TWI881799B - Aluminum alloy sheet for can cover - Google Patents

Abstract

One aspect of the present invention is an aluminum alloy plate for can lids, wherein the content of silicon is 0.27 mass % or more and 0.39 mass % or less, the content of iron is 0.35 mass % or more and 0.55 mass % or less, the content of copper is 0.17 mass % or more and 0.25 mass % or less, the content of manganese is 0.75 mass % or more and 0.95 mass % or less, and the content of magnesium is 2.2 mass % or more and 2.8 mass % or less. The aluminum alloy plate for can lids is respectively in the 0° direction, the 45° direction and the 90° direction relative to the rolling direction, and the minimum value is the minimum evaluation value S among the evaluation values S calculated by the following formula (1) using 0.2% proof stress σ _0.2 , tensile strength σ _B , and the average value σ _fm of 0.2% proof stress and tensile strength _min is 370 MPa or more and 410 MPa or less. S = σ _fm / (σ _0.2 / σ _B ) ‧‧‧ (1)

Description

Aluminum alloy sheet for can cover

The present invention relates to an aluminum alloy plate for can covers.

In recent years, due to the increasing environmental awareness, aluminum alloy plates with low carbon dioxide emissions during the manufacturing process are needed. In the aluminum manufacturing process, the ratio of the aluminum new casting in the casting step indirectly affects the carbon dioxide emissions.

The production of aluminum new castings uses a lot of electricity in its refining step, which in turn causes a lot of carbon dioxide emissions. Therefore, reducing the amount of aluminum new castings and increasing the horizontal recycling rate (or closed loop recycling rate) for the production of aluminum alloy plates will help reduce carbon dioxide emissions.

Generally speaking, when aluminum scrap is melted for casting, carbon dioxide emissions are thought to be reduced to about 1/30 compared to the case of making new aluminum ingots. In particular, the production volume of aluminum alloy plates for beverage cans used worldwide is very large, and further improving its horizontal recycling rate is of great significance for reducing environmental load.

Among them, the upper limit of the component specifications of silicon, iron, copper, manganese, etc. of the can lid formed of 5182 aluminum alloy (AA5182 alloy) is lower than that of the can body formed of 3104 aluminum alloy (AA3104 alloy), and it is difficult to mix the waste from the can body material mixed with 3104 aluminum alloy.

For example, if the can waste (UBC: Used Beverage Can) generated in the city is directly mixed, the weight ratio of the can body and the can lid makes the 3104 aluminum alloy contain more components, so it is easy to exceed the upper limit of the 5182 aluminum alloy composition, and it is necessary to dilute the composition with a new casting.

Therefore, compared with the aluminum alloy sheet for the can body, the aluminum alloy sheet for the can lid uses more new castings to adjust the composition of the 5182 aluminum alloy, and the recovery rate is low. Therefore, by changing the can lid to an alloy that is easy to mix with the composition of the 3104 aluminum alloy, the use rate of new castings for the can lid can be greatly reduced.

Patent documents 1 to 5 disclose aluminum alloy sheets for can lids that have a composition close to that of 3104 aluminum alloy and have excellent recyclability.

Patent document 1 is Japanese Patent Publication No. 2001-73106, Patent document 2 is Japanese Patent Publication No. 9-070925, Patent document 3 is Japanese Patent Publication No. 11-269594, Patent document 4 is Japanese Patent Publication No. 2000-160273, and Patent document 5 is Japanese Patent Publication No. 2016-160511.

When the composition of the alloy used for the can cover is close to that of 3104 aluminum alloy, the pressure resistance and toughness of the can cover are reduced. The pressure resistance of the can cover is the internal pressure value when the can cover is reversed relative to the pressure inside the can. It is the resistance value when the internal pressure of the can increases unexpectedly due to changes in the external environment.

In particular, high pressure resistance is required for pressure cans for beer or carbonated drinks. Generally speaking, the higher the strength of the material or the thicker the plate, the higher the pressure resistance. Therefore, the lid of the pressure can is made of high-strength 5182 aluminum alloy, which contains more magnesium, a component that helps increase strength.

In contrast, if the known 3104 aluminum alloy is used for can lids, the pressure resistance will be greatly reduced, and when the pressure inside the can increases unexpectedly, the lid will flip over, increasing the possibility of leakage of the contents. In addition, if the plate thickness is increased to improve the pressure resistance, the weight of the lid will increase and the original price of the lid will rise.

