Preparation and hemming performance characterization method of high-hemming aluminum alloy automobile sheet

Abstract

The invention discloses a high-curled-edge aluminum alloy automobile sheet preparation and curled-edge performance characterization method. The method comprises the following steps: (1) proportioning according to an alloy component proportion; (2) smelting the prepared raw materials, and casting after slagging-off, degassing and filtering treatment to obtain a cast ingot; (3) carrying out two-stage homogenization treatment on the cast ingot; (4) carrying out hot rolling on the homogenized cast ingot to obtain a hot-rolled coiled material; (5) carrying out primary cold rolling, intermediate annealing and secondary cold rolling on the hot-rolled plate to obtain a cold-rolled plate; and (6) the cold-rolled sheet is subjected to solution quenching treatment on a continuous annealing line, then pre-aging rolling treatment is conducted, and the high-curled-edge aluminum alloy automobile sheet is obtained. And (7) sampling the aluminum alloy automobile sheet, preparing a sample by using an electrolytic double-spraying method, obtaining the form and distribution of a precipitated phase at the grain boundary position of the aluminum alloy sheet through a scanning electron microscope, and visually characterizing the crimping performance of the sheet. The method can be used for preparing the aluminum alloy automobile plate with the high hemming performance, and characterization and evaluation of the hemming performance are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy profile preparation, and in particular to a method for preparing a high-curling aluminum alloy automobile plate and characterizing its curling performance. Background Art

[0002] With the continuous development of the automobile industry and the continuous increase in the number of cars, the three major issues of energy, environment and safety have become increasingly prominent. Energy shortage and environmental pollution have become the main reasons affecting the sustainable development of the automobile industry. To promote automobile energy conservation and emission reduction, we can consider optimizing the efficiency of power transmission, promoting the lightweight of automobile material structure, and improving aerodynamic parameters. Compared with other methods, automobile lightweighting is a measure to promote energy conservation and emission reduction that is easier to implement and has a better effect. Aluminum alloy has high specific strength, is easy to form, has good energy absorption effect, is corrosion-resistant, and has a high recycling value. Therefore, it is regarded as one of the ideal materials for automobile lightweighting.

[0003] Heat-treatable and strengthened 6xxx series Al-Mg-Si alloys are widely used as aluminum alloy automobile body panels due to their excellent formability, high bake hardening performance and corrosion resistance. It should be noted that during the forming process of aluminum alloy sheets, especially aluminum alloy automobile outer panels, they need to be bent 180° during the stamping process to surround the inner panel, and the surface of the bent component must remain smooth, otherwise, if the sheet hemming ability is insufficient, cracks will appear on the sheet surface, and even fractures will occur, resulting in substandard product performance. At present, although a lot of research has been done in the prior art on improving the hemming performance of 6 series aluminum alloys, there is still a situation of poor hemming performance, and the hemming performance relies on bending tests for testing, and after the bending test is completed, metallographic photography and grade evaluation of the outer surface are required, and the detection time is long, resulting in low production efficiency. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing high-curling aluminum alloy automobile plates and characterizing the curling performance, which can prepare aluminum alloy automobile plates with high curling performance and characterize and evaluate the curling performance through the precipitation phase at the grain boundary position of the aluminum alloy plate.

[0005] The technical solution adopted by the present invention is:

[0006] The present invention provides a method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance, comprising the steps of:

[0007] (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 0.7% to 1.0%, Fe 0.08% to 0.15%, Cu ≤ 0.2%, Mn 0.05% to 0.10%, Mg 0.4% to 0.6%, Cr ≤ 0.05%, Zn ≤ 0.20%, Ti ≤ 0.15%, and the balance is Al and other inevitable impurities, and the single content of the impurities is not more than 0.02%, and the total amount is not more than 0.1%;

[0008] (2) Melting and casting: The prepared aluminum alloy raw materials are placed in a melting furnace for melting, and after slagging, degassing and filtering, they are cast to obtain aluminum alloy ingots;

