The invention relates to an Al-Mg-Si series alloy and a preparation method thereof. The preparation method comprises the following steps: beta Carrying out apos; phase aluminum alloy and aluminum alloy sheet for automobile

Abstract

The invention relates to the technical field of aluminum alloy materials, in particular to an Al-Mg-Si alloy and a preparation method thereof, a beta ''-phase aluminum alloy and an aluminum alloy plate for an automobile. The Al-Mg-Si series alloy disclosed by the invention is prepared from the following chemical components in percentage by mass: 0.4 percent to 0.7 percent of Si, 0.5 percent to 0.6 percent of Fe, 0.1 percent to 0.25 percent of Cu, 0.4 percent to 0.8 percent of Mn, 0.5 percent to 0.8 percent of Mg, 0 to 0.3 percent of Zn, 0 to 0.2 percent of Ti, 0 to 0.15 percent of Cr, 0.05 percent to 0.2 percent of V, 0.05 percent to 0.2 percent of Mo and 94 percent to 98 percent of Al. The yield strength of the Al-Mg-Si alloy subjected to baking hardening treatment at 170-200 DEG C is greater than or equal to 200MPa; and the yield strength of the Al-Mg-Si alloy which is not subjected to baking hardening treatment at 170-200 DEG C is less than or equal to 130 MPa. According to the Al-Mg-Si alloy provided by the invention, impurity elements such as Fe and Mn can be utilized, so that recycling of the aluminum alloy with high impurity content is realized; and the initial yield strength is low, the yield strength is high after baking hardening treatment, and the stamping forming performance and the baking performance are good.

Description

Technical Field

[0001] The present application relates to the technical field of aluminum alloy materials, and in particular to Al-Mg-Si alloys and preparation methods thereof, β'' phase aluminum alloys, and aluminum alloy sheets for automobiles. Background Art

[0002] Al-Mg-Si alloys (also known as 6XXX series aluminum alloys or 6000 series aluminum alloys) have excellent formability and corrosion resistance, and they can further precipitate Mg-Si phase (β'' phase) through bake hardening to improve strength, so they are widely used in sheet materials such as automobile body panels and structural parts. Among them, Al-Mg-Si alloys used in sheet materials such as automobile body panels and structural parts must meet the following requirements: (1) the yield strength before bake hardening needs to be low, which is conducive to the subsequent stamping forming of Al-Mg-Si alloys; (2) the yield strength of Al-Mg-Si alloys after bake hardening needs to be high, which can meet the use requirements such as anti-dentation of automobile sheets. That is, Al-Mg-Si alloys used in sheet materials such as automobile body panels and structural parts must have both good stamping and baking properties.

[0003] Al-Mg-Si alloys primarily include virgin aluminum alloys and recycled aluminum alloys. Virgin aluminum alloys are products formed by smelting and preparing raw aluminum as the primary raw material, while recycled aluminum alloys are those formed by smelting and preparing scrap aluminum. Compared to virgin aluminum alloys, recycled aluminum alloys can reduce resource consumption and environmental impact through recycling, thus meeting the needs of green manufacturing. However, the scrap aluminum used to prepare recycled aluminum alloys, due to its repeated recycling, contains high levels of impurities (such as Fe and Mn). In particular, Fe (typically >0.5 wt.%) can form coarse Al-Fe-Si-Mn intermetallic compounds (such as α-AlFeSi or β-AlFeSi phases), which severely impair the precipitation of β' phase in Al-Mg-Si alloys and, consequently, their bake-hardenability. Simply increasing the content of alloying elements such as Mg and Si, which contribute to bake-hardenability, will increase the initial yield strength of Al-Mg-Si alloys, which in turn will negatively impact the stamping performance of the Al-Mg-Si alloy sheets after delivery. Summary of the Invention

[0004] Based on this, the present application provides an Al-Mg-Si alloy and its preparation method, a β'' phase aluminum alloy, and an aluminum alloy sheet for automobiles. The Al-Mg-Si alloy provided herein can utilize impurity elements such as Fe and Mn to recycle high-impurity aluminum alloys. It also has a low initial yield strength and a high yield strength after bake hardening, combining good stamping and baking properties.

[0005] In a first aspect of the present application, an Al-Mg-Si alloy is provided, wherein the chemical composition of the Al-Mg-Si alloy comprises, by mass percentage, 0.4% to 0.7% Si, 0.5% to 0.6% Fe, 0.1% to 0.25% Cu, 0.4% to 0.8% Mn, 0.5% to 0.8% Mg, 0 to 0.3% Zn, 0 to 0.2% Ti, 0 to 0.15% Cr, 0.05% to 0.2% V, 0.05% to 0.2% Mo, and 94% to 98% Al;

[0006] The yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C is ≥200MPa;

[0007] The yield strength of the Al-Mg-Si alloy before being subjected to a bake hardening treatment at 170° C. to 200° C. is ≤130 MPa.

[0008] In one embodiment, the chemical composition of the Al-Mg-Si alloy includes: 0.4%-0.7% Si, 0.5%-0.6% Fe, 0.1%-0.25% Cu, 0.4%-0.8% Mn, 0.5%-0.8% Mg, 0-0.3% Zn, 0-0.2% Ti, 0-0.15% Cr, 0.05%-0.1% V, 0.05%-0.1% Mo, and 96%-98% Al;

[0009] Among them, the ratio of the mass percentage of Mg to the mass percentage of Si is (1~1.6):1;

[0010] The ratio of the mass percentage of V to the mass percentage of Mo is (1~2):1.

[0011] In one embodiment, the yield strength of the Al-Mg-Si alloy after bake hardening at 170° C. to 200° C. is 204 MPa to 235 MPa.

[0012] In one embodiment, the yield strength of the Al-Mg-Si alloy before bake hardening at 170° C. to 200° C. is 96 MPa to 130 MPa.

[0013] In one embodiment, the yield strength of the Al-Mg-Si alloy after the bake hardening treatment at 170°C to 200°C is increased by 75 MPa to 120 MPa compared to the yield strength of the Al-Mg-Si alloy before the bake hardening treatment at 170°C to 200°C.

[0014] In one embodiment, the Al-Mg-Si alloy has a dispersed phase.

[0015] A second aspect of the present application provides a method for preparing the Al-Mg-Si alloy according to any one of the embodiments of the first aspect of the present application, comprising the following steps:

[0016] According to the chemical composition of the Al-Mg-Si alloy, the materials are prepared, and after melting and refining, an ingot is prepared;

[0017] The Al-Mg-Si alloy is prepared by subjecting the ingot to homogenization treatment, rolling treatment, solution treatment and pre-aging treatment.

[0018] In one embodiment, the homogenization step includes:

[0019] The ingot is subjected to a first-stage homogenization treatment at 260°C to 280°C, heated to 360°C to 390°C at a heating rate of 20°C / h to 40°C / h, and then subjected to a second-stage homogenization treatment. The ingot is subjected to a third-stage homogenization treatment after being heated to 540°C to 580°C at a heating rate of 20°C / h to 40°C / h.

