JP7724098B2 - Aluminum alloy plate - Google Patents

Description

The present invention relates to an aluminum alloy plate.

Automobile bodies have traditionally been made of steel. Car bodies are painted for the purposes of rust prevention and improved design. However, in recent years, with the advancement of electric vehicles and the growing demand for improved fuel efficiency, there is a strong demand for further weight reduction in car bodies. Therefore, aluminum alloys are increasingly being used in place of steel for car bodies.

Aluminum alloys commonly used in automobiles include sheet materials made from Al-Mg alloys (e.g., Patent Document 1), which have relatively high strength among aluminum alloys, and Al-Mg-Si alloys (e.g., Patent Document 2).

Japanese Patent Application Publication No. 8-165538 Japanese Patent Application Publication No. 11-71623

When a vehicle is traveling, various vibrations are generated, including those generated by the power source and those caused by uneven road surfaces. If these vibrations are transmitted to various parts of the vehicle via the body, etc., problems may arise due to the vibrations. Therefore, there is a need to further improve the vibration-damping properties of Al-Mg alloys and Al-Mg-Si alloys used in vehicles.

Furthermore, when using aluminum alloy materials for body panels, etc., it is desirable for the paint film to have excellent adhesion to the aluminum alloy material. One possible method for improving adhesion to the paint film is to anodize the aluminum alloy material and form an anodized film on the surface of the aluminum alloy material. However, if the chemical composition of aluminum alloy materials made from Al-Mg alloys or Al-Mg-Si alloys is changed to improve the vibration damping properties, the types of intermetallic compounds present in the alloy will change, which may make it difficult to apply a uniform surface treatment to the surface of the aluminum alloy material.

The present invention was made in light of this background, and aims to provide an aluminum alloy sheet that has excellent adhesion to coatings and resins, excellent vibration damping properties, and high strength.

One aspect of the present invention relates to a substrate having a chemical composition comprising Fe (iron): 0.10% by mass to 3.0% by mass , Mn (manganese): 0.10% by mass to 3.0% by mass, Si (silicon): 0.10% by mass to 0.40% by mass, Cu (copper): 0.005% by mass to 0.100% by mass, Cr (chromium): 0.01% by mass to 1.00% by mass, and Zn (zinc): 0.01% by mass to 0.50% by mass (excluding Zn: 0.1% by mass or less) , with the balance being Al (aluminum) and unavoidable impurities;
an anodic oxide coating provided on at least one surface of the substrate,
The aluminum alloy plate has the properties that after heating at a temperature of 250°C for 3 hours , the Young's modulus is 70 GPa or more, the 0.2% yield strength is 100 MPa or more, and the damping rate in damped free vibration is 1.5 × 10 ^-3 or more.

The aluminum alloy sheet has a substrate having the specific chemical composition and an anodized coating formed on at least one surface of the substrate. By adjusting the chemical composition of the substrate to fall within the specific range, the anodized coating can be formed uniformly on the substrate. Furthermore, by providing the anodized coating on the substrate, the aluminum alloy sheet can improve adhesion to paint films and resins.

Furthermore, by containing at least the specific chemical components, the aluminum alloy plate can achieve the Young's modulus, 0.2% proof stress, and damping rate of damped free vibration within the specific ranges after heating at a temperature of 100°C to 300°C for 0.5 to 10 hours. Aluminum alloy plates with such properties can exhibit high strength and excellent vibration damping after undergoing heat treatment, for example, for baking a coating.

As described above, the above-described embodiment makes it possible to provide an aluminum alloy sheet that has excellent adhesion to coatings and resins, vibration damping properties, and high strength.

FIG. 1 is a cross-sectional view showing a main part of an aluminum alloy plate according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a schematic diagram of the attenuation rate measuring device in the examples. FIG. 3 is an explanatory diagram showing a method for calculating the attenuation rate in the embodiment.

(aluminum alloy plate)
The aluminum alloy plate has a substrate and an anodized film formed on one or both sides of the substrate.

[Base material]
First, the chemical composition of the substrate of the aluminum alloy plate and the reasons for limiting it will be explained.

