JP2022139747A - Aluminum alloy sheet for car reinforcements and method for producing the same - Google Patents

Abstract

To provide an aluminum alloy sheet for car reinforcements that is made from aluminum scrap material to reduce the environmental load, while having moldability, product strength and corrosion resistance, and a method for producing the same.SOLUTION: An aluminum alloy sheet for car reinforcements contains Fe: 0.5 mass% or less, Si: 1.2 mass% or more and 1.6 mass% or less, Cu: 0.2 mass% or less, Mn: 0.8 mass% or more and 1.2 mass% or less, Mg: 0.45 mass% or more and 0.7 mass% or less, and Zn: 0.7 mass% or less with the balance being Al and inevitable impurities. The aluminum alloy sheet has an average crystal grain size of 30 μm or less, a 0.2% proof stress of 100 MPa or more and 155 MPa or less, and an elongation of 20% or more. The aluminum alloy sheet is subjected to 2% uniaxial strain in a rolling direction and then heated at 170°C for 20 minutes, resulting in the 0.2% proof stress of 170 MPa or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an aluminum alloy plate for automobile reinforcement and a method for producing the same.
Reinforcement is also called reinforcement, reinforcement, reinforcement, and reinforcement.

In recent years, in order to protect the global environment, there is a demand for the adoption of materials that can reduce environmental loads. As for aluminum alloy plates, there is a very high demand for reusing scraps of various used aluminum alloy parts (hereinafter referred to as aluminum scrap material) to manufacture aluminum alloy plates. If the aluminum scrap material is reused to produce an aluminum alloy plate, the amount of CO ₂ generated can be greatly suppressed and the environmental load can be reduced compared to the case of adopting the aluminum base metal. When aluminum alloys made from recycled aluminum scraps are used as automotive reinforcement parts, it is important to ensure press formability and paintability when molding parts, as well as structural strength and corrosion resistance as products. However, since aluminum alloy plates made from recycled aluminum scrap materials contain various additive elements, it has been difficult to satisfy all the properties required for these structures. For example, regarding material strength, it is necessary to keep the strength within a certain range in order to ensure press formability during part molding, and if the strength is too high or too low, the press formability is poor. On the other hand, the final product must have high strength in order to ensure structural strength. The material strength of these reinforcement members is improved by the temperature applied in the painting process (baking process) after press molding, and the strength of the final product is obtained. It was difficult to ensure both the structural strength of the product.
For example, an aluminum alloy plate described in Patent Document 1 is known as an aluminum alloy plate made by reusing such an aluminum scrap material.

For example, the aluminum alloy plate of Patent Document 1 has Si: 0.4 to 2.0% by mass, Fe: 0.2 to 0.6% by mass, Cu: 0.1 to 0.7% by mass, Mn: 0 .5 to 1.5% by mass, Mg: 0.5 to 2.0% by mass, Zn: 0.05 to 1.0% by mass, and the balance being Al and unavoidable impurities. there is The aluminum alloy plate described in Patent Document 1 has a recrystallized structure over the entire plate thickness cross section, and has a recrystallized grain size of 50 μm or less and an electrical conductivity of 43.0 to 49.5% IACS. , thereby improving press formability and corrosion resistance.

Japanese Patent No. 5323673

By the way, although Patent Document 1 describes the press formability and corrosion resistance of an aluminum alloy plate, the target product is a heat insulator for automobiles and the like, and is different from the aluminum alloy plate for automobile reinforcement of the invention. Required characteristics do not match. In addition, it is considered difficult to achieve the aforementioned press formability and ensure the structural strength of the final product.

The present invention has been made in view of the above circumstances, and an aluminum alloy sheet for automotive reinforcement having formability, product strength and corrosion resistance while suppressing environmental load by using aluminum scrap material as a raw material, and a method for producing the same. intended to provide

As a result of intensive research, the researchers analyzed the composition of the aluminum scrap materials generated in aluminum rolling mills, examined in detail the effects of the alloying elements contained in large amounts in the aluminum scrap materials, and selected the range of alloying compositions. , and by appropriately controlling the combination of subsequent manufacturing conditions, we discovered an aluminum alloy material for automotive reinforcement that has formability, product strength, and corrosion resistance.

That is, in view of the above problems, the inventors of the present invention optimized the composition of aluminum alloys that reused aluminum scrap materials, and also optimized the manufacturing processes such as casting, rolling, and heat treatment, thereby making each additive component a solid solution. By controlling the precipitation state, the size of various intermetallic compounds, the dispersion state such as the number density, and the texture, we were able to obtain an invention that satisfies all of the required properties required for automobile reinforcement at a high level. For example, regarding the state of dispersion of intermetallic compounds, by optimizing the existence ratio of coarse Mg-Si compounds, it is possible to ensure the material strength necessary for press formability during part molding, while maintaining heat resistance in the subsequent parts painting process. Loading can cause age hardening to result in higher strength in the final product.

The aluminum alloy plate for automobile reinforcement of the present invention has Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8 % by mass or more and 1.2% by mass or less, Mg: 0.45% by mass or more and 0.7% by mass or less, Zn: 0.7% by mass or less, and the balance being Al and unavoidable impurities. , The average grain size is 30 μm or less, the 0.2% proof stress is 100 MPa or more and 155 MPa or less, the elongation is 20% or more, and after applying 2% uniaxial strain in the rolling direction, heat treatment is performed at 170 ° C. for 20 minutes. The 0.2% yield strength after the sintering is 170 MPa or more.

