Aluminum alloy sheet and method for manufacturing the same

Abstract

The application provides an aluminum alloy plate and a preparation method thereof. The aluminum alloy plate comprises the following elements in percentage by mass: Si content is less than or equal to 0.6%, Fe content is less than or equal to 0.3%, Mn content is 0.2% to 0.4%, Mg content is 2.4% to 3.5%, Cr content is less than or equal to 0.3%, Cu content is 0.1 to 0.5%, total content of unavoidable impurities is less than or equal to 0.15%, content of single impurity is less than 0.05%, and the rest is Al, wherein the area 70 to 80 mu m away from the outer surface of the aluminum alloy plate in the thickness direction of the aluminum alloy plate is an oxide film layer, and the surface of the oxide film layer is attached with Ti element and Zr element. The above aluminum alloy plate has high strength, good paint film performance and anti-wire corrosion performance. The aluminum alloy plate is used in a body structure and / or a cover inner plate, so that the aluminum alloy plate has high strength, rigidity and good processing forming property.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy, in particular to an aluminum alloy plate and a preparation method thereof. BACKGROUND

[0002] With the development of economy, energy saving and emission reduction is increasingly put on the agenda, which brings great challenges to the development of automobile industry. Under this background, automobile lightweight becomes one of the few choices or inevitable trends in the industry. Reducing the overall weight of the automobile can not only improve the handling and safety, but also effectively reduce energy consumption. Aluminum alloy is the first choice for automobile lightweight due to its small density, easy processing, high strength, corrosion resistance and other advantages.

[0003] As an important vehicle body structural member and cover member material, the aluminum alloy plate is currently mainly applied to "four doors and two covers". It is required to have good mechanical properties, as well as good paint film properties and filiform corrosion properties. Electrophoresis is the first process for coating aluminum alloy materials, and a paint film is formed on the surface of the aluminum alloy through electrophoresis treatment to improve the corrosion resistance of the base aluminum material.

[0004] At present, domestic scholars have carried out some researches on the filiform corrosion properties of aluminum alloy plates. Zhang Yangguang's "Research Review of Aluminum Alloy Filiform Corrosion" reveals the generation, development mechanism, protection and standard evaluation of filiform corrosion. Yang Huan's "Influence of Pretreatment on 6063 Aluminum Alloy Material... Properties and Filiform Corrosion Resistance", Yang Bo's "Influence of Pretreatment on Filiform Corrosion Properties of Aluminum Alloy Spraying Layer" and the like improve the filiform corrosion properties by improving the pretreatment process. However, the filiform corrosion properties of the aluminum alloy plate obtained by the existing method are still poor. SUMMARY

[0005] The main purpose of the present application is to provide an aluminum alloy plate and a preparation method thereof, so as to solve the problem of poor filiform corrosion properties of the aluminum alloy plate in the prior art.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, an aluminum alloy plate is provided, which comprises the following elements in mass percentage: Si content ≤0.6%, Fe content ≤0.3%, Mn content 0.2%-0.4%, Mg content 2.4%-3.5%, Cr content ≤0.3%, Cu content 0.1-0.5%, total content of unavoidable impurities ≤0.15wt%, content of single impurity <0.05wt%, and the balance is Al, wherein the region 70-80μm away from the outer surface of the aluminum alloy plate in the thickness direction of the aluminum alloy plate is an oxide film layer, and the surface of the oxide film layer is attached with Ti element and Zr element.

[0007] Further, the content of the Ti element and the content of the Zr element are each independently 2-8mg / m2 ; preferably, the content of Ti element and the content of Zr element are each independently 2-5 mg / m 2 , preferably, the mass ratio of Ti element to Zr element is (1-1.5):1.

[0008] Further, the mass ratio of Mg element to Cu element is (4.8-16.7):1.

[0009] According to another aspect of the present application, there is provided a preparation method of the above-mentioned aluminum alloy plate, which comprises: step S1, sequentially subjecting an alloy raw material to a melting step, a casting step, a two-stage homogenization treatment, a hot rolling step, a first cold rolling step, an intermediate annealing step, a second cold rolling step, and a final annealing step to obtain a final annealed aluminum alloy; step S2, subjecting the final annealed aluminum alloy to a cleaning passivation treatment to obtain a passivated aluminum alloy; and step S3, subjecting the passivated aluminum alloy to a phosphating electrophoresis treatment to obtain the aluminum alloy plate.

[0010] Further, in the above-mentioned step S2, the cleaning passivation treatment process comprises sequentially performing a first degreasing treatment, a first water washing treatment, a cleaning treatment, a second water washing treatment, a passivation treatment, and a drying treatment; wherein the degreasing reagent used in the first degreasing treatment comprises 3-5 wt% of an alkaline degreasing agent and 0.6-1 wt% of a surfactant, and the free alkali point of the degreasing reagent is 8-12 pt; preferably, the temperature of the first degreasing treatment is 45-55℃, and preferably, the time of the first degreasing treatment is 8-12 s; preferably, the first water washing treatment and the second water washing treatment are each independently a cleaning treatment at a temperature of 20-30℃ for 6-10 s; preferably, the cleaning reagent used in the cleaning treatment comprises 2.5-3 wt% of a cleaning agent and 9-10 wt% of an additive, and the conductivity of the cleaning reagent is 50±5 ms / cm; preferably, the free fluorine of the cleaning reagent is 300±50 ppm; preferably, the temperature of the cleaning treatment is 45-55℃, and preferably, the time of the cleaning treatment is 10-30 s; preferably, the passivation reagent used in the passivation treatment comprises 4.5-5 wt% of a chromium-free treatment supplement and 1.8-2 wt% of a chromium-free passivation adjuster, preferably, the conductivity of the passivation reagent is 1800-2300 μs / cm, and preferably, the pH value of the passivation reagent is 3.8-4.2; preferably, the temperature of the passivation treatment is 45-55℃, and preferably, the time of the passivation treatment is 3-9 s; preferably, the unit m 2 The content of the passivation reagent on the final annealed aluminum alloy is 2-5 mg.