Fe (iron): 0.10% by mass or more and 3.0% by mass or less The base material contains 0.10% by mass or more and 3.0% by mass or less of Fe as an essential component. Fe is mainly present in the Al matrix as second-phase particles such as Al-Fe intermetallic compounds. The Al-Fe intermetallic compounds in the Al matrix improve the vibration damping properties of the aluminum alloy sheet and also improve the strength of the aluminum alloy sheet through dispersion strengthening. The remainder of Fe is present as a solid solution element in the Al matrix and has the effect of improving the strength of the aluminum alloy sheet.

The mechanism by which second-phase particles such as Al-Fe intermetallic compounds improve the vibration-damping properties of aluminum alloy sheets is thought to be, for example, as follows: When external vibrations are applied to the aluminum alloy sheet, viscous flow occurs at the interface between the Al matrix and the second-phase particles. This viscous flow is thought to absorb the vibration energy, resulting in early damping of the vibrations.

By setting the Fe content in the substrate to 0.10 mass% or more, the strength and vibration-damping properties of the aluminum alloy sheet can be improved. From the perspective of further improving the vibration-damping properties of the aluminum alloy sheet and increasing its strength, the Fe content in the substrate is preferably 0.40 mass% or more, and more preferably 1.0 mass% or more. If the Fe content in the substrate is less than 0.10 mass%, the number of second-phase particles such as Al-Fe intermetallic compounds formed in the substrate will be insufficient, which may result in a decrease in the strength and vibration-damping properties of the aluminum alloy sheet.

Furthermore, by setting the Fe content in the substrate to 3.0 mass% or less, preferably 2.0 mass% or less, and more preferably 1.7 mass% or less, a uniform anodic oxide film can be easily formed on the substrate. As a result, adhesion between the aluminum alloy sheet and the coating or resin can be improved. If the Fe content in the substrate is excessively high, coarse Al-Fe intermetallic compounds are likely to form in the substrate. If coarse Al-Fe intermetallic compounds are present in the substrate, reactions around the coarse Al-Fe intermetallic compounds are likely to be accelerated when anodizing is formed, which may make it difficult to form a uniform anodic oxide film on the substrate.

Mn (Manganese): 0.10% by mass or more and 3.0% by mass or less The substrate contains 0.10% by mass or more and 3.0% by mass or less of Mn as an essential component. Mn is mainly present in the Al matrix as second-phase particles such as Al-Mn intermetallic compounds. The Al-Mn intermetallic compounds in the Al matrix, like the Al-Fe intermetallic compounds, have the effect of improving the strength and vibration-damping properties of the aluminum alloy sheet. Furthermore, Mn can form Al-Fe-Mn intermetallic compounds in the substrate together with Fe. The Al-Fe-Mn intermetallic compounds have a small potential difference with the Al matrix, and therefore have the effect of suppressing local cell reactions during the formation of an anodic oxide film. By suppressing the local cell reactions during the formation of an anodic oxide film, a uniform anodic oxide film can be easily formed on the substrate.

By ensuring that the Mn content in the substrate is 0.10 mass% or more, preferably 0.20 mass% or more, and more preferably 0.40 mass% or more, the strength and vibration-damping properties of the aluminum alloy sheet are improved and a uniform anodic oxide coating can be easily formed on the substrate. If the Mn content in the substrate is less than 0.10 mass%, the number of second-phase particles such as Al-Mn intermetallic compounds formed in the substrate will be insufficient, which may result in a decrease in the strength and vibration-damping properties of the aluminum alloy sheet.

Furthermore, by setting the Mn content in the substrate to 3.0 mass% or less, preferably 2.0 mass% or less, and more preferably 1.0 mass% or less, it is possible to form a uniform anodized film on the substrate. As a result, it is possible to improve the adhesion between the aluminum alloy sheet and the coating or resin. If the Mn content in the substrate is excessively high, coarse Al-Mn intermetallic compounds are more likely to form in the substrate. Similar to Al-Fe intermetallic compounds, coarse Al-Mn intermetallic compounds have the effect of accelerating the reaction that occurs when forming the anodized film. Therefore, in this case, it may be difficult to form a uniform anodized film on the substrate.

The substrate further contains Si (silicon), Cu (copper), Cr (chromium), and Zn (zinc) in addition to Fe and Mn. The substrate may optionally contain one or more elements selected from the group consisting of Ti (titanium), B (boron), V (vanadium), and Ni (nickel).