[0009] (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for a two-stage homogenization treatment;

[0010] (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the hot rolled intermediate billet has a thickness of 51 to 53 mm, and the aluminum alloy sheet after hot rough rolling is subjected to five-stage finish rolling to obtain a hot rolled sheet with a thickness of 8 to 10 mm, which is then coiled at 300 to 350°C;

[0011] (5) Cold rolling: The hot-rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process to obtain a cold-rolled sheet with a thickness of 1.0 to 1.5 mm;

[0012] (6) Solution treatment and pre-aging: The cold-rolled sheet is solution-quenched in a continuous annealing line, and then the solution-quenched sheet is pre-aged and rolled in a box furnace to obtain a high-curling aluminum alloy automobile sheet;

[0013] (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile plates were taken and prepared using the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy plate were obtained using a scanning electron microscope to intuitively characterize the hemming performance of the plate.

[0014] Specifically, in the above technical solution, the present invention optimizes the alloy composition, mainly adjusts the content of Si and Fe elements, and reduces the content of the above two elements, which is beneficial to reduce the tendency of aluminum alloy to form coarse compounds, that is, it is beneficial to improve the curling performance of the plate.

[0015] Furthermore, the homogenization heat treatment process in step (3) is as follows: the aluminum alloy ingot is heated to 520-530° C. and kept warm for 6-8 hours, then heated to 555-565° C. and kept warm for 8-10 hours, and then air-cooled.

[0016] Specifically, in the above technical scheme, the present invention optimizes the homogenization process and adopts a two-stage homogenization process. In the first-stage homogenization process, the small-sized second phase is first fully dissolved, and the homogenization temperature is further increased in the second-stage homogenization process, which is beneficial to the further dissolution of the Mg2Si phase in the matrix and fully ensures the dissolution effect.

[0017] Furthermore, in the step (5), the cold rolling passes are distributed as follows: 8-10 mm→6-7.5 mm→4-5 mm→intermediate annealing→2-2.5 mm→1.0-1.5 mm.

[0018] Furthermore, in the step (5), the intermediate annealing process is carried out in a continuous annealing line, the intermediate annealing temperature is 400-450° C., and the intermediate annealing time is 20-30 seconds.

[0019] Specifically, in the above technical scheme, the present invention performs intermediate annealing between cold rolling passes, and the intermediate annealing is performed on a continuous annealing line. The rapid heating of the continuous annealing line production line can ensure that the second phase in the matrix does not have time to grow during the annealing process, and ensure that the second phase precipitated during the annealing process is completely dissolved in the solid solution stage, which is beneficial to reduce the second phase content in the matrix.

[0020] Furthermore, in step (6), the solution treatment temperature is 540-560°C, the solution treatment time is 20-30s, and the pre-aging temperature is 60-80°C.

[0021] Specifically, in the above technical solution, the above solid treatment system can ensure that the second phase of the plate is fully dissolved back during the solid solution process. At the same time, the low-temperature pre-aging makes the grain boundary phase precipitated from the plate less during the pre-aging process.

[0022] Furthermore, the quenching method in step (6) is water cooling.

[0023] Furthermore, the step (7) is specifically as follows:

[0024] (71) Cut the aluminum alloy plate along the rolling direction to a thickness of 1.0 to 1.5 mm using wire cutting, stick a transparent tape on the surface of the sample, place the sample in a fully automatic grinding and polishing machine for grinding and polishing, and use a punch to punch the polished sample into a small disc sample with a diameter of 3 mm;

[0025] (72) Methanol and nitric acid were measured in a beaker in a volume ratio of 3:1 and stirred evenly to prepare an electrolytic double spray solution;

[0026] (73) The small disc sample was placed in an electrolytic double-spray solution for electrolytic double-spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer to observe the grain boundary precipitation phase of the aluminum alloy plate.

[0027] Furthermore, in the step (73), during the electrolysis double spray process, the electrolysis voltage is 35 to 45 V, the current is 25 to 35 mA, the time is 1 min 30 s to 3 min, and the electrolyte temperature is controlled to -40 to -30 ° C by using liquid nitrogen to cool the electrolyte.