In the present invention, since the 0.2% proof stress is set to 100 MPa or more and 155 MPa or less and the elongation is set to 20% or more, press working can be performed appropriately. In addition, the 0.2% yield strength after heat treatment at 170° C. for 20 minutes after applying a uniaxial strain of 2% can be increased to 170 MPa or more, and the strength of the final product can be increased. In addition, since Cu is less than 0.2 mass % and Zn is less than 0.7 mass %, corrosion resistance can be improved. Furthermore, since the average crystal grain size is as small as 30 μm or less, workability can be improved.

In addition, if the average grain size exceeds 30 μm, workability is deteriorated. If the 0.2% proof stress is less than 100 MPa, the aluminum alloy plate may break during press working, and if it exceeds 150 MPa, the workability will deteriorate. Furthermore, if the elongation is less than 20%, workability is reduced. In addition, if the 0.2% proof stress after heat treatment at 170° C. for 20 minutes after applying uniaxial strain of 2% in the rolling direction is less than 170 MPa, the strength of the final product (automobile reinforcement) is reduced.

Fe contributes to the improvement of yield strength of the aluminum alloy plate, and if it exceeds 0.5% by mass, the ratio of intermetallic compounds increases, yield strength becomes too high, and formability deteriorates.
Si contributes to the improvement of yield strength of the aluminum alloy plate, and if it is less than 1.2% by mass, sufficient yield strength after heat treatment at 170° C. cannot be obtained, resulting in insufficient strength of the product. On the other hand, if it exceeds 1.6% by mass, the proportion of the intermetallic compound increases and the yield strength becomes too high, resulting in deterioration of formability.
Cu contributes to the improvement of yield strength and corrosion resistance of the aluminum alloy plate, and if it exceeds 0.2% by mass, the corrosion resistance is greatly reduced.
Mn contributes to the improvement of yield strength of the aluminum alloy plate, and if it is less than 0.8% by mass, sufficient yield strength after heat treatment at 170° C. cannot be obtained, resulting in insufficient strength of the product. On the other hand, if it exceeds 1.2% by mass, the intermetallic compound coarsens and a sufficient yield strength after heat treatment at 170° C. cannot be obtained.
Mg contributes to the yield strength improvement of the aluminum alloy plate, and if it is less than 0.45% by mass, sufficient yield strength after heat treatment at 170° C. cannot be obtained. On the other hand, if it exceeds 0.7% by mass, the proof stress becomes too high, the elongation decreases, and the formability deteriorates.
Zn contributes to the corrosion resistance of the aluminum alloy plate, and when it exceeds 0.7% by mass, the corrosion resistance deteriorates.

As a preferred embodiment of the aluminum alloy plate for automotive reinforcement of the present invention, Cr: 0.01% by mass or more and 0.10% by mass or less, Ti: 0.01% by mass or more and 0.10% by mass or less, Zr: 0.01% by mass or more and 0.10% by mass or less. Among 01% by mass or more and 0.10% by mass or less, one or more may be further contained.
Each of Cr and Zr contributes to the improvement of strength, refinement of crystal grains, and stabilization of the structure. In addition to saturating the effect, a large number of intermetallic compounds are generated, which may adversely affect moldability.
Ti contributes to the improvement of strength and the refinement of the ingot structure. Crystallized substances may form.

In a preferred embodiment of the aluminum alloy plate for automotive reinforcement of the present invention, the number of Mg—Si second phase particles having an equivalent circle diameter of 1.0 μm or more is 5.0×10 ³ particles/mm ² or less.
In the above aspect, by optimizing the existence ratio of coarse Mg—Si compounds to 5.0×10 ³ /mm ² or less, while ensuring the material strength necessary for press formability at the time of part molding, The load heat in the part coating process of 1 can cause age hardening to obtain high strength in the final product.

As a preferred embodiment of the aluminum alloy plate for automobile reinforcement of the present invention, the area ratio of crystal grains having an orientation difference from the cubic orientation of the cross section in the rolling direction within 15 ° to all crystal grains, and the Goss orientation It is preferable that the sum of the area ratio of crystal grains having an orientation difference of 15° or less with respect to all crystal grains is 3% or more.
Here, the expression of the texture in the EBSD (Electron Back Scatter Diffraction) method is expressed by the rolling surface and the rolling direction in the case of the texture of the sheet material by rolling, the rolling surface is expressed by {hkl}, and the rolling direction is It is represented by <uvw>. When using this expression, the cube orientation is expressed as {001}<100>, and the Goss orientation is expressed as {110}<001>.
In the above Cube orientation {001} <100> and Goss orientation {110} <001>, the slip lines on the crystal plane (rolling plane) should be symmetrical at 45° and 135° with respect to the bending axis. can be done. Therefore, in the above aspect, the area ratio of the crystal grains having the orientation difference from the cubic orientation in all the crystal grains of the rolled surface within 15° to all the crystal grains and the orientation difference between the Goss orientation and the Goss orientation are within 15°. By increasing the sum of the area ratio of crystal grains with a certain orientation to all crystal grains (hereinafter referred to as the oriented area ratio) above a certain level, the formation of shear bands on the outer side of the bend is suppressed, greatly improving bending workability. can.

