Aluminum alloy sheet and preparation method therefor

Abstract

Provided is aluminum alloy sheet and preparation method thereof. The aluminum alloy sheet includes the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element, wherein a total content of inevitable impurities is ≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%. The aluminum alloy sheet has low yield strength, high room-temperature storage stability, excellent paint-bake hardening performance, and good stamping formability.

Description

[0001] This application is based upon and claims priority to Chinese Patent Application No. 202411169284.7, filed on August 23, 2024, the invention of which is hereby incorporated by reference in its entirety.Technical Field

[0002] The present invention relates to the technical field of aluminum alloys, and in particular to aluminum alloy sheet and preparation method thereof.Background

[0003] Automotive lightweighting is a relatively economical and effective means to achieve energy conservation and emission reduction, while also improving safety. Aluminum alloy sheets are considered ideal materials for automotive lightweighting due to their advantages of light weight, high specific strength, and excellent overall performance. 6xxx series aluminum alloys have excellent surface quality and heat-treatable strengthening properties, making them the most widely used materials in automotive applications. However, at present, the cost of aluminum alloy automotive sheets is much higher than that of conventional steel, and further cost reduction is urgently needed. While meeting the formability and rigidity requirements of components, increasing the strength of 6xxx series aluminum alloys can reduce the amount of aluminum used, thereby lowering component costs and further enhancing the lightweighting effect. In addition, it is also necessary to maintain excellent formability and room-temperature storage stability of the sheet as the strength increases.

[0004] In recent years, some domestic universities and research institutes have conducted studies on 6xxx series aluminum alloy automotive sheets. For example: Chinese Patent with Authorization Announcement No. CN112095039B discloses a method for improving paint-bake performance through two-stage pre-aging, but it does not concern room-temperature storage stability. Especially with microalloying of Sn and Cu, the preparation process becomes more complex, making it difficult to meet requirements. Chinese Patent with Authorization Announcement No. CN103740988B discloses a preparation method of a high-performance aluminum alloy for an automotive component, but the addition of elements such as Zr and Sr increases cost. Chinese Patent Application with Publication No. CN117467873A discloses an Al-Mg-Si-Sn-Sc alloy and a preparation method thereof, in which Sc element is added. In addition, the alloy is supplied in a T6 temper. Summary

[0005] A main objective of the present invention is to provide aluminum alloy sheet and preparation method thereof, so as to solve the problems in the related art that formability, room-temperature storage stability, and paint-bake hardening performance of the aluminum alloy sheet are difficult to achieve simultaneously.

[0006] In order to achieve the above objective, according to one aspect of the present invention, an aluminum alloy sheet is provided. The aluminum alloy sheet includes the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element. A total content of inevitable impurities is≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%.

[0007] Further, the above aluminum alloy sheet includes the following elements, by mass percentage: 0.40-1.25wt% of Si element, 0.1-0.3wt% of Fe element, 0.15-0.25wt% of Cu element, 0.10-0.18wt% of Mn element, 0.4-0.8wt% of Mg element, 0.01-0.05wt% of Cr element, 0.02-0.04wt% of Ti element, and 0.010-0.025wt% of Sn element, with the balance being Al. The total content of inevitable impurities is ≤0.15wt%, and the content of any single impurity is less than or equal to 0.05wt%.

[0008] Further, a mass ratio of the above Sn element to the Cu element is 1:8-20.

[0009] Further, a yield strength of the above aluminum alloy sheet after being stored at 25 °C for 7 days is less than 100 MPa; and / or, an increment in the yield strength of the aluminum alloy sheet after being stored at 25 °C for 180 days compared with that after being stored for 7 days does not exceed 24 MPa; and / or, the aluminum alloy sheet after being stored at 25 °C for 7 days is sequentially subjected to a 2% pre-stretching treatment and a paint baking treatment at 185 °C for 20 min to obtain a treated aluminum alloy sheet. A yield strength of the treated aluminum alloy sheet is greater than 220 MPa, and a paint bake response is greater than 140 MPa.

[0010] According to another aspect of the present invention, a preparation method of the above-mentioned aluminum alloy sheet is provided. The preparation method includes: melting, refining, and casting raw materials including metals in proportion to obtain an aluminum alloy ingot; and subjecting the aluminum alloy ingot sequentially to a homogenization treatment, a hot rolling treatment, a cold rolling treatment, a solution treatment, a first-stage pre-aging treatment, and a second-stage pre-aging treatment to obtain an aluminum alloy sheet. A temperature of the first-stage pre-aging treatment is greater than that of the second-stage pre-aging treatment, and a cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment is ≥5 °C / min.

[0011] Further, the temperature of the above first-stage pre-aging treatment is 140-200 °C; and / or, a holding time of the first-stage pre-aging treatment is 5-180 s; and / or, the temperature of the second-stage pre-aging treatment is 70-130 °C; and / or, a holding time of the second-stage pre-aging treatment is 1-12 h.

[0012] Further, the above homogenization treatment includes a first-stage homogenization treatment and a second-stage homogenization treatment performed sequentially. A heating rate of the first-stage homogenization treatment is 30-80 °C / h; and / or, a temperature of the first-stage homogenization treatment is 480-520 °C; and / or, a holding time of the first-stage homogenization treatment is 4-10 h; and / or, a heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment is 20-40 °C / h; and / or, a temperature of the second-stage homogenization treatment is 560-580 °C; and / or, a holding time of the second-stage homogenization treatment is 6-10 h.

[0013] Further, the above solution treatment is performed using an air-cushion continuous annealing furnace, and the solution treatment includes a heating process, a holding process, and a cooling process performed sequentially; and / or, a heating rate of the heating process is ≥5 °C / s; and / or, a temperature of the holding process is 565-585 °C; and / or, a holding time of the holding process is 0.5-5 min; and / or, a cooling rate of the cooling process is ≥30 °C / s.

[0014] Further, a material obtained from the homogenization treatment is directly subjected to the above hot rolling treatment without being cooled; and / or, a thickness of the material after the hot rolling treatment is 3-8 mm.

[0015] Further, a thickness of the material after the above cold rolling treatment is 0.5-3.0 mm.

[0016] By applying the technical solution of the present invention, compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn atoms to fully re-dissolve into the Al matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.Detailed Description of the Embodiments

[0017] It is to be noted that the embodiments in the present invention and features in the embodiments may be combined with each other without conflict. The present invention is illustrated in detail below in conjunction with the embodiments.

[0018] It is to be noted that mass percentage refers to a percentage of a mass (weight) of a certain alloy component relative to a total mass of the alloy.

[0019] Yield strength refers to the stress at which the aluminum alloy begins to yield, defined as the stress value that produces 0.2% residual deformation. A stress-strain curve is obtained through a uniaxial tensile test, and yield strength data is obtained from this curve.

