JP6289153B2 - Aluminum alloy plate for can lid - Google Patents

Description

  The present invention relates to an aluminum alloy plate for can lids, and more particularly to an aluminum alloy plate for easy open can lids having a good balance between material strength and rivet formability.

Properties required for the aluminum alloy plate for can lids include formability that can withstand lid processing, pressure resistance that can withstand internal pressure after beverage filling, and can openability for normal and easy opening.
On the other hand, in recent years, thinning of the aluminum alloy plate for can lids is required from the viewpoint of cost reduction. However, when the aluminum alloy plate is thinned, the pressure resistance of the can lid decreases. As one of the methods for suppressing the decrease in the pressure resistance of the can lid, it is conceivable to increase the strength of the aluminum alloy itself. However, there arises a problem that the formability decreases as the strength is increased. For this reason, in order to reduce the thickness of the aluminum alloy plate for can lids, it is necessary to improve the balance between strength and formability.

  As one of the techniques for improving the formability while maintaining the material strength of the aluminum alloy plate for can lids (Al-Mg alloy plate for can lids), the control of the presence of intermetallic compounds and the texture is performed. I came. For example, in Patent Document 1, the number of particles of an intermetallic compound having a diameter of 3 μm or more existing in a visual field having a diameter of 50 μm and the number of particles of an intermetallic compound having a diameter of 1 μm or more existing in 0.2 mm 2 are defined. An aluminum alloy plate is described. Patent Document 2 describes an aluminum alloy plate for can lids that defines the number of intermetallic compound particles having a length of 1 μm or more existing in 1 mm 2 and the rolling texture component in a portion in the plate thickness direction 1/4. ing. Patent Document 3 describes an aluminum alloy plate for can lids that defines the number of particles of an intermetallic compound having an equivalent circle diameter of 0.7 μm or more present within 1 mm 2 and the proof stress after coating film formation.

JP 05-302139 A JP 2002-105574 A JP 2007-277694 A

The intermetallic compound having a size described in Patent Documents 1 to 3 (equivalent circle diameter is 0.7 μm or more) becomes a starting point of cracking during rivet molding. For this reason, as described in Patent Documents 1 to 3, by reducing the number of particles per unit area of the intermetallic compound of this size, or by reducing the area ratio, cracks that occur during rivet molding Can be suppressed.
However, even if cracks do not occur during rivet molding, if constriction occurs, cracks may occur during stake (processing to strike the rivet portion to attach the tab to the lid). In the conventional technique, the constriction at the time of rivet forming cannot be controlled, and better rivet formability with reduced constriction is required.

  An object of this invention is to provide the aluminum alloy plate for can lids which has the outstanding rivet formability, without reducing material strength.

  As a means to improve the rivet formability without reducing the material strength of the aluminum alloy plate for can lids (Al-Mg alloy plate), the amount of solid solution strengthening increased by increasing the concentration of solid solution elements, and work hardening characteristics (uniform) Improvement of deformation ability is conceivable. Solid solution strengthening and work hardening occur because dislocation movement is hindered by the interaction between dislocations and solute atoms. In an aluminum alloy, it is said that the difference in atomic radius between the parent phase (Al) and the solute atoms (Mg, Cu, Mn) dominates the magnitude of the interaction. Mg, Cu, and Mn have a large atomic radius difference from the parent phase (Al) and a large amount of solid solution strengthening, but Mg and Mn increase not only the amount of solid solution but also the amount of crystallized matter. Formability decreases due to an increase in the amount of products. For this reason, the present inventors paid attention to an increase in the solid solution amount of Cu, and decided to improve the formability without reducing the material strength, and particularly to suppress the occurrence of necking during rivet forming.

  The aluminum alloy plate for can lids according to the present invention has Mg: 3.8 to 5.5% by mass, Fe: 0.1 to 0.5% by mass, Si: 0.05 to 0.3% by mass, Mn: An aluminum alloy plate containing 0.01 to 0.6 mass%, Cu: 0.06 to 0.3 mass% or less, with the balance being Al and inevitable impurities, and the Cu solid solution concentration is 0.06 mass %, And the area ratio of the intermetallic compound having an equivalent circle diameter of more than 300 nm is 0.3% or more and 2.0% or less.