In addition, the toughness of the material affects the formability and opening of the lid. If the toughness of the material is low, forming cracks will occur especially at the rivet and countersink parts of the lid. Also, when the pressure inside the can increases unexpectedly, cracks will occur at the scored part, increasing the possibility of leakage of the contents of the can. Such cracks will occur especially along the rolling direction. Therefore, toughness against tensile stress and bending stress in the direction perpendicular to the rolling direction is required.

However, aluminum alloy sheets for can lids that are closer to the known 3104 aluminum alloy cannot meet either or both of the above two issues, namely, material strength (i.e., pressure resistance of the lid) and toughness (i.e., formability and opening properties).

One aspect of the present invention is to preferably provide an aluminum alloy plate for can lids, which is made from waste materials from cans and has both high strength and high toughness.

One aspect of the present invention is an aluminum alloy plate for can lids, wherein the content of silicon is 0.27 mass % or more and 0.39 mass % or less, the content of iron is 0.35 mass % or more and 0.55 mass % or less, the content of copper is 0.17 mass % or more and 0.25 mass % or less, the content of manganese is 0.75 mass % or more and 0.95 mass % or less, the content of magnesium is 2.2 mass % or more and 2.8 mass % or less, and the remainder is composed of aluminum and inevitable impurities, or the remainder includes aluminum and inevitable impurities, and the aluminum alloy plate for can lids has 0.2% proof strength σ _0.2 , tensile strength σ _B in the 0° direction, 45° direction and 90° direction relative to the rolling direction, respectively. Among the evaluation _values S calculated by the following formula (1), the minimum value, i.e., the minimum evaluation value S _min, is greater than 370 MPa and less than 410 MPa.

S=σ _fm /(σ _0.2 /σ _B )‧‧‧(1)

In this way, it is possible to prepare scrap raw materials from can materials while taking into account the high strength and high toughness of aluminum alloy plates. In other words, a certain amount of scrap 3104 aluminum alloy for can bodies can be prepared, which can reduce the use rate of new castings and reduce carbon dioxide emissions. In addition, aluminum alloy plates for can lids with high formability that can be used for anodic can lids that require high pressure resistance can be obtained.

R: Curved ridge

D: Rolling direction

L: Long side direction

LT: Width direction

ST: Plate thickness direction

[Figure 1] Figure 1 is a schematic diagram of the repeated bending test.

[Figure 2] Figure 2 is an explanatory diagram of the L-ST cross section.

[Figure 3] Figure 3 is a graph showing the relationship between the V value of the embodiment and the shell unit's pressure resistance strength.

The following diagrams are used to illustrate the applicable implementation forms of the present invention.

[1. First implementation form]

〔1-1. Architecture〕

<Composition>

The aluminum alloy plate for can lids of the present invention (hereinafter also referred to as "alloy plate") contains aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn) and magnesium (Mg).

The lower limit of silicon content is 0.27% by mass, preferably 0.30% by mass. If the silicon content is less than 0.27% by mass, the amount of silicon precipitated by the processing heat of hot rolling and cold rolling after solution treatment will decrease, and there is a concern that the strength of the alloy plate will be insufficient.

In addition, the average value of the silicon content of 3104 aluminum alloy in the JIS-H-4000:2014 standard is 0.30% by mass. Therefore, the silicon content is 0.27% by mass or more, preferably 0.30% by mass or more, so that more 3104 aluminum alloy scrap can be prepared.

The upper limit of the silicon content is 0.39 mass %, preferably 0.35 mass %. If the silicon content exceeds 0.39 mass %, the number of Mg ₂ Si particles increases, and the toughness of the alloy plate decreases.

The lower limit of the iron content is 0.35% by mass, preferably 0.40% by mass. The average value of the iron content specification of 3104 aluminum alloy is 0.40% by mass. Therefore, by making the iron content above 0.35% by mass, preferably above 0.40% by mass, more scrap of 3104 aluminum alloy can be prepared.

The upper limit of the iron content is 0.55% by mass. If the iron content exceeds 0.55% by mass, the intermetallic compounds (i.e., second phase particles) of the aluminum-iron-manganese or aluminum-iron-manganese-silicon system will increase. As a result, the propagation path of the crack will be generated, reducing the toughness of the alloy plate.

The lower limit of the copper content is 0.17% by mass, preferably 0.20% by mass. If the copper content is less than 0.17% by mass, the copper that increases the strength by solid solution or precipitation is insufficient, and the strength of the alloy plate decreases. In addition, the strength of the alloy plate can be significantly increased by precipitating copper during hot rolling and solution treatment followed by cold rolling.