[0011] Further, in the above-mentioned step S3, the phosphating electrophoresis treatment process comprises sequentially performing a second degreasing treatment, a third water washing treatment, a surface conditioning treatment, a phosphating treatment, a fourth water washing treatment, an electrophoresis treatment, a fifth water washing treatment, and a baking treatment.

[0012] Further, in the step S1, the two-stage homogenization treatment includes a first-stage homogenization treatment and a second-stage homogenization treatment, preferably, the temperature of the first-stage homogenization treatment is 400-480℃, preferably, the time of the first-stage homogenization treatment is 2-6h; preferably, the temperature of the second-stage homogenization treatment is 500-550℃, preferably, the time of the second-stage homogenization treatment is 2-6h.

[0013] Further, in the step S1, the thickness of the hot-rolled plate obtained by the hot-rolling step is 6.0-8.0mm; and / or, the thickness of the plate obtained by the first-stage cold-rolling step is 1.8-6.0mm; and / or, the thickness of the plate obtained by the second-stage cold-rolling step is 0.8-2.0mm.

[0014] Further, in the step S1, the intermediate annealing step includes: heating the plate to 320-350℃ at a speed of 20-50℃ / h and then holding for 2-3h; and / or, the final annealing step includes: heating the plate to 450-530℃ at a speed of 15-20℃ / s and then holding for 15s-5min for continuous annealing, and then cooling at a speed of 5-10℃ / s.

[0015] Further, the passivation aluminum alloy is straightened, and the straightening amount is 0.5-1%.

[0016] By controlling the content of each element within the above range, especially by controlling the content of Cu and Mg elements and the Ti element and Zr element attached to the surface of the oxide film layer, the synergistic effect between each element is improved, so that the aluminum alloy plate has high strength, good paint film performance and anti-wire corrosion performance. When the aluminum alloy plate is used in the body structure and / or cover inner plate, not only the high strength, stiffness and good processing formability of the aluminum alloy plate are exerted, but also the adhesion of the paint film after electrophoresis and the cup convex performance are improved; at the same time, good anti-wire corrosion performance is provided, and the alloy wire corrosion performance meets the certification requirements of the host factory. BRIEF DESCRIPTION OF DRAWINGS

[0017] The drawings accompanying the specification of this application form a part thereof, serve to provide further understanding of the application, and together with the description of the exemplary embodiments of the application, serve to explain the application. The drawings provided herein are for illustrative purposes only and are not intended to limit the scope of the application. In the drawings:

[0018] Figure 1 The figure shows the oxide film thickness test of the aluminum alloy plate in Example 1 of the application;

[0019] Figure 2 The figure shows the oxide film thickness test of the aluminum alloy plate in Comparative Example 1 of the application;

[0020] Figure 3A figure showing the front side impact resistance test of the aluminum alloy plate in Example 1 of the present application after the test is shown;

[0021] Figure 4 A figure showing the back side impact resistance test of the aluminum alloy plate in Example 1 of the present application after the test is shown;

[0022] Figure 5 A figure showing the front side impact resistance test of the aluminum alloy plate in Comparative Example 1 of the present application after the test is shown;

[0023] Figure 6 A figure showing the back side impact resistance test of the aluminum alloy plate in Comparative Example 1 of the present application after the test is shown;

[0024] Figure 7 A figure showing the paint adhesion and filamentous corrosion test of the aluminum alloy plate in Example 1 of the present application is shown; and

[0025] Figure 8 A figure showing the paint adhesion and filamentous corrosion test of the aluminum alloy plate in Comparative Example 1 of the present application is shown; DETAILED DESCRIPTION

[0026] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] As analyzed in the background art of the present application, there is a problem of poor filamentous corrosion performance of the aluminum alloy plate in the prior art. In order to solve the above problem, the present application provides an aluminum alloy plate and a preparation method thereof.

[0028] In a typical embodiment of the present application, an aluminum alloy plate is provided, which comprises the following elements in mass percentage: Si content ≤0.6%, Fe content ≤0.3%, Mn content 0.2%-0.4%, Mg content 2.4%-3.5%, Cr content ≤0.3%, Cu content 0.1-0.5%, total content of unavoidable impurities ≤0.15wt%, content of single impurity <0.05wt%, and the balance being Al, wherein a region 70-80μm away from the outer surface of the aluminum alloy plate in the thickness direction of the aluminum alloy plate is an oxide film layer, and the surface of the oxide film layer is attached with Ti element and Zr element.

[0029] The application improves the synergistic effect among the elements by controlling the content of each element within the above range, especially by controlling the content of Cu and Mg elements and the Ti element and Zr element attached to the surface of the oxide film layer, so that the aluminum alloy sheet has high strength, good paint film performance and anti-wire corrosion performance. When the aluminum alloy sheet is used in the inner panel of a vehicle body structural member and / or a cover member, the high strength, rigidity and good processing formability of the aluminum alloy sheet are exerted, and the adhesion and cupping performance of the paint film after electrophoresis are improved. At the same time, good anti-wire corrosion performance is provided, and the alloy wire corrosion performance meets the certification requirements of the main machine factory.

