respectively.

[0028] A second aspect of the present invention provides a method for preparing the above-mentioned 5-series aluminum alloy sheet with low-temperature baking hardening response, wherein the preparation method includes melting, casting, homogenization, hot rolling, cold rolling, annealing, and cooling;

[0029] The homogenization process includes two stages: the temperature T1 of the first stage is 440-480℃ and the time of the first stage is 8-24h; the temperature T2 of the second stage is 490-510℃ and the time of the second stage is 4-10h.

[0030] The heat treatment adaptation function f in homogenization step It is 19-90;

[0031] Formula IV,

[0032] In Equation IV, ω(Cu), ω(Zn), ω(Fe), and ω(Si) are the weight fractions of Cu, Zn, Fe, and Si, respectively, T1 is the temperature of the first homogenization stage, and T2 is the temperature of the second homogenization stage.

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

[0034] (1) The present invention uses a specific two-stage homogenization process to make Cu and Zn elements in a “pre-dissolved / easily soluble” state before entering a specific short-term continuous annealing process. During the short annealing process, Cu and Zn elements can still be effectively activated to form a high solute supersaturation, which significantly improves the baking hardening potential.

[0035] (2) The present invention adopts a specific alloy composition that satisfies Formula I, preferably Formula II, and Formula III, which takes into account both low-temperature aging kinetics and solute strengthening effect. Through the multi-component composite regulation of Mn, Cr, Zr, Ti, Sc / rare earth, a stable dispersed phase is formed, which inhibits recrystallization and coarse grains, and ensures the microstructure stability of the plate during large deformation processing and annealing. A good balance is established between composition, microstructure and performance, and the dual characteristics of high elongation and high bake hardening response are achieved.

[0036] (3) The sheet metal provided by the present invention has low yield strength (<120MPa) and high elongation (>25%), which is suitable for complex stamping of automotive body panels; after baking cycle, the yield strength increases by ≥100MPa and the final yield strength is ≥220MPa, which is significantly better than traditional 5 series alloys and meets the requirements for anti-denting and anti-sagging.

[0037] (4) The sheet metal provided by the present invention has high formability, corrosion resistance and good welding performance comparable to 5 series alloys, and is suitable for use in key parts such as body panels and electric vehicle battery pack housings. Compared with 6 series alloys, the preparation method provided by the present invention avoids the complex solid solution-aging process, and the production cost and process are closer to the traditional 5 series alloys, which has industrialization feasibility and economic advantages. Detailed Implementation

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] In the existing technology, 5-series aluminum alloys have technical problems in automotive sheet metal, such as insufficient bake hardening response and difficulty in balancing strength and formability.

[0040] In this invention, the inventors discovered that by employing specific homogenization methods, combined with other optimization methods and specific alloy ratios, it is possible to produce 5-series aluminum alloys that possess low yield strength, high elongation, guaranteed paint hardening, high formability, and high dent resistance.

[0041] Therefore, in a first aspect, the present invention provides a 5-series aluminum alloy sheet with a low-temperature bake-hardening response, wherein the components and their weight percentages in the 5-series aluminum alloy sheet are as follows:

[0042] The Mg content is 2.5-5.0%;

[0043] The Zn content is 1.5-3.5%;

[0044] The Cu content is 0.3-1.2%;

[0045] The Mn content is 0.1-0.3%;

[0046] The Cr content is 0.03-0.15%;

[0047] The Zr content is 0.05-0.15%;

[0048] The Ti content is 0.01-0.10%;

[0049] Si content ≤ 0.2%;

[0050] Fe content ≤ 0.25%;

[0051] La content ≤ 0.2%;

[0052] Ce content ≤0.2%;

[0053] Yb content ≤ 0.2%;

[0054] The content of a single impurity is ≤0.03%;

[0055] The total content of other impurity elements is ≤0.1%;

[0056] The balance is Al;

[0057] Among them, the bake hardening response efficiency function Φ of 5-series aluminum alloy sheets BH The value is 0.15-1.2;

[0058] Formula I,

[0059] In Formula I, ω(Zn), ω(Cu), ω(Mg), and ω(Zn / 6) represent the weight fractions of Zn, Cu, Mg, and one-sixth of the Zn content, respectively.

[0060] In this invention, the contents of Zn, Cu, and Mg meet the specific range required by Formula I, which changes the characteristic that traditional 5-series alloys do not possess age-hardening properties, and induces the formation of Zn / Cu-rich pre-precipitated clusters or I-phase. " This ensures that solute atoms are in a metastable state most easily precipitated at low temperatures.