In addition, the average copper content of 3104 aluminum alloy is 0.15% by mass. Therefore, by increasing the copper content to 0.17% by mass or more, more 3104 aluminum alloy scrap can be prepared.

The upper limit of the copper content is 0.25% by mass. If the copper content exceeds 0.25% by mass, the toughness of the alloy plate will decrease.

The lower limit of the manganese content is 0.75% by mass, preferably 0.80% by mass. If the manganese content is less than 0.75% by mass, there is insufficient manganese to increase the strength by solid solution or precipitation, and the average strength of the alloy plate is reduced.

In addition, the average value of the manganese content of 3104 aluminum alloy is 1.1% by mass, and the average value of the manganese content of 5182 aluminum alloy is 0.35% by mass. Therefore, by making the manganese content above 0.75% by mass, more scrap of 3104 aluminum alloy can be prepared compared to the known 5182 aluminum alloy.

The upper limit of manganese content is 0.95% by mass, preferably 0.90% by mass. If the manganese content exceeds 0.95% by mass, the intermetallic compounds (i.e., second phase particles) of the aluminum-iron-manganese system or the aluminum-iron-manganese-silicon system will increase. As a result, the propagation path of the tortoise crack will be generated, reducing the toughness of the alloy plate.

The lower limit of the magnesium content is 2.2% by mass. If the magnesium content is less than 2.2% by mass, the magnesium that increases the strength by solid solution or precipitation is insufficient, and the average strength of the alloy plate decreases. In addition, by precipitating magnesium during cold rolling after hot rolling and solution treatment, the strength of the alloy plate can be significantly increased.

The upper limit of the magnesium content is 2.8% by mass. The average magnesium content of 3104 aluminum alloy is 1.05% by mass, and the average magnesium content of 5182 aluminum alloy is 4.5% by mass. Therefore, by keeping the magnesium content below 2.8% by mass, more scrap of 3104 aluminum alloy can be prepared and the amount of additional magnesium-containing raw materials can be reduced.

The alloy plate may contain titanium (Ti). The upper limit of the content of titanium is preferably 0.10 mass%. By containing titanium, the structure of the casting of the alloy plate is refined. In addition, the alloy plate may contain zinc (Zn). The upper limit of the content of zinc is preferably 0.25 mass%. Furthermore, the alloy plate may contain chromium (Cr). The upper limit of the content of chromium is preferably 0.10 mass%.

The alloy plate may contain unavoidable impurities within the range that does not significantly impair the performance of the alloy plate. That is, the alloy plate contains silicon, iron, copper, manganese, magnesium, titanium, zinc and chromium in the above ranges, respectively, and the balance is composed of aluminum and unavoidable impurities, or the balance contains aluminum and unavoidable impurities. The upper limit of the total amount of unavoidable impurities is preferably 0.15% by mass. The balance may contain substances other than aluminum and unavoidable impurities.

<Material strength and pressure resistance>

Aluminum alloy rolled plates have material anisotropy, and their strength exhibits different values in the 0°, 45°, and 90° directions relative to the rolling direction. When the pressure inside the tank increases, the deformation starts from the direction with the lowest strength.

Therefore, in the alloy plate of the present invention, in the evaluation values S (S0°, S45° and S90°) calculated by the following formula (1) using 0.2% proof stress σ _0.2 , tensile strength σ _B , and the average value σ _fm of 0.2% proof stress and tensile strength, the minimum value, i.e., the minimum evaluation value S _min (=min(S0°, S45°, S90°)), is 370 MPa or more and 410 MPa or less.

S=σ _fm /(σ _0.2 /σ _B )‧‧‧(1)

From experience, the withstand voltage of the cover formed of the aluminum alloy plate has a strong positive correlation with the value V of the following formula (2) represented by the minimum evaluation value _Smin and the plate thickness t.

V=t ^2.27 ×S _min ‧‧‧(2)

Therefore, by setting the minimum evaluation value S _min of the alloy plate to 370 MPa or more, a cover body having sufficient pressure resistance can be formed without increasing the plate thickness.

If the minimum evaluation value _Smin exceeds 410MPa, the material strength is too high and the toughness of the material is reduced. That is, shear bands are easily generated relative to the tensile stress and bending stress generated in the material during forming, and forming cracks are easily caused. By making the minimum evaluation value _Smin less than 410MPa, the strength of the material (that is, the pressure resistance of the cover) and toughness (that is, formability and opening property) can be taken into account.