The method for producing an aluminum alloy plate for automotive reinforcement according to the present invention includes an aluminum scrap material, Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2 % by mass or less, Mn: 0.8% by mass or more and 1.2% by mass or less, Mg: 0.45% by mass or more and 0.7% by mass or less, Zn: 0.7% by mass or less, and the balance being Al and After melting and casting an aluminum alloy containing unavoidable impurities, homogenization treatment is performed by holding at 500 ° C. or higher and 600 ° C. or lower for 2 hours or longer, and then multiple passes of hot rolling are performed at a rolling speed of 50 m / min or higher. A plate material having a thickness of 0.8 mm or more and 2.5 mm or less is formed by cold rolling, and the plate material is heated to 500 ° C. or more and 550 ° C. Hold for 20 seconds or less, then apply solution treatment to cool to 100°C or lower at a cooling rate of 200°C/second or higher, then perform aging treatment by storing at room temperature for 14 days or longer or aging treatment at 50°C for 72 hours. .

In the present invention, a plate material having a final thickness of 0.8 mm or more and 2.5 mm or less is formed by hot rolling and cold rolling. By performing aging treatment by storage, an aluminum alloy sheet for automobile reinforcement having formability, strength and corrosion resistance can be produced.

If the homogenization temperature is less than 500°C, segregation that occurs during casting will remain and sufficient homogenization will not be possible, and if the holding temperature exceeds 600°C, the ingot may melt. Further, when the holding time is less than 2 hours, homogenization may not proceed sufficiently.
When the rolling speed of one pass of hot rolling is less than 50 m / min, the elongation of the material and the area ratio of the crystal grains having an orientation difference from the cubic orientation within 15 ° to all crystal grains , the sum of the area ratio of the crystal grains having an orientation difference from the Goss orientation within 15° with respect to all crystal grains (orientation area ratio) decreases, and the 0.2% yield strength after heat treatment at 170 ° C. decreases. As a result, the formability and product strength of the aluminum alloy plate are lowered.
If the heating rate for the solution treatment is less than 100°C/sec, the productivity of the aluminum alloy sheet will be reduced, and if the holding temperature is less than 500°C, the redissolution of the solute elements will not proceed sufficiently, resulting in a 600 If the temperature exceeds °C, the plate may melt and break. Further, if the holding time is less than 15 seconds, the redissolution will not proceed sufficiently, and if it exceeds 120 seconds, the productivity of the aluminum alloy sheet will decrease.
Moreover, if the cooling rate of the solution treatment is less than 10° C./second, the productivity of the aluminum alloy sheet is lowered.
If the room temperature storage after the solution treatment is less than 14 days, the age hardening is insufficient, the strength of the aluminum alloy sheet is insufficient, and the formability is deteriorated.

According to the present invention, it is possible to provide an automobile reinforcement member that has excellent formability, strength and corrosion resistance while suppressing environmental load by using aluminum scrap material as a raw material.

An embodiment of an aluminum alloy plate for automobile reinforcement (hereinafter referred to as an aluminum alloy plate) according to the present invention will be described below.

[Structure of aluminum alloy plate]
The aluminum alloy plate of the present embodiment is, for example, inserted inside the hood and trunk of an automobile, and is processed into a so-called reinforcement material used as a reinforcement or the like used to increase the rigidity of the structure. This aluminum alloy plate is formed from an aluminum alloy made from an aluminum scrap material. Specifically, the aluminum alloy used as the aluminum alloy plate contains 50 or 60% by mass or more of aluminum scrap material, and may be entirely made of aluminum scrap material.
Also, such aluminum scrap material consists of scraps from aluminum rolling mills and various used aluminum alloy parts.

In addition, as described above, the aluminum alloy plate contains a plurality of elements because the main raw material is the aluminum scrap material. Specifically, the aluminum alloy plate has Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8% by mass. 1.2% by mass or less, Mg: 0.45% by mass or more and 0.7% by mass or less, Zn: 0.7% by mass or less, and the balance being Al and unavoidable impurities.

Fe contributes to the improvement of yield strength of the aluminum alloy plate, and if it exceeds 0.5% by mass, the ratio of intermetallic compounds increases, yield strength becomes too high, and formability deteriorates.
Si contributes to the improvement of yield strength of the aluminum alloy plate, and if it is less than 1.2% by mass, sufficient yield strength after heat treatment at 170° C. described below cannot be obtained, resulting in insufficient strength of the product. On the other hand, if it exceeds 1.6% by mass, the proportion of the intermetallic compound increases and the yield strength becomes too high, resulting in deterioration of formability.
Cu contributes to the improvement of yield strength and corrosion resistance of the aluminum alloy plate, and if it exceeds 0.2% by mass, the corrosion resistance is greatly reduced.
Mn contributes to the improvement of yield strength of the aluminum alloy plate, and if it is less than 0.8% by mass, sufficient yield strength after heat treatment at 170° C. cannot be obtained, resulting in insufficient strength of the product. On the other hand, if it exceeds 1.2% by mass, the intermetallic compound coarsens and a sufficient yield strength after heat treatment at 170° C. cannot be obtained.
Mg contributes to the yield strength improvement of the aluminum alloy plate, and if it is less than 0.45% by mass, sufficient yield strength after heat treatment at 170° C. cannot be obtained. On the other hand, if it exceeds 0.7% by mass, the proof stress becomes too high, the elongation decreases, and the formability deteriorates.
Zn contributes to the corrosion resistance of the aluminum alloy plate, and when it exceeds 0.7% by mass, the corrosion resistance deteriorates.