[0020] Paint bake response refers to the difference in yield strength of the aluminum alloy sheet before and after a 2% pre-stretching treatment followed by a paint baking treatment, e.g. at 185 °C for 20 min.

[0021] As analyzed in the background of the present invention, there is a problem with 6xxx series aluminum alloy sheets in that formability, room temperature storage stability, and paint-bake hardening performance are difficult to achieve simultaneously. In order to solve the problems, the present invention provides aluminum alloy sheet and preparation method thereof.

[0022] In a typical implementation of the present invention, an aluminum alloy sheet is provided. The aluminum alloy sheet includes the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element. A total content of inevitable impurities is ≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%.

[0023] Compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn atoms to fully re-dissolve into the Al matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0024] In order to further enhance the synergistic effects among different elements, thereby further reducing the yield strength of the aluminum alloy sheet and improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet, in one embodiment of the present invention, the above aluminum alloy sheet preferably includes the following elements, by mass percentage: 0.40-1.25wt% of Si element, 0.1-0.3wt% of Fe element, 0.15-0.25wt% of Cu element, 0.10-0.18wt% of Mn element, 0.4-0.8wt% of Mg element, 0.01-0.05wt% of Cr element, 0.02-0.04wt% of Ti element, and 0.010-0.025wt% of Sn element, with the balance being Al. The total content of inevitable impurities is ≤0.15wt%, and the content of any single impurity is less than or equal to 0.05wt%.

[0025] In one embodiment of the present invention, a mass ratio of the above Sn element to the Cu element is 1:8-20.

[0026] If the mass ratio of the Sn element to the Cu element is excessively high, the paint-bake strength and paint bake response of the sheet may decrease. If the mass ratio of the Sn element to the Cu element is excessively low, the strength of the sheet may be excessively high, and the room-temperature storage stability may be reduced, thereby resulting in insufficient formability of the sheet. Preferably, controlling the mass ratio of the Sn element to the Cu element within the above range helps to fully exert the synergistic interaction between the Sn element and the Cu element, thereby further improving paint-bake hardening performance and the room-temperature storage stability of the aluminum alloy sheet to a certain extent.

[0027] In one embodiment of the present invention, a yield strength of the above aluminum alloy sheet after being stored at 25 °C for 7 days is less than 100 MPa; and / or, an increment in the yield strength of the aluminum alloy sheet after being stored at 25 °C for 180 days compared with that after being stored for 7 days does not exceed 24 MPa; and / or, the aluminum alloy sheet after being stored at 25 °C for 7 days is sequentially subjected to a 2% pre-stretching treatment and a paint baking treatment at 185 °C for 20 min to obtain a treated aluminum alloy sheet. A yield strength of the treated aluminum alloy sheet is greater than 220 MPa, and a paint bake response is greater than 140 MPa.

[0028] The aluminum alloy sheet of the present invention is an aluminum alloy sheet in a T4P temper, and the treated aluminum alloy sheet is an aluminum alloy sheet in a T8X temper. The aluminum alloy sheet having the above ranges of yield strength and paint bake response helps to achieve thickness reduction of the aluminum alloy sheet under equal-strength conditions, thereby reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0029] In another typical implementation of the present invention, a preparation method of the above-mentioned aluminum alloy sheet is provided. The preparation method includes: melting, refining, and casting raw materials including metals in proportion to obtain an aluminum alloy ingot; and subjecting the aluminum alloy ingot sequentially to a homogenization treatment, a hot rolling treatment, a cold rolling treatment, a solution treatment, a first-stage pre-aging treatment, and a second-stage pre-aging treatment to obtain an aluminum alloy sheet. A temperature of the first-stage pre-aging treatment is greater than that of the second-stage pre-aging treatment, and a cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment is ≥5 °C / min.

[0030] In the present invention, subjecting the aluminum alloy ingot to the homogenization treatment helps to enable effective re-dissolution of alloying elements, particularly the Sn element, thereby helping to improve the distribution uniformity of the alloying elements within the matrix, and in turn helping to improve the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet. Subjecting the alloy after the homogenization treatment to the hot rolling treatment helps to improve the plasticity of the alloy, thereby facilitating subsequent processing of the alloy. In addition, the hot rolling treatment also helps to refine grains, eliminate casting defects, and improve microstructural uniformity. Subjecting the alloy after the hot rolling treatment to the cold rolling treatment helps to improve the dimensional accuracy of the aluminum alloy sheet, relieve the internal stress of the material, and improve the surface quality of the material. Subjecting the alloy after the cold rolling treatment to the solution treatment helps to dissolve the alloying elements, particularly the Sn element, into the Al matrix, thereby helping to improve the paint-bake hardening performance of the aluminum alloy sheet. Employing a two-stage pre-aging treatment helps to further improve the paint-bake hardening performance of the aluminum alloy sheet. Specifically, the first-stage pre-aging treatment helps to form clusters that are more favorable for transformation into β" strengthening phase during the paint-bake process. The second-stage pre-aging treatment helps to improve the room-temperature storage stability of the aluminum alloy sheet, thereby enabling the aluminum alloy sheet to achieve both high room-temperature storage stability and paint-bake hardening performance. Preferably controlling the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment within the above range helps to reduce the risk of excessive formation or coarsening of clusters, which may result in an excessively high initial yield strength and a decline in formability of the aluminum alloy sheet.

[0031] In one embodiment of the present invention, the temperature of the above first-stage pre-aging treatment is 140-200 °C; and / or, a holding time of the first-stage pre-aging treatment is 5-180 s; and / or, the temperature of the second-stage pre-aging treatment is 70-130 °C; and / or, a holding time of the second-stage pre-aging treatment is 1-12 h.

[0032] An excessively high temperature of the first-stage pre-aging treatment leads to excessive formation, of clusters, thereby resulting in an excessively high initial strength of the sheet. Conversely, an excessively low temperature of the first-stage pre-aging treatment also cannot achieve the effect of first-stage pre-aging, leading to insufficient paint-bake strength of the sheet. Preferably controlling the temperature and holding time of the first-stage pre-aging treatment within the above ranges helps to form more clusters that are favorable for transformation into the β" strengthening phase during the paint-bake process. An excessively high temperature of the second-stage pre-aging treatment promotes excessive formation of clusters, thereby resulting in an excessively high initial strength of the sheet. Conversely, an excessively low temperature of the second-stage pre-aging treatment cannot achieve the effect of pre-aging, leading to a deterioration in room-temperature storage stability. Preferably controlling the temperature and holding time of the second-stage pre-aging treatment within the above ranges helps to further improve the room-temperature storage stability of the aluminum alloy sheet.