[0020] In one embodiment, the rolling treatment step includes: hot rolling and cold rolling the intermediate after homogenization treatment in sequence; wherein the hot rolling step includes: a starting rolling temperature of 500°C to 520°C, a finishing rolling temperature ≥ 350°C, and a thickness of the intermediate after hot rolling of 5mm to 8mm; the process parameters of the cold rolling include: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after cold rolling of 0.8mm to 1.2mm;

[0021] The pre-aging treatment step comprises: holding the intermediate after the solution treatment at 100°C to 115°C for 3 minutes to 10 minutes, and then cooling the intermediate to 25°C to 35°C at a cooling rate of 0.5°C / h to 1.8°C / h; wherein the interval time between the end of the solution treatment and the start of the pre-aging treatment is ≤ 10 minutes;

[0022] Alternatively, the pre-aging treatment step includes: keeping the intermediate after the solution treatment at 120°C~135°C for 3min~10min, and then cooling it to 25°C~35°C at a cooling rate of 1.5°C / h~2.5°C / h; wherein the interval time between the end of the solution treatment and the start of the pre-aging treatment is ≤10min.

[0023] In another embodiment, the rolling treatment step includes: sequentially hot rolling, first cold rolling, annealing, and second cold rolling the intermediate after homogenization treatment; the process parameters of the hot rolling include: a starting rolling temperature of 500°C to 520°C, a finishing rolling temperature ≥350°C, and a thickness of the intermediate after hot rolling of 5mm to 8mm; the process parameters of the first cold rolling meet: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after the first cold rolling of 2mm to 3.5mm; the process parameters of the annealing include: heating to 450°C to 470°C at a heating rate of 12°C / min to 23°C / min; the process parameters of the second cold rolling include: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after the second cold rolling of 0.98mm to 1.05mm;

[0024] The pre-aging treatment step includes: keeping the intermediate after solution treatment at 115°C~125°C for 3min~10min, and then cooling it to 25°C~35°C at a cooling rate of 0.9°C / h~1.8°C / h; wherein the interval time between the end of solution treatment and the start of pre-aging treatment is ≤10min.

[0025] In one embodiment, the step of solution treatment comprises:

[0026] The rolled intermediate is heated to 550°C~570°C at a heating rate of 3°C / s~10°C / s, kept at this temperature for 2min~8min, and then cooled to room temperature at a quenching rate of ≥400°C / s.

[0027] In a third aspect of the present application, a β'' phase aluminum alloy is provided, wherein the β'' phase aluminum alloy is obtained by baking and hardening the Al-Mg-Si alloy according to any one of the first aspects of the present application;

[0028] The baking hardening temperature is 170℃~200℃.

[0029] The fourth aspect of the present application provides an aluminum alloy plate for automobiles, which is obtained by baking and hardening the Al-Mg-Si alloy described in the first aspect of the present application; or includes the β'' phase aluminum alloy described in the third aspect of the present application.

[0030] The Al-Mg-Si alloy provided in this application has at least the following beneficial effects:

[0031] The Al-Mg-Si alloy provided in the present application can improve the morphology of the iron-rich phase and inhibit the formation of α-AlFeSi or β-AlFeSi phases by rationally matching the chemical components and chemical component ratios, thereby effectively utilizing impurity elements such as Fe and Mn in scrap aluminum, thereby reducing production costs and improving the resource utilization rate of scrap aluminum, and ensuring the bake hardening performance of the Al-Mg-Si alloy.

[0032] Furthermore, the Al-Mg-Si alloy provided in the present application can have a yield strength of ≤130MPa before the bake hardening treatment at 170℃~200℃, which is beneficial to the subsequent stamping and forming of the Al-Mg-Si alloy. And the Al-Mg-Si alloy can have a yield strength of ≥200MPa after the bake hardening treatment at 170℃~200℃, which can meet the use requirements such as the dent resistance of automotive sheet materials. Therefore, the Al-Mg-Si alloy provided in the present application can utilize impurity elements such as Fe and Mn to achieve the recycling of aluminum alloys with high impurity content; it has both good stamping and baking properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 1. A comparison diagram of engineering stress-strain curves of Al-Mg-Si alloys before and after bake hardening in Example 1 and Comparative Examples 1-1 to 1-3 of the present application;

[0035] Figure 2 2-1 of the present application, the engineering stress-strain curve comparison diagram of the Al-Mg-Si alloy before and after bake hardening;

[0036] Figure 3 This is a bending performance diagram of the Al-Mg-Si alloy of Example 2-1 of the present application before bake hardening;

[0037] Figure 4 A line graph showing the aging stability of the Al-Mg-Si alloys of Example 2-2, Comparative Example 2-1, and Comparative Example 3-1 of the present application before bake hardening;

[0038] Figure 5 This is a comparison diagram of the engineering stress-strain curves of the Al-Mg-Si alloy of Example 3-1 of the present application before and after bake hardening;

[0039] Figure 6 This is a diagram showing the bending performance of the Al-Mg-Si alloy of Example 3-1 of the present application before bake hardening. DETAILED DESCRIPTION

[0040] The following, in conjunction with specific examples, provides a further, more complete and clear description of the Al-Mg-Si alloy and its preparation method, β″ phase aluminum alloy, and automotive aluminum alloy sheet of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to facilitate a more thorough and comprehensive understanding of the disclosure.

[0041] It should be understood that the terms used in this application are intended only to describe specific embodiments and are not intended to limit this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are intended only to describe specific embodiments and are not intended to limit this application.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art described in this application. Although this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0043] As used herein, "one or more" refers to any one, any two, or any two or more of the listed items.

[0044] In this application, terms such as "first aspect," "second aspect," "third aspect," "fourth aspect," and "fifth aspect" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," "fourth," and "fifth" serve only as non-exhaustive enumeration and description, and should not constitute a closed-ended limitation on quantity.

[0045] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0046] In addition, for numerical ranges in this application, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range and any other stated value or intervening value in the stated range is also included in this application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0047] Unless otherwise specified, the percentage contents mentioned in this application refer to mass percentage for solid-liquid mixture and solid-solid mixture, and refer to volume percentage for liquid-liquid mixture.

[0048] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0049] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

[0050] Al-Mg-Si alloys used in automotive body panels and structural parts require a low yield strength before bake hardening to ensure good workability during subsequent stamping. They also need a high yield strength after bake hardening to meet the strength requirements of automotive sheet metal for applications such as dent resistance.

[0051] The high content of impurity elements in scrap aluminum negatively impacts its bake-hardening properties in multiple ways. First, impurities interfere with the formation of key strengthening phases. Coarse second-phase particles hinder the diffusion of Mg / Si atoms, directly inhibiting the normal precipitation of β' phase. Fe impurities promote heterogeneous nucleation, leading to a disordered distribution of precipitated phases. Second, impurity elements degrade the alloy's microstructure and mechanical properties. Mn segregation at grain boundaries exacerbates brittleness and reduces alloy plasticity. In Al-Mg-Si alloys containing Mn, the peak time of β' phase precipitation is significantly delayed, and the bake hardening rate is significantly reduced. Furthermore, impurities consume available solute atoms. Fe preferentially combines with Si, reducing the free Si content and weakening the driving force for the formation of Mg-Si precipitates. Finally, impurities hinder the recrystallization process. During hot working, coarse second-phase particles hinder dislocation movement and grain boundary migration, resulting in incomplete dynamic recrystallization. The residual deformed microstructure significantly reduces the alloy's aging potential. It is worth noting that there is a synergistic effect between Fe and Mn elements. The two will jointly promote the coarsening of the second phase particles, forming a larger and more densely distributed Al-Fe-Mn-Si phase, which seriously destroys the continuity of the matrix and further reduces the baking performance of the alloy.