Further, the aluminum alloy plate has Cr: 0.01% by mass or more and 0.10% by mass or less, Ti: 0.01% by mass or more and 0.1% by mass or less, Zr: 0.01% by mass or more and 0.10% by mass. It is preferable to further contain one or more of the following.
Each of Cr and Zr contributes to the improvement of strength, refinement of crystal grains, and stabilization of the structure. In addition to saturating the effect, a large number of intermetallic compounds are generated, which may adversely affect moldability.
Ti contributes to the improvement of strength and the refinement of the ingot structure. Crystallized substances may form.

This aluminum alloy plate has an average grain size of 30 μm or less, a 0.2% proof stress of 100 MPa or more and 155 MPa or less, an elongation of 20% or more, and 20% at 170° C. after applying 2% uniaxial strain in the rolling direction. The 0.2% yield strength after heat treatment for 1 minute is 170 MPa or more. The application of 2% uniaxial strain is a condition assuming press molding as a reinforcement, and the heat treatment at 170° C. for 20 minutes is a condition assuming painting after processing to reinforce. In other words, the 0.2% yield strength (sometimes referred to as the yield strength after heat treatment at 170 ° C.) after applying 2% uniaxial strain in the rolling direction and then performing heat treatment at 170 ° C. for 20 minutes is the Reinforce product. Assuming strength.

Also, if the average crystal grain size exceeds 30 μm, the workability is lowered. Furthermore, if the 0.2% proof stress is less than 100 MPa, the aluminum alloy plate may break during press working, and if it exceeds 150 MPa, the workability will deteriorate. In addition, if the elongation is less than 20%, workability is reduced. Further, if the 0.2% proof stress after heat treatment at 170° C. for 20 minutes after imparting uniaxial strain of 2% in the rolling direction is less than 170 MPa, the strength of the final product (automobile reinforcement) is reduced.
It should be noted that the average crystal grain size is more preferably 25 μm or less. The 0.2% proof stress is more preferably 125 MPa or more and 150 MPa or less. Moreover, the yield strength after heat treatment at 170° C. is more preferably 185 MPa or more.

Further, the aluminum alloy plate contains 5.0×10 ³ particles/mm ² or less of Mg—Si-based second phase particles having an equivalent circle diameter of 1.0 μm or more. If the number of Mg—Si-based second-phase particles with an equivalent circle diameter of 1.0 μm or more exceeds 5.0×10 ³ particles/mm ² , it is difficult to ensure the material strength necessary for press formability when molding parts. , the heat load in the subsequent part coating process may make age hardening less likely.

Furthermore, the aluminum alloy plate has an area ratio (Cube orientation area ratio) of crystal grains having an orientation difference with the cubic orientation of the cross section in the rolling direction within 15 ° with respect to all crystal grains, and an orientation difference between the Goss orientation The sum (orientation area ratio) of crystal grains having an orientation within 15° with respect to all crystal grains (Goss orientation area ratio) is 3% or more. If the azimuth area ratio is 3% or more, it contributes to the improvement of bending workability. . If the area ratio of the crystal grains to all crystal grains is less than 3%, it is difficult to suppress the formation of shear bands on the outer side of the bend, making it difficult to significantly improve the bending workability.

Further, the aluminum alloy plate preferably has a material conductivity of 40%IACS or more and 45%IACS or less. The electrical conductivity is also an index representing the solid solution/precipitation state of each additive element (especially Si and Mg), and the strength of the aluminum alloy plate (0.2% proof stress and 0.2% after heat treatment at 170 ° C. for 20 minutes strength), etc. As the dissolution into the aluminum matrix progresses, the conductivity decreases, and as the precipitation as an intermetallic compound progresses, the conductivity increases. Therefore, if the conductivity of the material is too low or too high, the strength of the material and the strength after aging tend to decrease, and the above range is desirable.
If the conductivity is less than 40% IACS or exceeds 45% IACS, the solid solubility of each additive element in the aluminum alloy plate is outside the appropriate range, so at 0.2% proof stress and 170 ° C. The 0.2% yield strength after heat treatment for 20 minutes may decrease. In addition, if the electrical conductivity exceeds 45% IACS, the intermetallic compound tends to coarsen, which may slightly reduce the corrosion resistance.
This conductivity is more preferably 42%IACS or more and 44%IACS or less.

[Method for producing aluminum alloy plate]
An aluminum alloy plate is manufactured by the following procedures. First, an aluminum alloy having the above composition containing 50% by mass or more of aluminum scrap material is subjected to melting and casting treatment, homogenization treatment, soaking treatment, hot rolling treatment, cold rolling treatment, solution treatment and aging treatment. It is manufactured by applying in this order. A specific description will be given below.