[0030] In an embodiment of the present application, in order to further improve the synergistic effect of Ti element, Zr element, Cu element and Mg element, the content of the Ti element and the content of the Zr element are each independently 2-8 mg / m 2 ; preferably, the content of the Ti element and the content of the Zr element are each independently 2-5 mg / m 2 , and the mass ratio of the Ti element to the Zr element is (1-1.5):1.

[0031] In an embodiment of the present application, the mass ratio of the Mg element to the Cu element is (4.8-16.7):1.

[0032] Preferably, the mass ratio of the Mg element to the Cu element is within the above range, which helps to balance the wire corrosion resistance and strength of the aluminum alloy sheet.

[0033] In another typical embodiment of the present application, a preparation method of the above-mentioned aluminum alloy sheet is provided, which comprises: step S1, sequentially subjecting an alloy raw material to melting, casting, two-stage homogenization treatment, hot rolling step, first cold rolling step, intermediate annealing step, second cold rolling step, and finished product annealing step to obtain a finished product annealed aluminum alloy; step S2, subjecting the finished product annealed aluminum alloy to cleaning and passivation treatment to obtain a passivated aluminum alloy; and step S3, subjecting the passivated aluminum alloy to phosphating and electrophoresis treatment to obtain the aluminum alloy sheet.

[0034] By subjecting the finished product annealed aluminum alloy to cleaning and passivation treatment, the Ti element and the Zr element are attached to the surface oxide film layer of the aluminum alloy sheet. Through the synergistic effect of the Cu element, the Mg element, the Ti element and the Zr element, the wire corrosion resistance of the aluminum alloy sheet is improved. Then, by subjecting the passivated aluminum alloy to phosphating and electrophoresis treatment, the paint film performance of the aluminum alloy sheet is improved, so that the aluminum alloy sheet can have excellent wire corrosion resistance and paint film performance, and thus it is easier to meet the corrosion prevention requirements of the automobile sheet.

[0035] In one embodiment of the present application, the cleaning and passivation process in step S2 comprises first degreasing, first water washing, cleaning, second water washing, passivation and drying in sequence. The degreasing reagent used in the first degreasing comprises 3-5 wt% of alkaline degreasing agent and 0.6-1 wt% of surfactant, and the free alkali point of the degreasing reagent is 8-12 pt. Preferably, the temperature of the first degreasing is 45-55°C, and the time of the first degreasing is 8-12 s, thereby helping to remove the oil and other impurities on the surface of the aluminum alloy.

[0036] Preferably, the first water washing and the second water washing are each independently cleaned at a temperature of 20-30°C for 6-10 s, thereby facilitating the cleaning of the impurities on the surface of the aluminum alloy.

[0037] Preferably, the cleaning reagent used in the cleaning process comprises 2.5-3 wt% of cleaning agent and 9-10 wt% of additive, and the conductivity of the cleaning reagent is 50±5 ms / cm. Preferably, the free fluorine of the cleaning reagent is 300±50 ppm. Preferably, the temperature of the cleaning is 45-55°C, and the time of the cleaning is 10-30 s, thereby helping to improve the efficiency and effect of cleaning the impurities on the surface of the aluminum alloy.

[0038] Preferably, the passivation reagent used in the passivation process comprises 4.5-5 wt% of chromium-free treatment supplement and 1.8-2 wt% of chromium-free passivation adjuster. Preferably, the conductivity of the passivation reagent is 1800-2300 μs / cm, and the pH value of the passivation reagent is 3.8-4.2. Preferably, the temperature of the passivation is 45-55°C, and the time of the passivation is 3-9 s. Preferably, the content of the passivation reagent on the surface of the aluminum alloy after annealing of the finished product is 2-5 mg, thereby helping to form a corrosion-resistant passivation film on the surface of the aluminum alloy oxide film, which comprises Ti element and Zr element, thereby effectively reducing the corrosion sensitivity of the surface of the aluminum alloy sheet and preventing oxidation and corrosion. 2 Preferably, the content of the passivation reagent on the surface of the aluminum alloy after annealing of the finished product is 2-5 mg, thereby helping to form a corrosion-resistant passivation film on the surface of the aluminum alloy oxide film, which comprises Ti element and Zr element, thereby effectively reducing the corrosion sensitivity of the surface of the aluminum alloy sheet and preventing oxidation and corrosion.