[0061] According to the present invention, the solute activation equilibrium index I of the 5-series aluminum alloy sheet act The value is 1.2-10.0;

[0062] Formula II,

[0063] In Formula II, ω(Zn), ω(Cu), ω(Mg), ω(Fe), and ω(Si) represent the weight fractions of Zn, Cu, Mg, Fe, and Si, respectively.

[0064] In this invention, the contents of Zn, Cu, Mg, Fe and Si meet the specific range required by Formula II, maximizing the reduction of coarse non-equilibrium phases and ensuring that even with a certain amount of impurities, sufficient "active solute atoms" can still enter the solid solution through the specific two-stage homogenization in the preparation method, thereby achieving high ductility in the finished board.

[0065] According to the present invention, the dispersed phase thermal stability factor K of the 5-series aluminum alloy sheet is... stab ≥0.77;

[0066] Formula III,

[0067] In Equation III, ω(Zr), ω(Sc), ω(Mn), ω(Cr), and ω(Ti) represent the weight fractions of Zr, Sc, Mn, Cr, and Ti, respectively.

[0068] In this invention, the contents of Zr, Sc, Mn, Cr and Ti meet the specific range required by Formula III. Mn and Cr can significantly increase the volume fraction of the dispersed phase and form a multi-scale interception system with Zr. This ensures that the plate does not undergo complete recrystallization or abnormal grain growth after high-temperature continuous annealing, thus avoiding abnormal strength reduction caused by grain coarsening.

[0069] According to the present invention, the 5-series aluminum alloy sheet has a yield strength of <120MPa, a tensile strength of 190-210MPa, an elongation of >25%, and a strain hardening index n≥0.28.

[0070] A second aspect of the present invention provides a method for preparing the above-mentioned 5-series aluminum alloy sheet with low-temperature baking hardening response, wherein the preparation method includes melting, casting, homogenization, hot rolling, cold rolling, annealing, and cooling;

[0071] The homogenization process includes two stages: the temperature T1 of the first stage is 440-480℃ and the time of the first stage is 8-24h; the temperature T2 of the second stage is 490-510℃ and the time of the second stage is 4-10h.

[0072] The heat treatment adaptation function f in homogenization step It is 19-90;

[0073] Formula IV,

[0074] In Equation IV, ω(Cu), ω(Zn), ω(Fe), and ω(Si) are the weight fractions of Cu, Zn, Fe, and Si, respectively, T1 is the temperature of the first homogenization stage, and T2 is the temperature of the second homogenization stage.

[0075] In this invention, the first homogenization stage is a specific low-temperature, long-duration stage that dissolves and spheroidizes the low-melting-point T and η phases, preventing over-burning. The second homogenization stage is a specific high-temperature, short-duration stage that promotes the dissolution / refinement of the S phase and coarse Al-Fe-Mn-Si phases, placing Cu and Zn elements in a "pre-dissolved" or "easily soluble" state, significantly reducing coarse, undissolved phases, and obtaining a clean and uniform microstructure; the dispersed phases (Al3Zr, Al6Mn, Al...) 12 (FeMn)3Si is uniformly distributed, effectively suppressing grain coarsening.

[0076] In the first stage, Cu has a high diffusion activation energy in 5-series aluminum alloys and is very easy to form low-melting-point eutectics (such as S phase). If directly heated at high temperature, it is easy to cause grain boundary overburning. The role of the temperature T1 in the first stage, which is 440-460℃, is to provide initial kinetic energy to allow Cu atoms to initially diffuse into the matrix (pre-dissolve) without overburning.

[0077] In the second stage, although Zn atoms diffuse relatively quickly, in order to achieve a baking hardening increment ΔYS≥100MPa, the ultimate solid solution state must be reached. The temperature T2 of the second stage, 490-510℃, provides a high-energy driving force to ensure that Zn is completely pushed into the aluminum lattice and promotes the ideal precipitation of the Mn / Zr dispersed phase.

[0078] In this invention, the homogenization process satisfies Formula IV, enabling the aluminum alloy composition, especially high concentrations of Zn and Cu, to be transformed from the as-cast state into a sheet material with a high baking response.