[0033] In one embodiment of the present invention, the above homogenization treatment includes a first-stage homogenization treatment and a second-stage homogenization treatment performed sequentially. A heating rate of the first-stage homogenization treatment is 30-80 °C / h; and / or, a temperature of the first-stage homogenization treatment is 480-520 °C; and / or, a holding time of the first-stage homogenization treatment is 4-10 h; and / or, a heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment is 20-40 °C / h; and / or, a temperature of the second-stage homogenization treatment is 560-580 °C; and / or, a holding time of the second-stage homogenization treatment is 6-10 h.

[0034] An excessively high temperature of the first-stage homogenization treatment may cause overheating, resulting in material failure. Conversely, an excessively low temperature of the first-stage homogenization treatment cannot ensure sufficient re-dissolution of low-melting-point phases. Preferably controlling the temperature, holding time, and heating rate of the first-stage homogenization treatment within the above ranges helps to ensure sufficient re-dissolution of low-melting-point phases of the material while preventing overheating, and also takes into account the practical requirements of industrial-scale production. An excessively high temperature of the second-stage homogenization treatment may also cause overheating, resulting in material failure. Conversely, an excessively low temperature of the second-stage homogenization treatment may lead to insufficient solubility of elements such as Sn, which is unfavorable for improving the room-temperature storage stability of the aluminum alloy sheet. Preferably, controlling the temperature, holding time, and heating rate of the second-stage homogenization treatment within the above ranges helps to prevent overheating while improving both the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet.

[0035] In order to further re-dissolve the alloying elements, particularly the Sn element, into the Al matrix, thereby improving the paint-bake hardening performance of the aluminum alloy sheet, in one embodiment of the present invention, the above solution treatment is preferably performed using an air-cushion continuous annealing furnace, and the solution treatment includes a heating process, a holding process, and a cooling process performed sequentially; and / or, a heating rate of the heating process is ≥5 °C / s; and / or, a temperature of the holding process is 565-585 °C; and / or, a holding time of the holding process is 0.5-5 min; and / or, a cooling rate of the cooling process is ≥30 °C / s.

[0036] In order to further improve the plasticity of the alloy, refine grains, eliminate casting defects, and improve microstructural uniformity, in one embodiment of the present invention, a material obtained from the homogenization treatment is preferably directly subjected to the above hot rolling treatment without being cooled; and / or, a thickness of the material after the hot rolling treatment is 3-8 mm.

[0037] In order to further improve the dimensional accuracy of the aluminum alloy sheet, relieve the internal stress of the material, and improve the surface quality of the material, in one embodiment of the present invention, the thickness of the material after the above cold rolling treatment is 0.5-3.0 mm.

[0038] The beneficial effects of the present invention will be further illustrated below in conjunction with embodiments.Embodiments 1-8, Comparative Embodiments 1-3

[0039] First, pure aluminum and various master alloys were melted according to the composition ratios shown in Table 1. The melt was refined and then cast into ingots using a Direct Chill (DC) casting equipment. After cropping and scalping, the ingots were placed in a heat-treatment furnace for first-stage homogenization treatment and second-stage homogenization treatment. The heating rate of the first-stage homogenization treatment was 50 °C / h, and the heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 30 °C / h. The ingots after the homogenization treatment were directly discharged for hot rolling, and the thickness of the material after the hot rolling treatment was 5 mm. Upon completion of hot rolling, the obtained hot-rolled sheets were cold-rolled, and the thickness of the material after the cold rolling treatment was 2.0 mm. The obtained cold-rolled sheets were subjected to the solution treatment, the first-stage pre-aging treatment, and the second-stage pre-aging treatment, followed by edge trimming and blanking to obtain aluminum alloy sheets in the T4P temper. The heating rate of the solution treatment was 5 °C / s, and the cooling rate of the solution treatment was 30 °C / s. The specific values for the temperatures and holding times of the first-stage homogenization treatment and the second-stage homogenization treatment, the temperature and holding time of the solution treatment, the temperatures and holding times of the first-stage pre-aging treatment and the second-stage pre-aging treatment, and the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment are shown in Table 2. Table 1Alloy numberMass percentage (wt%)SiMnCuFeMgCrTiSnAl1#0.200.050.150.11.00.020.010.060Balance2#1.450.100.060.30.20.010.020.025Balance3#0.900.150.300.40.40.100.100.005Balance4#0.550.180.200.10.80.050.020.020Balance5#0.950.160.700.20.70.020.030.000Balance6#1.250.180.010.20.40.030.040.300Balance Table 2 Embodiment / Comparative EmbodimentAlloy numberHomogenization treatmentSolution TreatmentPre-aging treatmentFirst-stageSecond-stageFirst-stageTransferSecond-stageTemperatureHolding timeTemperatureHolding timeTemperatureHolding timeTemperatureHolding timeCooling rateTemperatureHolding time°Ch°Ch°Cmin°Cs°C / min°ChEmbodiment 11#4805570656521503057012Embodiment 21#500456585700.5200561302Embodiment 32#520456010570316012010808Embodiment 42#520658065750.51703015908Embodiment 53#50045757585118020101204Embodiment 63#51085709580115018081105Embodiment 74#490105701057021606061004Embodiment 84#48010575856551701505903Comparative Embodiment 12#51075757575318012011008Comparative Embodiment 25#4901057585755160307858Comparative Embodiment 36#49585601058032006061006 Embodiment 9

[0040] Different from Embodiment 7, the content of the Sn element was 0.025wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:8. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 10

[0041] Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:20. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 11

[0042] Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.25wt%, and the mass ratio of the Sn element to the Cu element was 1:25. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 12

[0043] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 140 °C, the holding time of the first-stage pre-aging treatment was 180 s, the temperature of the second-stage pre-aging treatment was 70 °C, and the holding time of the second-stage pre-aging treatment was 12 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 13

[0044] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 200 °C, the holding time of the first-stage pre-aging treatment was 5 s, the temperature of the second-stage pre-aging treatment was 130 °C, and the holding time of the second-stage pre-aging treatment was 1 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 14

[0045] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 205 °C, the holding time of the first-stage pre-aging treatment was 4 s, the temperature of the second-stage pre-aging treatment was 135 °C, and the holding time of the second-stage pre-aging treatment was 0.5 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 15

[0046] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 30 °C / h, the temperature of the first-stage homogenization treatment was 480 °C, and the holding time of the first-stage homogenization treatment was 10 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 20 °C / h, the temperature of the second-stage homogenization treatment was 560 °C, and the holding time of the second-stage homogenization treatment was 10 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 16

[0047] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 80 °C / h, the temperature of the first-stage homogenization treatment was 520 °C, and the holding time of the first-stage homogenization treatment was 4 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 40 °C / h, the temperature of the second-stage homogenization treatment was 580 °C, and the holding time of the second-stage homogenization treatment was 6 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 17