In the formula (1), 0.2% proof stress σ _0.2 and tensile strength σ _B are measured by the method specified in JIS-Z-2241: 2011. The plate thickness t is measured by, for example, a micrometer.

The pressure resistance of aluminum alloy plates can be measured by, for example, the following steps. First, fix the shell formed by the aluminum alloy plate to a jig and apply internal pressure. Then, gradually increase the internal pressure, and the internal pressure value when the shell is reversed (i.e. buckled) is used as the pressure resistance value.

Specifically, the shell is formed using a shell mold in the shape of φ204 Fullform (B64). The internal pressure value is measured using the buckling and injection testing machine DV036E from VERSATILE TECHNOLOGY. Specifically, after the shell formed with a dedicated fixture is fixed, the internal pressure is increased by a program, and the internal pressure value when the shell is reversed is read. For example, the internal pressure is increased at a rate of about 175kPa/s, and when it reaches a time point of about 350kPa to 400kPa, the internal pressure is increased at a rate of 10kPa/s.

<Resilience>

The formability of the cover and the force required to open the notched portion (i.e., the opening force) are known to be affected by the toughness of the aluminum alloy sheet.

(Number of repeated bends)

One of the evaluation indicators of the toughness of aluminum alloy plates is the repeated bending test. If the plate thickness is the same, the more times the aluminum alloy plate is repeatedly bent, the better its toughness.

The repeated bending test is performed using the following steps. For example, as shown in Figure 1, a test piece cut into a strip of 12.5 mm in width and 200 mm in length is arranged in a direction parallel to the bending edge R and the rolling direction D of the alloy plate. The two ends of the test piece are fixed with a clamp and a tensile force of 200 N is applied.

In this state, a jig with a bending radius of R2.0mm is placed at a position of 150mm in the long side direction of the test piece fixed by one of the fixed clamps as a fulcrum, and the other clamp is rotated 90° to the left and right to perform repeated bending, and the number of bends until the test piece breaks is measured.

The number of bends is calculated by bending 90° to either side and returning to the original position as one time each. In the case of breakage during the process, read the angle θ (0°~90°) and calculate the number of repeated bends N using the following formula (3). In formula (3), _N0 is the total number of times the test piece is bent 90° to either side and returned from the 90° bend position to the original 0° position until it breaks.

N = N ₀ + Θ / 90‧‧‧ (3)

The evaluation of repeated bending is more disadvantageous as the plate thickness increases, so it is necessary to make corrections based on the plate thickness as a reference. Here, the normalized number of repeated bending times N _s normalized by the following formula (4) is calculated based on a plate thickness of 0.235 mm. In addition, t (mm) is the plate thickness of the test piece.

_Ns =N×t/0.235‧‧‧(4)

The standardized repeated bending number _Ns of the aluminum alloy plate of the present invention is preferably 14.0 times or more.

(Second phase particles)

Toughness is affected by strength and the distribution of second-phase particles. That is, the higher the strength or the higher the density of second-phase particles, the lower the toughness. In particular, if the content of magnesium and silicon is higher, Mg ₂ Si particles are more likely to form. As a result, Mg ₂ Si particles form the starting point and propagation path of cracks, which affects the reduction of toughness.

In the L-ST cross section of the aluminum alloy plate of the present invention in the central part in the width direction indicated by the diagonal lines in Fig. 2, the total area of Mg ₂ Si particles with an area of 0.3 μm ² or more in the L-ST cross section preferably accounts for 0.2% or less of the area of the L-ST cross section. In Fig. 2, L is the longitudinal direction, ST is the plate thickness direction, and LT is the width direction.

The area ratio of _Mg2Si particles can be measured, for example, by the following method. First, the sample to be measured is cut, and the surface to be measured (i.e., L-ST cross section) is mechanically polished to a mirror surface. Then, the polished surface (i.e., L-ST cross section) is observed using a SEM (scanning electron microscope) to obtain 10 fields of view. The SEM has an accelerating voltage of 15 kV, a magnification of 500 times, and a field of view range of 0.049 ^mm2 for photography to obtain a COMPO (reflected electron composition) image.

The photographed COMPO images were analyzed using the image analysis software "ImageJ". Specifically, the brightness of the 256-color image was taken as the background brightness, and particles with a brightness lower than the value of the brightness of the majority minus 30 were determined to be Mg ₂ Si particles.