  Conventional aluminum alloy plates for lid materials have a reduced rivet formability when the strength is increased. Conversely, in order to obtain an excellent rivet formability, it is necessary to reduce the material strength. On the other hand, the aluminum alloy plate for a lid material according to the present invention has excellent rivet formability despite having high material strength. According to the present invention, even when the aluminum alloy plate for can lids is thinned, there is provided an aluminum alloy plate for can lids that has no deficiency in pressure resistance after beverage filling and is excellent in rivet formability and can openability. be able to.

It is a top view of the can lid by an aluminum alloy plate. It is sectional drawing of the score of the can lid used at the time of evaluation of can opening property. It is a schematic diagram of the can open load measuring machine used at the time of evaluation of can openability. FIG. 3A is a perspective view of an open load measuring machine. FIG.3 (b) is a cross-sectional schematic diagram of can-lid vicinity at the time of the measurement of an open can load measuring machine. FIG.3 (c) is a front schematic diagram which shows the direction of a can lid when installing a can lid in a can opening load measuring machine.

Hereinafter, the aluminum alloy plate for can lids and the manufacturing method thereof according to the present invention will be described in detail.
(Component composition of aluminum alloy)
Mg: 3.8 to 5.5% by mass
Mg has the effect of improving the strength of the aluminum alloy plate. However, when the Mg content is less than 3.8% by mass, the strength of the aluminum alloy plate is insufficient, and the pressure resistance when formed into a can lid is insufficient. On the other hand, when the Mg content exceeds 5.5% by mass, the strength of the aluminum alloy plate becomes excessive, and the rivet formability decreases. Therefore, the Mg content is set to 3.8 to 5.5% by mass.

Fe: 0.1 to 0.5% by mass
Fe forms Al-Fe (-Mn) -based and Al-Fe (-Mn) -Si-based intermetallic compounds in the aluminum alloy plate, and improves the tearability of the score part when it is molded into a can lid. There is an effect of improving canability. However, if the Fe content is less than 0.1% by mass, the tearability of the score part does not improve, and score derailment at the time of can open (crack propagates to other than the score part at the time of can open) and can opening force Opening defects such as tab breakage due to increase are likely to occur. On the other hand, when the Fe content exceeds 0.5% by mass, the area ratio of intermetallic compounds exceeding 300 nm in the aluminum alloy plate is larger than a predetermined range, and the rivet formability is lowered. Therefore, the Fe content is 0.1 to 0.5 mass%.

Si: 0.05-0.3 mass%
Si forms a Mg-Si, Al-Fe (-Mn), Al-Fe (-Mn) -Si intermetallic compound in an aluminum alloy plate, and tears the score part when formed into a can lid It has the effect of improving the performance and improving the can openability. However, when the Si content is less than 0.05% by mass, the openability is not improved as in the case of Fe. In addition, the amount of scrap that can be used as the raw material for the aluminum alloy plate is reduced, and the required purity of the aluminum ingot is increased, which increases the cost. On the other hand, when the Si content exceeds 0.3% by mass, the area ratio of the intermetallic compound exceeding 300 nm in the aluminum alloy plate becomes larger than the predetermined range, and the rivet formability decreases. Therefore, the Si content is set to 0.05 to 0.3% by mass.

Mn: 0.01 to 0.6% by mass
Mn has the effect of improving the strength of the aluminum alloy sheet, and when Al-Fe-Mn and Al-Fe-Mn-Si intermetallic compounds are formed in the aluminum alloy sheet and formed into a can lid. There is an effect of improving the tearability of the score part and improving the can openability. However, when the content of Mn is less than 0.01% by mass, the effect of improving the strength of the aluminum alloy plate or the effect of improving the openability when formed into a can lid cannot be obtained. On the other hand, when the content of Mn exceeds 0.6% by mass, the area ratio of intermetallic compounds exceeding 300 nm in the aluminum alloy plate becomes larger than a predetermined range, and the rivet formability decreases. Therefore, the content of Mn is set to 0.01 to 0.6% by mass.