[Melting and casting process]
Fe containing 50% by mass or more of aluminum scrap material: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8% by mass % or more and 1.2 mass % or less, Mg: 0.45 mass % or more and 0.7 mass % or less, Zn: 0.7 mass % or less, and the balance being Al and unavoidable impurities. Produce aluminum alloy molten metal. Then, the molten aluminum alloy is cast by a semi-continuous casting method (DC casting).
The casting method is not limited to the semi-continuous casting method, and other common methods such as continuous casting method may be used. Further, the aluminum alloy ingot may be subjected to facing processing before and after the homogenization treatment.

[Homogenization treatment]
The ingot obtained by the semi-continuous casting method is homogenized for the purpose of removing non-homogeneous structure such as segregation. Due to the high-temperature homogenization treatment, the additive element supersaturated in solid solution in the matrix during casting precipitates as an intermetallic compound. Since the size and dispersion amount of the precipitated intermetallic compound are affected by the temperature and time of the homogenization treatment, it is necessary to select heat treatment conditions according to the type of additive element.

For example, since the aluminum alloy containing the aluminum scrap material has the above composition, the obtained ingot is subjected to a homogenization treatment at a temperature of 500° C. or more and 600° C. or less for 2 hours or more. More preferably, this homogenization treatment is held at a temperature of 535-595° C. for 3-8 hours.
If the holding temperature of the homogenization treatment is less than 500°C, the segregation that occurs during casting remains and sufficient homogenization cannot be performed, and if the holding temperature exceeds 600°C, the ingot may melt. be. Further, when the holding time is less than 2 hours, homogenization may not proceed sufficiently.

[Soaking treatment]
A soaking treatment is performed on the homogenized ingot. This soaking treatment is performed at a temperature slightly lower than that of the homogenization treatment, and is maintained at a temperature of 480° C. or higher and 550° C. or lower, for example, for one hour or longer. Note that the soaking treatment and the soaking treatment before hot rolling may be performed together.

[Hot rolling treatment]
Hot rolling is performed on the homogenized ingot (or the soaked ingot if soaked). This hot rolling is performed at a high temperature of around 500°C. Specifically, after hot rough rolling at a delivery side temperature of 400 ° C. to 460 ° C., the plate material is passed through a single reverse type hot finish rolling mill three times at a rolling speed of 50 m / min or more. The thickness is 2 mm to 6 mm. Specifically, the first pass of hot finishing is performed under the conditions of a rolling speed of 50 m/min or more and 150 m/min or less and a coiling temperature of 350° C. or more and 400° C. or less. Next, a second pass of hot finishing is performed under the conditions of a rolling speed of 50 m/min or more and 150 m/min or less and a coiling temperature of 330° C. or more and 380° C. or less. Finally, a third pass of hot finishing is performed under the conditions of a rolling speed of 150 m/min or more and 300 m/min or less and a coiling temperature of 230° C. or more and 330° C. or less.

If the rolling speed of hot rolling is less than 50 m/min, the elongation and cubic orientation of the material will decrease, and the 0.2% proof stress after heat treatment at 170 ° C. will decrease, so the formability of the aluminum alloy plate and product strength is reduced.
In this embodiment, the texture of the material is controlled by variously changing the conditions of the hot finish rolling, and crystal grains having an orientation difference from the cubic orientation of the rolled surface in the final rolled product within 15 ° and the area ratio of crystal grains having an orientation difference of 15° or less from the Goss orientation to all crystal grains (orientation area ratio) was adjusted to a desired range.

[Cold rolling]
Next, a cold rolling process is performed with respect to the plate|board material after hot rolling. The method of this cold rolling treatment is not particularly limited, but it can be carried out, for example, by passing the sheet material through a rolling mill. The thickness of the sheet after cold rolling is, for example, 0.8 mm or more and 2.5 mm or less.

[Solution treatment]
Solution treatment is performed on the sheet material after the cold rolling treatment. In this solution treatment, the plate material is heated to 500° C. or more and 550° C. or less at a heating rate of 100° C./second or more, held for 15 seconds or more and 120 seconds or less, and then cooled to 100° C. or less at a cooling rate of 200° C./second or more. cool to
If the heating rate for the solution treatment is less than 100°C/sec, the productivity of the aluminum alloy plate will decrease, and if the holding temperature is less than 500°C, recrystallization will not proceed sufficiently, and the temperature will be 600°C. , the aluminum alloy plate may melt and break. Further, if the holding time is less than 15 seconds, recrystallization will not proceed sufficiently, and if it exceeds 120 seconds, the productivity of the aluminum alloy sheet will decrease. Moreover, if the cooling rate of the solution treatment is less than 200° C./sec, the productivity of the aluminum alloy sheet will be lowered.

[Aging treatment]
Finally, the plate material subjected to the solution treatment is stored at room temperature for 14 days or more, or is subjected to aging treatment corresponding to room temperature by holding at 50° C. for 72 hours. The yield strength and elongation of these aluminum alloy sheets after aging treatment after completion of rolling greatly affect the press formability of the product. The 0.2% proof stress of the aluminum alloy plate after this aging treatment is 100 MPa or more and 155 MPa or less, and the elongation is 20% or more.