Among the _Mg2Si particles to be judged, the total area of particles with an area of ^0.3μm2 or more was calculated and divided by 10 parts of the photographed area of the field of view (i.e., the total area photographed), thereby calculating the ratio of the total area of _Mg2Si particles with an area of 0.3μm2 or ^more in the L-ST cross section to the area of the L-ST cross section.

<Intensity anisotropy>

It is known that materials with low cold rolling rates have high toughness, and materials with high cold rolling rates have high strength. In addition, the higher the cold rolling rate, the greater the 0.2% proof stress σ _{0.2_90°} in the 90° direction relative to the rolling direction than the 0.2% proof stress σ _{0.2_0°} in the 0° direction. Therefore, the difference in 0.2% proof stress in the 0° direction and the 90° direction relative to the rolling direction, that is, the strength anisotropy, can be related to the cold rolling rate of the material.

In order to achieve toughness that can ensure the formability of the cover, the alloy sheet of the present invention preferably has a D value obtained by formula (5) of -20 MPa or more. The D value is the value obtained by subtracting the 0.2% proof stress σ _{0.2_0°} in the 0° direction relative to the rolling direction from the 0.2% proof stress σ _{0.2_90°} in the 90° direction relative to the rolling direction. However, if the D value is higher than -10 MPa, the cold rolling rate is reduced, and there is a possibility of insufficient strength. Therefore, the D value of strength anisotropy is preferably less than -10 MPa.

D=σ _{0.2_0°} -σ _{0.2_90°} ‧‧‧(5)

The strength anisotropy of 0.2% proof stress σ _{0.2_0°} in the 0° direction relative to the rolling direction minus 0.2% proof stress σ _{0.2_90°} in the 90° direction relative to the rolling direction can be explained as follows in terms of the significance of material structure.

The material after hot rolling or annealing is in a recrystallized state, and the aggregation degree of the isotropic cube orientation is high. Therefore, through the plastic deformation of cold rolling, the cube orientation is deformed into a rolled aggregate structure with anisotropy in the rolling direction. Furthermore, if the cold rolling rate is larger, the grains are stretched in the rolling direction, so the grain size along the 0° direction relative to the rolling direction increases. On the other hand, the grain size change along the 90° direction relative to the rolling direction is smaller than that in the 0° direction.

The relationship between the change in the structure caused by such rolling and the 0.2% proof stress σ _0.2 is shown in equation (6) by referring to the Hall-Petch equation. In equation (6), κ is the resistance of the grain boundary to slip, and d is the grain size.

The resistance κ has different values for stretching in the 0° direction or 90° direction relative to the rolling direction. This is because the aggregation of the rolled aggregate structure with anisotropy in the rolling direction increases with the increase in the cold rolling rate, causing the resistance of the grain boundary to slip to change depending on the stretching direction.

In addition, in the 0° direction relative to the rolling direction, as the cold rolling rate increases, the grains elongate and the grain size increases. On the other hand, in the 90° direction relative to the rolling direction, the change in grain size relative to the cold rolling rate is relatively small. Through the accumulation of these effects, strength anisotropy is generated relative to the increase in the cold rolling rate.

<Manufacturing method of aluminum alloy plate>

The aluminum alloy plate of the present invention can be manufactured, for example, as follows. First, an aluminum alloy having the composition ratio of the aluminum alloy plate of the present invention is subjected to conventional semi-continuous casting (i.e., DC casting) to manufacture a casting.

Next, the four faces of the casting except the front and rear ends are plane-cut. After that, the casting is put into a homogenizing furnace for homogenization. The temperature of the homogenization treatment is preferably above 470°C and below 620°C. The time of the homogenization treatment is preferably above 1 hour and below 20 hours.

When the temperature of the homogenization treatment is above 400°C, the segregation of the casting structure is easily eliminated. Furthermore, when the temperature of the homogenization treatment is above 450°C, the _Mg2Si particles can be re-solidified, thereby improving the strength and toughness of the alloy plate. Furthermore, if the temperature of the homogenization treatment is above 470°C, preferably above 550°C, the re-solidification of the _Mg2Si particles can be promoted, thereby further improving the strength and toughness of the alloy plate. On the other hand, when the temperature of the homogenization treatment is below 620°C, local melting of the aluminum alloy is not likely to occur.

When the homogenization time is more than 1 hour, the temperature of the entire plate becomes uniform, the segregation of the casting structure is easily eliminated, and the Mg ₂ Si particles are easily re-dissolved. The longer the homogenization time is, the more Mg ₂ Si particles can be re-dissolved. However, if the homogenization time exceeds 20 hours, the effect of the homogenization is saturated.