[0028] Furthermore, in the step (7), when the precipitated phase at the grain boundary of the aluminum alloy plate is discontinuously distributed and the precipitated phase is ≤2μm, it means that the curling performance meets the requirements and the curling coefficient is ≤0.5; when the precipitated phase at the grain boundary of the aluminum alloy plate is continuously distributed or agglomerated and the precipitated phase at the grain boundary is greater than 2μm, it means that the curling performance does not meet the requirements and the curling coefficient is >0.5.

[0029] The beneficial effects of the present invention are:

[0030] The present invention provides a method for preparing a high-curling aluminum alloy automobile plate and characterizing its curling performance. The curling performance of the aluminum alloy automobile plate is improved by optimizing the alloy component ratio and optimizing production processes such as hot rolling, primary cold rolling, intermediate annealing, secondary cold rolling, solid solution, and pre-aging. The production and manufacturing process is simple, the cost is low, and the performance is stable. In addition, the present invention obtains the distribution of precipitated phases at the grain boundary position of the aluminum alloy plate by low-temperature electrolysis, and can intuitively characterize and evaluate the curling performance of the aluminum alloy plate through the distribution of precipitated phases at the grain boundary. The detection time is short, and the production efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 is a flow chart of the present invention;

[0033] Figure 2 This is a distribution diagram of the grain boundary precipitation phase of Example 1 of the present invention;

[0034] Figure 3 This is a distribution diagram of the grain boundary precipitation phase of Example 2 of the present invention;

[0035] Figure 4 This is a distribution diagram of the grain boundary precipitation phase of Example 3 of the present invention;

[0036] Figure 5 This is the distribution diagram of the grain boundary precipitation phase of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention provides a method for preparing a high-curling aluminum alloy automobile plate and characterizing the curling performance. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Example 1

[0039] Reference Figure 1 This embodiment provides a method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance, comprising the steps of:

[0040] (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 0.8%, Fe 0.09%, Cu 0.05%, Mn 0.08%, Mg 0.40%, Cr 0.04%, Zn 0.03%, Ti 0.03%, and the balance is Al and other inevitable impurities, and the single content of the impurities is not more than 0.02%, and the total amount is not more than 0.1%;

[0041] (2) Melting and casting: placing the prepared aluminum alloy raw material in a melting furnace for melting, and casting after slagging, degassing and filtering to obtain an aluminum alloy ingot; specifically, the aluminum alloy raw material uses industrial pure aluminum, master alloy Al-Si, master alloy Al-Fe, master alloy Al-Mn, master alloy Al-Cu, the melting temperature is 750°C, the stirring method is electromagnetic stirring, Cl-Ar mixed gas is used for refining, the refining temperature is 730°C, and the filtering treatment uses deep bed filtering equipment;

[0042] (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for double-stage homogenization treatment; the homogenization heat treatment process is as follows: the aluminum alloy ingot is heated to 520°C and kept at this temperature for 6 hours, then heated to 555°C and kept at this temperature for 8 hours, and then air-cooled; in the first-stage homogenization, the homogenizing furnace is first heated to the target temperature and then the aluminum alloy ingot is placed in the furnace; in the subsequent second-stage homogenization process, the ingot is heated to the target temperature in the furnace;

[0043] (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the thickness of the hot rolled intermediate billet is 53 mm, and the aluminum alloy plate after hot rough rolling is subjected to five continuous rolling and finish rolling to obtain a 10 mm thick hot rolled plate, and the hot rolling coiling temperature is 330°C;

[0044] (5) Cold rolling: The hot rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process, i.e., the cold rolling process is carried out according to the pass reduction of 10 mm → 7.5 mm → 5 mm → intermediate annealing → 2.5 mm → 1.2 mm to obtain a 1.2 mm thick cold rolled sheet. The intermediate annealing process is carried out on a continuous annealing line. The intermediate annealing temperature is 420 °C and the intermediate annealing time is 20 s.