Furthermore, the aluminum alloy plate (aluminum alloy plate after aging treatment) produced in this way assumes a thermal load in the painting process after press forming in the product, and the 0.2% proof stress is measured by the following method. did. Specifically, a test piece subjected to a strain of 2% by a tensile test based on JISZ2241 is heated to 170 ° C. at a heating rate of 10 ° C./sec or more and held for 20 minutes, and then heated to 10 ° C. The yield strength was measured after the heat treatment was performed at a cooling rate of 1/sec or higher. The yield strength of these aluminum alloy plates after heat treatment at 170° C. is equivalent to the product strength of the product. The 0.2% yield strength of the aluminum alloy plate after this 170° C. heat treatment is 170 MPa or more.

Next, the crystal orientation will be explained. The cubic orientation (cube orientation) is expressed as {001}<100> in terms of texture in the EBSD method, and the Goss orientation is expressed as {110}<001>. The Cube orientation and the Goss orientation show similar characteristics in the three directions of the thickness direction ND of the rolled surface, the rolling direction LD, and the direction perpendicular to the rolling direction TD. In the Cube orientation {001} <100> and the Goss orientation {110} <001>, the slip lines on the crystal plane (rolled plane) should have good symmetry at 45° and 135° with respect to the bending axis. can be done. For this reason, the area ratio of crystal grains having an orientation difference of 15° or less from the cubic orientation in all crystal grains to all crystal grains, and the crystal grain having an orientation having an orientation difference of 15° or less from the Goss orientation It was found that by increasing the sum of the area ratios of all crystal grains (orientation area ratio) to a certain level, the formation of shear bands on the outer side of the bend can be suppressed and the bending workability can be greatly improved.

The aluminum alloy plate thus produced has an average grain size of 30 μm or less, a 0.2% proof stress of 100 MPa or more and 155 MPa or less, an elongation of 20% or more, and 170% after 2% uniaxial strain is applied. An aluminum alloy sheet having a 0.2% proof stress of 170 MPa or more after being heat-treated at °C for 20 minutes, that is, an aluminum alloy sheet for automotive reinforcement having formability, strength and corrosion resistance. Moreover, since the aluminum alloy plate can be produced from the aluminum alloy containing 50% by mass or more of the aluminum scrap material, the environmental load can be reduced.

Specifically, since the aluminum alloy plate of the present embodiment has a 0.2% proof stress of 100 MPa or more and 155 MPa or less and an elongation of 20% or more, it can be appropriately press-worked. In addition, the 0.2% proof stress after heat treatment at 170 ° C. for 20 minutes after applying 2% uniaxial strain in the rolling direction can be extremely high at 170 MPa or more, and the strength of the final product (automobile reinforcement) can be increased. can be done. In addition, since Cu is less than 0.2 mass % and Zn is less than 0.7 mass %, corrosion resistance can be improved. Furthermore, since the average crystal grain size is as small as 30 μm or less, workability can be improved.

In addition, by optimizing the existence ratio of coarse Mg—Si compounds to 5.0×10 ³ pieces/mm ² or less, the material strength necessary for press formability at the time of part molding is ensured, and the subsequent parts The applied heat in the coating process can cause age hardening to achieve high strength in the final product. Furthermore, the area ratio of crystal grains having an orientation difference from the cubic orientation of the rolled surface within 15° to all crystal grains, and the total area ratio of crystal grains having an orientation difference from the Goss orientation within 15° The sum of the area ratio with respect to the crystal grain (orientation area ratio) is 3% or more, and the cube orientation (Cube orientation) {001} <100> and Goss orientation {110} <001> have Since the upper slip line can be made symmetrical at 45° and 135° with respect to the bending axis, the constant increase in the azimuthal area ratio suppresses the formation of shear bands on the outside of the bend, Machinability can be greatly improved. In addition, since the conductivity is set to 40% IACS or more and 45% IACS or less, the 0.2% proof stress of the aluminum alloy plate and the 0.2% proof stress after heat treatment at 170 ° C. for 20 minutes are each within the above numerical range. can be In addition, if the electrical conductivity is 45% IACS or less, the intermetallic compound will not coarsen, so it is possible to suppress the deterioration of the corrosion resistance.

By subjecting the aluminum alloy plate for automobile reinforcement as described above to press forming and then painting, it is possible to provide an automobile reinforcement having excellent formability, strength and corrosion resistance.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

The aluminum alloys of Examples 1 to 17 and Comparative Examples 1 to 12 were produced by the method shown below, and the 0.2% proof stress and elongation of each of the obtained samples were measured, and then the formability was evaluated. A detailed description is given below.
The compositions (components) of the aluminum alloys used as raw materials for Examples 1 to 17 and Comparative Examples 1 to 12 were as shown in Table 1.