[0039] In an embodiment of the present application, the phosphating electrophoresis process in step S3 comprises second degreasing treatment, third water washing treatment, surface conditioning treatment, phosphating treatment, fourth water washing treatment, electrophoresis treatment, fifth water washing treatment and baking treatment in sequence. The degreasing reagent used in the second degreasing treatment comprises 3-5 wt% of alkaline degreasing agent and 0.6-1 wt% of surfactant, preferably the free alkali point of the reagent is 8-12 pt, preferably the temperature of the first degreasing treatment is 45-55°C, and preferably the time of the first degreasing treatment is 1-10 min. Preferably, the third water washing treatment, the fourth water washing treatment and the fifth water washing treatment are each independently washing at a temperature of 20-30°C for 1-5 min. The surface conditioning reagent used in the surface conditioning treatment comprises 0.1-0.2 wt% of polyphosphoric acid titanium surface conditioning agent, preferably the temperature of the surface conditioning treatment is 20-35°C, and preferably the time of the surface conditioning treatment is 0.5-5 min. The phosphating reagent used in the phosphating treatment comprises 4-5 wt% of main film-forming agent, 2-3 wt% of neutralizing agent, 0.1-0.2 wt% of accelerator, 0.1-0.5 wt% of manganese additive, 0.1-0.5 wt% of nickel additive, 0.5-1 wt% of fluorosilicate and 0.1-0.5 wt% of fluoride ion additive, preferably the free acid point of the phosphating reagent is 1.5-2.0, preferably the total acid point of the phosphating reagent is 25-30, preferably the fluoride ion concentration of the phosphating reagent is 150-200 ppm, and preferably the gas point of the accelerator is 2-4. Preferably, the temperature of the phosphating treatment is 40-60°C, and preferably the time of the phosphating treatment is 3-5 min. The electrophoresis reagent used in the electrophoresis treatment comprises 34-38 wt% of emulsion, 58-60 wt% of color paste and 10-15 wt% of acetic acid, preferably the temperature of the electrophoresis treatment is 28-30°C, and preferably the time of the electrophoresis treatment is 180-210 s. Preferably, the electrophoresis voltage of the electrophoresis treatment is 180-260 V. Preferably, the solid content of the electrophoresis reagent is 19-24%, preferably the ash content of the electrophoresis reagent is 14-21%, preferably the pH value of the electrophoresis reagent is 5.2-5.6, preferably the conductivity of the electrophoresis reagent is 1300-2400 μs / cm, and preferably the MEQ value of the electrophoresis reagent is 20-30. Preferably, the temperature of the baking treatment is 180-185°C, and preferably the time of the baking treatment is 20-25 min.

[0040] The above conditions help to improve the phosphating treatment activity, promote the compact and uniform growth of the phosphating film on the surface of the aluminum alloy sheet, and provide good corrosion resistance. The electrophoresis treatment makes the paint film on the surface of the aluminum alloy sheet evenly covered, so that the paint film has excellent adhesion and cupping performance. Finally, the aluminum alloy sheet has good anti-wire corrosion performance and paint film performance, so as to ensure that the alloy wire corrosion performance meets the certification requirements of the main machine factory.

[0041] In an embodiment of the present application, the two-stage homogenization treatment in step S1 includes a first-stage homogenization treatment and a second-stage homogenization treatment, preferably the temperature of the first-stage homogenization treatment is 400-480℃, and preferably the time of the first-stage homogenization treatment is 2-6h; preferably the temperature of the second-stage homogenization treatment is 500-550℃, and preferably the time of the second-stage homogenization treatment is 2-6h.

[0042] The two-stage homogenization treatment is advantageous to improve the non-uniform crystalline structure formed in the casting process and improve the performance of the aluminum alloy plate after rolling. The specific operation mode can refer to the prior art, which will not be described here.

[0043] In an embodiment of the present application, the thickness of the hot-rolled plate obtained by the hot-rolling step in step S1 is 6.0-8.0mm; and / or, the intermediate annealing step includes: heating the plate to 320-350℃ at a speed of 20-50℃ / h and then holding for 2-3h; and / or, the thickness of the plate obtained by the first cold-rolling step is 1.8-6.0mm; and / or, the thickness of the plate obtained by the second cold-rolling step is 0.8-2.0mm.

[0044] Those skilled in the art can easily determine the implementation method and parameter index of the above steps according to the prior art. For example, hot rolling can be performed in one pass or multiple passes, which will not be described here. The preferred intermediate annealing temperature is low, and the main function is to eliminate work hardening to facilitate the subsequent cold working.

[0045] In an embodiment of the present application, the intermediate annealing step in step S1 includes: heating the plate to 320-350℃ at a speed of 20-50℃ / h and then holding for 2-3h; and / or, the final annealing step includes: heating the plate to 450-530℃ at a speed of 15-20℃ / s and then holding for 15s-5min for continuous annealing, and then cooling at a speed of 5-10℃ / s.

[0046] The above final annealing step is preferably mainly to realize complete recrystallization of the plate, adjust the grain structure and second phase re-dissolution and precipitation behavior, so as to be advantageous to form suitable texture, which is helpful to improve the plasticity and toughness of the aluminum alloy plate, and further improve the adhesion of the paint film after electrophoresis, the cupping performance and the anti-wire corrosion performance.

[0047] In order to facilitate the subsequent phosphating treatment and use, it is preferred to straighten the plate after the final annealing step, and the straightening amount is 0.5-1%.

[0048] The beneficial effects of the present application will be further illustrated below with examples.