Si: 0.10% by mass or more and 0.40% by mass or less The substrate contains 0.10 % by mass or more and 0.40% by mass or less of Si. Si forms second-phase particles such as Si particles in the substrate, and has the effect of improving the strength and vibration-damping properties of the aluminum alloy sheet, similar to Al-Fe-based intermetallic compounds. Si can also form Al-Si-Mn-based intermetallic compounds in the substrate together with Mn. Al-Si-Mn-based intermetallic compounds have a small potential difference with the Al parent phase, and therefore have the effect of suppressing local cell reactions when forming an anodic oxide film. By suppressing local cell reactions when forming an anodic oxide film, a uniform anodic oxide film can be easily formed on the substrate.

By setting the Si content in the substrate to 0.10% by mass or more and 0.40% by mass or less, and more preferably 0.15% by mass or more and 0.30% by mass or less, the strength and vibration damping properties of the aluminum alloy sheet can be further improved, and the anodized film can be formed more uniformly on the substrate.

Cu: 0.005% by mass or more and 0.100% by mass or less The substrate contains 0.005 % by mass or more and 0.100% by mass or less of Cu. Cu forms second-phase particles such as Al-Cu intermetallic compounds in the substrate, and has the effect of improving the strength and vibration-damping properties of the aluminum alloy sheet, similar to Al-Fe intermetallic compounds. However, while Al-Cu intermetallic compounds improve vibration-damping properties, they may precipitate at the grain boundaries of the Al matrix upon heat treatment, causing intergranular corrosion. By setting the Cu content in the substrate to 0.005% by mass or more and 0.100% by mass or less, more preferably 0.010% by mass or more and 0.070% by mass or less, the strength and vibration-damping properties of the aluminum alloy sheet can be further improved while suppressing the occurrence of intergranular corrosion.

Cr: 0.01% by mass or more and 1.00% by mass or less The base material contains 0.01 % by mass or more and 1.00% by mass or less of Cr. Cr forms second-phase particles such as Al-Cr intermetallic compounds in the base material, and has the effect of improving the strength and vibration-damping properties of the aluminum alloy sheet, similar to Al-Fe intermetallic compounds and the like.

On the other hand, if the Cr content in the substrate is excessively high, coarse Al-Cr intermetallic compounds are more likely to form in the substrate. Because coarse Al-Cr intermetallic compounds have the effect of accelerating the reaction that occurs when an anodic oxide film is formed, the presence of excessively large coarse Al-Cr intermetallic compounds in the substrate may make it difficult to form a uniform anodic oxide film on the substrate. By setting the Cr content in the substrate to 0.01 mass% or more and 1.00 mass% or less, and more preferably 0.10 mass% or more and 0.50 mass% or less, the strength and vibration-damping properties of the aluminum alloy sheet are further improved, the formation of coarse Al-Cr intermetallic compounds in the substrate is suppressed, and a more uniform anodic oxide film can be formed on the substrate.

Zn: 0.01% by mass or more and 0.50% by mass or less (excluding Zn: 0.1% by mass or less)
The substrate contains 0.01 % by mass or more and 0.50% by mass or less (excluding 0.1% by mass or less) . A portion of the Zn forms second-phase particles in the Al matrix together with other alloying elements, further improving the strength and vibration-damping properties of the aluminum alloy sheet. The remainder of the Zn dissolves in the Al matrix, thereby lowering the potential of the substrate and improving the reactivity during the formation of an anodized film. However, an excessively high Zn content may make the substrate more susceptible to corrosion. By setting the Zn content in the substrate to 0.01% by mass or more and 0.50% by mass or less (excluding 0.1% by mass or less) , more preferably 0.10% by mass or more and 0.40% by mass or less (excluding 0.1% by mass or less) , the strength and vibration-damping properties of the aluminum alloy sheet can be further improved, and the potential of the substrate can be appropriately lowered to a lower potential, further accelerating the formation of an anodized film.

Ti, B, and V: total of 0.005% by mass or more and 0.500% by mass or less. The substrate may contain, as an optional component, one or more elements selected from the group consisting of Ti, B, and V. These elements have the effect of refining the crystal grains of the ingot during the manufacturing process of the aluminum alloy sheet. By setting the total content of Ti, B, and V within the specific range, the crystal grains of the ingot can be refined and the variation in size of second-phase particles formed in the substrate can be reduced. As a result, the variation in vibration-damping properties of the aluminum alloy sheet can be reduced. Furthermore, the reduced variation in size of second-phase particles reduces the variation in reactivity during the formation of an anodized film, allowing the anodized film to be formed more uniformly on the substrate. From the viewpoint of further enhancing these effects, the total content of Ti, B, and V is more preferably 0.20% by mass or less.