[0045] (6) Solution treatment and pre-aging: The cold-rolled sheet was solution treated at 560°C / 20s in a continuous annealing line and quenched in water to room temperature. The sheet was then pre-aged and rolled at 75°C in a box furnace and air-cooled to room temperature. After aging for 7 days, a high-curling aluminum alloy automotive sheet was obtained.

[0046] (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile sheets are taken and prepared by the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy sheet are obtained by scanning electron microscopy, and the hemming performance of the sheet is intuitively characterized; specifically:

[0047] (71) The pre-aged aluminum alloy sheet was cut into 1.2 mm × 10 mm × 10 mm specimens along the rolling direction by wire cutting, and transparent tape was adhered to the surface of the specimen. The specimen was placed in a fully automatic grinding and polishing machine for grinding and polishing. First, the specimen was polished to 400 μm with 200# sandpaper, and then polished to 220 μm with 800# and 2000# sandpaper in sequence. After completion, the specimen was water-polished with a polishing cloth for 3 min, and then the polished specimen was punched into a small disc specimen with a diameter of 3 mm using a puncher;

[0048] (72) Take 150 mL of high-purity methanol solution in a 500 mL beaker, add 50 mL of 1 mol / L nitric acid, stir well with a glass rod, and prepare an electrolytic double spray solution;

[0049] (73) The small disc sample was placed in an electrolytic double-spray solution for electrolytic double-spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer. The electrolytic voltage was 40 V, the current was 35 mA, and the electrolyte temperature was controlled to -40 °C by cooling the electrolyte with liquid nitrogen. Then, a scanning electron microscope was used to observe the grain boundary precipitation phase of the sample, such as Figure 2 As shown, through Figure 2 It can be seen that the precipitated phases at the grain boundaries of the aluminum alloy sheet prepared in this embodiment are intermittently distributed, and no large-sized phases exist, indicating that the hemming performance is good and meets the hemming requirements. In this case, the hemming coefficient is ≤0.5.

[0050] In addition, in order to verify the accuracy of using the distribution of grain boundary precipitation phase to characterize and evaluate the curling performance, this embodiment also carried out a bending test on the aluminum alloy plate after pre-aging, and the plate curling coefficient was 0.40, indicating that the curling performance was good and met the requirements.

[0051] Example 2

[0052] This embodiment provides a method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance, comprising the steps of:

[0053] (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 0.85%, Fe 0.13%, Cu 0.04%, Mn 0.07%, Mg 0.55%, Cr 0.04%, Zn 0.02%, Ti 0.03%, and the balance is Al and other inevitable impurities, and the single content of the impurities is not more than 0.02%, and the total amount is not more than 0.1%;

[0054] (2) Melting and casting: placing the prepared aluminum alloy raw material in a melting furnace for melting, and casting after slagging, degassing and filtering to obtain an aluminum alloy ingot; specifically, the aluminum alloy raw material uses industrial pure aluminum, master alloy Al-Si, master alloy Al-Fe, master alloy Al-Mn, master alloy Al-Cu, the melting temperature is 750°C, the stirring method is electromagnetic stirring, Cl-Ar mixed gas is used for refining, the refining temperature is 730°C, and the filtering treatment uses deep bed filtering equipment;

[0055] (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for double-stage homogenization treatment; the homogenization heat treatment process is as follows: the aluminum alloy ingot is heated to 530°C and kept at this temperature for 6 hours, then heated to 560°C and kept at this temperature for 8 hours, and then air-cooled; in the first-stage homogenization, the homogenizing furnace is first heated to the target temperature and then the aluminum alloy ingot is placed in the furnace; in the subsequent second-stage homogenization process, the ingot is heated to the target temperature in the furnace;

[0056] (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the thickness of the hot rolled intermediate billet is 53 mm, and the aluminum alloy plate after hot rough rolling is subjected to five continuous rolling and finish rolling to obtain a 10 mm thick hot rolled plate, and the hot rolling coiling temperature is 350°C;

[0057] (5) Cold rolling: The hot rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process, i.e., the cold rolling process is carried out according to the pass reduction of 10 mm → 7.5 mm → 5 mm → intermediate annealing → 2.5 mm → 1.2 mm to obtain a 1.2 mm thick cold rolled sheet. The intermediate annealing process is carried out on a continuous annealing line. The intermediate annealing temperature is 420 °C and the intermediate annealing time is 20 s.