[0048] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 85 °C / h, the temperature of the first-stage homogenization treatment was 475 °C, and the holding time of the first-stage homogenization treatment was 3 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 45 °C / h, the temperature of the second-stage homogenization treatment was 555 °C, and the holding time of the second-stage homogenization treatment was 5 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 18

[0049] Different from Embodiment 7, the temperature of the solution treatment was 565 °C and the holding time of the solution treatment was 5 min. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 19

[0050] Different from Embodiment 7, the temperature of the solution treatment was 585 °C and the holding time of the solution treatment was 0.5 min. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 20

[0051] Different from Embodiment 7, the temperature of the solution treatment was 555 °C and the holding time of the solution treatment was 0.4 min. An aluminum alloy sheet in the T4P temper was finally obtained.Performance testing

[0052] The aluminum alloy sheets in the T4P temper prepared in the above embodiments and comparative embodiments were tested for yield strength after being stored at 25 °C for 7 days and 180 days, respectively. The paint-bake performance was evaluated according to the standards of most original equipment manufacturers. Specifically, the aluminum alloy sheets in the T4P temper stored at 25°C for 7 days were subjected to a 2% pre-stretching treatment, followed by a paint baking treatment in an oil bath at 185 °C for 20 min, and then water quenched to room temperature to obtain aluminum alloy sheets in the T8X temper. The yield strength and paint bake response of the sheets were then measured. The above test results are shown in Table 3. Table 3Embodiment / Comparative EmbodimentAluminum alloy sheet in T4P temperAluminum alloy sheet in T8X temperYield strength after 7 days / MPaYield strength after 180 days / MPaYield strength increment from 7 to 180 Days / MPaYield strength / MPaPaint-bake increment / MPaEmbodiment 19010717235145Embodiment 29010818230140Embodiment 39511520244149Embodiment 49711720246149Embodiment 58811224244156Embodiment 69211523246154Embodiment 79411218268174Embodiment 88710619260173Embodiment 99311017269176Embodiment 109611519273177Embodiment 119811820256158Embodiment 129511116261166Embodiment 139611418265169Embodiment 149911920255156Embodiment 159010919260170Embodiment 169511217271176Embodiment 179611620253157Embodiment 189311118265172Embodiment 199611519270174Embodiment 209511520254159Comparative Embodiment 114415612262118Comparative Embodiment 29712730232135Comparative Embodiment 313314512284151

[0053] From Table 3, it can be seen that in Comparative Embodiment 1, the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment was excessively slow, resulting in excessive formation of clusters, an excessively high yield strength of the sheet in the T4P temper, and poor stamping performance. In Comparative Embodiment 2, insufficient amounts of Sn element and Cu element were added, leading to inadequate room-temperature storage stability in the T4P temper and insufficient paint-bake strength in the T8X temper. In Comparative Embodiment 3, the contents of the Cu element and the Sn element were excessively high, resulting in an excessively high yield strength of the sheet in the T4P temper.

[0054] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects.

[0055] Compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn element to fully re-dissolve into a matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0056] The above is only the preferred embodiments of the present invention, and is not intended to limit the present invention, and for those of ordinary skill in the art, various modifications and changes may be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Examples

embodiment 9

[0040]Different from Embodiment 7, the content of the Sn element was 0.025wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:8. An aluminum alloy sheet in the T4P temper was finally obtained.

embodiment 10

[0041]Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:20. An aluminum alloy sheet in the T4P temper was finally obtained.

embodiment 11

[0042]Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.25wt%, and the mass ratio of the Sn element to the Cu element was 1:25. An aluminum alloy sheet in the T4P temper was finally obtained.

[0001] This application is based upon and claims priority to Chinese Patent Application No. 202411169284.7, filed on August 23, 2024, the invention of which is hereby incorporated by reference in its entirety.Technical Field

[0002] The present invention relates to the technical field of aluminum alloys, and in particular to aluminum alloy sheet and preparation method thereof.Background

[0003] Automotive lightweighting is a relatively economical and effective means to achieve energy conservation and emission reduction, while also improving safety. Aluminum alloy sheets are considered ideal materials for automotive lightweighting due to their advantages of light weight, high specific strength, and excellent overall performance. 6xxx series aluminum alloys have excellent surface quality and heat-treatable strengthening properties, making them the most widely used materials in automotive applications. However, at present, the cost of aluminum alloy automotive sheets is much higher than that of conventional steel, and further cost reduction is urgently needed. While meeting the formability and rigidity requirements of components, increasing the strength of 6xxx series aluminum alloys can reduce the amount of aluminum used, thereby lowering component costs and further enhancing the lightweighting effect. In addition, it is also necessary to maintain excellent formability and room-temperature storage stability of the sheet as the strength increases.

[0004] In recent years, some domestic universities and research institutes have conducted studies on 6xxx series aluminum alloy automotive sheets. For example: Chinese Patent with Authorization Announcement No. CN112095039B discloses a method for improving paint-bake performance through two-stage pre-aging, but it does not concern room-temperature storage stability. Especially with microalloying of Sn and Cu, the preparation process becomes more complex, making it difficult to meet requirements. Chinese Patent with Authorization Announcement No. CN103740988B discloses a preparation method of a high-performance aluminum alloy for an automotive component, but the addition of elements such as Zr and Sr increases cost. Chinese Patent Application with Publication No. CN117467873A discloses an Al-Mg-Si-Sn-Sc alloy and a preparation method thereof, in which Sc element is added. In addition, the alloy is supplied in a T6 temper. Summary

[0005] A main objective of the present invention is to provide aluminum alloy sheet and preparation method thereof, so as to solve the problems in the related art that formability, room-temperature storage stability, and paint-bake hardening performance of the aluminum alloy sheet are difficult to achieve simultaneously.

[0006] In order to achieve the above objective, according to one aspect of the present invention, an aluminum alloy sheet is provided. The aluminum alloy sheet includes the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element. A total content of inevitable impurities is≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%.

[0007] Further, the above aluminum alloy sheet includes the following elements, by mass percentage: 0.40-1.25wt% of Si element, 0.1-0.3wt% of Fe element, 0.15-0.25wt% of Cu element, 0.10-0.18wt% of Mn element, 0.4-0.8wt% of Mg element, 0.01-0.05wt% of Cr element, 0.02-0.04wt% of Ti element, and 0.010-0.025wt% of Sn element, with the balance being Al. The total content of inevitable impurities is ≤0.15wt%, and the content of any single impurity is less than or equal to 0.05wt%.

[0008] Further, a mass ratio of the above Sn element to the Cu element is 1:8-20.