[0049] Example 1

[0050] The alloy is in mass percentage: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 2.4%; Cr: 0.05%; Cu: 0.5%, and the balance is Al. The alloy composition is allocated as above, the melt is treated by refining, and then cast into ingot by semi-continuous casting equipment; the ingot is cut and milled after the head, and then homogenized at 450℃ for 2h, and then at 530℃ for 2h; then hot rolled to 6mm thick; the hot rolled plate is cold rolled to 4mm, and then intermediate annealed at a temperature of 350℃ for 2h, and then air cooled to room temperature; then further cold rolled to obtain a cold rolled plate with a thickness of 1.5mm, and then finished annealing treatment is performed on the finished annealed aluminum alloy at a temperature of 530℃ for 30s, and then water quenched at a rate of 20℃ / s. Then the finished annealed aluminum alloy is cleaned and passivated, and the cleaning and passivation treatment includes:

[0051] First degreasing treatment: the degreasing reagent used in the first degreasing treatment includes 5wt% of alkaline degreasing agent and 1wt% of surfactant, and the free alkali point of the degreasing reagent is 12pt; the temperature of the first degreasing treatment is 50℃, and the time of the first degreasing treatment is 12s;

[0052] First water washing treatment: the first water washing treatment is cleaning at a temperature of 20-30℃ for 6s;

[0053] Cleaning treatment: the cleaning reagent used in the cleaning treatment includes 3wt% of cleaning agent and 10wt% of additive, and the conductivity of the cleaning reagent is 50±5ms / cm; the free fluorine of the cleaning reagent is 300±50ppm; the temperature of the cleaning treatment is 50℃, and the time of the cleaning treatment is 30s;

[0054] Second water washing treatment: the second water washing treatment is cleaning at a temperature of 20-30℃ for 6s;

[0055] Passivation treatment: the passivation reagent used in the passivation treatment includes 5wt% of chromium-free treatment supplement and 2wt% of chromium-free passivation adjuster, and the conductivity of the passivation reagent is 1800μs / cm, and the pH value of the passivation reagent is 3.8; the temperature of the passivation treatment is 50℃, and the time of the passivation treatment is 9s; the unit m 2 The content of the passivation reagent on the finished annealed aluminum alloy is 3.6mg.

[0056] Drying treatment: strong air drying. Finally, straightening is performed on a straightening machine, and the straightening amount is 1%, and the front impact test diagram of the aluminum alloy plate after the impact test is shown in Figure 3 , and the back impact test diagram after the impact test is shown in Figure 4 .

[0057] Example 2

[0058] The difference from Example 1 is that the alloy is in mass percentage: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 2.4%; Cr: 0.05%; Cu: 0.5%, the balance being Al. Melting is carried out according to the above alloy composition ratio, and the melt is cast into ingots after refining treatment using a semi-continuous casting device; after the ingots are cut and milled, homogenization treatment is carried out, the homogenization process being 450°C for 2h, and then 530°C for 2h; then hot rolling to 6mm thick; the hot rolled plate is cold rolled to 4mm, and intermediate annealing is carried out, heating to 350°C at a rate of 30°C / h, holding for 2h, and air cooling to room temperature after discharge; then subsequent cold rolling is carried out, obtaining a cold rolled plate of 1.5mm thick, and then finished annealing treatment is carried out, water quenching after holding at 530°C for 30s at a heating rate of 30°C / s, and cooling at a rate of 20°C / s. Then cleaning and passivation treatment is carried out, the cleaning temperature being 50°C, the cleaning time being 15s, the passivation temperature being 45°C, and the passivation time being 9s. Finally, straightening is carried out on a straightening machine, and the straightening amount is 1%.

[0059] Example 3

[0060] The difference from Example 1 is that the alloy is in mass percentage: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 3.0%; Cr: 0.05%; Cu: 0.18%, the balance being Al. Melting is carried out according to the above alloy composition ratio, and the melt is cast into ingots after refining treatment using a semi-continuous casting device; after the ingots are cut and milled, homogenization treatment is carried out, the homogenization process being 450°C for 2h, and then 530°C for 2h; then hot rolling to 6mm thick; the hot rolled plate is cold rolled to 4mm, and intermediate annealing is carried out, heating to 350°C at a rate of 30°C / h, holding for 2h, and air cooling to room temperature after discharge; then subsequent cold rolling is carried out, obtaining a cold rolled plate of 1.5mm thick, and then finished annealing treatment is carried out, water quenching after holding at 530°C for 30s at a heating rate of 30°C / s, and cooling at a rate of 20°C / s. Then cleaning and passivation treatment is carried out, the cleaning temperature being 50°C, the cleaning time being 10s, the passivation temperature being 50°C, and the passivation time being 9s. Finally, straightening is carried out on a straightening machine, and the straightening amount is 1%.

[0061] Example 4

[0062] The difference from Example 1 is that the alloy is in mass percent: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 3.0%; Cr: 0.05%; Cu: 0.18%, the balance being Al. Melting is carried out according to the above alloy composition ratio, and the melt is cast into ingots after refining treatment using a semi-continuous casting device; after the ingots are cut and milled, homogenization treatment is carried out, the homogenization process being 450°C for 2h, and then 530°C for 2h; then hot rolling to 6mm thick; the hot-rolled plate is cold-rolled to 4mm, and intermediate annealing is carried out, heating to 350°C at a rate of 30°C / h, holding for 2h, and air cooling to room temperature after discharge; then subsequent cold rolling is carried out, obtaining a cold-rolled plate of 1.5mm thick, and then finished annealing treatment is carried out, water quenching after holding at 530°C for 30s at a heating rate of 30°C / s, and cooling at a rate of 20°C / s. Then cleaning and passivation treatment is carried out, the cleaning temperature being 50°C, the cleaning time being 15s, the passivation temperature being 45°C, and the passivation time being 6s. Finally, straightening is carried out on a straightening machine, and the straightening amount is 1%.