Ni: 0.10% by mass or less The substrate may contain 0.10% by mass or less of Ni as an optional component. Ni forms second-phase particles such as Al-Ni intermetallic compounds in the substrate, and has the effect of improving the strength and vibration-damping properties of the aluminum alloy sheet, similar to Al-Fe intermetallic compounds. However, while Al-Ni intermetallic compounds improve vibration-damping properties, they may become cathode sites when exposed to corrosive substances, accelerating corrosion. Furthermore, since Al-Ni intermetallic compounds have the effect of accelerating the reaction when forming an anodized film, if the number of Al-Ni intermetallic compounds present on the surface of the substrate increases, it may become difficult to form a uniform anodized film on the substrate.

By keeping the Ni content in the substrate to 0.10% by mass or less, and more preferably 0.05% by mass or less, it is possible to further improve the strength and vibration-damping properties of the aluminum alloy plate while suppressing the occurrence of corrosion. In addition, in this case, it is easier to form a uniform anodic oxide film on the substrate.

Other Elements In addition to the elements described above, the base material contains unavoidable impurities that are inevitably mixed in during the manufacturing process. Elements contained as unavoidable impurities include, for example, Zr (zirconium), Pb (lead), Ga (gallium), and Sn (tin). The content of each element as an unavoidable impurity is 0.1% by mass or less for each individual element, and the total content of the unavoidable impurities is 0.2% by mass or less.

[Anodic oxide film]
An anodized film is provided on the substrate. By adjusting the chemical composition of the substrate to fall within the specific range, second-phase particles such as Al-Fe intermetallic compounds can be formed in the substrate. These second-phase particles can improve the strength and vibration-damping properties of the aluminum alloy sheet. Furthermore, the second-phase particles formed in the substrate of the aluminum alloy sheet are unlikely to interfere with the dissolution and growth reactions of aluminum oxide during anodizing. Therefore, by adjusting the chemical composition of the substrate to fall within the specific range, an anodized film can be uniformly formed on the substrate, and the second-phase particles can improve the strength and vibration-damping properties of the aluminum alloy sheet after heating.

In the aluminum alloy sheet, the provision of an anodized film on the substrate not only inhibits oxidation of the substrate, but also creates fine irregularities on the surface of the aluminum alloy sheet, improving adhesion to coatings and resins through an anchoring effect. From the perspective of further enhancing the effect of improving adhesion to coatings and resins, the thickness of the anodized film is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

The anodized film on the aluminum alloy plate is preferably a porous anodized film with numerous pores. In this case, when the aluminum alloy plate is painted, the paint easily penetrates into the pores of the anodized film. This further improves adhesion to the paint film and resin. In this case, it is also possible to color the aluminum alloy plate by enclosing a dye in the pores of the anodized film.

[Physical properties of aluminum alloy sheet]
The aluminum alloy sheet has the properties that, after heating at a temperature of 250°C for 3 hours , the Young's modulus is 70 GPa or more, the 0.2% proof stress is 100 MPa or more, and the damping rate in damped free vibration is 1.5 × 10 ^-3 or more. An aluminum alloy sheet with a high Young's modulus and a high damping rate in damped free vibration can efficiently damp vibrations applied from the outside. Furthermore, an aluminum alloy sheet with a high 0.2% proof stress can improve the rigidity of final products such as automobile bodies, and can also suppress the occurrence of cracks and wrinkles during forming.

Therefore, aluminum alloy sheets whose Young's modulus, 0.2% proof stress, and damping rate of damped free vibration after heating under the specified conditions are each within the specified ranges can exhibit excellent vibration-damping properties after heat treatment, such as baking, performed after painting. Furthermore, aluminum alloy sheets with such properties are particularly suitable for automobile bodies.

From the viewpoint of further improving the vibration-damping property of the aluminum alloy plate, it is more preferable that the aluminum alloy plate has a damping rate of damped free vibration of 2.0 × 10 ^-3 or more after heating for 3 hours at a temperature of 250° C. A specific method for measuring the damping rate of damped free vibration will be described in detail in the Examples.