[0009] Further, a yield strength of the above aluminum alloy sheet after being stored at 25 °C for 7 days is less than 100 MPa; and / or, an increment in the yield strength of the aluminum alloy sheet after being stored at 25 °C for 180 days compared with that after being stored for 7 days does not exceed 24 MPa; and / or, the aluminum alloy sheet after being stored at 25 °C for 7 days is sequentially subjected to a 2% pre-stretching treatment and a paint baking treatment at 185 °C for 20 min to obtain a treated aluminum alloy sheet. A yield strength of the treated aluminum alloy sheet is greater than 220 MPa, and a paint bake response is greater than 140 MPa.

[0010] According to another aspect of the present invention, a preparation method of the above-mentioned aluminum alloy sheet is provided. The preparation method includes: melting, refining, and casting raw materials including metals in proportion to obtain an aluminum alloy ingot; and subjecting the aluminum alloy ingot sequentially to a homogenization treatment, a hot rolling treatment, a cold rolling treatment, a solution treatment, a first-stage pre-aging treatment, and a second-stage pre-aging treatment to obtain an aluminum alloy sheet. A temperature of the first-stage pre-aging treatment is greater than that of the second-stage pre-aging treatment, and a cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment is ≥5 °C / min.

[0011] Further, the temperature of the above first-stage pre-aging treatment is 140-200 °C; and / or, a holding time of the first-stage pre-aging treatment is 5-180 s; and / or, the temperature of the second-stage pre-aging treatment is 70-130 °C; and / or, a holding time of the second-stage pre-aging treatment is 1-12 h.

[0012] Further, the above homogenization treatment includes a first-stage homogenization treatment and a second-stage homogenization treatment performed sequentially. A heating rate of the first-stage homogenization treatment is 30-80 °C / h; and / or, a temperature of the first-stage homogenization treatment is 480-520 °C; and / or, a holding time of the first-stage homogenization treatment is 4-10 h; and / or, a heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment is 20-40 °C / h; and / or, a temperature of the second-stage homogenization treatment is 560-580 °C; and / or, a holding time of the second-stage homogenization treatment is 6-10 h.

[0013] Further, the above solution treatment is performed using an air-cushion continuous annealing furnace, and the solution treatment includes a heating process, a holding process, and a cooling process performed sequentially; and / or, a heating rate of the heating process is ≥5 °C / s; and / or, a temperature of the holding process is 565-585 °C; and / or, a holding time of the holding process is 0.5-5 min; and / or, a cooling rate of the cooling process is ≥30 °C / s.

[0014] Further, a material obtained from the homogenization treatment is directly subjected to the above hot rolling treatment without being cooled; and / or, a thickness of the material after the hot rolling treatment is 3-8 mm.

[0015] Further, a thickness of the material after the above cold rolling treatment is 0.5-3.0 mm.

[0016] By applying the technical solution of the present invention, compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn atoms to fully re-dissolve into the Al matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.Detailed Description of the Embodiments

[0017] It is to be noted that the embodiments in the present invention and features in the embodiments may be combined with each other without conflict. The present invention is illustrated in detail below in conjunction with the embodiments.

[0018] It is to be noted that mass percentage refers to a percentage of a mass (weight) of a certain alloy component relative to a total mass of the alloy.

[0019] Yield strength refers to the stress at which the aluminum alloy begins to yield, defined as the stress value that produces 0.2% residual deformation. A stress-strain curve is obtained through a uniaxial tensile test, and yield strength data is obtained from this curve.

[0020] Paint bake response refers to the difference in yield strength of the aluminum alloy sheet before and after a 2% pre-stretching treatment followed by a paint baking treatment, e.g. at 185 °C for 20 min.

[0021] As analyzed in the background of the present invention, there is a problem with 6xxx series aluminum alloy sheets in that formability, room temperature storage stability, and paint-bake hardening performance are difficult to achieve simultaneously. In order to solve the problems, the present invention provides aluminum alloy sheet and preparation method thereof.

[0022] In a typical implementation of the present invention, an aluminum alloy sheet is provided. The aluminum alloy sheet includes the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element. A total content of inevitable impurities is ≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%.

[0023] Compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn atoms to fully re-dissolve into the Al matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0024] In order to further enhance the synergistic effects among different elements, thereby further reducing the yield strength of the aluminum alloy sheet and improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet, in one embodiment of the present invention, the above aluminum alloy sheet preferably includes the following elements, by mass percentage: 0.40-1.25wt% of Si element, 0.1-0.3wt% of Fe element, 0.15-0.25wt% of Cu element, 0.10-0.18wt% of Mn element, 0.4-0.8wt% of Mg element, 0.01-0.05wt% of Cr element, 0.02-0.04wt% of Ti element, and 0.010-0.025wt% of Sn element, with the balance being Al. The total content of inevitable impurities is ≤0.15wt%, and the content of any single impurity is less than or equal to 0.05wt%.

[0025] In one embodiment of the present invention, a mass ratio of the above Sn element to the Cu element is 1:8-20.

[0026] If the mass ratio of the Sn element to the Cu element is excessively high, the paint-bake strength and paint bake response of the sheet may decrease. If the mass ratio of the Sn element to the Cu element is excessively low, the strength of the sheet may be excessively high, and the room-temperature storage stability may be reduced, thereby resulting in insufficient formability of the sheet. Preferably, controlling the mass ratio of the Sn element to the Cu element within the above range helps to fully exert the synergistic interaction between the Sn element and the Cu element, thereby further improving paint-bake hardening performance and the room-temperature storage stability of the aluminum alloy sheet to a certain extent.

[0027] In one embodiment of the present invention, a yield strength of the above aluminum alloy sheet after being stored at 25 °C for 7 days is less than 100 MPa; and / or, an increment in the yield strength of the aluminum alloy sheet after being stored at 25 °C for 180 days compared with that after being stored for 7 days does not exceed 24 MPa; and / or, the aluminum alloy sheet after being stored at 25 °C for 7 days is sequentially subjected to a 2% pre-stretching treatment and a paint baking treatment at 185 °C for 20 min to obtain a treated aluminum alloy sheet. A yield strength of the treated aluminum alloy sheet is greater than 220 MPa, and a paint bake response is greater than 140 MPa.

[0028] The aluminum alloy sheet of the present invention is an aluminum alloy sheet in a T4P temper, and the treated aluminum alloy sheet is an aluminum alloy sheet in a T8X temper. The aluminum alloy sheet having the above ranges of yield strength and paint bake response helps to achieve thickness reduction of the aluminum alloy sheet under equal-strength conditions, thereby reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0029] In another typical implementation of the present invention, a preparation method of the above-mentioned aluminum alloy sheet is provided. The preparation method includes: melting, refining, and casting raw materials including metals in proportion to obtain an aluminum alloy ingot; and subjecting the aluminum alloy ingot sequentially to a homogenization treatment, a hot rolling treatment, a cold rolling treatment, a solution treatment, a first-stage pre-aging treatment, and a second-stage pre-aging treatment to obtain an aluminum alloy sheet. A temperature of the first-stage pre-aging treatment is greater than that of the second-stage pre-aging treatment, and a cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment is ≥5 °C / min.