[0058] (6) Solution treatment and pre-aging: The cold-rolled sheet was solution treated at 540°C / 30s in a continuous annealing line and quenched in water to room temperature. The sheet was then pre-aged and rolled in a box furnace at 65°C and air-cooled to room temperature. After aging for 7 days, a high-curling aluminum alloy automotive sheet was obtained.

[0059] (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile sheets are taken and prepared by the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy sheet are obtained by scanning electron microscopy, and the hemming performance of the sheet is intuitively characterized; specifically:

[0060] (71) The pre-aged aluminum alloy sheet was cut into 1.2 mm × 10 mm × 10 mm specimens along the rolling direction by wire cutting, and transparent tape was adhered to the surface of the specimen. The specimen was placed in a fully automatic grinding and polishing machine for grinding and polishing. First, the specimen was polished to 400 μm with 200# sandpaper, and then polished to 220 μm with 800# and 2000# sandpaper in sequence. After completion, the specimen was water-polished with a polishing cloth for 3 min, and then the polished specimen was punched into a small disc specimen with a diameter of 3 mm using a puncher;

[0061] (72) Take 150 mL of high-purity methanol solution in a 500 mL beaker, add 50 mL of 1 mol / L nitric acid, stir well with a glass rod, and prepare an electrolytic double spray solution;

[0062] (73) The small disc sample was placed in an electrolytic double spray solution for electrolytic double spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer. The electrolytic voltage was 40 V, the current was 30 mA, and the electrolyte temperature was controlled to -35 °C by cooling the electrolyte with liquid nitrogen. Then, a scanning electron microscope was used to observe the grain boundary precipitation phase of the sample, such as Figure 3 As shown, through Figure 3 It can be seen that the precipitated phases at the grain boundaries of the aluminum alloy sheet prepared in this embodiment are intermittently distributed, and no large-sized phases exist, indicating that the hemming performance is good and meets the hemming requirements. In this case, the hemming coefficient is ≤0.5.

[0063] In addition, in order to verify the accuracy of using the distribution of grain boundary precipitation phase to characterize and evaluate the curling performance, this embodiment also carried out a bending test on the aluminum alloy plate after pre-aging, and the plate curling coefficient was 0.40, indicating that the curling performance was good and met the requirements.

[0064] Example 3

[0065] This embodiment provides a method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance, comprising the steps of:

[0066] (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 0.98%, Fe 0.12%, Cu 0.04%, Mn 0.06%, Mg 0.50%, Cr 0.03%, Zn 0.01%, Ti 0.02%, and the balance is Al and other inevitable impurities, and the single content of the impurities is not more than 0.02%, and the total amount is not more than 0.1%;

[0067] (2) Melting and casting: placing the prepared aluminum alloy raw material in a melting furnace for melting, and casting after slagging, degassing and filtering to obtain an aluminum alloy ingot; specifically, the aluminum alloy raw material uses industrial pure aluminum, master alloy Al-Si, master alloy Al-Fe, master alloy Al-Mn, master alloy Al-Cu, the melting temperature is 750°C, the stirring method is electromagnetic stirring, Cl-Ar mixed gas is used for refining, the refining temperature is 730°C, and the filtering treatment uses deep bed filtering equipment;

[0068] (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for double-stage homogenization treatment; the homogenization heat treatment process is as follows: the aluminum alloy ingot is heated to 520°C and kept at this temperature for 6 hours, then heated to 560°C and kept at this temperature for 8 hours, and then air-cooled; in the first-stage homogenization, the homogenizing furnace is first heated to the target temperature and then the aluminum alloy ingot is placed in the furnace; in the subsequent second-stage homogenization process, the ingot is heated to the target temperature in the furnace;