[Application]
As described above, the aluminum alloy sheet has improved adhesion to paint films and resins and has excellent vibration-damping properties after heating, due to the chemical composition of the substrate being within the above-mentioned specific range and the anodized coating being provided on the substrate, and is therefore suitable for applications requiring excellent vibration-damping properties after paint baking, such as automobile body panel materials.

When heating the aluminum alloy plate during paint baking or other processes, it is preferable to set the heating temperature to 300°C or less and the heating time to 10 hours or less. If the heating temperature of the aluminum alloy plate is excessively high or the heating time is excessively long, this may result in a decrease in the strength of the aluminum alloy plate.

(Method for manufacturing aluminum alloy plate)
In producing the aluminum alloy plate, a substrate made of an aluminum alloy having the specific chemical composition is cold-rolled to a desired thickness, and then the substrate is anodized to form an anodized coating.

The method for producing the substrate is not particularly limited. For example, the substrate may be produced by DC casting an ingot having the specific chemical composition, optionally heating the ingot for homogenization, and then hot rolling it.

In DC casting, the cooling rate of the ingot after casting is preferably in the range of 0.1°C/sec to 1000°C/sec. When homogenizing, the ingot should be held at a temperature of 500°C to 650°C for 0.5 hours or more.

When hot rolling an ingot without homogenizing it, it is preferable to start rolling while the ingot temperature is in the range of 300°C or higher and 550°C or lower. Also, when hot rolling an ingot after homogenizing it, it is preferable to start rolling while the ingot temperature is in the range of 300°C or higher and lower than 380°C. In either case, the temperature of the substrate at the end of hot rolling should be in the range of 100°C or higher and lower than 380°C.

In addition, a plate material having the above-mentioned specific chemical composition produced by CC casting can also be used as the substrate. The cooling rate of the substrate after casting in CC casting is preferably in the range of 0.1°C/sec or more and 1000°C/sec or less.

The substrate thus obtained is then cold-rolled to reduce its thickness to the desired thickness. The thickness of the substrate after cold rolling may be set appropriately within the range of, for example, 1.0 mm to 2.0 mm. Furthermore, the total reduction ratio in cold rolling, i.e., the ratio of the reduction in thickness of the substrate due to cold rolling to the thickness of the substrate before cold rolling, is preferably 10% to 95%.

When cold rolling the substrate, the substrate can also be heated and annealed, if necessary. Annealing can be performed before cold rolling or during cold rolling. Annealing can also be performed both before and during cold rolling. Annealing can be performed using a batch annealing furnace or a continuous annealing furnace. For example, when annealing using a batch annealing furnace, it is preferable to hold the substrate at a temperature of 200°C or higher but lower than 380°C for 0.1 hours to 10 hours.

The aluminum alloy sheet can be obtained by anodizing the substrate after cold rolling, forming an anodic oxide film on the substrate. In anodizing, the substrate and a counter electrode are immersed in an acidic electrolyte such as sulfuric acid, oxalic acid, or phosphoric acid, and a direct current is passed between the substrate and the counter electrode, causing the dissolution reaction and growth reaction of aluminum oxide to proceed in parallel. This allows a porous anodic oxide film with numerous pores to be formed on the substrate.

The thickness of the anodic oxide film can be controlled to some extent by the amount of electricity applied to the substrate. The amount of electricity applied to the substrate can be controlled by the magnitude of the voltage applied between the substrate and the counter electrode, the magnitude of the current flowing between the substrate and the counter electrode, and the duration of the current flow. In anodizing, for example, the voltage applied between the substrate and the counter electrode can be kept constant and the current can be varied, or the current applied between the substrate and the counter electrode can be kept constant and the voltage can be varied. It is also possible to vary both the voltage and the current in anodizing. Furthermore, when attempting to form a porous anodic oxide film on a substrate, the diameter and number of pores per unit area formed in the anodic oxide film can be controlled to some extent by the type of electrolyte.

Anodizing may be performed at any time between the completion of cold rolling and the application of coating. For example, anodizing may be performed by uncoiling a coiled substrate, bringing it into contact with an electrolyte together with a counter electrode, and passing a direct current through it. Alternatively, anodizing may be performed by bringing a substrate that has been cut to a desired size, or a substrate that has been formed and processed, into contact with an electrolyte together with a counter electrode, and passing a direct current through it.