[0030] In the present invention, subjecting the aluminum alloy ingot to the homogenization treatment helps to enable effective re-dissolution of alloying elements, particularly the Sn element, thereby helping to improve the distribution uniformity of the alloying elements within the matrix, and in turn helping to improve the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet. Subjecting the alloy after the homogenization treatment to the hot rolling treatment helps to improve the plasticity of the alloy, thereby facilitating subsequent processing of the alloy. In addition, the hot rolling treatment also helps to refine grains, eliminate casting defects, and improve microstructural uniformity. Subjecting the alloy after the hot rolling treatment to the cold rolling treatment helps to improve the dimensional accuracy of the aluminum alloy sheet, relieve the internal stress of the material, and improve the surface quality of the material. Subjecting the alloy after the cold rolling treatment to the solution treatment helps to dissolve the alloying elements, particularly the Sn element, into the Al matrix, thereby helping to improve the paint-bake hardening performance of the aluminum alloy sheet. Employing a two-stage pre-aging treatment helps to further improve the paint-bake hardening performance of the aluminum alloy sheet. Specifically, the first-stage pre-aging treatment helps to form clusters that are more favorable for transformation into β" strengthening phase during the paint-bake process. The second-stage pre-aging treatment helps to improve the room-temperature storage stability of the aluminum alloy sheet, thereby enabling the aluminum alloy sheet to achieve both high room-temperature storage stability and paint-bake hardening performance. Preferably controlling the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment within the above range helps to reduce the risk of excessive formation or coarsening of clusters, which may result in an excessively high initial yield strength and a decline in formability of the aluminum alloy sheet.

[0031] In one embodiment of the present invention, the temperature of the above first-stage pre-aging treatment is 140-200 °C; and / or, a holding time of the first-stage pre-aging treatment is 5-180 s; and / or, the temperature of the second-stage pre-aging treatment is 70-130 °C; and / or, a holding time of the second-stage pre-aging treatment is 1-12 h.

[0032] An excessively high temperature of the first-stage pre-aging treatment leads to excessive formation, of clusters, thereby resulting in an excessively high initial strength of the sheet. Conversely, an excessively low temperature of the first-stage pre-aging treatment also cannot achieve the effect of first-stage pre-aging, leading to insufficient paint-bake strength of the sheet. Preferably controlling the temperature and holding time of the first-stage pre-aging treatment within the above ranges helps to form more clusters that are favorable for transformation into the β" strengthening phase during the paint-bake process. An excessively high temperature of the second-stage pre-aging treatment promotes excessive formation of clusters, thereby resulting in an excessively high initial strength of the sheet. Conversely, an excessively low temperature of the second-stage pre-aging treatment cannot achieve the effect of pre-aging, leading to a deterioration in room-temperature storage stability. Preferably controlling the temperature and holding time of the second-stage pre-aging treatment within the above ranges helps to further improve the room-temperature storage stability of the aluminum alloy sheet.

[0033] In one embodiment of the present invention, the above homogenization treatment includes a first-stage homogenization treatment and a second-stage homogenization treatment performed sequentially. A heating rate of the first-stage homogenization treatment is 30-80 °C / h; and / or, a temperature of the first-stage homogenization treatment is 480-520 °C; and / or, a holding time of the first-stage homogenization treatment is 4-10 h; and / or, a heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment is 20-40 °C / h; and / or, a temperature of the second-stage homogenization treatment is 560-580 °C; and / or, a holding time of the second-stage homogenization treatment is 6-10 h.

[0034] An excessively high temperature of the first-stage homogenization treatment may cause overheating, resulting in material failure. Conversely, an excessively low temperature of the first-stage homogenization treatment cannot ensure sufficient re-dissolution of low-melting-point phases. Preferably controlling the temperature, holding time, and heating rate of the first-stage homogenization treatment within the above ranges helps to ensure sufficient re-dissolution of low-melting-point phases of the material while preventing overheating, and also takes into account the practical requirements of industrial-scale production. An excessively high temperature of the second-stage homogenization treatment may also cause overheating, resulting in material failure. Conversely, an excessively low temperature of the second-stage homogenization treatment may lead to insufficient solubility of elements such as Sn, which is unfavorable for improving the room-temperature storage stability of the aluminum alloy sheet. Preferably, controlling the temperature, holding time, and heating rate of the second-stage homogenization treatment within the above ranges helps to prevent overheating while improving both the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet.

[0035] In order to further re-dissolve the alloying elements, particularly the Sn element, into the Al matrix, thereby improving the paint-bake hardening performance of the aluminum alloy sheet, in one embodiment of the present invention, the above solution treatment is preferably performed using an air-cushion continuous annealing furnace, and the solution treatment includes a heating process, a holding process, and a cooling process performed sequentially; and / or, a heating rate of the heating process is ≥5 °C / s; and / or, a temperature of the holding process is 565-585 °C; and / or, a holding time of the holding process is 0.5-5 min; and / or, a cooling rate of the cooling process is ≥30 °C / s.

[0036] In order to further improve the plasticity of the alloy, refine grains, eliminate casting defects, and improve microstructural uniformity, in one embodiment of the present invention, a material obtained from the homogenization treatment is preferably directly subjected to the above hot rolling treatment without being cooled; and / or, a thickness of the material after the hot rolling treatment is 3-8 mm.

[0037] In order to further improve the dimensional accuracy of the aluminum alloy sheet, relieve the internal stress of the material, and improve the surface quality of the material, in one embodiment of the present invention, the thickness of the material after the above cold rolling treatment is 0.5-3.0 mm.