Cu: 0.06-0.3 mass%
Cu has the effect of improving the strength of the aluminum alloy plate. Moreover, a moldability improves also by making it dissolve. However, when the Cu content is less than 0.06% by mass, the amount of solid solution in the parent phase is small, the balance between strength and formability is lowered, and rivet formability is not improved. On the other hand, when the Cu content exceeds 0.3% by mass, the strength of the aluminum alloy plate becomes excessive, and the rivet formability decreases. Therefore, the Cu content is set to 0.06 to 0.30 mass%.

Inevitable Impurities The aluminum alloy according to the present invention contains the balance Al and inevitable impurities in addition to the additive components. Inevitable impurities are 0.3 mass% or less for Cr, 0.3 mass% or less for Zn, 0.1 mass% or less for Ti, 0.1 mass% or less for Zr, 0.1 mass% or less for B, etc. Are permitted within a range of 0.05% by mass or less. If the content of inevitable impurities is within this range, it does not affect the characteristics of the aluminum alloy sheet according to the present invention.

(Cu solid solution concentration)
As described above, when the Cu solid solution concentration in the parent phase (Al) is large, the material strength is increased due to the increase in the solid solution strengthening amount, and the work hardening characteristics (uniform deformation ability) are improved. Constriction can be suppressed. However, if the Cu solid solution concentration is less than 0.06% by mass, the effect is insufficient. Therefore, the Cu solid solution concentration is 0.06% by mass or more, preferably 0.09% by mass or more, and more preferably 0.12% by mass or more. In addition, the ratio of the solid solution amount to the added amount of Cu (Cu solid solution concentration / Cu content) is preferably 0.75 or more, and more preferably 0.87 or more.

(Intermetallic compounds in aluminum alloy plates)
The effect of increasing the tearability of the score part when aluminum alloy plates are molded into can lids and improving the can openability by appropriately distributing intermetallic compounds with equivalent circle diameters exceeding 300 nm in aluminum alloy plates Is obtained. On the surface of the aluminum alloy plate, when the area ratio of the intermetallic compound having an equivalent circle diameter of more than 300 nm is smaller than 0.3%, the tearability of the score portion is lowered and the openability is deteriorated. On the other hand, when the area ratio of the intermetallic compound with an equivalent circle diameter exceeding 300 nm exceeds 2.0% on the plate surface, cracks are generated by the intermetallic compound during rivet forming, and it is easy to propagate and formability. Decreases. Therefore, the area ratio of the intermetallic compound having an equivalent circle diameter exceeding 300 nm is set to be 0.3% or more and 2.0% or less. The upper limit of this area ratio is preferably 1.0%, and the lower limit is preferably 0.4%.

(Aluminum alloy plate manufacturing method)
The aluminum alloy sheet according to the present invention can be produced by the steps of casting, homogenizing heat treatment, hot rolling, primary cold rolling, intermediate annealing, and secondary cold rolling. The method for producing an aluminum alloy sheet according to the present invention is particularly characterized in that the homogenization heat treatment is maintained in a temperature range of 400 ° C. to 550 ° C. for 1 to 10 hours, and the intermediate annealing is performed twice continuously. Hereinafter, each step will be described.

First, an aluminum alloy is cast by a known semi-continuous casting method such as a DC casting method.
Next, after removing the area | region used as an inhomogeneous structure | tissue of an ingot surface layer by chamfering, homogenization heat processing is performed. The homogenization heat treatment is held in a temperature range of 400 to 550 ° C. for 1 to 10 hours. When the homogenization heat treatment temperature is less than 400 ° C. or the holding time is less than 1 hour, the area ratio of the intermetallic compound having an equivalent circle diameter of more than 300 nm is smaller than a predetermined range, and the openability is lowered. When the homogenization heat treatment temperature exceeds 550 ° C., burning occurs during hot rolling. Moreover, when holding time exceeds 10 hours, productivity will fall.
After the homogenization heat treatment, the hot rolling is continued without cooling, and the hot rolling is preferably finished at 300 ° C. or higher. The produced hot rolled material has a recrystallized structure.