[0052] Therefore, it is crucial to achieve the recycling of aluminum alloys with high impurity content and to ensure that they have both good stamping and baking properties.

[0053] Based on this, a first aspect of the present application provides an Al-Mg-Si alloy, wherein the chemical composition of the Al-Mg-Si alloy includes, by mass percentage, 0.4%-0.7% Si, 0.5%-0.6% Fe, 0.1%-0.25% Cu, 0.4%-0.8% Mn, 0.5%-0.8% Mg, 0-0.3% Zn, 0-0.2% Ti, 0-0.15% Cr, 0.05%-0.2% V, 0.05%-0.2% Mo, and 94%-98% Al;

[0054] The yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C is ≥200MPa;

[0055] The yield strength of the Al-Mg-Si alloy before being subjected to a bake hardening treatment at 170° C. to 200° C. is ≤130 MPa.

[0056] It can be understood that the bake hardening temperature of 170°C to 200°C corresponds to the precipitation temperature of the β" phase. In the present application, the mass percentage of Si can be selected from any value between 0.4% and 0.7%. For example, the mass percentage of Si is but not limited to 0.4%, 0.5%, 0.53%, 0.55%, 0.56%, 0.57%, 0.6%, 0.65% or 0.7%, or within the range consisting of any two of the above point values ​​as endpoint values. In Al-Mg-Si alloys, Si is a key solute element, which can form M The g-Si precipitate phase (such as β' phase) improves the yield strength after bake hardening. At the same time, controlling its content within a reasonable range can avoid excessive work hardening rate caused by excess Si, thereby taking into account both stamping and baking properties. To prevent excessive Fe from forming coarse Al-Fe-Si phases that hinder the diffusion of Mg / Si atoms, the mass percentage of Fe includes but is not limited to 0.5%, 0.52%, 0.53%, 0.54%, 0.55%, 0.57%, 0.58% or 0.6%, or a range consisting of any two of the above points as endpoints.

[0057] The mass percentage of Cu includes, but is not limited to, 0.1%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24% or 0.25%, or a range formed by any two of the above values ​​as endpoints. 0.1% to 0.25% Cu can improve the matrix strength through solid solution strengthening, and synergistically promote the uniform distribution of the precipitate phase with Mg / Si, thereby enhancing the bake hardening effect without significantly reducing the plasticity of stamping. The mass percentage of Mn includes, but is not limited to, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.66%, 0.67%, 0.68%, 0.7%, 0.75% or 0.8%, or a range formed by any two of the above values ​​as endpoints. Mn can inhibit the growth of recrystallized grains by forming a dispersed Al-Mn-Si phase, thereby improving the precipitation kinetics of the β' phase during baking. The mass percentage of Mg includes, but is not limited to, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.72%, 0.73%, 0.74%, 0.75%, 0.78%, or 0.8%, or any two of the above values ​​as endpoints. Mg, as a key alloying element, forms a Mg-Si precipitate phase with Si, which dominates the bake hardening effect. At the same time, its solid solution strengthening effect, within a reasonable content range, can balance the work hardening ability during stamping and the improved strength after baking.

[0058] The mass percentage of Zn includes, but is not limited to, 0%, 0.01%, 0.03%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%, or any two of the above values ​​as endpoints. The mass percentage of Ti includes, but is not limited to, 0%, 0.01%, 0.02%, 0.03%, 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, 0.18%, or 0.2%, or any two of the above values ​​as endpoints. The mass percentage of Cr includes, but is not limited to, 0%, 0.05%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, or 0.15%, or any two of the above values ​​as endpoints. 0~0.3% Zn can assist in strengthening the matrix and optimize the distribution of precipitated phases. 0~0.2% Ti inhibits the growth of recrystallized grains by forming Al3Ti dispersed phase to retain deformation energy storage. 0~0.15% Cr and Mn synergistically form a stable Al-Cr-Mn-Si phase to refine the grains. The three act within a low content range and can provide favorable conditions for precipitation strengthening during baking by regulating the microstructure without significantly affecting the plasticity of stamping.

[0059] The mass percentage of V includes but is not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18% or 0.2%, or any two of the above point values ​​are used as endpoint values. The mass percentage of Mo includes but is not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18% or 0.2%, or any two of the above point values ​​are used as endpoint values. The present application uses V and Mo in combination, which can make the primary large-sized iron-rich phase obtain a certain degree of rounding or refinement, thereby promoting the formation of more initial α-AlFeSi or α-AlFeMnVCrSi and other secondary phases, so as to reduce the consumption of Si by impurity elements Fe, Mn, etc., so as to ensure the baking performance of Al-Mg-Si alloy.

[0060] The mass percentage of Al includes but is not limited to 94%, 94.5%, 95%, 96%, 97%, 97.1%, 97.12%, 97.13%, 97.14%, 97.15%, 97.16%, 97.2%, 97.5% or 98%, or within the range consisting of any two of the above endpoints.

[0061] The Al-Mg-Si alloy provided in the present application can improve the morphology of the iron-rich phase, inhibit the formation of α-AlFeSi or β-AlFeSi phase, and facilitate the precipitation of β'' phase by rationally matching the chemical components and chemical component ratios, thereby effectively utilizing impurity elements such as Fe and Mn in scrap aluminum, thereby reducing production costs and improving the resource utilization rate of scrap aluminum, and ensuring the bake hardening performance of the Al-Mg-Si alloy.

[0062] Furthermore, the Al-Mg-Si alloy provided in the present application can have a yield strength of ≤130MPa before the bake hardening treatment at 170℃~200℃, which is beneficial to the subsequent stamping and forming of the Al-Mg-Si alloy. And the Al-Mg-Si alloy can have a yield strength of ≥200MPa after the bake hardening treatment at 170℃~200℃, which can meet the use requirements such as the dent resistance of automotive sheet materials. Therefore, the Al-Mg-Si alloy provided in the present application can utilize impurity elements such as Fe and Mn to achieve the recycling of aluminum alloys with high impurity content; it has both good stamping and baking properties.

[0063] In some examples, the chemical composition of the Al-Mg-Si alloy includes: 0.4%-0.7% Si, 0.5%-0.6% Fe, 0.1%-0.25% Cu, 0.4%-0.8% Mn, 0.5%-0.8% Mg, 0-0.3% Zn, 0-0.2% Ti, 0-0.15% Cr, 0.05%-0.1% V, 0.05%-0.1% Mo, and 96%-98% Al.

[0064] The ratio of the mass percentage of Mg to the mass percentage of Si is (1-1.6):1. The ratio of the mass percentage of Mg to the mass percentage of Si includes but is not limited to 1:1, 1.1:1, 1.2:1, 1.25:1, 1.28:1, 1.29:1, 1.3:1, 1.31:1, 1.32:1, 1.35:1, 1.4:1, 1.5:1, or 1.6:1, or a range formed by any two of the above points as endpoints. The ratio of the mass percentage of Mg to the mass percentage of Si is within the above range, which can ensure that the effective Si content does not exceed the maximum content maintained at the maximum yield strength that causes stamping difficulties, and is not lower than the minimum content at which the minimum baking strength cannot be obtained after being consumed by impurities.

[0065] The ratio of V to Mo by mass is (1-2):1. For example, the ratio includes, but is not limited to, 1:1, 1.1:1, 1.2:1, 1.2:1, 1.5:1, 1.8:1, or 2:1, or a range consisting of any two of the aforementioned endpoints. Adding V to Mo in a ratio of (1-2):1 allows for a certain degree of rounding or refinement of the primary, large-scale, iron-rich phase, thereby promoting the formation of more secondary phases such as initial α-AlFeSi or α-AlFeMnVCrSi, thereby reducing Si consumption by impurity elements and providing a foundation for subsequent baking performance.