[0038] The beneficial effects of the present invention will be further illustrated below in conjunction with embodiments.Embodiments 1-8, Comparative Embodiments 1-3

[0039] First, pure aluminum and various master alloys were melted according to the composition ratios shown in Table 1. The melt was refined and then cast into ingots using a Direct Chill (DC) casting equipment. After cropping and scalping, the ingots were placed in a heat-treatment furnace for first-stage homogenization treatment and second-stage homogenization treatment. The heating rate of the first-stage homogenization treatment was 50 °C / h, and the heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 30 °C / h. The ingots after the homogenization treatment were directly discharged for hot rolling, and the thickness of the material after the hot rolling treatment was 5 mm. Upon completion of hot rolling, the obtained hot-rolled sheets were cold-rolled, and the thickness of the material after the cold rolling treatment was 2.0 mm. The obtained cold-rolled sheets were subjected to the solution treatment, the first-stage pre-aging treatment, and the second-stage pre-aging treatment, followed by edge trimming and blanking to obtain aluminum alloy sheets in the T4P temper. The heating rate of the solution treatment was 5 °C / s, and the cooling rate of the solution treatment was 30 °C / s. The specific values for the temperatures and holding times of the first-stage homogenization treatment and the second-stage homogenization treatment, the temperature and holding time of the solution treatment, the temperatures and holding times of the first-stage pre-aging treatment and the second-stage pre-aging treatment, and the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment are shown in Table 2. Table 1Alloy numberMass percentage (wt%)SiMnCuFeMgCrTiSnAl1#0.200.050.150.11.00.020.010.060Balance2#1.450.100.060.30.20.010.020.025Balance3#0.900.150.300.40.40.100.100.005Balance4#0.550.180.200.10.80.050.020.020Balance5#0.950.160.700.20.70.020.030.000Balance6#1.250.180.010.20.40.030.040.300Balance Table 2 Embodiment / Comparative EmbodimentAlloy numberHomogenization treatmentSolution TreatmentPre-aging treatmentFirst-stageSecond-stageFirst-stageTransferSecond-stageTemperatureHolding timeTemperatureHolding timeTemperatureHolding timeTemperatureHolding timeCooling rateTemperatureHolding time°Ch°Ch°Cmin°Cs°C / min°ChEmbodiment 11#4805570656521503057012Embodiment 21#500456585700.5200561302Embodiment 32#520456010570316012010808Embodiment 42#520658065750.51703015908Embodiment 53#50045757585118020101204Embodiment 63#51085709580115018081105Embodiment 74#490105701057021606061004Embodiment 84#48010575856551701505903Comparative Embodiment 12#51075757575318012011008Comparative Embodiment 25#4901057585755160307858Comparative Embodiment 36#49585601058032006061006 Embodiment 9

[0040] Different from Embodiment 7, the content of the Sn element was 0.025wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:8. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 10

[0041] Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:20. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 11

[0042] Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.25wt%, and the mass ratio of the Sn element to the Cu element was 1:25. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 12

[0043] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 140 °C, the holding time of the first-stage pre-aging treatment was 180 s, the temperature of the second-stage pre-aging treatment was 70 °C, and the holding time of the second-stage pre-aging treatment was 12 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 13

[0044] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 200 °C, the holding time of the first-stage pre-aging treatment was 5 s, the temperature of the second-stage pre-aging treatment was 130 °C, and the holding time of the second-stage pre-aging treatment was 1 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 14

[0045] Different from Embodiment 7, the temperature of the first-stage pre-aging treatment was 205 °C, the holding time of the first-stage pre-aging treatment was 4 s, the temperature of the second-stage pre-aging treatment was 135 °C, and the holding time of the second-stage pre-aging treatment was 0.5 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 15

[0046] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 30 °C / h, the temperature of the first-stage homogenization treatment was 480 °C, and the holding time of the first-stage homogenization treatment was 10 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 20 °C / h, the temperature of the second-stage homogenization treatment was 560 °C, and the holding time of the second-stage homogenization treatment was 10 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 16

[0047] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 80 °C / h, the temperature of the first-stage homogenization treatment was 520 °C, and the holding time of the first-stage homogenization treatment was 4 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 40 °C / h, the temperature of the second-stage homogenization treatment was 580 °C, and the holding time of the second-stage homogenization treatment was 6 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 17

[0048] Different from Embodiment 7, the heating rate of the first-stage homogenization treatment was 85 °C / h, the temperature of the first-stage homogenization treatment was 475 °C, and the holding time of the first-stage homogenization treatment was 3 h. The heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment was 45 °C / h, the temperature of the second-stage homogenization treatment was 555 °C, and the holding time of the second-stage homogenization treatment was 5 h. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 18

[0049] Different from Embodiment 7, the temperature of the solution treatment was 565 °C and the holding time of the solution treatment was 5 min. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 19

[0050] Different from Embodiment 7, the temperature of the solution treatment was 585 °C and the holding time of the solution treatment was 0.5 min. An aluminum alloy sheet in the T4P temper was finally obtained.Embodiment 20

[0051] Different from Embodiment 7, the temperature of the solution treatment was 555 °C and the holding time of the solution treatment was 0.4 min. An aluminum alloy sheet in the T4P temper was finally obtained.Performance testing

[0052] The aluminum alloy sheets in the T4P temper prepared in the above embodiments and comparative embodiments were tested for yield strength after being stored at 25 °C for 7 days and 180 days, respectively. The paint-bake performance was evaluated according to the standards of most original equipment manufacturers. Specifically, the aluminum alloy sheets in the T4P temper stored at 25°C for 7 days were subjected to a 2% pre-stretching treatment, followed by a paint baking treatment in an oil bath at 185 °C for 20 min, and then water quenched to room temperature to obtain aluminum alloy sheets in the T8X temper. The yield strength and paint bake response of the sheets were then measured. The above test results are shown in Table 3. Table 3Embodiment / Comparative EmbodimentAluminum alloy sheet in T4P temperAluminum alloy sheet in T8X temperYield strength after 7 days / MPaYield strength after 180 days / MPaYield strength increment from 7 to 180 Days / MPaYield strength / MPaPaint-bake increment / MPaEmbodiment 19010717235145Embodiment 29010818230140Embodiment 39511520244149Embodiment 49711720246149Embodiment 58811224244156Embodiment 69211523246154Embodiment 79411218268174Embodiment 88710619260173Embodiment 99311017269176Embodiment 109611519273177Embodiment 119811820256158Embodiment 129511116261166Embodiment 139611418265169Embodiment 149911920255156Embodiment 159010919260170Embodiment 169511217271176Embodiment 179611620253157Embodiment 189311118265172Embodiment 199611519270174Embodiment 209511520254159Comparative Embodiment 114415612262118Comparative Embodiment 29712730232135Comparative Embodiment 313314512284151

[0053] From Table 3, it can be seen that in Comparative Embodiment 1, the cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment was excessively slow, resulting in excessive formation of clusters, an excessively high yield strength of the sheet in the T4P temper, and poor stamping performance. In Comparative Embodiment 2, insufficient amounts of Sn element and Cu element were added, leading to inadequate room-temperature storage stability in the T4P temper and insufficient paint-bake strength in the T8X temper. In Comparative Embodiment 3, the contents of the Cu element and the Sn element were excessively high, resulting in an excessively high yield strength of the sheet in the T4P temper.

[0054] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects.