An example of the aluminum alloy sheet will be described with reference to Figures 1 to 3. As shown in Figure 1, the aluminum alloy sheet 1 of this example includes a substrate 2 having a chemical composition containing 0.10 to 3.0 mass% Fe and 0.10 to 3.0 mass% Mn, with the balance being Al and unavoidable impurities, and an anodized coating 3 provided on at least one surface of the substrate 2. Furthermore, as shown in Table 1, the aluminum alloy sheet 1 of this example has properties such that after heating at a temperature of 100°C to 300°C for 0.5 to 10 hours, the Young's modulus is 70 GPa or more, the 0.2% proof stress is 100 MPa or more, and the damping factor in damped free vibration is 1.5 x ^10-3 or more.

To produce the aluminum alloy plate 1 of this example, first, an ingot having the chemical composition shown in Table 1 is produced by DC casting. In Table 1, the symbol "Bal." indicates that the corresponding element is the remainder, and the symbol "-" indicates that the corresponding element is not included. The surface of the ingot is ground to remove the surface segregation layer, and then the ingot is held at a temperature of 520°C for one hour for homogenization. Hot rolling is then initiated while the ingot temperature is still 460°C, producing a substrate 2 with a thickness of 3.0 mm. The temperature of substrate 2 at the completion of hot rolling is 280°C. Next, substrate 2 is cold-rolled to reduce the thickness of substrate 2 to 1.0 mm.

One side of the substrate 2 thus obtained is masked, and then the substrate 2 is immersed together with a counter electrode in a 15% by mass aqueous sulfuric acid solution at a temperature of 20°C. Anodizing treatment is then performed by passing a direct current at a current density of 10 mA/ ^cm2 between the substrate 2 as the anode and the counter electrode. The current application time in the anodizing treatment is as shown in Table 1. As a result, a porous anodic oxide film 3 is formed on the substrate 2, and test materials S1 to S3 shown in Table 1 can be obtained. The cross section of each test material was observed using an electron microscope, and the thickness of the anodic oxide film 3 was measured. The results are shown in Table 1.

Note that test materials R1 and R2 shown in Table 1 are test materials for comparison with test materials S1 to S3. Test material R1 has the same structure as test materials S1 to S3, except that the chemical composition of the base material has been changed as shown in Table 1. Furthermore, test material R2 has a different chemical composition of the base material as shown in Table 1. For test material R2, even if the base material is anodized under the same conditions as test materials S1 to S3, it is difficult to form a uniform anodized film on the base material. Therefore, the symbol "-" is entered in the anodized film thickness column for test material R2 in Table 1.

The methods for measuring the Young's modulus, 0.2% proof stress, and damping rate of damped free vibration of the aluminum alloy plate 1 in this example after heating are as follows.

Young's modulus and damping rate: After heat treatment by heating each test material at the holding temperature and holding time shown in Table 2, strip-shaped test pieces measuring 80 mm in length and 8 mm in width were taken from the test material with the rolling direction and longitudinal direction parallel. These test pieces were attached to a free-resonance internal friction measuring device ("JE-RT" manufactured by Nippon Technoplus Co., Ltd.), and the Young's modulus and damping rate were measured using the damping method. As shown in FIG. 2, the measuring device 4 used in this example has a driving electrode 41 and an amplitude sensor 42 facing the driving electrode 41. The test piece S is horizontally placed between the driving electrode 41 and the amplitude sensor 42, and the test piece S is fixed with a thin wire 43 at a vibration node position. In this state, an AC current is passed through the driving electrode 41 to apply a Coulomb force to the test piece S, thereby vibrating the test piece S. The amplitude of the test piece S is then measured using the amplitude sensor 42, thereby obtaining a vibration waveform.

In this example, an AC current is passed through the driving electrode 41 to forcibly vibrate the test piece S, and then the AC current is stopped, allowing the test piece S to vibrate freely due to its restoring force. The vibration of the test piece S is so-called damped free vibration, in which the amplitude exponentially decays while oscillating periodically with a period T, as shown in the waveform in Figure 3. Note that in damped free vibration, the amplitude is thought to decrease exponentially due to losses of vibration energy caused by atmospheric resistance and internal friction due to dislocations and grain boundaries within the test piece.