[0066] In some examples, the yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C is 204MPa to 235MPa. For example, the yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C includes but is not limited to 204MPa, 205MPa, 208MPa, 210MPa, 215MPa, 220MPa, 225MPa, 230MPa or 235MPa, or a range consisting of any two of the above point values ​​as endpoint values. The yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C reaches 204MPa to 235MPa, which can give the component higher service strength and deformation resistance through aging strengthening while retaining good stamping formability.

[0067] In some examples, the yield strength of the Al-Mg-Si alloy before bake hardening treatment at 170°C to 200°C is 96MPa to 130MPa. For example, the yield strength of the Al-Mg-Si alloy before bake hardening treatment at 170°C to 200°C includes but is not limited to 96MPa, 98MPa, 100MPa, 108MPa, 110MPa, 115MPa, 118MPa, 120MPa, 125MPa or 130MPa, or a range consisting of any two of the above point values ​​as endpoint values. The Al-Mg-Si alloy has a yield strength of 96MPa to 130MPa before bake hardening treatment, and has excellent stamping plasticity, which facilitates its processing and is not easy to crack.

[0068] In some examples, the yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C increased by 75MPa to 120MPa compared to the yield strength of the Al-Mg-Si alloy before bake hardening at 170°C to 200°C. The yield strength increase of 75MPa to 120MPa after bake hardening can be achieved through a step-by-step "machining-aging hardening" process, achieving performance matching from easy formability to high strength in components, meeting the dual requirements of material formability and load-bearing capacity for lightweighting in automobiles. For example, the yield strength of the Al-Mg-Si alloy after bake hardening treatment at 170°C~200°C compared to the yield strength of the Al-Mg-Si alloy without bake hardening treatment at 170°C~200°C includes but is not limited to 75MPa, 80MPa, 85MPa, 90MPa, 95MPa, 100MPa, 105MPa, 110MPa, 115MPa or 120MPa, or in a range consisting of any two of the above point values ​​as endpoint values.

[0069] In some examples, the Al-Mg-Si alloy has a dispersed phase. The Al-Mg-Si alloy provided herein, through the synergistic combination of various chemical components, can improve the morphology of the initial iron-rich phase and optimize and regulate the distribution and grain morphology of the dispersed phase. Furthermore, the dispersed phase in the Al-Mg-Si alloy stabilizes the microstructure during hot working and bake hardening, ensuring the material's formability and aging-strengthening effects.

[0070] A second aspect of the present application provides a method for preparing the Al-Mg-Si alloy according to any one of the embodiments of the first aspect of the present application, comprising the following steps:

[0071] S10: preparing the Al-Mg-Si alloy according to its chemical composition, melting and refining the alloy, and then producing an ingot.

[0072] S20: preparing the Al-Mg-Si alloy by subjecting the ingot to homogenization treatment, rolling treatment, solution treatment and pre-aging treatment.

[0073] In some examples, in step S20, the homogenization step includes:

[0074] The ingot is subjected to a first-stage homogenization treatment at 260°C to 280°C, heated to 360°C to 390°C at a heating rate of 20°C / h to 40°C / h, and then subjected to a second-stage homogenization treatment. The ingot is subjected to a third-stage homogenization treatment after being heated to 540°C to 580°C at a heating rate of 20°C / h to 40°C / h.

[0075] Furthermore, the first level homogenization treatment takes 1 to 3 hours, the second level homogenization treatment takes 1 to 3 hours, and the third level homogenization treatment takes 6 to 10 hours.

[0076] The temperature of the first homogenization treatment includes, but is not limited to, 260°C, 265°C, 270°C, 273°C, 274°C, 275°C, 276°C, 278°C, or 280°C. The time of the first homogenization treatment includes, but is not limited to, 1 hour, 1.3 hours, 1.5 hours, 1.8 hours, 2 hours, 2.1 hours, 2.3 hours, 2.5 hours, 2.8 hours, or 3 hours. The heating rate includes, but is not limited to, 20°C / h, 22°C / h, 24°C / h, 25°C / h, 28°C / h, 29°C / h, 30°C / h, 31°C / h, 32°C / h, 35°C / h, 38°C / h, or 40°C / h. The temperature of the second homogenization treatment includes, but is not limited to, 360°C, 370°C, 373°C, 374°C, 375°C, 376°C, 380°C, 385°C, or 390°C. The duration of the second homogenization treatment includes, but is not limited to, 1 hour, 1.3 hours, 1.5 hours, 1.8 hours, 2 hours, 2.1 hours, 2.3 hours, 2.5 hours, 2.8 hours, or 3 hours. The temperature of the third homogenization treatment includes, but is not limited to, 540°C, 545°C, 550°C, 555°C, 558°C, 560°C, 562°C, 565°C, 570°C, 575°C, or 580°C. The duration of the third homogenization treatment includes, but is not limited to, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 7.8 hours, 8 hours, 8.2 hours, 8.5 hours, 9 hours, 9.5 hours, or 10 hours.

[0077] The present application adopts a multi-stage homogenization treatment step, which can improve the distribution of the dispersed phase and provide a nucleation site for β" in the subsequent baking hardening process, thereby improving the baking performance.

[0078] In some examples, the rolling process includes: hot rolling and cold rolling the intermediate after homogenization treatment in sequence; wherein the hot rolling process includes: a starting rolling temperature of 500°C to 520°C, a finishing rolling temperature ≥ 350°C, and a thickness of the intermediate after hot rolling of 5mm to 8mm. The process parameters of cold rolling include: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after cold rolling of 0.8mm to 1.2mm. For example, the starting rolling temperature in this example includes but is not limited to 500°C, 505°C, 510°C, 515°C or 520°C. The finishing rolling temperature includes but is not limited to 350°C, 370°C, 380°C or 400°C. The single-pass cold rolling reduction rate includes but is not limited to 20%, 25%, 30%, 35% or 40%.

[0079] When the rolling process includes hot rolling and cold rolling, the pre-aging treatment step includes: holding the intermediate after solution treatment at 100°C to 115°C for 3 minutes to 10 minutes, and then cooling it to 25°C to 35°C at a cooling rate of 0.5°C / h to 1.8°C / h; wherein the interval between the end of solution treatment and the start of pre-aging treatment is ≤ 10 minutes. For example, the holding temperature includes but is not limited to 100°C, 102°C, 105°C, 110°C, or 115°C. The cooling rate includes but is not limited to 0.5°C / h, 0.8°C / h, 0.9°C / h, 1°C / h, 1.5°C / h, 1.6°C / h, 1.7°C / h, or 1.8°C / h.

[0080] Alternatively, the pre-aging step includes holding the solution-treated intermediate at 120°C to 135°C for 3 to 10 minutes, then cooling the temperature to 25°C to 35°C at a cooling rate of 1.5°C / h to 2.5°C / h; wherein the interval between the end of the solution treatment and the start of the pre-aging treatment is ≤ 10 minutes. For example, the holding temperature includes, but is not limited to, 120°C, 121°C, 122°C, 125°C, 130°C, or 135°C. The cooling rate includes, but is not limited to, 1.5°C / h, 1.7°C / h, 1.8°C / h, 1.9°C / h, 2°C / h, 2.2°C / h, or 2.5°C / h.