After homogenization, the casting is hot rolled. The hot rolling step includes a rough rolling step and a finishing rolling step. In the rough rolling step, the casting is processed into a plate with a thickness of about tens of mm by reciprocating rolling. In the finishing rolling step, the thickness of the plate is reduced to about several mm by, for example, tandem rolling, and a hot rolled coil is formed to roll the plate into a coil.

If the total pressing rate of the finishing rolling is high, a recrystallized structure will be formed after coiling, which can improve the aggregation of the cube orientation. If the coiling temperature of the finishing rolling is high, a recrystallized structure will be formed after coiling, which can improve the aggregation of the cube orientation.

In addition, the hot rolled coil is subjected to solution treatment to dissolve magnesium and other elements, thereby obtaining a high-strength alloy plate. For example, a continuous annealing furnace (CAL) is used to perform heat treatment (i.e. annealing) at a target solid body temperature of 440°C or above for more than 30 seconds, followed by intensive cooling such as air cooling, which can effectively increase the strength of the alloy plate.

After hot rolling, the plate is cold rolled. Cold rolling is to roll the hot rolled plate to the plate thickness of the product. Cold rolling can be either single-seat rolling or tandem rolling. It is better to implement rolling in multiple passes or more in single-seat cold rolling.

In addition, by setting the finishing temperature of the cold rolling of the intermediate pass other than the final pass to above 120°C, silicon, copper and magnesium will be finely precipitated and age-hardened, thereby increasing the strength of the alloy plate. Further setting the finishing temperature to above 130°C can further increase the strength of the alloy plate.

The cold rolling rate (i.e. the total rolling rate to be achieved) is preferably above 80%. When the cold rolling rate is above 80%, the strength of the alloy plate can be improved. In addition, the lower the cold rolling rate, the more cube orientation will be left, so the cold rolling rate is preferably below 92%.

The cold rolling ratio R (%) is calculated by the following formula (7) using the plate thickness t ₀ (mm) after hot rolling or solution treatment and the product plate thickness t ₁ (mm) after cold rolling.

R=(t ₀ -t ₁ )/t ₀ ×100‧‧‧(7)

The thickness of the product plate can be appropriately selected to obtain the desired withstand voltage. As shown in the above formula (2), the greater the plate thickness, the higher the withstand voltage. The plate thickness of the product can be selected corresponding to the V value of formula (2), so that the V value is greater than 13.0, preferably greater than 14.0. As described above, according to the aluminum alloy plate of the present invention, the increase in plate thickness can be suppressed in order to maintain high withstand voltage.

For coils that are cold-rolled to the thickness of the product plate, pre-coating is carried out in the coating production line. The cold-rolled coils are subjected to surface degreasing, cleaning and chemical treatment, and then the coating baking treatment is carried out after the coating is applied.

In the chemical treatment, chromate-based, zirconium-based, and other chemicals are used. Epoxy-based or polyester-based coatings are used. These can be selected according to the application. In the coating baking treatment, the coil is heated within about 30 seconds when the solid temperature (PMT: Peak Metal Temperature) is above 220°C and below 270°C. At this time, the lower the PMT, the more the recovery of the material is suppressed, and the strength of the alloy plate can be maintained higher.

〔1-2. Effect〕

According to the implementation described in detail above, the following effects can be obtained.

(1a) It is possible to prepare scrap raw materials from can materials while taking into account the high strength and high toughness of aluminum alloy plates. In other words, a certain amount of scrap 3104 aluminum alloy for can bodies can be prepared, which can reduce the use rate of new castings and reduce carbon dioxide emissions. In addition, aluminum alloy plates for can covers that can be used for anodic can covers that require high pressure resistance and have high formability can be obtained.

[2. Other implementation forms]

The above describes the implementation form of the present invention, but the present invention is certainly not limited to the above implementation form, and various implementation forms can be adopted.

(2a) In addition to the aluminum alloy plate of the above-mentioned embodiment, the present invention also includes various forms such as components formed by the aluminum alloy plate and the manufacturing method of the aluminum alloy plate.

(2b) The function of one component of the above-mentioned implementation form may be distributed to multiple components, or the functions of multiple components may be integrated into one component. In addition, part of the components of the above-mentioned implementation form may be omitted. In addition, at least part of the components of the above-mentioned implementation form may be added to or replaced with the components of other above-mentioned implementation forms. In addition, all aspects included in the technical ideas defined by the textual language described in the scope of the patent application are implementation forms of the present invention.