[0079] Impurity elements Fe and Si will form coarse, insoluble intermetallic compounds (such as Al-Fe-Mn-Si phase) with Al, Mn, and Cu. The denominator in Formula IV is the weight fraction of Fe and Si. The more impurities in the alloy, the larger the denominator, satisfying f step The temperature needs to be adjusted accordingly to achieve a uniformity of 19-90°C, forming a dynamic balance between "heat input / impurity sensitivity". Otherwise, solute atoms will be "captured" by the impurity phase, leading to failure of baking and hardening in the later stage.

[0080] According to the present invention, the hot rolling conditions include: a hot-rolled coil thickness of 3.5-5 mm and a coiling temperature of 305-335°C.

[0081] According to the present invention, the cold rolling conditions include: cold rolling the hot-rolled sheet to 0.8-2 mm.

[0082] According to the present invention, the annealing conditions include holding at 500-560°C for 60-120 seconds.

[0083] In this invention, since Cu and Zn elements have been pretreated during the ingot casting stage, the specific short-time annealing of this invention can still partially activate them, resulting in high solute supersaturation.

[0084] Traditional annealing of 5-series aluminum alloys is only to obtain an O-state (soft state) microstructure to facilitate stamping. However, due to the presence of specific amounts of Zn and Cu, the annealing process of this invention essentially serves as a "secondary activation." The annealing process provided by this invention uses high temperature (500-560℃) and extremely short time (60–120 s) thermal activation to completely push the solute atoms that have been "pre-dissolved" during the homogenization stage into the aluminum matrix, and then "locks" them in through rapid cooling. This allows for the retention of extremely high bake hardening potential while maintaining excellent formability.

[0085] Since the solid solubility of Cu and Zn in aluminum increases dramatically with increasing temperature, the high temperature of 500-560℃ can be used to instantly dissolve the fine strengthening phases that may precipitate during cold rolling. The extremely short time (60-120s) ensures that solute atoms can "enter the site" but not "grow". Combined with subsequent specific rapid cooling, a highly supersaturated single-phase solid solution structure can be obtained, so that the present invention provides 5-series aluminum alloy plates with a yield strength ≤120MPa and an elongation ≥25%.

[0086] During the high-temperature continuous annealing stage, the present invention forms a highly thermally stable nano-dispersed phase through the composite addition of Mn / Cr / Zr. These dispersed phases strongly lock grain boundary movement through the "Zener pinning" effect, ensuring that grains do not grow abnormally even at annealing temperatures as high as 560°C, thus maintaining the excellent n-value and forming limit of the plate.

[0087] According to the present invention, the cooling conditions include cooling to 50-70°C at a cooling rate of 450-600°C / min.

[0088] In this invention, specific annealing conditions can maintain the soft structure in the annealed state, so that the 5-series aluminum alloy sheet provided by this invention has high elongation and low yield strength.

[0089] According to the present invention, the smelting conditions include: a smelting temperature of 720-780°C and a smelting time of 2-6 hours.

[0090] Test methods

[0091] The yield strength was measured according to ISO 6892-1 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0092] The tensile strength was measured according to ISO 6892-1 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0093] The elongation was measured according to ISO 6892-1 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0094] The strain hardening index n was measured according to ISO 6892-1 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0095] Baking hardening properties include yield strength increment and final yield strength. Baking hardening properties refer to the properties after 2% pre-stretching, baking in an air-heated furnace at 185°C for 20 minutes, and then stretching. Yield strength increment refers to the increase in yield strength before and after baking. Final yield strength refers to the yield strength after baking hardening. It is measured according to ISO 6892-1 "Metallic materials, tensile testing - Part 1: Tests at room temperature".

[0096] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0097] Example 1

[0098] The components and their weight percentages in 5-series aluminum alloy sheets are as follows: Mg 3.8%, Zn 2.4%, Cu 0.8%, Mn 0.20%, Cr 0.08%, Zr 0.10%, Ti 0.05%, Si 0.08%, Fe 0.15%, La content ≤0.2%, Ce content ≤0.2%, Yb content ≤0.2%, the balance being Al and individual impurities ≤0.03%, and the total content of other impurity elements ≤0.1%. The bake hardening efficiency function Φ BH The solute activation equilibrium index is 0.56. Iact The thermal stability factor K of the dispersed phase is 4.58. stab It is 1.61;

[0099] Melting: Melting temperature 750℃, melting time 5 hours;

[0100] Casting: DC casting, ingot size 500×1500 mm;

[0101] Homogenization: The first stage of homogenization was carried out at 460℃ for 10 hours, and the second stage was carried out at 500℃ for 8 hours. The heat treatment adaptation function was f. step It is 68.17;

[0102] Hot-rolled: 4mm thickness, hot-rolled coiling temperature 315℃;

[0103] Cold rolling: Cold rolling to a sheet thickness of 1mm;

[0104] Annealing: Annealing temperature 540 ℃, holding time 90 s;

[0105] Cooling: Cool to 60°C at a cooling rate of 500°C / min to obtain 5-series aluminum alloy sheet A1.