[0081] In other examples, the rolling step includes sequentially subjecting the homogenized intermediate to hot rolling, a first cold rolling step, annealing, and a second cold rolling step. The hot rolling process parameters include a starting rolling temperature of 500°C to 520°C, a finishing rolling temperature ≥ 350°C, and a thickness of 5mm to 8mm after hot rolling. The first cold rolling process parameters include a single-pass cold rolling reduction of 20% to 40%, and a thickness of 2mm to 3.5mm after the first cold rolling step. The annealing process parameters include heating to 450°C to 470°C at a heating rate of 12°C / min to 23°C / min. The second cold rolling process parameters include a single-pass cold rolling reduction of 20% to 40%, and a thickness of 0.98mm to 1.05mm after the second cold rolling step. For example, in the hot rolling step, the starting rolling temperature includes, but is not limited to, 500°C, 505°C, 510°C, 515°C, or 520°C. During the hot rolling step, the finishing temperature includes, but is not limited to, 350°C, 370°C, 380°C, or 400°C. During the annealing step, the heating rate includes, but is not limited to, 12°C / min, 15°C / min, 18°C / min, 20°C / min, 22°C / min, or 23°C / min, and the annealing temperature includes, but is not limited to, 450°C, 455°C, 460°C, 465°C, or 470°C. The annealing time is 1 to 3 hours. Furthermore, when the annealing temperature is 460°C, the annealing time is 2 hours.

[0082] When the rolling treatment also includes annealing, the pre-aging treatment step includes: keeping the intermediate after the solution treatment at 115°C~125°C for 3min~10min, and then cooling it to 25°C~35°C at a cooling rate of 0.9°C / h~1.8°C / h; wherein the interval time from the end of the solution treatment to the start of the pre-aging treatment is ≤10min.

[0083] The present application can be processed with or without intermediate annealing rolling system, and both can obtain good forming properties and baking properties. The present application found that Al-Mg-Si alloys with an additional intermediate annealing step have better impact forming properties and baking properties. This is because the intermediate annealing treatment can make the hot-rolled plate obtain a more sufficient recrystallized structure to provide power for subsequent baking hardening; at the same time, Al-Mg-Si alloys have a large amount of Mg2Si precipitated during the hot rolling process, and the dispersed precipitated Mg2Si has a strong inhibitory effect on recrystallization, resulting in the hot-rolled plate after hot rolling being difficult to recrystallize. Therefore, adopting a certain degree of intermediate annealing process can reduce the deformation structure and improve the aging potential.

[0084] The pre-aging process parameters of this application, in conjunction with the rolling and solution treatment steps, maximize the baking increment by controlling the initial and final temperatures and cooling rates during the pre-aging process. Because impurity elements significantly affect effective Si, the amount of Si available for baking performance is limited. Therefore, increasing the pre-aging temperature and time can maximize baking performance.

[0085] The interval time from the end of solution treatment to the start of pre-aging treatment is ≤10min. At this time, it is easy to obtain and retain enough solid solution atoms in the aluminum matrix, providing sufficient driving force for precipitation during the aging process.

[0086] In some examples, the solution treating steps include:

[0087] The rolled intermediate is heated to 550°C~570°C at a heating rate of 3°C / s~10°C / s, kept at this temperature for 2min~8min, and then cooled to room temperature at a quenching rate of ≥400°C / s.

[0088] For example, in the solution treatment step, the heating rate includes but is not limited to 3°C / s, 4°C / s, 5°C / s, 6°C / s, 7°C / s, 8°C / s, 9°C / s or 10°C / s. The holding temperature includes but is not limited to 550°C, 555°C, 560°C, 565°C or 570°C. The holding time includes but is not limited to 2 min, 3 min, 4 min, 5 min, 6 min, 7 min or 8 min. The quenching rate includes but is not limited to 400°C / s, 500°C / s, 600°C / s, 700°C / s, 800°C / s or 900°C / s. Furthermore, the quenching rate is 400°C / s to 900°C / s.

[0089] In a third aspect of the present application, a β'' phase aluminum alloy is provided, wherein the β'' phase aluminum alloy is obtained by baking and hardening the Al-Mg-Si alloy according to any one of the first aspects of the present application;

[0090] The baking hardening temperature is 170℃~200℃.

[0091] For example, the bake hardening temperature includes, but is not limited to, 170°C, 180°C, 183°C, 185°C, 186°C, 190°C, 195°C, or 200°C. The bake hardening time is 10 to 30 minutes. For example, the bake hardening time includes, but is not limited to, 10 minutes, 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, or 30 minutes.

[0092] In one example, the heating step for bake hardening further includes: a 2% pre-stretching along the RD direction.

[0093] The following further specific examples are provided to illustrate the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application belong to the scope of protection of the present application. The specific process parameters and the like in the following embodiments are only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not necessarily limited to the specific values ​​of the embodiments below.

[0094] In the following examples and comparative examples, unless otherwise specified, the definitions of the terms are as follows:

[0095] "T4P" refers to the state of Al-Mg-Si alloys before bake hardening. The corresponding yield strength (YS), ultimate tensile strength (UTS), and elongation at break (A50) in the T4P state are measured after one week of pre-aging and storage.

[0096] "T6B" refers to the bake-hardened state. For hardness results, "T6B" corresponds to the bake-hardened state at 185°C for 20 minutes. For strength results, "T6B" corresponds to the bake-hardened state at 185°C for 20 minutes after a 2% pre-stretch in the RD direction. The yield strength (YS), ultimate tensile strength (UTS), and elongation at break (A50) in the T6B state are measured after one week of storage after bake-hardening.

[0097] "BH" refers to the bake hardening response performance or bake increase, and its value corresponds to the yield strength in the T6B state - the yield strength in the T4p state.

[0098] Bendability is measured by bending Al-Mg-Si alloys before bake hardening. Bend angle = 180°. A larger bend angle indicates better formability. The bend line is parallel to the rolling direction, and the bending tool R is 0.2mm.

[0099] "Aging stability" refers to the performance stability of Al-Mg-Si alloys stored at room temperature in a pre-aged state before bake hardening. Because Al-Mg-Si alloys require time from production to delivery to the OEM for stamping, coating, and bake hardening, lower aging stability in the pre-aged state (before bake hardening) facilitates subsequent stamping.

[0100] Example 1

[0101] (1) Preparation of ingot: The ingot was prepared by mixing the ingredients according to the mass percentage of each chemical component in Table 1, and then melting and refining the ingredients.

[0102] (2) Homogenization treatment: The ingot in step (1) was subjected to a first-stage homogenization treatment at 275°C for 2 h, heated to 375°C at a heating rate of 30°C / h, and then subjected to a second-stage homogenization treatment for 2 h. The ingot was heated to 560°C at a heating rate of 30°C / h, and then subjected to a third-stage homogenization treatment for 8 h.

[0103] (3) Rolling treatment: The intermediate prepared in step (2) is sequentially hot-rolled and cold-rolled; the process parameters of hot rolling are: the starting rolling temperature is 520°C, the final rolling temperature is 360°C, and the thickness of the intermediate after hot rolling is 6 mm; the process parameters of cold rolling are: single-stand reversible rolling, the rolling rate of each pass is 28%~32%, and the thickness of the finished product after cold rolling is controlled at about 1.0 mm.