[0069] (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the thickness of the hot rolled intermediate billet is 53 mm, and the aluminum alloy plate after hot rough rolling is subjected to five continuous rolling and finish rolling to obtain a 10 mm thick hot rolled plate, and the hot rolling coiling temperature is 340°C;

[0070] (5) Cold rolling: The hot rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process, i.e., the cold rolling process is carried out according to the pass reduction of 10 mm → 7.5 mm → 5 mm → intermediate annealing → 2.5 mm → 1.2 mm to obtain a 1.2 mm thick cold rolled sheet. The intermediate annealing process is carried out on a continuous annealing line. The intermediate annealing temperature is 420 °C and the intermediate annealing time is 20 s.

[0071] (6) Solution treatment and pre-aging: The cold-rolled sheet was solution treated at 540°C / 20s in a continuous annealing line and quenched in water to room temperature. The sheet was then pre-aged and rolled at 75°C in a box furnace and air-cooled to room temperature. After aging for 7 days, a high-curling aluminum alloy automotive sheet was obtained.

[0072] (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile sheets are taken and prepared by the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy sheet are obtained by scanning electron microscopy, and the hemming performance of the sheet is intuitively characterized; specifically:

[0073] (71) The pre-aged aluminum alloy sheet was cut into 1.2 mm × 10 mm × 10 mm specimens along the rolling direction by wire cutting, and transparent tape was adhered to the surface of the specimen. The specimen was placed in a fully automatic grinding and polishing machine for grinding and polishing. First, the specimen was polished to 400 μm with 200# sandpaper, and then polished to 220 μm with 800# and 2000# sandpaper in sequence. After completion, the specimen was water-polished with a polishing cloth for 3 min, and then the polished specimen was punched into a small disc specimen with a diameter of 3 mm using a puncher;

[0074] (72) Take 150 mL of high-purity methanol solution in a 500 mL beaker, add 50 mL of 1 mol / L nitric acid, stir well with a glass rod, and prepare an electrolytic double spray solution;

[0075] (73) The small disc sample was placed in an electrolytic double-spray solution for electrolytic double-spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer. The electrolytic voltage was 40 V, the current was 35 mA, and the electrolyte temperature was controlled to -40 °C by cooling the electrolyte with liquid nitrogen. Then, a scanning electron microscope was used to observe the grain boundary precipitation phase of the sample, such as Figure 4 As shown, through Figure 4 It can be seen that the precipitated phases at the grain boundaries of the aluminum alloy sheet prepared in this embodiment are intermittently distributed, and no large-sized phases exist, indicating that the hemming performance is good and meets the hemming requirements. In this case, the hemming coefficient is ≤0.5.

[0076] In addition, in order to verify the accuracy of using the distribution of grain boundary precipitation phase to characterize and evaluate the curling performance, this embodiment also carried out a bending test on the aluminum alloy plate after pre-aging, and the curling coefficient of the plate was 0.45, indicating that the curling performance was good and met the requirements.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance, comprising the steps of:

[0079] (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 1.02%, Fe 0.18%, Cu 0.04%, Mn 0.08%, Mg 0.55%, Cr 0.03%, Zn 0.02%, Ti 0.02%, and the balance is Al and other inevitable impurities, and the single content of the impurities is not more than 0.02%, and the total amount is not more than 0.1%;

[0080] (2) Melting and casting: placing the prepared aluminum alloy raw material in a melting furnace for melting, and casting after slagging, degassing and filtering to obtain an aluminum alloy ingot; specifically, the aluminum alloy raw material uses industrial pure aluminum, master alloy Al-Si, master alloy Al-Fe, master alloy Al-Mn, master alloy Al-Cu, the melting temperature is 750°C, the stirring method is electromagnetic stirring, Cl-Ar mixed gas is used for refining, the refining temperature is 730°C, and the filtering treatment uses deep bed filtering equipment;