[0106] Example 2

[0107] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were as follows: Mg 2.5%, Zn 1.5%, Cu 0.3%, Mn 0.1%, Cr 0.03%, Zr 0.05%, Ti 0.01%, Si 0.10%, Fe 0.12%, La content ≤0.2%, Ce content ≤0.2%, Yb content ≤0.2%, and the balance being Al. The bake hardening efficiency function Φ BH The solute activation equilibrium index is 0.20. Iact The thermal stability factor K of the dispersed phase is 3.82. stab The heat treatment adaptation function is 15.27. step The alumina was 40.4, and A2 5-series aluminum alloy sheet was obtained.

[0108] Example 3

[0109] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were as follows: Mg 5.0%, Zn 3.5%, Cu 1.2%, Mn 0.3%, Cr 0.15%, Zr 0.15%, Ti 0.10%, Si 0.20%, Fe 0.25%, La content ≤0.2%, Ce content ≤0.2%, Yb content ≤0.2%, and the balance being Al. The bake hardening efficiency function Φ BH The solute activation equilibrium index is 0.95. Iact The thermal stability factor K of the dispersed phase is 2.62. stab The heat treatment adaptation function is 2.5. step The value is 51.16, and A3 5-series aluminum alloy sheet is obtained.

[0110] Example 4

[0111] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 3.25%, Zn 1.5%, Cu 0.3%, and the bake hardening efficiency function Φ was used. BH With a value of 0.15, A4 5-series aluminum alloy sheet was obtained.

[0112] Example 5

[0113] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 3.5%, Zn 3.0%, Cu 1.20%, and the bake hardening efficiency function Φ was used. BH With a value of 1.2, A5 5-series aluminum alloy sheet was obtained.

[0114] Example 6

[0115] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 5.0%, Zn 1.8%, Cu 0.45%, Si 0.20%, Fe 0.25%, and solute activation equilibrium index I. act With a value of 1.2, A6 5-series aluminum alloy sheet was obtained.

[0116] Example 7

[0117] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 2.5%, Zn 2.4%, Cu 0.8%, Si 0.08%, Fe 0.08%, and solute activation equilibrium index I. act The value is 10, and A7 5-series aluminum alloy sheet is obtained.

[0118] Example 8

[0119] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Zr 0.05%, Mn 0.10%, Cr 0.03%, Ti 0.01%, and the dispersed phase thermal stability factor K. stab With a value of 0.77, A8 5-series aluminum alloy sheet was obtained.

[0120] Example 9

[0121] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Cu 0.3%, Zn 1.5%, Fe 0.25%, Si 0.20%, and the heat treatment adaptability function f. step The value is 19.7, and A9 5-series aluminum alloy sheet is obtained.

[0122] Example 10

[0123] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 5%, Cu 1.2%, Zn 3.5%, Fe 0.25%, Si 0.11%, and the heat treatment adaptability function f. stepThe alumina content was 88.5, and A10 5-series aluminum alloy sheet was obtained.

[0124] Example 11

[0125] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the homogenization first stage was carried out at 440°C for 8 hours, and the second stage was carried out at 490°C for 4 hours, with the heat treatment adaptability function f. step The value is 66.4, and 5-series aluminum alloy sheet A11 is obtained.

[0126] Example 12

[0127] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the homogenization first stage was carried out at 480°C for 24 hours, and the second stage was carried out at 510°C for 10 hours, with the heat treatment adaptation function f. step The value is 69.9, and A12 5-series aluminum alloy sheet is obtained.

[0128] Example 13

[0129] A 5-series aluminum alloy sheet was prepared according to the preparation method of Example 1, except that the annealing temperature was 500 ℃ and the holding time was 60 s, and the A13 5-series aluminum alloy sheet was obtained.

[0130] Example 14

[0131] A 5-series aluminum alloy sheet was prepared according to the preparation method of Example 1, except that the annealing temperature was 560 ℃ and the holding time was 120 s, and the A14 5-series aluminum alloy sheet was obtained.