[0104] (4) Solution treatment: The intermediate after rolling treatment in step (3) was heated to 560°C at a heating rate of 7°C / s, kept at this temperature for 3 min, and then cooled to room temperature at a quenching rate of 500°C / s.

[0105] (5) Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes, kept at 100°C for 5 minutes, and then cooled to 30°C at a cooling rate of 1.8°C / h for pre-aging treatment to prepare an Al-Mg-Si alloy (thickness 1mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment. The corresponding test results are as follows: Figure 1 and as shown in Table 2.

[0106] (6) Baking and hardening:

[0107] 1. The Al-Mg-Si alloy in step (5) was pre-stretched 2% along the RD direction and bake-hardened at 185°C for 20 minutes to obtain a β' phase aluminum alloy. This corresponds to the T6B state of the Al-Mg-Si alloy after bake-hardening. The strength properties of the Al-Mg-Si alloy were measured in this state. The corresponding test results are shown in Table 2 for T6B (2% PS + 185°C for 20 minutes).

[0108] 2. After the Al-Mg-Si alloy in step (5) is bake-hardened at 185°C for 20 minutes, a β' phase aluminum alloy is obtained. This corresponds to the T6B state of the Al-Mg-Si alloy after bake-hardening. The hardness properties of the Al-Mg-Si alloy are measured in this state.

[0109] The corresponding test results under the above T4P and T6B states are as follows Figure 1 and as shown in Table 2.

[0110] Comparative Example 1-1

[0111] (1) Preparation of ingot: The ingot was prepared by mixing the ingredients according to the mass percentage of each chemical component in Table 1, and then melting and refining the ingredients.

[0112] (2) Homogenization treatment: The ingot in step (1) was subjected to a single-stage homogenization treatment at 560°C for 8 hours.

[0113] (3) Rolling treatment: The intermediate prepared in step (2) is sequentially hot-rolled and cold-rolled; the process parameters of hot rolling are: the starting rolling temperature is 520°C, the final rolling temperature is 360°C, and the thickness of the intermediate after hot rolling is 6 mm; the process parameters of cold rolling are: single-stand reversible rolling, the rolling rate of each pass is 28%~32%, and the thickness of the finished product after cold rolling is controlled at about 1.0 mm.

[0114] (4) Solution treatment: The intermediate after rolling treatment in step (3) was heated to 560°C at a heating rate of 7°C / s, kept at this temperature for 3 min, and then cooled to room temperature at a quenching rate of 500°C / s.

[0115] (5) Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes, kept at 100°C for 5 minutes, and then cooled to 30°C at a cooling rate of 1.8°C / h for pre-aging treatment to prepare an Al-Mg-Si alloy (thickness 1mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment. The corresponding test results are as follows: Figure 1 and as shown in Table 2.

[0116] (6) Baking and hardening:

[0117] 1. The Al-Mg-Si alloy in step (5) was pre-stretched 2% along the RD direction and bake-hardened at 185°C for 20 minutes to obtain a β' phase aluminum alloy. This corresponds to the T6B state of the Al-Mg-Si alloy after bake-hardening. The strength properties of the Al-Mg-Si alloy were measured in this state. The corresponding test results are shown in Table 2 for T6B (2% PS + 185°C for 20 minutes).

[0118] 2. After the Al-Mg-Si alloy in step (5) is bake-hardened at 185°C for 20 minutes, a β' phase aluminum alloy is obtained. This corresponds to the T6B state of the Al-Mg-Si alloy after bake-hardening. The hardness properties of the Al-Mg-Si alloy are measured in this state.

[0119] The corresponding test results under the above T4P and T6B states are as follows Figure 1 and as shown in Table 2.

[0120] Comparative Example 1-2

[0121] Comparative Example 1-2 is substantially the same as Comparative Example 1-1, with the main difference being that the ratio of chemical components in the preparation of the ingot in step (1) of Comparative Example 1-2 is different.

[0122] Comparative Examples 1-3

[0123] Comparative Example 1-3 is substantially the same as Comparative Example 1-1, with the main difference being that the ratio of chemical components in the preparation of the ingot in step (1) of Comparative Example 1-3 is different.

[0124] Table 1

[0125]

[0126] Table 2

[0127]

[0128] Depend on Figure 1 As can be seen from Table 2, the yield strength of the Al-Mg-Si alloy T4p state in Example 1 before bake hardening treatment is 117 MPa, which is beneficial to the subsequent stamping forming step of the Al-Mg-Si alloy. After testing, the yield strength before bake hardening treatment is ≤130 MPa, which is beneficial to the stamping process without cracking and wrinkling. The yield strength of the Al-Mg-Si alloy T6B state in Example 1 after bake hardening treatment is 208 MPa, and the yield strength increment BH reaches 91 MPa, which also has excellent bake hardening performance. That is, Example 1 of the present application can make the Al-Mg-Si alloy have both recyclability, stamping forming performance and bake hardening performance when containing impurity elements such as Mn and Fe. At the same time, from the perspective of chemical composition, Example 1 contains impurity elements such as Fe and Mn, which is suitable for the preparation of recyclable aluminum alloys.

[0129] Comparative Examples 1-1 and 1-2 have relatively low Mg and Fe contents, corresponding to newly produced aluminum alloys. However, their high Si content and other factors result in Al-Mg-Si alloys with unsatisfactory chemical compositions. Their corresponding T4p yield strengths exceed 130 MPa, hindering cracking and wrinkling during stamping, resulting in poor impact forming performance.

[0130] The Al-Mg-Si alloys of Comparative Examples 1-3 and Example 1 have the same chemical composition, but are prepared using different procedures. The yield strength of the Al-Mg-Si alloys of Comparative Examples 1-3 in the T6B state after bake hardening is 177 MPa, which is less than 200 MPa. Testing revealed that the Al-Mg-Si alloys of Comparative Examples 1-3 were susceptible to deformation and denting after forming and bake curing, failing to meet service performance requirements.

[0131] Comparative Example 2-1

[0132] Comparative Example 2-1 is basically the same as Example 1, with the main difference being that the pre-aging treatment in step (5) of Comparative Example 2-1 is different from that in Example 1. Specifically, step (5) of Comparative Example 2-1 is:

[0133] Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes and kept at 80°C for 8 hours to prepare an Al-Mg-Si alloy (thickness 1 mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment.

[0134] Comparative Example 2-2 to Comparative Example 2-6

[0135] Comparative Examples 2-2 to 2-6 are essentially the same as Comparative Example 2-1, with the main difference being that the pre-aging treatments in step (5) of Comparative Examples 2-2 to 2-6 are different. Specifically, the process parameters for the pre-aging treatments in step (5) of Comparative Examples 2-2 to 2-6 are shown in Table 3.

[0136] Comparative Example 3-1

[0137] Comparative Example 3-1 is basically the same as Comparative Example 1-2, with the main difference being that the homogenization treatment in step (2) and the pre-aging treatment in step (5) of Comparative Example 3-1 are different. Specifically, step (2) of Comparative Example 3-1 is:

[0138] Homogenization treatment: The ingot in step (1) was subjected to a first-stage homogenization treatment at 275°C for 2 hours, heated to 375°C at a heating rate of 30°C / h, and then subjected to a second-stage homogenization treatment for 2 hours. The ingot was heated to 560°C at a heating rate of 30°C / h, and then subjected to a third-stage homogenization treatment for 8 hours.