[3. Implementation examples]

The following describes the test contents and evaluation results conducted to confirm the efficacy of this invention.

<Manufacturing of aluminum alloy plates>

The aluminum alloy plates S1 to S8 shown in Table 1 and Table 2 are manufactured as implementation examples and comparative examples. The specific manufacturing steps are described as follows.

First, a casting is produced by a semi-continuous casting method. The casting contains the components (mass %) of alloy numbers 1 to 4 shown in Table 3, and the remainder is composed of aluminum and inevitable impurities. The casting contains less than 0.10 mass % of titanium, less than 0.25 mass % of zinc, less than 0.10 mass % of chromium, and less than 0.15 mass % of inevitable impurities.

Next, the four faces of the casting except the front and rear ends are flattened. After that, the casting is put into the furnace for homogenization. The temperature of the homogenization treatment is shown in Table 1. After the homogenization treatment, the casting is taken out of the furnace and hot rolling is immediately started to form a rolled plate.

Furthermore, regarding S1~S6 and S8, the rolled plate after hot rolling is cold rolled to the CAL plate thickness shown in Table 1. After that, the rolled plate with the CAL plate thickness is annealed in a continuous annealing furnace (CAL). The CAL temperature during annealing is shown in Table 1. After annealing, the rolled plate is cooled to room temperature by air cooling. After cooling, the rolled plate is cold rolled again. The cold rolling rate to be achieved by cold rolling after annealing is shown in Table 1.

Regarding S7, the rolled sheet after hot rolling is not annealed but cold rolled. The cold rolling rate to be achieved by cold rolling is shown in Table 1.

The thickness of the product after cold rolling from S1 to S8 (i.e., t ₁ in formula (7)) is set to be in the range of about 0.235±0.03mm.

In S1~S8, after cold rolling, the coating is applied on the plate surface and the coating baking treatment is carried out for about 30 seconds. The physical temperature (PMT) during coating baking is shown in Table 1. By coating baking, aluminum alloy plates of S1~S8 are obtained. In addition, the plate thickness (i.e., product plate thickness) of the aluminum alloy plates of S1~S8 measured by a micrometer is shown in Table 1.

<Evaluation of aluminum alloy plates>

(Tensile properties)

Three No. 5 test pieces specified in JIS-Z-2241:2011 were made from aluminum alloy plates of S1~S8 by milling. The long sides of the three test pieces extend in the 0°, 45° and 90° directions relative to the rolling direction.

The test pieces were subjected to a tensile test based on JIS-Z-2241: 2011 to determine the 0.2% proof stress and tensile strength. The results of the 0.2% proof stress σ _0.2 and tensile strength σ _B and the average values of the 0.2% proof stress and tensile strength σ _fm are shown in Tables 1 and 2.

Furthermore, three evaluation values S are calculated from the measurement results of the tensile tests in the 0° direction, 45° direction and 90° direction relative to the rolling direction and formula (1). The minimum evaluation value _Smin of the evaluation values S is shown in Table 2.

(Resilience)

For aluminum alloy plates S1 to S8, the ratio of the total area of Mg ₂ Si particles with an area of 0.3 μm ² or more to the area of the L-ST cross section (area ratio) was calculated by implementing the measurement method described above. The measurement results are shown in Table 2.

For aluminum alloy plates of S1~S8, the number of repeated bending and the standardized number of repeated bending are calculated by the measurement method described in the implementation form, formula (3) and formula (4). The results are shown in Table 2.

(Intensity anisotropy)

For aluminum alloy plates of S1~S8, the strength anisotropy (i.e., D value) is calculated using the formula (5) described in the implementation form. The results are shown in Table 2.

(Shell unit pressure resistance strength)

For the aluminum alloy plates of S1~S8, the withstand voltage was measured by the measuring method described in the implementation form. The results are shown in Table 2. The aluminum alloy plates of S1~S6 and S8 exhibited a high withstand voltage of more than 550kPa.

(Waste allocation rate)

Regarding the composition ratio of aluminum alloy plates S1~S8, determine whether the available ratio of 3104 aluminum alloy scrap is above 50% by mass. The results are shown in Table 2.

In Table 2, the aluminum alloy plates with a result of "≧50" can be mixed with 3104 aluminum alloy with a mass percentage of more than 50%. In addition, the mixing rate of 3104 aluminum alloy scrap is determined based on Table 4.