These aluminum alloys were melted to produce molten aluminum alloys, which were cast by semi-continuous casting. The ingot obtained by the semi-continuous casting method was subjected to a homogenization treatment at 565 ° C. for 2 hours, and then subjected to soaking at 510 ° C. for 1 hour. After the rolling, a plate material having a thickness of 1.5 mm was formed by cold rolling. This plate material is heated to 520°C at a heating rate of 100°C/second or more, held for 20 seconds or less, and then cooled to 100°C or less at a cooling rate of 50°C/second. Each sample was prepared by subjecting it to an aging treatment in which it was held at room temperature for 72 hours.
In addition, in the hot rolling conditions of Table 2, the rolling speed ranges from the lower limit value to less than the upper limit value for each column of rolling conditions B to D (for example, 20 m in the first pass of rolling condition D /min or more and less than 50 m/min), and in each column of the rolling conditions A, the range is indicated by the lower limit or more and the upper limit or less (100 m/min or more and 150 m/min or less for the first pass).

(Measurement of 0.2% yield strength)
The 0.2% yield strength was measured by a method according to JISZ2241. Specifically, from each obtained sample, a sample was cut out parallel to the rolling direction to prepare a JIS No. 5-shaped test piece, and a tensile test was performed at room temperature to measure yield strength (MPa). The tensile speed was set to 5 mm/min.

(Elongation measurement)
Elongation was measured by a method according to JISZ2241. Specifically, from each obtained sample, a sample was cut out parallel to the rolling direction to prepare a JIS No. 5 test piece, and a tensile test was performed at room temperature to measure the elongation. The elongation referred to herein is the permanent elongation after rupture based on JISZ2241 expressed as a percentage of the original gauge length.

(conductivity)
The electrical conductivity was measured by the four-probe method. A current of 500 mA was passed through the sample in a room temperature environment of 20 to 25° C., the resistance was calculated from the voltage value, and then the conductivity was calculated.

(Observation of compound particle distribution state)
A cross section parallel to the rolling direction was observed for the produced aluminum alloy. Observation was performed with a field emission scanning electron microscope (FE-SEM) on a cross section subjected to CP processing (cross section processing) based on the ion milling method. Based on the observed image, the equivalent circle diameter and distribution density of the compound particles (Mg—Si compound particles) were calculated by image analysis.

(Crystal grain size)
As a method of exposing the metal structure, a cross section cut parallel to the rolling direction of the aluminum alloy plate is polished with emery paper, rough buffed, finish polished, washed with water, dried, and further treated with a barker. A method of anodizing in a liquid under the conditions of bath temperature: 25° C., applied voltage: 30 V, and applied time: 120 seconds was applied. The treated sample was photographed using a polarized optical microscope, and the average crystal grain size was calculated by the section method.

(azimuth area ratio)
The crystal grain has an orientation difference of 15° or less from the Cube orientation of the crystal grain, and has an orientation difference of 15° or less from the Goss orientation. The sum of the area ratio (Goss orientation area ratio) of the crystal grains to all the crystal grains (orientation area ratio) is obtained by measuring the crystal grain orientation distribution map OIM (Orientation Imaging Microscopy) image measured by the EBSD (Electron Backscatter Diffraction) method. {001} <100> orientation with a misorientation within 15° area fraction of all grains, and crystal grains with a misorientation with a Goss orientation within 15° The sum of the area fraction with respect to all crystal grains was measured as the azimuthal area fraction. Specifically, an electron beam is scanned at a pitch of 1 μm for a measurement area of 0.20 mm × 1.5 mm (plate thickness) of the plate thickness cross section in the rolling direction of the aluminum alloy plate described above, and each measurement point Among the crystal grains determined from the orientation difference between the measurement points, the crystal grains having an orientation difference with the Cube orientation within 15 ° and the orientation difference with the Goss orientation within 15 ° For each crystal grain having a certain orientation, the average area ratio (%) with respect to the measured area was measured to calculate the Cube orientation area ratio and the Goss orientation area ratio, and the sum of these was taken as the orientation area ratio.

(Evaluation of moldability)
Regarding the evaluation of formability, the degree of occurrence of cracks and wrinkles generated when 180° close contact bending based on JISZ2248 was performed was visually evaluated. In this case, those with almost no wrinkles and no cracks were evaluated as very good (◎), and those with some wrinkles but no cracks were evaluated as good (○), and cracks were evaluated. was evaluated as unsatisfactory (x).

(Evaluation of product strength)
After imparting 2% uniaxial strain in the rolling direction to the sample, 0.2% proof stress after heat treatment at 170°C for 20 minutes was assumed to be the product strength. Those with a yield strength of 190 MPa or more were evaluated as very good (⊚), those with a yield strength of 170 MPa or more and less than 190 MPa were evaluated as good (◯), and those with less than 170 MPa were evaluated as unsatisfactory (×).

(Evaluation of corrosion resistance)
As a corrosion resistance evaluation, a salt spray test (SST) was performed for 1000 hours. For the samples after this corrosion test, corrosion weight loss was measured after removing corrosion products with chromium phosphate. Based on these results, samples with a corrosion weight loss of less than 15.0 mg/cm ² were evaluated as good (◯), and samples with a corrosion weight loss of 15.0 mg/cm ² or more were evaluated as unsatisfactory (×).
These yield strength, elongation, conductivity, number density of Mg—Si compound, crystal grain size, Cube orientation area ratio, Goss orientation area ratio, Goss orientation area ratio, and yield strength after heat treatment at 170 ° C. are shown in Table 3, and various evaluations are performed. is shown in Table 4.