The method for calculating the value of the damping rate δ is as follows: first, the nth cycle (n is a positive integer) and the n+mth cycle (m is an integer of 2 or more) are arbitrarily selected from the waveform of the damped free vibration, and the value of the amplitude a _n in the nth cycle and the value of the amplitude a n _+m in the n+mth cycle are obtained. Since the damping rate δ is the natural logarithm ln(a _k /a k _{+1 ) of the ratio between the amplitude a k in} the kth cycle and the amplitude a _k+1 in the next cycle, the natural logarithm ln(a _n /a _n+m ) of the ratio between the amplitude a _n and the amplitude a n+ _m can be expanded as shown in the following formula.
ln(a _n /a _n+m )=ln{(a _n /a _n+1 )×(a _n+1 /a _n+2 )×...×(a _n+m-1 /a _n+m )}=mδ

Therefore, the value of the attenuation rate δ can be expressed as follows using the value of the amplitude a _n in the nth period and the value of the amplitude a _n+m in the (n+m)th period:
δ=(1/m)・ln(a _n /a _n+m )

Table 2 shows the Young's modulus and damping rate of damped free vibration for each test material after heating. Note that the damping rate for test material R2 was not calculated, so the symbol "-" is entered in the damping rate column.

0.2% Yield Strength After heat treatment by heating each test material at the holding temperature and holding time shown in Table 2, JIS No. 5 test pieces were taken from the test material so that the rolling direction and longitudinal direction were parallel. Using these test pieces, tensile tests were conducted using a method in accordance with JIS Z2241:2011. The 0.2% yield strength of each test material was then calculated based on the load-displacement curve obtained from the tensile test. Table 2 shows the 0.2% yield strength of each test material after heating. Note that the 0.2% yield strength of test material R2 was not calculated, so the symbol "-" is entered in the 0.2% yield strength column.

As shown in Table 1, test materials S1 to S3 have a substrate 2 with the specific chemical composition and an anodized coating 3 formed on the substrate 2, resulting in excellent adhesion to paint films and resins. Furthermore, test materials S1 to S3 have properties such that after heat treatment at the temperatures and times shown in Table 2, their Young's modulus, 0.2% proof stress, and damping rate of damped free vibration are all within the specific ranges. Aluminum alloy sheets with such properties can exhibit high strength and excellent vibration damping after heating, such as paint baking, and are therefore suitable for use in automobile bodies.

Because the Fe content and Mn content in the base material of test material R1 are lower than the specified ranges, second-phase particles such as Al-Fe intermetallic compounds and Al-Mn intermetallic compounds are less likely to form in the base material. As a result, test material R1 has a low Young's modulus and damping rate after heating, and is inferior in vibration damping properties to test material S1.

Test material R2 had a substrate with an Fe content and Mn content lower than the specified ranges, and an excessively high Si content, making it difficult to form a uniform anodized film on the substrate during anodizing.

The above describes examples of specific configurations of aluminum alloy sheets according to the present invention, but the specific configurations of aluminum alloy sheets according to the present invention are not limited to the configurations in the examples, and the configurations can be modified as appropriate within the scope of the spirit of the present invention.

1 Aluminum alloy plate 2 Base material 3 Anodic oxide film

Claims (4)

a base material having a chemical composition containing Fe: 0.10% by mass or more and 3.0% by mass or less , Mn: 0.10% by mass or more and 3.0% by mass or less, Si: 0.10% by mass or more and 0.40% by mass or less, Cu: 0.005% by mass or more and 0.100% by mass or less, Cr: 0.01% by mass or more and 1.00% by mass or less, and Zn: 0.01% by mass or more and 0.50% by mass or less (excluding Zn: 0.1% by mass or less) , with the balance being Al and unavoidable impurities;
an anodic oxide coating provided on at least one surface of the substrate,
An aluminum alloy plate having properties such that after heating at a temperature of 250°C for 3 hours , the Young's modulus is 70 GPa or more, the 0.2% proof stress is 100 MPa or more, and the damping rate in damped free vibration is 1.5 × 10 ^-3 or more. 2. The aluminum alloy plate according to claim 1, wherein the base material further contains one or more elements selected from the group consisting of Ti, B, and V , and the total content of these elements is 0.005% by mass or more and 0.500% by mass or less. The aluminum alloy plate according to claim 1 or 2 , wherein the substrate further contains Ni: 0.10 mass % or less. The aluminum alloy plate according to any one of claims 1 to 3 , wherein the anodized film has a thickness of 2 µm or more.