[0063] Example 5

[0064] The difference from Example 1 is that the alloy is in mass percent: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 3.5%; Cr: 0.05%; Cu: 0.37%, the balance being Al. Melting is carried out according to the above alloy composition ratio, and the melt is cast into ingots after refining treatment using a semi-continuous casting device; after the ingots are cut and milled, homogenization treatment is carried out, the homogenization process being 450°C for 2h, and then 530°C for 2h; then hot rolling to 6mm thick; the hot-rolled plate is cold-rolled to 4mm, and intermediate annealing is carried out, heating to 350°C at a rate of 30°C / h, holding for 2h, and air cooling to room temperature after discharge; then subsequent cold rolling is carried out, obtaining a cold-rolled plate of 1.5mm thick, and then finished annealing treatment is carried out, water quenching after holding at 530°C for 30s at a heating rate of 30°C / s, and cooling at a rate of 20°C / s. Then cleaning and passivation treatment is carried out, the cleaning temperature being 50°C, the cleaning time being 10s, the passivation temperature being 50°C, and the passivation time being 9s. Finally, straightening is carried out on a straightening machine, and the straightening amount is 1%.

[0065] Example 6

[0066] The difference from Example 1 is that the alloy is in mass percentage: Si: 0.15%; Fe: 0.3%; Mn: 0.4%; Mg: 3.5%; Cr: 0.05%; Cu: 0.37%, and the balance is Al. The alloy composition is allocated and melted as above, and the melt is cast into an ingot after refining treatment using a semi-continuous casting device; the ingot is cut and milled after cutting, and then homogenized at 450°C for 2h, and then at 530°C for 2h; then hot-rolled to 6mm thick; the hot-rolled plate is cold-rolled to 4mm, and then intermediate annealed at a temperature of 350°C for 2h, and then cooled to room temperature; then further cold-rolled to obtain a cold-rolled plate of 1.5mm thick, and then finished annealed at a temperature of 530°C for 30s, and then water quenched at a cooling rate of 20°C / s. Then cleaned and passivated at a temperature of 50°C for 15s, and then passivated at a temperature of 45°C for 6s. Finally straightened on a straightening machine, and the straightening amount is 1%.

[0067] Example 7

[0068] The difference from Example 1 is that the cleaning treatment: the temperature of the cleaning treatment is 45°C, and the time of the cleaning treatment is 30s, and finally a passivated aluminum alloy is obtained.

[0069] Example 8

[0070] The difference from Example 1 is that the cleaning treatment: the temperature of the cleaning treatment is 55°C, and the time of the cleaning treatment is 10s, and finally a passivated aluminum alloy is obtained.

[0071] Example 9

[0072] The difference from Example 1 is that the passivation treatment: the temperature of the passivation treatment is 55°C, and finally a passivated aluminum alloy is obtained.

[0073] Example 10

[0074] The difference from Example 1 is that the passivation treatment: the time of the passivation treatment is 3s, and finally a passivated aluminum alloy is obtained.

[0075] Example 11

[0076] The difference from Example 1 is that the passivation treatment: the time of the passivation treatment is 7s, and finally a passivated aluminum alloy is obtained.

[0077] Example 12

[0078] The difference from Example 1 is that the passivation treatment: the time of the passivation treatment is 10s, and finally a passivated aluminum alloy is obtained.

[0079] Example 13

[0080] The difference from Example 1 is that the passivation treatment: unit m 2 The content of the passivation agent on the aluminum alloy after the finished product annealing is 2, and the passivated aluminum alloy is finally obtained.

[0081] Example 14

[0082] The difference from Example 1 is that the passivation treatment: unit m 2 The content of the passivation agent on the aluminum alloy after the finished product annealing is 5, and the passivated aluminum alloy is finally obtained.

[0083] Example 15

[0084] The difference from Example 1 is that the passivation treatment: unit m 2 The content of the passivation agent on the aluminum alloy after the finished product annealing is 6, and the passivated aluminum alloy is finally obtained.

[0085] Example 16

[0086] The difference from Example 1 is that the passivation treatment: the pH value of the passivation agent is 4.2, and the passivated aluminum alloy is finally obtained.

[0087] Example 17

[0088] The difference from Example 1 is that the passivation treatment: the conductivity of the passivation agent is 2300 μs / cm, and the passivated aluminum alloy is finally obtained.

[0089] Example 18

[0090] The difference from Example 1 is that the mass ratio of Mg element to Cu element is 13.3:1, and the passivated aluminum alloy is finally obtained.

[0091] Example 19

[0092] The difference from Example 1 is that the mass ratio of Mg element to Cu element is 7:1, and the passivated aluminum alloy is finally obtained.

[0093] Example 20

[0094] The difference from Example 1 is that the mass ratio of Mg element to Cu element is 17.5:1, and the passivated aluminum alloy is finally obtained.

[0095] Example 21

[0096] The difference from Example 1 is that the content of Cu element is 0.37%, and the passivated aluminum alloy is finally obtained.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that the passivation treatment: unit m The content of the passivation agent on the aluminum alloy after the finished product annealing is 2, and the passivated aluminum alloy is finally obtained.Figure 5 The picture of the back of the impact-resistant test is shown in Figure 6 .

[0099] The oxide film thickness and surface TiZr content of the aluminum alloy finished plate prepared in the above examples and comparative examples were detected, and the detection method was as follows: the oxide film thickness was detected by glow discharge spectroscopy, 40*50mm samples were taken along the rolling direction, and after alcohol wiping, the distribution curves of the contents of O, Mg, and Al elements along the thickness direction were determined, wherein the depth corresponding to 10% content of O element was marked as the oxide film thickness, wherein the oxide film thickness test chart of the aluminum alloy plate in Example 1 is shown in Figure 1 The oxide film thickness test chart of the aluminum alloy plate in Comparative Example 1 is shown in Figure 2 The surface TiZr content was detected by X fluorescence, and the sample size was 30mm in diameter, which was cleaned with ether, and then the blank sample was calibrated, and then the surface TiZr content was determined, and the detection results are shown in Table 1.