As shown in Tables 3 and 4, Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8% by mass % or more and 1.2 mass% or less, Mg: 0.45 mass% or more and 0.7 mass% or less, Zn: 0.7 mass% or less, with the balance being Al and unavoidable impurities, The average grain size is 30 μm or less, the 0.2% proof stress is 100 MPa or more and 155 MPa or less, the elongation is 20% or more, and after applying 2% uniaxial strain in the rolling direction, heat treatment was performed at 170 ° C. for 20 minutes. Examples 1 to 17 having a later 0.2% yield strength of 170 MPa or more had good or very good moldability and product strength, and all had good corrosion resistance.

On the other hand, in Comparative Example 1, since the Fe component was too large and the 0.2% proof stress was high, the formability deteriorated and was not acceptable. In Comparative Example 2, since the Si component was too small, both the 0.2% yield strength and the 0.2% yield strength after heat treatment at 170 ° C. were low, so both formability and product strength were unsatisfactory. became. In Comparative Example 3, since the Si component was too large, the 0.2% proof stress and elongation were low, and the formability was not good. Comparative Example 4 had too much Cu component, so the corrosion resistance was unsatisfactory. In Comparative Example 5, the Mn component was too small, the electrical conductivity was lowered, and the 0.2% yield strength after heat treatment at 170° C. was lowered, so the product strength was unsatisfactory. In Comparative Example 6, the number density of the Mg—Si compound became too large as the conductivity increased due to the excessive Mn component, and as a result, the 0.2% yield strength after heat treatment at 170 ° C. decreased. Strength is disabled.

In addition, in Comparative Example 7, since the Mg component was too small, both the 0.2% proof stress and the 0.2% proof stress after heat treatment at 170 ° C. were low, so both the formability and the product strength were poor. became impossible. In Comparative Example 8, since the Mg component was too large, the 0.2% proof stress and elongation were low, and the formability was not good. In Comparative Example 9, since the Zn content was too large, the corrosion resistance was unsatisfactory, and the oriented area ratio was low, so that the formability was also unsatisfactory. In Comparative Examples 10 and 11, the hot rolling condition was D, and the rolling speeds in the first pass and the second pass were lower than those in the other conditions A to C. Therefore, in Comparative Example 10, the elongation and the azimuthal area ratio were low, and the formability was not good. Moreover, in Comparative Example 11, the elongation and the azimuthal area ratio were low, and the 0.2% yield strength after heat treatment at 170° C. was low, so both formability and product strength were unsatisfactory.

Claims (5)

Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8% by mass or more and 1.2% by mass or less, Mg: 0.45% by mass or more and 0.7% by mass or less, Zn: 0.7% by mass or less, with the balance being Al and unavoidable impurities, an average crystal grain size of 30 μm or less, and 0 2% proof stress is 100 MPa or more and 155 MPa or less, elongation is 20% or more, and 0.2% proof stress is 170 MPa or more after heat treatment at 170 ° C. for 20 minutes after applying 2% uniaxial strain in the rolling direction. An aluminum alloy plate for automobile reinforcement, characterized by: Cr: 0.01 mass% or more and 0.10 mass% or less, Ti: 0.01 mass% or more and 0.10 mass% or less, Zr: 0.01 mass% or more and 0.10 mass% or less, one or 2. The aluminum alloy plate for automobile reinforcement according to claim 1, further comprising two or more kinds. 3. The aluminum alloy for automotive reinforcement according to claim 1 or 2, wherein the number of Mg—Si-based second phase particles having an equivalent circle diameter of 1.0 μm or more is 5.0×10 ³ particles/mm ² or less. board. The area ratio of crystal grains having an orientation difference from the cubic orientation of the cross section in the rolling direction within 15° to all crystal grains, and the total area ratio of crystal grains having an orientation difference from the Goss orientation within 15° The aluminum alloy plate for automobile reinforcement according to any one of claims 1 to 3, wherein the sum of the area ratio with respect to the crystal grains is 3% or more. Including aluminum scrap material, Fe: 0.5% by mass or less, Si: 1.2% by mass or more and 1.6% by mass or less, Cu: 0.2% by mass or less, Mn: 0.8% by mass or more and 1.2% After melting and casting an aluminum alloy containing Mg: 0.45 mass% or more and 0.7 mass% or less, Zn: 0.7 mass% or less, and the balance being Al and inevitable impurities, 500 ° C. or higher Homogenization treatment is performed by holding at 600 ° C. or less for 2 hours or more, then hot rolling is performed in multiple passes at a rolling speed of 50 m / min or more, and then cold rolling is performed to obtain a thickness of 0.8 mm or more 2 Forming a plate material of 5 mm or less, heating the plate material to 500° C. or more and 550° C. or less at a heating rate of 100° C./second or more, holding it for 15 seconds or more and 120 seconds or less, and then cooling it at a rate of 200° C./second or more. A method for producing an aluminum alloy plate for automobile reinforcement, characterized by subjecting the aluminum alloy plate to solution treatment by cooling to 100°C or less at 100°C or less, followed by aging treatment by storage at room temperature for 14 days or more or aging treatment at 50°C for 72 hours. .