[0055] Compared with the Mg element and the Si element, the Sn element and the Cu element have higher vacancy binding energy. By adding the Sn element and the Cu element, the present invention helps to improve the room-temperature storage stability of the aluminum alloy sheet. Moreover, at high temperature, the release of vacancies in the aluminum alloy sheet and the precipitation of Sn-containing phase and Cu-containing phase help to improve the paint-bake hardening performance of the aluminum alloy sheet. When the content of the Sn element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Sn element is excessively high, it is unfavorable for the Sn element to fully re-dissolve into a matrix, thereby being unfavorable for improving the microstructural distribution uniformity of the aluminum alloy sheet. When the content of the Cu element is excessively low, the effects of improving the room-temperature storage stability and paint-bake hardening performance of the aluminum alloy sheet are not significant. When the content of the Cu element is excessively high, it is unfavorable for improving the stamping performance and corrosion resistance of the aluminum alloy sheet. The addition of Si, Fe, Mn, Mg, Cr, and Ti elements to the aluminum alloy sheet helps to improve the overall performance such as formability, paint baking performance, and corrosion resistance of the aluminum alloy sheet. Preferably controlling the mass content of each element in the aluminum alloy sheet within the above range enhances the synergistic effects among different elements, thereby further improving the room-temperature storage stability, paint-bake hardening performance, and stamping formability of the aluminum alloy sheet. Consequently, the aluminum alloy sheet of the present invention may meet the forming requirements of more complex components. Furthermore, due to the high paint-bake hardening performance, the aluminum alloy sheet of the present invention enables thickness reduction of the aluminum alloy sheet under equal-strength conditions, reducing the amount of aluminum alloy sheet used and further enhancing the lightweighting effect of the aluminum alloy sheet.

[0056] The above is only the preferred embodiments of the present invention, and is not intended to limit the present invention, and for those of ordinary skill in the art, various modifications and changes may be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Examples

embodiment 9

[0040]Different from Embodiment 7, the content of the Sn element was 0.025wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:8. An aluminum alloy sheet in the T4P temper was finally obtained.

embodiment 10

[0041]Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.20wt%, and the mass ratio of the Sn element to the Cu element was 1:20. An aluminum alloy sheet in the T4P temper was finally obtained.

embodiment 11

[0042]Different from Embodiment 7, the content of the Sn element was 0.010wt%, the content of the Cu element was 0.25wt%, and the mass ratio of the Sn element to the Cu element was 1:25. An aluminum alloy sheet in the T4P temper was finally obtained.

Claims

1. An aluminum alloy sheet, comprising the following elements, by mass percentage: 0.20-1.45wt% of Si element, ≤0.40wt% of Fe element, 0.06-0.30wt% of Cu element, 0.05-0.2wt% of Mn element, 0.2-1.0wt% of Mg element, ≤0.1wt% of Cr element, 0.01-0.10wt% of Ti element, and 0.005-0.06wt% of Sn element, with the balance being Al element, wherein a total content of inevitable impurities is ≤0.15wt%, and a content of any single impurity is less than or equal to 0.05wt%.

2. The aluminum alloy sheet according to claim 1, comprising the following elements, by mass percentage: 0.40-1.25wt% of Si element, 0.1-0.3wt% of Fe element, 0.15-0.25wt% of Cu element, 0.10-0.18wt% of Mn element, 0.4-0.8wt% of Mg element, 0.01-0.05wt% of Cr element, 0.02-0.04wt% of Ti element, and 0.010-0.025wt% of Sn element, with the balance being Al, wherein the total content of inevitable impurities is ≤0.15wt%, and the content of any single impurity is less than or equal to 0.05wt%.

3. The aluminum alloy sheet according to claim 1 or 2, wherein a mass ratio of the Sn element to the Cu element is 1:8-20.

4. The aluminum alloy sheet according to any one of claims 1 to 3, wherein a yield strength of the aluminum alloy sheet after being stored at 25 °C for 7 days is less than 100 MPa; and / or, an increment in the yield strength of the aluminum alloy sheet after being stored at 25 °C for 180 days compared with that after being stored for 7 days does not exceed 24 MPa; and / or, the aluminum alloy sheet after being stored at 25 °C for 7 days is sequentially subjected to a 2% pre-stretching treatment and a paint baking treatment at 185 °C for 20 min to obtain a treated aluminum alloy sheet, wherein a yield strength of the treated aluminum alloy sheet is greater than 220 MPa, and a paint bake response is greater than 140 MPa.

5. A preparation method of the aluminum alloy sheet according to any one of claims 1 to 4, comprising: melting, refining, and casting raw materials comprising metals in proportion to obtain an aluminum alloy ingot; subjecting the aluminum alloy ingot sequentially to a homogenization treatment, a hot rolling treatment, a cold rolling treatment, a solution treatment, a first-stage pre-aging treatment, and a second-stage pre-aging treatment to obtain an aluminum alloy sheet; wherein a temperature of the first-stage pre-aging treatment is greater than that of the second-stage pre-aging treatment, and a cooling rate from the first-stage pre-aging treatment to the second-stage pre-aging treatment is ≥5 °C / min.

6. The preparation method according to claim 5, wherein the temperature of the first-stage pre-aging treatment is 140-200 °C; and / or, a holding time of the first-stage pre-aging treatment is 5-180 s; and / or, the temperature of the second-stage pre-aging treatment is 70-130 °C; and / or, a holding time of the second-stage pre-aging treatment is 1-12 h.

7. The preparation method according to claim 5 or 6, wherein the homogenization treatment comprises a first-stage homogenization treatment and a second-stage homogenization treatment performed sequentially; wherein a heating rate of the first-stage homogenization treatment is 30-80 °C / h; and / or, a temperature of the first-stage homogenization treatment is 480-520 °C; and / or, a holding time of the first-stage homogenization treatment is 4-10 h; and / or, a heating rate from the first-stage homogenization treatment to the second-stage homogenization treatment is 20-40 °C / h; and / or, a temperature of the second-stage homogenization treatment is 560-580 °C; and / or, a holding time of the second-stage homogenization treatment is 6-10 h.

8. The preparation method according to any one of claims 5 to 7, wherein the solution treatment is performed using an air-cushion continuous annealing furnace, and the solution treatment comprises a heating process, a holding process, and a cooling process performed sequentially; and / or, a heating rate of the heating process is ≥5 °C / s; and / or, a temperature of the holding process is 565-585 °C; and / or, a holding time of the holding process is 0.5-5 min; and / or, a cooling rate of the cooling process is ≥30 °C / s.

9. The preparation method according to any one of claims 5 to 8, wherein a material obtained from the homogenization treatment is directly subjected to the hot rolling treatment without being cooled; and / or, a thickness of the material after the hot rolling treatment is 3-8 mm.

10. The preparation method according to any one of claims 5 to 9, wherein a thickness of the material after the cold rolling treatment is 0.5-3.0 mm.

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