[0100] Evaluation criteria: the oxide film thickness of 70-80nm indicates that the oxide film is completely removed; the Ti content is 2-5mg / m 2 , the Zr content is 2-5mg / m 2 , and the mass ratio of Ti element to Zr element is (1-1.5):1.

[0101] Table 1

[0102]

[0103]

[0104] The degreased plate was subjected to phosphating electrophoresis treatment, and the specific method was as follows:

[0105] The phosphating electrophoresis process consisted of 8 processes, including degreasing, water washing 1, surface conditioning, phosphating, water washing 2, electrophoresis, water washing 3, and baking.

[0106] Degreasing: using a mixture of 5% alkaline degreasing agent and 1% surfactant, treating for 5min, degreasing temperature 50℃, and the free alkali point of the mixture was 10pt.

[0107] Water washing 1: washing with tap water for 3min, washing temperature 25℃.

[0108] Surface conditioning: using 0.2% titanium polyphosphate surface conditioning agent, treating for 3min, surface conditioning temperature 30℃.

[0109] Phosphating: using a mixture of 5% main film forming agent, 2.5% neutralizing agent, 0.2% accelerator, 0.3% manganese additive, 0.3% nickel additive, 0.75% fluorosilicate and 0.3% fluoride ion additive, free acid point 1.8, total acid point 30, fluoride ion concentration 180 ppm, accelerator gas point 3, phosphating temperature 50°C, treatment 5 min.

[0110] Water washing 2: washing with tap water for 3 min, washing temperature 25°C.

[0111] Electrophoresis: using a mixture of 34% emulsion, 58% color paste and 10% acetic acid, treatment time 180-210 s, treatment temperature 28-30°C, electrophoresis voltage 180-260 V, solid content of the mixture 19-24%, ash content 14-21%, pH value 5.2-5.6, conductivity 1300-2400 μs / cm, MEQ value 20-30.

[0112] Water washing 3: washing with tap water for 3 min, washing temperature 25°C.

[0113] Baking: using a high temperature drying oven, baking time 20-25 min, baking temperature 180-185°C.

[0114] The phosphating and electrophoresis of the plate prepared by the above process are followed by evaluation of the paint film performance and filamentous corrosion performance, and the specific methods are as follows:

[0115] I. Evaluation of paint film performance

[0116] Adhesion: after electrophoresis, the sample is placed on a hard and flat surface, a grid is drawn with a spacing of 1 mm, a single blade is used, a 90° mesh pattern is cut for each sample, and a soft brush is used to sweep several times, and the grid area is bonded with adhesive tape.

[0117] Evaluation standard: according to the grid shedding, the level is evaluated according to the ISO 2409 standard, and 0 level is qualified.

[0118] Impact resistance: using a DuPont impact tester, adjusting the four screws at the bottom of the instrument to fix it so that the instrument remains horizontal and does not shake. Choose appropriate mold seat and corresponding impact head, place the mold seat in the mold seat fixing groove, place the test plate with the paint film facing up above the mold seat, place the corresponding impact head in the impact head guide groove and press it on the test plate, select a 1000 g weight, set the bracket to a certain height (electrophoresis test plate at 50 cm, topcoat test plate at 30 cm), fix the weight on the bracket, push the test handle outward to make the weight fall freely, lift the impact head and remove the test plate, check the damage and deformation of the test plate, check whether there are cracks on the surface of the test plate, select other parts of the test plate, repeat the test for 3 times, and observe whether the coating is broken or cracked.

[0119] Evaluation criteria: The coating is considered acceptable if it is not cracked.

[0120] II. Evaluation of Filamentous Corrosion Performance

[0121] The sample size was 70*150mm. Before the test, the sample surface was wiped with anhydrous ethanol. Referring to GB / T30786-2014 Guidelines for Scratch Marking of Metal Plate Coatings for Corrosion Testing of Paints and Varnishes, the initial scratch width was 1mm. Horizontal and vertical line segments were simultaneously scratched on the sample surface, penetrating to the substrate surface. The scratches were at least 25mm away from each edge of the test plate. The environmental conditions were (23±2)℃ and (50±5)%RH. The test cycle included steps one and two (see Table 2).

[0122] Table 2

[0123]

[0124]

[0125] The corroded sample was rinsed with water, cleaned with anhydrous ethanol, dried, and the corrosion width was recorded in accordance with ISO 4628-10.

[0126] Evaluation criteria: Average corrosion width on one side ≤ 2mm, maximum corrosion width on one side ≤ 4mm; no blistering, poor adhesion, peeling, etc.

[0127] Table 3

[0128]

[0129]

[0130]

[0131] The test results for paint film adhesion and filamentous corrosion in Example 1 are shown in the figure. Figure 7 The test results for paint film adhesion and filamentous corrosion in Comparative Example 1 are shown in the figure. Figure 8 .

[0132] As can be seen from the above description, the aluminum alloy sheet preparation method provided in this application improves the adhesion and impact resistance of the paint film after electrophoresis by optimizing the content of each component, especially the trace elements Cu and Mg, and controlling the TiZr content on the surface; at the same time, it provides good resistance to filamentous corrosion, ensuring that the alloy's filamentous corrosion performance meets the certification requirements of the OEM.