[0132] Comparative Example 1

[0133] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were as follows: Mg 2.4%, Zn 1.4%, Cu 0.1%, Mn 0.05%, Cr 0.02%, Zr 0.04%, Ti 0.005%, Si 0.12%, Fe 0.15%, La content ≤0.2%, Ce content ≤0.2%, Yb content ≤0.2%, and the balance being Al. The bake hardening efficiency function Φ BH The solute activation equilibrium index is 0.06. Iact The thermal stability factor K of the dispersed phase is 2.47. stab The heat treatment adaptation function f is 0.55. step The value is 27.6, and DA1 5-series aluminum alloy sheet is obtained.

[0134] Comparative Example 2

[0135] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were as follows: Mg 6.0%, Zn 3.6%, Cu 1.5%, Mn 0.4%, Cr 0.16%, Zr 0.17%, Ti 0.20%, Si 0.20%, Fe 0.25%, La content ≤0.2%, Ce content ≤0.2%, Yb content ≤0.2%, and the balance being Al. The bake hardening efficiency function Φ BH The solute activation equilibrium index is 1.0. Iact The thermal stability factor K of the dispersed phase is 2.44. stab The heat treatment adaptation function is 3.02. step The value was 55.3, and DA2 5-series aluminum alloy sheet was obtained.

[0136] Comparative Example 3

[0137] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 5.0%, Zn 1.5%, Cu 0.3%, and the bake hardening efficiency function Φ was used. BH With a value of 0.095, DA3 5-series aluminum alloy sheet was obtained.

[0138] Comparative Example 4

[0139] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 2.5%, Zn 3.5%, Cu 1.2%, and the bake hardening efficiency function Φ was used. BH The value is 2.19, and DA4 5-series aluminum alloy sheet is obtained.

[0140] Comparative Example 5

[0141] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 5.0%, Zn 2.1%, Cu 0.45%, Si 0.25%, Fe 0.35%, and solute activation equilibrium index I. act The value was 1.0, and DA5 5-series aluminum alloy sheet was obtained.

[0142] Comparative Example 6

[0143] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Mg 2.5%, Zn 2.4%, Cu 0.8%, Si 0.06%, Fe 0.06%, and solute activation equilibrium index I. act The value is 13.3, and DA6 5-series aluminum alloy sheet is obtained.

[0144] Comparative Example 7

[0145] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Zr 0.02%, Sc 0%, Mn 0.05%, Cr 0.01%, Ti 0.01%, and the dispersed phase thermal stability factor K. stab With a value of 0.32, DA7 5-series aluminum alloy sheet was obtained.

[0146] Comparative Example 8

[0147] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Cu 0.3%, Zn 1.5%, Fe 0.3%, Si 0.25%, and the heat treatment adaptability function f. step The value is 15.8, and DA8 5-series aluminum alloy sheet is obtained.

[0148] Comparative Example 9

[0149] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the components and their weight percentages in the 5-series aluminum alloy sheets were: Cu 1.2%, Zn 3.5%, Fe 0.13%, Si 0.12%, and the heat treatment adaptability function f. step The alumina content was 93.5, and DA9 5-series aluminum alloy sheet was obtained.

[0150] Comparative Example 10

[0151] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the homogenization first stage was carried out at 400°C for 7 hours, and the second stage was carried out at 450°C for 3 hours, with the heat treatment adaptability function f. step The value is 60.9, and DA10 5-series aluminum alloy sheet is obtained.

[0152] Comparative Example 11

[0153] 5-series aluminum alloy sheets were prepared according to the preparation method of Example 1, except that the homogenization first stage was carried out at 490°C for 25 hours, and the second stage was carried out at 520°C for 11 hours, with the heat treatment adaptation function f. step The value is 71.3, and DA11 5-series aluminum alloy sheet is obtained.

[0154] Comparative Example 12

[0155] The 5-series aluminum alloy sheet was prepared according to the preparation method of Example 1, except that the annealing temperature was 490 ℃ and the holding time was 50s, and the 5-series aluminum alloy sheet DA12 was obtained.

[0156] Comparative Example 13

[0157] The 5-series aluminum alloy sheet was prepared according to the preparation method of Example 1, except that the annealing temperature was 570 ℃ and the holding time was 140 s, and the 5-series aluminum alloy sheet DA13 was obtained.