[0081] (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for double-stage homogenization treatment; the homogenization heat treatment process is as follows: the aluminum alloy ingot is heated to 520°C and kept at this temperature for 6 hours, then heated to 560°C and kept at this temperature for 8 hours, and then air-cooled; in the first-stage homogenization, the homogenizing furnace is first heated to the target temperature and then the aluminum alloy ingot is placed in the furnace; in the subsequent second-stage homogenization process, the ingot is heated to the target temperature in the furnace;

[0082] (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the hot rolled intermediate billet has a thickness of 53 mm, and the aluminum alloy sheet after hot rough rolling is subjected to five consecutive rolling and finish rolling to obtain a 10 mm thick hot rolled sheet, and the hot rolling coiling temperature is 300°C;

[0083] (5) Cold rolling: The hot rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process, i.e., the cold rolling process is carried out with a pass reduction of 10 mm → 7.5 mm → 5 mm → intermediate annealing → 2.5 mm → 1.2 mm to obtain a 1.2 mm thick cold rolled sheet. The intermediate annealing process is carried out on a continuous annealing line, the intermediate annealing temperature is 380 °C, and the intermediate annealing time is 10 s;

[0084] (6) Solution treatment and pre-aging: The cold-rolled sheet was solution treated at 540°C / 20s in a continuous annealing line and quenched in water to room temperature. The sheet was then pre-aged and rolled at 75°C in a box furnace and air-cooled to room temperature. After aging for 7 days, a high-curling aluminum alloy automotive sheet was obtained.

[0085] (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile sheets are taken and prepared by the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy sheet are obtained by scanning electron microscopy, and the hemming performance of the sheet is intuitively characterized; specifically:

[0086] (71) The pre-aged aluminum alloy sheet was cut into 1.2 mm × 10 mm × 10 mm specimens along the rolling direction by wire cutting, and transparent tape was adhered to the surface of the specimen. The specimen was placed in a fully automatic grinding and polishing machine for grinding and polishing. First, the specimen was polished to 400 μm with 200# sandpaper, and then polished to 220 μm with 800# and 2000# sandpaper in sequence. After completion, the specimen was water-polished with a polishing cloth for 3 min, and then the polished specimen was punched into a small disc specimen with a diameter of 3 mm using a puncher;

[0087] (72) Take 150 mL of methanol solution in a 500 mL beaker, add 50 mL of nitric acid, stir thoroughly with a glass rod, and prepare an electrolytic double spray solution;

[0088] (73) The small disc sample was placed in an electrolytic double-spray solution for electrolytic double-spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer. The electrolytic voltage was 40 V, the current was 35 mA, and the electrolyte temperature was controlled to -40 °C by cooling the electrolyte with liquid nitrogen. Then, a scanning electron microscope was used to observe the grain boundary precipitation phase of the sample, such as Figure 5 As shown, through Figure 5 It can be seen that the precipitated phase at the grain boundary of the aluminum alloy plate prepared in this comparative example is large in size, reaching tens of microns, with sharp morphology and agglomeration, indicating that the curling performance is good and meets the curling requirements. In this case, the curling coefficient is greater than 0.5.

[0089] In addition, in order to verify the accuracy of using the distribution of grain boundary precipitation phase to characterize and evaluate the curling performance, this comparative example also conducted a bending test on the aluminum alloy plate after pre-aging, and the curling coefficient of the plate was 0.55, indicating that the curling performance was poor.