[0133] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0134] This invention enhances the synergistic effect between elements by controlling the content of each element within the above range, especially by controlling the content of Cu and Mg elements and the Ti and Zr elements adhering to the surface of the oxide film. This results in aluminum alloy sheets possessing high strength, good paint film performance, and resistance to filamentous corrosion. When this aluminum alloy sheet is used in the inner panels of body structural parts and / or body panels, it not only leverages the high strength, rigidity, and good processability of the aluminum alloy sheet, but also improves the adhesion and cupping performance of the paint film after electrophoresis; at the same time, it provides good resistance to filamentous corrosion, ensuring that the alloy's filamentous corrosion performance meets the certification requirements of OEMs.

[0135] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An aluminum alloy sheet, characterized in that, The aluminum alloy sheet comprises the following elements by mass percentage: Si content ≤0.6%, Fe content ≤0.3%, Mn content 0.2%~0.4%, Mg content 2.4%~3.5%, Cr content ≤0.3%, Cu content 0.1~0.5%, total unavoidable impurities ≤0.15wt%, single impurity content less than 0.05wt%, and the balance being Al. The area 70~80nm from the outer surface of the aluminum alloy sheet in the thickness direction is an oxide film layer, and the surface of the oxide film layer is coated with Ti and Zr elements. The mass ratio of Ti to Zr is (1~1.5):1; The content of Ti and the content of Zr are each independently 2~8 mg / m³. 2 .

2. The aluminum alloy sheet according to claim 1, characterized in that, The mass ratio of Mg to Cu is (4.8~16.7):

1.

3. A method for preparing the aluminum alloy sheet according to claim 1 or 2, characterized in that, The preparation method includes: Step S1 involves sequentially performing melting, casting, two-stage homogenization treatment, hot rolling, first cold rolling, intermediate annealing, second cold rolling, and finished product annealing on the alloy raw materials to obtain the finished annealed aluminum alloy. Step S2 involves cleaning and passivating the annealed aluminum alloy to obtain a passivated aluminum alloy; and Step S3: Perform phosphating electrophoresis on the passivated aluminum alloy to obtain the aluminum alloy sheet.

4. The preparation method according to claim 3, characterized in that, In step S2, the cleaning and passivation process includes a first degreasing treatment, a first water washing treatment, a cleaning treatment, a second water washing treatment, a passivation treatment, and a drying treatment performed sequentially. Wherein, the degreasing agent used in the first degreasing treatment includes 3-5 wt% alkaline degreasing agent and 0.6-1 wt% surfactant, the free alkaline point of the degreasing agent is 8-12 pt; and / or the temperature of the first degreasing treatment is 45-55℃, and / or the time of the first degreasing treatment is 8-12 s; And / or the first water wash and the second water wash are each independently performed at a temperature of 20~30°C for 6~10 seconds; And / or the cleaning reagent used in the cleaning process comprises 2.5~3wt% cleaning agent and 9~10wt% additive, the conductivity of the cleaning reagent is 50±5ms / cm; and / or the free fluorine of the cleaning reagent is 300±50ppm; and / or the temperature of the cleaning process is 45~55℃; and / or the time of the cleaning process is 10~30s. And / or the passivation reagent used in the passivation treatment includes 4.5-5 wt% of a chromium-free treatment supplement and 1.8-2 wt% of a chromium-free passivation adjuster, and / or the conductivity of the passivation reagent is 1800-2300 μS / cm, and / or the pH value of the passivation reagent is 3.8-4.2; and / or the passivation treatment temperature is 45-55°C, and / or the passivation treatment time is 3-9 s; and / or the unit is m 2 The content of the passivating agent on the aluminum alloy after annealing is 2~5mg.

5. The preparation method according to claim 4, characterized in that, In step S3, the phosphating electrophoresis process includes the following steps performed sequentially: a second degreasing treatment, a third water washing treatment, a surface conditioning treatment, a phosphating treatment, a fourth water washing treatment, an electrophoresis treatment, a fifth water washing treatment, and a baking treatment.

6. The preparation method according to claim 3, characterized in that, In step S1, the two-stage homogenization process includes a first-stage homogenization process and a second-stage homogenization process, and / or the temperature of the first-stage homogenization process is 400~480℃, and / or the time of the first-stage homogenization process is 2~6h; and / or the temperature of the second-stage homogenization process is 500~550℃, and / or the time of the second-stage homogenization process is 2~6h.

7. The method according to claim 6, characterized in that, In step S1, the thickness of the hot-rolled plate obtained by the hot rolling step is 6.0~8.0 mm; And / or, the thickness of the sheet obtained by the first cold rolling step is 1.8~6.0 mm; And / or, the thickness of the sheet obtained by the secondary cold rolling step is 0.8~2.0 mm.

8. The method according to claim 6, characterized in that, In step S1, the intermediate annealing step includes: heating the plate to 320-350°C at a rate of 20-50°C / h and then holding it at that temperature for 2-3 hours; And / or, the finished product annealing step includes: heating the plate to 450~530℃ at a heating rate of 15~20℃ / s and holding it at that temperature for 15s~5min for continuous annealing, and then cooling it at a rate of 5~10℃ / s.

9. The preparation method according to claim 3, characterized in that, The passivated aluminum alloy is straightened by a straightening amount of 0.5-1%.

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