  The hot-rolled sheet is cold-rolled (primary cold-rolling) at a total rolling rate of 50 to 80%. When the total rolling rate is less than 50%, the accumulated strain due to rolling becomes insufficient, the recrystallized grain size becomes large in the subsequent intermediate annealing, and the formability including the rivet formability is deteriorated. On the other hand, when the total rolling rate exceeds 80%, the number of rolling passes increases and productivity decreases.

  Next, the cold-rolled sheet is annealed and recrystallized, and the solid solution concentration of Cu is increased. This intermediate annealing is performed twice continuously. The first intermediate annealing is performed under conditions where the material temperature is in the range of 380 ° C. to 550 ° C. and the holding time is within 10 minutes, and after cooling to room temperature, reheating is performed to perform the second intermediate annealing. Similarly, the second intermediate annealing is performed under conditions where the material temperature is in the range of 380 ° C. to 550 ° C. and the holding time is within 10 minutes. The cooling rate after the second intermediate annealing is set to 100 ° C./min or more. When the holding temperature of the intermediate annealing exceeds 550 ° C., or when the holding time exceeds 10 minutes, the recrystallized grains after the annealing process are finished, and the formability of the product plate is lowered. When the holding temperature of the intermediate annealing is less than 380 ° C., the solid solution concentration of Cu does not fall within a predetermined range, and the rivet formability is not improved. In addition, when the number of intermediate annealing is one or when the second cooling rate is less than 100 ° C./min, the solid solution concentration of Cu does not fall within a predetermined range and the rivet formability is not improved.

  Subsequently, the annealed cold rolled sheet is cold rolled again (secondary cold rolling) at a total rolling rate of 50 to 85%. When the total rolling rate is less than 50%, the work hardening by rolling is small and the strength is lowered, and the pressure strength when formed into a can lid is insufficient. On the other hand, when the total rolling rate exceeds 85%, the strength of the aluminum alloy plate for can lids becomes too high, and the formability of the product plate including the rivet formability is lowered. Accordingly, the total rolling rate is 50 to 85%.

  The aluminum alloy plate for can lids manufactured by the above process is subjected to surface treatment such as chromate or zircon, and an organic resin such as epoxy resin, vinyl chloride sol or polyertel is applied, and PMT (Peak Metal Temperature: After being baked at a metal reached temperature of about 230 to 280 ° C., it is formed into a can lid.

Hereinafter, examples in which the effects of the present invention have been confirmed will be specifically described in comparison with comparative examples that do not satisfy the requirements of the present invention. In addition, this invention is not limited to this Example.
Aluminum alloys shown in Table 1 (excluding No. 27) were cast by a semi-continuous casting method (DC), and the ingot surface layer was chamfered to produce a slab. After subjecting this slab to homogenization heat treatment, it is hot-rolled to form a hot-rolled sheet. The hot-rolled sheet is subjected to primary cold rolling (rolling rate 70%), intermediate annealing, and secondary cold. Rolling (rolling rate 79%) was sequentially performed to produce an aluminum alloy plate for can lids having a plate thickness of 0.215 mm. No. The aluminum alloy No. 27 was cast by the continuous casting method (CC) in order to simulate the invention of Patent Document 1, and the primary cast cold rolling (rolling rate 70%) and intermediate annealing without homogenizing the continuous cast plate. Secondary cold rolling (rolling rate 79%) was sequentially performed to produce an aluminum alloy plate for can lids having a plate thickness of 0.215 mm. Tables 1 and 2 show the homogenization heat treatment and intermediate annealing conditions.

  No. manufactured 1 to 33 aluminum alloy plates as test materials, the solid solution concentration of Cu, the area ratio of the intermetallic compound having an equivalent circle diameter exceeding 300 nm, 0.2% proof stress, rivet formability and can open load are as follows: Measured as indicated. The results are shown in Table 2.