[0139] Specifically, step (5) of Comparative Example 3-1 is:

[0140] Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes and kept at 80°C for 8 hours to prepare an Al-Mg-Si alloy (thickness 1 mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment.

[0141] Comparative Example 3-2 to Comparative Example 3-6

[0142] Comparative Examples 3-2 to 3-6 are substantially the same as Comparative Example 3-1, with the main difference being that the pre-aging treatment steps in step (5) of Comparative Examples 3-2 to 3-6 are different. Specifically, the process parameters for the pre-aging treatment in step (5) of Comparative Examples 3-2 to 3-6 are shown in Table 3.

[0143] The corresponding hardness test results of Comparative Examples 2-1 to 2-6 and Comparative Examples 3-1 to 3-6 are shown in Table 3.

[0144] Table 3

[0145]

[0146] Comparative Examples 2-1 to 2-6 are basically the same as Example 1 of the present application, and the main difference is that the parameters of the pre-aging treatment and the rolling treatment are different. After conversion between hardness and yield strength, it is found that the strength of Comparative Examples 2-1 to 2-5 after bake hardening is lower than 200 MPa, which causes the Al-Mg-Si alloys of Comparative Examples 2-1 to 2-5 to be easily deformed and dented after forming and bake curing, and do not meet the service performance requirements. The strength of Comparative Example 2-6 before bake hardening is higher than 130 MPa. After testing, it is not conducive to cracking and wrinkling during the stamping forming process, that is, its impact forming performance is poor. It can be seen from Comparative Examples 2-1 to 2-6 that the process parameters of pre-aging play an important role in ensuring the yield strength of the Al-Mg-Si alloy before and after bake hardening treatment.

[0147] Comparative Examples 2-1 to 2-6 show that low-temperature or short-time (<8h) pre-aging systems in the pre-aging step all yield low baking performance, while high-temperature (≥140°C) pre-aging systems significantly improve initial hardness. Therefore, this application employs a medium-high temperature of 100-120°C and a long cooling pre-aging system (as in Example 1). This not only promotes β" precipitation during the high-temperature phase to improve baking performance, but also avoids the coarsening of β" that can occur during extended high-temperature periods, which reduces baking performance. Furthermore, the low-temperature pre-aging process further ensures aging stability, facilitating long-term storage.

[0148] The chemical compositions and pre-aging treatment parameters in Comparative Examples 3-1 to 3-6 are all different, resulting in the yield strength of the Al-Mg-Si alloy before and after bake hardening treatment not meeting the requirements.

[0149] Example 2-1

[0150] Example 2-1 is basically the same as Example 1, with the main difference being that the pre-aging treatment step (5) of Example 2-1 is different. Specifically, step (5) of Example 2-1 is:

[0151] Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes, kept at 100°C for 5 minutes, and then cooled to 30°C at a cooling rate of 0.9°C / h for pre-aging treatment to prepare an Al-Mg-Si alloy (thickness 1 mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment.

[0152] Example 2-2

[0153] Example 2-2 is basically the same as Example 2-1, with the main difference being that the pre-aging treatment step (5) of Example 2-2 is different. Specifically, step (5) of Example 2-2 is:

[0154] Pre-aging treatment: The intermediate after quenching in step (4) was transferred to an aging furnace within 5 minutes, kept at 120°C for 5 minutes, and then cooled to 30°C at a cooling rate of 1.8°C / h for pre-aging treatment to prepare an Al-Mg-Si alloy (thickness 1 mm). This corresponds to the T4P state of the Al-Mg-Si alloy before bake hardening treatment.

[0155] Comparative Example 4-1 to Comparative Example 4-9

[0156] Comparative Examples 4-1 to 4-9 are substantially the same as Example 2-1, with the main difference being that the pre-aging treatment steps in step (5) of Comparative Examples 4-1 to 4-9 are different. Specifically, the parameters for the pre-aging treatment in step (5) of Comparative Examples 4-1 to 4-9 are shown in Table 4.

[0157] The corresponding hardness test results of Example 2-1 to Example 2-2 and Comparative Example 4-1 to Comparative Example 4-9 are shown in Table 4.

[0158] Table 4

[0159]

[0160] The yield strength, tensile strength, and elongation of the Al-Mg-Si alloys of Examples 2-1 and 2-2 and Comparative Examples 4-1 to 4-6 before bake hardening, and the yield strength, tensile strength, elongation, and bake hardening value (BH) after bake hardening were further characterized, and the data are shown in Table 5 below. Since the Al-Mg-Si alloys of Examples 2-1 and 2-2 and Comparative Examples 4-1 to 4-6 were initially screened for hardness, Table 5 primarily tests the samples that met the hardness requirements in Table 4.

[0161] Table 5

[0162]

[0163] As can be seen from the Al-Mg-Si alloys of Examples 2-1 and 2-2 and Comparative Examples 4-1 to 4-9, a pre-aging system with an initial temperature of 100°C and a cooling rate of 0.9°C / h can achieve good delivery and baking performance, with a bending angle of 154° meeting forming requirements. Similarly, a pre-aging system with an initial temperature of 120°C and a cooling rate of 1.8°C / h can also achieve good delivery and baking performance, with a bending angle of 159° meeting forming requirements. Furthermore, the YS values ​​of Examples 2-1 and 2-2 before bake hardening are ≤130 MPa, and the YS values ​​of Examples 2-1 and 2-2 after bake hardening are ≥200 MPa.

[0164] The engineering stress-strain curve comparison of the Al-Mg-Si alloy of Example 2-1 before and after bake hardening is shown in the figure below: Figure 2 The bending performance of the Al-Mg-Si alloy of Example 2-1 before bake hardening is shown in FIG. Figure 3 shown.

[0165] The aging stability of Example 2-1 was further evaluated, and the corresponding test results are shown in Tables 6 and Figure 4 As shown. Example 2-1 adopts a cooling pre-aging system of 120℃-1.8℃ / h, while Comparative Examples 2-1 and Comparative Examples 3-1 adopt an isothermal pre-aging system of 80℃×8h respectively. After 2170h of parking after pre-aging, the hardness increment of Example 2-1 is only 5.3HV, and the aging stability remains very good, while the increment of Comparative Example 3-1 reaches 12HV, and the yield strength of the Al-Mg-Si alloy increases significantly, resulting in subsequent stamping difficulties, or a large amount of springback after stamping, and the forming accuracy of parts is greatly reduced. Although the parking hardness increment of Comparative Example 2-1 is also low, only 4.8HV, the baking hardness increment of Comparative Example 2-1 is also low, which does not meet the service performance requirements of automotive plates.

[0166] Table 6

[0167]

[0168] Example 3-1~Example 3-2, Comparative Example 5-1~Comparative Example 5-3

[0169] Example 3-1 to Example 3-2, Comparative Example 5-1 to Comparative Example 5-3 are basically the same as Example 1, and the main difference is that step (3) and step (5) of Example 3-1 to Example 3-2, Comparative Example 5-1 to Comparative Example 5-3 are different.