[0158] Table 1

[0159]

[0160]

[0161] By comparing the examples and comparative examples, it can be seen that the 5-series aluminum alloys prepared in Examples 1-14 have low yield strength, high elongation, guaranteed paint hardening, high formability and high dent resistance.

[0162] This invention, by employing specific homogenization methods, combined with other optimization methods and specific alloy ratios, satisfies Formulas I to IV, and can produce 5-series aluminum alloys that combine low yield strength, high elongation, guaranteed paint hardening, high formability, and high dent resistance.

[0163] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A 5-series aluminum alloy sheet with low-temperature bake hardening response, characterized in that, The components and their weight percentages in the 5-series aluminum alloy sheet are as follows: The Mg content is 2.5-5.0%; The Zn content is 1.5-3.5%; The Cu content is 0.3-1.2%; The Mn content is 0.1-0.3%; The Cr content is 0.03-0.15%; The Zr content is 0.05-0.15%; The Ti content is 0.01-0.10%; Si content ≤ 0.2%; Fe content ≤ 0.25%; La content ≤ 0.2%; Ce content ≤0.2%; Yb content ≤ 0.2%; The content of a single impurity is ≤0.03%; The total content of other impurity elements is ≤0.1%; The balance is Al; wherein the bake hardening response efficiency function Φ of the 5-series aluminum alloy sheet is BH 0.15-1.2; Equation I, In Formula I, ω(Zn), ω(Cu), ω(Mg), and ω(Zn / 6) represent the weight fractions of Zn, Cu, Mg, and one-sixth of the Zn content, respectively.

2. The 5-series aluminum alloy sheet with low-temperature baking hardening response according to claim 1, characterized in that, The solute activation equilibrium index I of the 5-series aluminum alloy sheet act It is 1.2-10; Formula II, In Formula II, ω(Zn), ω(Cu), ω(Mg), ω(Fe), and ω(Si) represent the weight fractions of Zn, Cu, Mg, Fe, and Si, respectively.

3. The 5-series aluminum alloy sheet with low-temperature baking hardening response according to claim 1, characterized in that, The dispersed phase thermal stability factor K of the 5-series aluminum alloy sheet stab ≥0.77; Formula III, In Equation III, ω(Zr), ω(Sc), ω(Mn), ω(Cr), and ω(Ti) represent the weight fractions of Zr, Sc, Mn, Cr, and Ti, respectively.

4. The 5-series aluminum alloy sheet with low-temperature baking hardening response according to claim 1, characterized in that, The 5-series aluminum alloy sheet has a yield strength of <120MPa, a tensile strength of 190-210MPa, an elongation of >25%, and a strain hardening index n≥0.

28.

5. A method for preparing a 5-series aluminum alloy sheet with a low-temperature bake-hardening response as described in any one of claims 1-4, characterized in that, The preparation method includes smelting, casting, homogenization, hot rolling, cold rolling, annealing, and cooling; The homogenization process includes two stages: the temperature T1 of the first stage is 440-480℃ and the time of the first stage is 8-24h; the temperature T2 of the second stage is 490-510℃ and the time of the second stage is 4-10h. The heat treatment adaptation function f in homogenization step It is 19-90; Formula IV, In Equation IV, ω(Cu), ω(Zn), ω(Fe), and ω(Si) are the weight fractions of Cu, Zn, Fe, and Si, respectively, T1 is the temperature of the first homogenization stage, and T2 is the temperature of the second homogenization stage.

6. The method for preparing 5-series aluminum alloy sheet with low-temperature bake hardening response according to claim 5, characterized in that, The hot rolling conditions include: a hot-rolled coil thickness of 3.5-5 mm and a coiling temperature of 305-335℃.

7. The method for preparing 5-series aluminum alloy sheet with low-temperature bake hardening response according to claim 5, characterized in that, The conditions for cold rolling include: cold rolling the hot-rolled sheet to 0.8-2 mm.

8. The method for preparing 5-series aluminum alloy sheet with low-temperature bake hardening response according to claim 5, characterized in that, The annealing conditions include holding at 500-560°C for 60-120 seconds.

9. The method for preparing a 5-series aluminum alloy sheet with low-temperature bake hardening response according to claim 5, characterized in that, The cooling conditions include cooling to 50-70°C at a cooling rate of 450-600°C / min.

10. The method for preparing a 5-series aluminum alloy sheet with low-temperature bake-hardening response according to claim 5, characterized in that, The smelting conditions include: a smelting temperature of 720-780℃ and a smelting time of 2-6 hours.

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