(Cu solid solution concentration)
After the aluminum alloy plate is decomposed with phenol, it is filtered using a 0.1 μm pore filter, and the filtrate is introduced into an ICP (Inductively Coupled Plasma) emission spectrophotometer, and is nebulized with a nebulizer so that only a small mist is contained in the plasma. The solid solution concentration of Cu was measured. In addition, even if the filtrate contains a precipitate of less than 0.1 μm, it is discharged without being analyzed as a large mist when it is atomized. Not included.

(Area ratio of intermetallic compound with equivalent circle diameter exceeding 300 nm)
A parallel section in the rolling direction of the aluminum alloy plate is mirror-finished by buffing, and 20 views of a composition image (COMPO image) at an acceleration voltage of 15 kV and a magnification of 500 times are obtained on this mirror-finished surface with a scanning electron microscope (SEM). (Total area 0.75 mm2 or more) Photographed. Among these composition images, particles obtained with white contrast from the parent phase are regarded as Al-Fe (-Mn) -based and Al-Fe (-Mn) -Si-based intermetallic compounds, and particles obtained with black contrast are Mg-- It was regarded as a Si-based intermetallic compound. From this composition image, the area ratio (percentage of the photographing area) of the intermetallic compound exceeding the equivalent circle diameter of 300 nm was calculated by image processing.

(0.2% yield strength)
The aluminum alloy plate was heat treated at 255 ° C. for 20 seconds using an oil bath simulating a painting / baking process, and then a JIS-5 tensile test piece was prepared so that the tensile direction was parallel to the rolling direction. Using this test piece, a tensile test was performed according to JIS-Z2241, and a 0.2% yield strength was obtained. An appropriate range of 0.2% proof stress is 300 MPa or more, and within this range, even a thin can lid satisfies the compressive strength.

(Rivet formability)
The rivet forming process includes a bubble forming process for projecting the center of the can lid, a button forming process for reducing the diameter of the projecting part (bubble) in steps 1 to 3 and a steep protrusion, and a tab on the protrusion (button). And a stake process in which the protrusion is crushed and the tab is crimped. In order to fix the tab normally, it is necessary to ensure the size of the rivet diameter after stake. Therefore, an aluminum alloy plate that can be formed with a sufficiently high protrusion (button) height after the button forming process is required. It is done.
Here, rivet formability was evaluated by a test simulating a bubble process. That is, after the aluminum alloy sheet was heat-treated at 255 ° C for 20 seconds using an oil bath simulating the painting and baking process, a micro-extrusion test of φ6 mm was performed, and the limit overhang height at which no constriction or cracking occurred Asked. The appropriate range of the limit overhang height was 1.45 mm or more. If the limit overhang height of the aluminum alloy plate is 1.45 mm or more, a button having a sufficient height can be formed during actual forming.

(Opening load)
After aluminum alloy plate is heat treated at 255 ° C for 20 seconds using an oil bath that simulates the painting and baking process, after shell molding, conversion molding, and tab stake using a 204-diameter full-form end mold A can open test was conducted. FIG. 1 is a plan view of a can lid used in a can open test. FIG. 2 is a cross-sectional view of the score 3 of the can lid used in the can open test. FIG. 3 is a schematic view of a can opening load measuring machine that measures the load at the time of opening the can. FIG. 3A is a perspective view of the can opening load measuring machine 5. FIG. 3B is a schematic cross-sectional view of the vicinity of the can lid 1 at the time of measurement by the can open load measuring device 5. FIG. 3C is a schematic front view showing the direction of the can lid 1 when the can lid 1 is installed in the can opening load measuring device 5. The can lid 1 is placed on the can opening load measuring device 5 so that the tab 4 is located above the score 3 with respect to the score 3 (FIG. 3C). A hook 6 is hooked on the tab 4 of the can lid 1 to form a hook 7 (FIG. 3B). The latch 6 was pulled in the horizontal direction to apply a 3N tensile load, and the latch 6 was stationary in that state, and then the can lid 1 was rotated in the X direction. The load was measured with a load cell, and the highest load was taken as the can open load. The appropriate range of the can opening load was 25 N or less. For aluminum alloys whose limit overhang height is less than 1.45 mm in the micro overhang test, the necessary protrusion (button) height cannot be obtained and the tab cannot be properly attached. There was no test to measure.