[0090] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0091] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing high-curling aluminum alloy automobile sheet and characterizing the curling performance, characterized in that: Includes steps: (1) Ingredients: The aluminum alloy raw material for preparing the high-curling aluminum alloy automobile sheet is prepared according to the following weight percentages: Si 0.7% to 1.0%, Fe 0.08% to 0.15%, Cu ≤ 0.2%, Mn 0.05% to 0.10%, Mg 0.4% to 0.6%, Cr ≤ 0.05%, Zn ≤ 0.20%, Ti ≤ 0.15%, and the balance is Al and other inevitable impurities; (2) Melting and casting: The prepared aluminum alloy raw materials are placed in a melting furnace for melting, and after slagging, degassing and filtering, they are cast to obtain aluminum alloy ingots; (3) Homogenization: The aluminum alloy ingot is placed in a homogenizing furnace for a two-stage homogenization treatment; (4) Hot rolling: The homogenized aluminum alloy ingot is placed in a rolling mill for hot rough rolling and hot finish rolling, wherein the hot rolled intermediate billet has a thickness of 51 to 53 mm, and the aluminum alloy sheet after hot rough rolling is subjected to five-stage finish rolling to obtain a hot rolled sheet with a thickness of 8 to 10 mm, which is then coiled at 300 to 350°C; (5) Cold rolling: The hot-rolled sheet is subjected to a first cold rolling, intermediate annealing, and a second cold rolling process to obtain a cold-rolled sheet with a thickness of 1.0 to 1.5 mm; (6) Solution treatment and pre-aging: The cold-rolled sheet is solution-quenched in a continuous annealing line, and then the solution-quenched sheet is pre-aged and rolled in a box furnace to obtain a high-curling aluminum alloy automobile sheet; (7) Characterization of hemming performance: Samples of high-hemming aluminum alloy automobile plates were taken and prepared using the electrolytic double-spray method. The morphology and distribution of the precipitated phase at the grain boundary of the aluminum alloy plate were obtained using a scanning electron microscope to intuitively characterize the hemming performance of the plate.

2. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: The homogenization heat treatment process in step (3) is as follows: the aluminum alloy ingot is heated to 520-530° C. and kept at this temperature for 6-8 hours, then heated to 555-565° C. and kept at this temperature for 8-10 hours, and then air-cooled.

3. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: In the step (5), the cold rolling passes are distributed as follows: 8-10 mm→6-7.5 mm→4-5 mm→intermediate annealing→2-2.5 mm→1.0-1.5 mm.

4. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: The intermediate annealing process in step (5) is carried out in a continuous annealing line, the intermediate annealing temperature is 400-450° C., and the intermediate annealing time is 20-30 seconds.

5. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: In the step (6), the solution treatment temperature is 540-560°C, the solution treatment time is 20-30s, and the pre-aging temperature is 60-80°C.

6. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: The quenching method in step (6) is water cooling.

7. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: The step (7) is specifically: (71) Cut the aluminum alloy plate along the rolling direction to a thickness of 1.0 to 1.5 mm using wire cutting, stick a transparent tape on the surface of the sample, place the sample in a fully automatic grinding and polishing machine for grinding and polishing, and use a punch to punch the polished sample into a small disc sample with a diameter of 3 mm; (72) Methanol and nitric acid were measured in a beaker in a volume ratio of 3:1 and stirred evenly to prepare an electrolytic double spray solution; (73) The small disc sample was placed in an electrolytic double-spray solution for electrolytic double-spray treatment, then cleaned with anhydrous ethanol and dried with a hair dryer to observe the grain boundary precipitation phase of the aluminum alloy plate.

8. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 7, characterized in that: In the step (73), during the electrolysis double spray process, the electrolysis voltage is 35 to 45 V, the current is 25 to 35 mA, the time is 1 min 30 s to 3 min, and the electrolyte temperature is controlled to -40 to -30 ° C by using liquid nitrogen to cool the electrolyte.

9. The method for preparing a high-curling aluminum alloy automobile sheet and characterizing the curling performance according to claim 1, characterized in that: In the step (7), when the precipitated phase at the grain boundary of the aluminum alloy plate is discontinuously distributed and the precipitated phase size is ≤2μm, it means that the curling performance meets the requirements; when the precipitated phase at the grain boundary of the aluminum alloy plate is continuously distributed or agglomerated and the precipitated phase at the grain boundary is larger than 2μm, it means that the curling performance does not meet the requirements.

Images