[0170] Specifically, step (3) of Example 3-1 to Example 3-2 and Comparative Example 5-1 to Comparative Example 5-3 is:

[0171] Rolling treatment: the intermediate after the homogenization treatment in step (2) is subjected to hot rolling, first cold rolling, annealing, and second cold rolling in sequence; wherein the hot rolling step includes: the starting rolling temperature is 520°C, and the final rolling temperature is 360°C, and the thickness of the intermediate after hot rolling is 6 mm; the first cold rolling step includes: the cold rolling is a single-stand reversible rolling, the rolling rate of a single pass is 28%~30%, and the thickness of the plate after the first cold rolling is controlled at 3 mm; the annealing step includes: heating the plate to 460°C at a heating rate of 15°C / min and annealing for 2 hours; the second cold rolling step includes: the cold rolling is a single-stand reversible rolling, the rolling rate of a single pass is 28%~30%, and the thickness of the finished plate after the second cold rolling is controlled at 1-1.05 mm.

[0172] Specifically, the specific parameters of the pre-aging temperature and cooling rate and the corresponding test results of step (5) of Example 3-1 to Example 3-2 and Comparative Example 5-1 to Comparative Example 5-3 are shown in Table 7 and Figure 5 、 Figure 6 shown.

[0173] Table 7

[0174]

[0175] The test results show that the Al-Mg-Si alloys of Examples 3-1 and 3-2 that have undergone intermediate annealing can obtain a lower yield strength than those without intermediate annealing (the yield strength of the pre-aged alloy after intermediate annealing is 96-115 MPa, while the yield strength of the pre-aged alloy without intermediate annealing is 116-129 MPa), a higher bake increment (the bake increment BH value after intermediate annealing reaches 108-117 MPa, while the bake increment BH value without intermediate annealing is 77-94 MPa), and better formability (the bending angle after intermediate annealing reaches 173-174°, while the bending angle without intermediate annealing is 154-159°). This allows the sheet to be used for components with higher formability requirements, such as door inner panels, engine hood inner panels, trunk inner panels, and the like.

[0176] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0177] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. An Al-Mg-Si alloy, characterized in that: The chemical composition of the Al-Mg-Si alloy includes, by mass percentage, 0.4%-0.7% Si, 0.5%-0.6% Fe, 0.1%-0.25% Cu, 0.4%-0.8% Mn, 0.5%-0.8% Mg, 0-0.3% Zn, 0-0.2% Ti, 0-0.15% Cr, 0.05%-0.2% V, 0.05%-0.2% Mo, and 94%-98% Al; The yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C is ≥200MPa; The yield strength of the Al-Mg-Si alloy before being subjected to a bake hardening treatment at 170° C. to 200° C. is ≤130 MPa.

2. The Al-Mg-Si alloy according to claim 1, wherein The chemical composition of the Al-Mg-Si alloy includes: 0.4%-0.7% Si, 0.5%-0.6% Fe, 0.1%-0.25% Cu, 0.4%-0.8% Mn, 0.5%-0.8% Mg, 0-0.3% Zn, 0-0.2% Ti, 0-0.15% Cr, 0.05%-0.1% V, 0.05%-0.1% Mo, and 96%-98% Al; Among them, the ratio of the mass percentage of Mg to the mass percentage of Si is (1~1.6):1; The ratio of the mass percentage of V to the mass percentage of Mo is (1~2):

1.

3. The Al-Mg-Si alloy according to claim 1 or 2, characterized in that: The Al-Mg-Si alloy satisfies one or more of the following characteristics: (1) The yield strength of the Al-Mg-Si alloy after bake hardening at 170°C to 200°C is 204 MPa to 235 MPa; (2) The yield strength of the Al-Mg-Si alloy before bake hardening at 170°C to 200°C is 96 MPa to 130 MPa; (3) the yield strength of the Al-Mg-Si alloy after the bake hardening treatment at 170°C to 200°C is increased by 75 MPa to 120 MPa compared to the yield strength of the Al-Mg-Si alloy before the bake hardening treatment at 170°C to 200°C; (4) The Al-Mg-Si alloy has a dispersed phase.

4. A method for preparing an Al-Mg-Si alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: According to the chemical composition of the Al-Mg-Si alloy, the materials are prepared, and after melting and refining, an ingot is prepared; The Al-Mg-Si alloy is prepared by subjecting the ingot to homogenization treatment, rolling treatment, solution treatment and pre-aging treatment.

5. The method for preparing an Al-Mg-Si alloy according to claim 4, wherein: The steps of homogenization treatment include: The ingot is subjected to a first-stage homogenization treatment at 260°C to 280°C, heated to 360°C to 390°C at a heating rate of 20°C / h to 40°C / h, and then subjected to a second-stage homogenization treatment. The ingot is subjected to a third-stage homogenization treatment after being heated to 540°C to 580°C at a heating rate of 20°C / h to 40°C / h.

6. The method for preparing an Al-Mg-Si alloy according to claim 4, wherein: The rolling process comprises: hot rolling and cold rolling the intermediate after homogenization treatment in sequence; wherein the hot rolling process comprises: a starting rolling temperature of 500° C. to 520° C., a finishing rolling temperature ≥ 350° C., and a thickness of the intermediate after hot rolling of 5 mm to 8 mm; and the process parameters of the cold rolling process comprise: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after cold rolling of 0.8 mm to 1.2 mm; The pre-aging treatment step comprises: holding the intermediate after the solution treatment at 100°C to 115°C for 3 minutes to 10 minutes, and then cooling the intermediate to 25°C to 35°C at a cooling rate of 0.5°C / h to 1.8°C / h; wherein the interval time between the end of the solution treatment and the start of the pre-aging treatment is ≤ 10 minutes; Alternatively, the pre-aging treatment step includes: keeping the intermediate after the solution treatment at 120°C~135°C for 3min~10min, and then cooling it to 25°C~35°C at a cooling rate of 1.5°C / h~2.5°C / h; wherein the interval time between the end of the solution treatment and the start of the pre-aging treatment is ≤10min.

7. The method for preparing an Al-Mg-Si alloy according to claim 4, wherein: The rolling treatment step includes: sequentially hot rolling, first cold rolling, annealing, and second cold rolling the intermediate after homogenization treatment; the process parameters of the hot rolling include: a starting rolling temperature of 500°C to 520°C, a finishing rolling temperature ≥350°C, and a thickness of the intermediate after hot rolling of 5mm to 8mm; the process parameters of the first cold rolling meet: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after the first cold rolling of 2mm to 3.5mm; the process parameters of the annealing include: heating to 450°C to 470°C at a heating rate of 12°C / min to 23°C / min; the process parameters of the second cold rolling include: a single-pass cold rolling reduction rate of 20% to 40%, and a thickness of the intermediate after the second cold rolling of 0.98mm to 1.05mm; The pre-aging treatment step includes: keeping the intermediate after solution treatment at 115°C~125°C for 3min~10min, and then cooling it to 25°C~35°C at a cooling rate of 0.9°C / h~1.8°C / h; wherein the interval time between the end of solution treatment and the start of pre-aging treatment is ≤10min.

8. The method for preparing an Al-Mg-Si alloy according to any one of claims 4 to 7, wherein: The steps of solution treatment include: The rolled intermediate is heated to 550°C~570°C at a heating rate of 3°C / s~10°C / s, kept at this temperature for 2min~8min, and then cooled to room temperature at a quenching rate of ≥400°C / s.

9. A β'' phase aluminum alloy, characterized in that: The β'' phase aluminum alloy is obtained by baking and hardening the Al-Mg-Si alloy according to any one of claims 1 to 3; The baking hardening temperature is 170℃~200℃.

10. An aluminum alloy plate for automobiles, characterized in that: It is obtained by baking and hardening the Al-Mg-Si alloy according to any one of claims 1 to 3; or includes the β'' phase aluminum alloy according to claim 9.

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