  As shown in Tables 1 and 2, the component composition, the solid solution concentration of Cu, and the area ratio of the intermetallic compound having an equivalent circle diameter exceeding 300 nm (hereinafter referred to as the area ratio of the intermetallic compound exceeding 300 nm) No. within the specified range. Nos. 1 to 16 (Examples) have appropriate 0.2% yield strength and can open load, and excellent rivet formability. Therefore, no. The aluminum alloy plates 1 to 16 have a thin thickness of 0.215 mm, but can be suitably used for easy open can lids.

On the other hand, no. 17-33 (comparative example) is any one of the component composition, the solid solution concentration of Cu, and the area ratio of the intermetallic compound exceeding 300 nm is not within the specified range of the present invention. Either the can opening load or the rivet formability does not satisfy the appropriate value.
No. No. 17 has an excessive Mg content, so the rivet formability is inferior. No. 18 has a low 0.2% yield strength due to insufficient Mg content.
No. No. 19 has an excessive Fe content, so that the area ratio of the intermetallic compound exceeding 300 nm is large and the rivet formability is inferior. Since the Fe content of 20 is insufficient, the area ratio of intermetallic compounds exceeding 300 nm is small and the can opening load is large.
No. In No. 21, since the Si content is excessive, the area ratio of the intermetallic compound exceeding 300 nm is large and the rivet formability is inferior. No. 22 has an insufficient Si content, so the area ratio of the intermetallic compound exceeding 300 nm is small and the can opening load is large.

No. No. 23 has an excessive Mn content, so that the area ratio of intermetallic compounds exceeding 300 nm is large and the rivet formability is inferior. No. 24 has a low Mn content, so the 0.2% yield strength is low, the area ratio of intermetallic compounds exceeding 300 nm is small, and the opening load is large.
No. No. 25 has an excessive Cu content, resulting in poor rivet formability. No. 26 has insufficient Cu content, so the solid solution concentration of Cu is low and the rivet formability is poor.
No. Since No. 27 is not subjected to homogenization heat treatment, the area ratio of intermetallic compounds exceeding 300 nm is small and the can opening load is large. No. Since No. 28 has a low holding temperature in the homogenization treatment, the area ratio of the intermetallic compound exceeding 300 nm is small and the opening load is large. No. Since No. 29 has a short holding time for the homogenization treatment, the area ratio of the intermetallic compound exceeding 300 nm is small and the can opening load is large.

  No. No. 30 has a low holding temperature for intermediate annealing, so the solid solution concentration of Cu does not increase and the rivet formability is poor. No. Since No. 31 and 32 are only subjected to intermediate annealing once, the solid solution concentration of Cu does not increase and the rivet formability is inferior. No. No. 33 has a low cooling rate after the second intermediate annealing, so the Cu solid solution concentration is low and the rivet formability is poor.

DESCRIPTION OF SYMBOLS 1 Can lid 2 Rivet part 3 Score 4 Tab 5 Opening load measuring machine 6 Latching tool 7 Latching part

Claims (1)

Mg: 3.8 to 5.5% by mass, Fe: 0.1 to 0.5% by mass, Si: 0.05 to 0.3% by mass, Mn: 0.08 to 0.6% by mass , Cu: It is an aluminum alloy plate containing 0.06 to 0.3% by mass or less, the balance being Al and inevitable impurities, the Cu solid solution concentration is 0.06% by mass or more, and the equivalent circle diameter exceeds 300 nm An aluminum alloy plate for can lids, wherein the area ratio of the intermetallic compound is 0.3% or more and 2.0% or less.

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