Table 4 shows the correspondence between the blending ratios of 3104 aluminum alloy and 5182 aluminum alloy and the average values of the composition specifications. The first row of Table 4 is the average value of the composition specifications of 3104 aluminum alloy, and the second row is the average value of the composition specifications of 5182 aluminum alloy.

For example, when the mixing ratio of 3104 aluminum alloy is 50 mass%, the average silicon content is 0.20 mass%, the average iron content is 0.29 mass%, the average copper content is 0.11 mass%, the average manganese content is 0.7 mass%, and the average magnesium content is 2.8 mass%.

Therefore, when the ratio of each component of the aluminum alloy plate is above the above-mentioned values of silicon, iron, copper, manganese, and magnesium, the blending rate of 3104 aluminum alloy scrap is above 50 mass%. The greater the blending ratio of 3104 aluminum alloy scrap, the higher the content of silicon, iron, copper, and manganese, and the lower the content of magnesium. S1~S10 aluminum alloy plates can blend 3104 aluminum alloy scrap of more than 50 mass%.

(Evaluation)

Figure 3 shows the relationship between the V value and the shell compressive strength of each of the aluminum alloy plates S1 to S8. As can be seen from the graph in Figure 3, there is a high correlation between the V value and the compressive strength. Therefore, an alloy plate with a minimum evaluation value _Smin of 370MPa or more can have a high compressive strength equivalent to that of an alloy plate formed of the conventional A5182 aluminum alloy without increasing the plate thickness.

Compared with S8, S1~S6 aluminum alloy plates have lower magnesium content but higher strength. In addition, S4~S6 aluminum alloy plates have higher homogenization temperature than S1~S3 aluminum alloy plates, so even if the steps and coating baking temperature are the same, they have higher strength and can withstand more repeated bending times.

Moreover, the lower the coating baking temperature (PMT), the higher the strength of the alloy plate. For example, comparing S1 to S3 and S4 to S6, the examples with lower coating baking temperatures show higher minimum evaluation values S _min .

The area ratio of Mg ₂ Si particles in aluminum alloys S4 to S6 is small, less than 0.2%. Comparing S1 to S3 with S4 to S6, it can be seen that the area ratio of Mg ₂ Si particles can be greatly reduced by increasing the homogenization temperature.

The number of repeated bends also varies with strength. Comparing S4 to S6, which have a smaller area ratio of Mg ₂ Si particles and the same cold rolling ratio, it can be seen that as PMT increases, the strength decreases and the number of repeated bends increases.

R: bending ridge D: rolling direction

Claims (2)

An aluminum alloy plate for can lids, wherein the content of silicon is 0.27 mass % or more and 0.39 mass % or less, the content of iron is 0.35 mass % or more and 0.55 mass % or less, the content of copper is 0.17 mass % or more and 0.25 mass % or less, the content of manganese is 0.75 mass % or more and 0.95 mass % or less, the content of magnesium is 2.2 mass % or more and 2.8 mass % or less, and the remainder is aluminum and unavoidable impurities, wherein the aluminum alloy plate for can lids is respectively measured in the 0° direction, the 45° direction and the 90° direction relative to the rolling direction, using 0.2% proof stress σ _0.2 , tensile strength σ _B , and the average value of 0.2% proof stress and tensile strength σ Among the evaluation values _S calculated by the following formula (1), the minimum value, i.e., the minimum evaluation value S _min, is 370 MPa or more and 410 MPa or less. S=σ _fm /(σ _0.2 /σ _B ) ‧‧‧(1) The value obtained by subtracting the 0.2% proof stress σ _{0.2_90°} in the direction of 90° relative to the rolling direction from the 0.2% proof stress σ _{0.2_0° in the direction of 0° relative to the rolling direction is -20 MPa} or more and -10 MPa or less. In the L-ST cross section in the central part in the width direction, the ratio of the total area of Mg ₂ Si particles with an area of 0.3 μm ² or more in the L-ST cross section to the area of the L-ST cross section is less than 0.2%. For the aluminum alloy plate for can lids of claim 1, for a test piece cut into a strip with a width of 12.5 mm and a length of 200 mm, when the bending operation of repeatedly bending 90° and returning to the 0° position in a direction parallel to the bending edge and the rolling direction is performed, the number of repeated bending operations until the test piece breaks is the number of repeated bending times N, and the normalized number of repeated bending times _Ns normalized by the plate thickness t of the test piece and the following formula (2) is 14.0 times or more, _Ns = N × t / 0.235 ‧‧‧ (2).

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