JP2891620B2 - High strength aluminum alloy hard plate excellent in stress corrosion cracking resistance and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet having excellent resistance to stress corrosion cracking (hereinafter referred to as SCC resistance), high strength even after baking, and good formability, and a method for producing the same. In particular, the present invention relates to a material suitably used for a can lid material.

[0002]

^2. Description of the Related Art In recent years, the use of high-strength materials having a proof stress of 300 N / mm ² or more after baking has been required for lids of cans having a high internal pressure for beer and carbonated beverages in accordance with the trend of thinning in recent years.
H18 and H of the 5182 alloy among the series aluminum alloys
Thirty-eight materials have come to be used.

[0003]

However, although the strength and formability of the 5182 alloy are excellent, the Mg content is increased to 4.0 to 5.0.
%, And is an alloy in which Mg easily precipitates at the grain boundary due to aging, so when exposed to an environment where corrosion is likely to occur, such as a high-temperature, high-humidity warehouse in summer under high internal pressure, In many cases, stress corrosion cracking was generated from the can lid score part and caused to break.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an aluminum alloy hard plate which has improved SCC resistance without impairing strength and formability, and which can be suitably used particularly for can lids, and a method of manufacturing the same. It is intended to provide a method.

[0005]

In order to solve the above-mentioned problems, the present inventors have conducted various experiments and studies. As a result, instead of reducing Mg which adversely affects the SCC resistance, the Mn content was reduced to 5182 alloy. In addition, the amount of Al ₆ Mn precipitates is appropriately precipitated in the ingot homogenization treatment, and the recrystallization grain size of the intermediate material after hot rolling or after intermediate annealing is refined, so that the final hardened The present inventors have found that the SCC resistance can be improved without impairing the strength and formability of the sheet, and have accomplished the present invention.

[0006] More specifically, Mg 2.0 or more
3.5% (weight%, the same applies hereinafter), Mn 1.0% to 1.8
%, The content of Fe as an impurity is restricted to 0.20% or less, Mn + Fe is 1.8% or less, the balance is Al and unavoidable impurities, and the particle size of A is 1 μm or more.
The number of l ₆ Mn precipitate particles is not less than 1000 per 0.1 mm ² , and the yield strength after painting baking at 270 ° C. × 20 seconds is not less than 280 N / mm ² ,
High strength aluminum alloy hard plate with excellent stress corrosion cracking resistance.

[0007] Further, Mg of 2.0 to 3.5% according to claim 2,
Fe containing 1.0% to 1.8% of Mn and Fe as an impurity
Is controlled to 0.20% or less, and an alloy containing Mn + Fe of 1.8% or less and the balance of Al and unavoidable impurities is cast at a casting temperature of 680 ° C. or more at a casting speed of 40 mm / min or more. The ingot was subjected to a homogenization treatment at a temperature in the range of 500 to 600 ° C. for 1 to 48 hours, and a particle size of 1 μm
The above Al ₆ Mn particles are precipitated at a rate of 1,000 or more per 0.1 mm ² , and then subjected to hot rolling, and then subjected to cold rolling and intermediate annealing as necessary, in order to obtain a required final sheet thickness. Finally, a method for producing a high-strength aluminum alloy hard plate excellent in stress corrosion cracking resistance, characterized by finally performing cold rolling of 60% or more.

[0008]

First, the reasons for limiting the component composition in the present invention will be described.

Mg: Mg is an element that is effective for improving strength, but is also an element that lowers SCC resistance. If the Mg content is less than 2.0%, the strength of the can lid material used in the present invention is insufficient, while if it exceeds 3.5%, the SCC resistance deteriorates. Therefore, the amount of Mg was set in the range of 2.0 to 3.5%.

Mn: Mn is forcibly formed into a solid solution at the time of casting, and not only is effective for improving strength by solid solution strengthening, but also Al ₆ Mn precipitated by high-temperature soaking (homogenizing treatment) on the ingot is hot-melt. Refines the recrystallized grains in the intermediate material after rolling or after intermediate annealing, effectively acting to improve the strength of the final plate, and reducing the anisotropy and ear ratio, improving the Erichsen value, etc. It also contributes to the improvement of However, when the Mn content is less than 1.0%, the solid solution amount of Mn is insufficient, and the number and size of Al ₆ Mn particles precipitated by high-temperature soaking are not sufficient, so that hot rolling is completed or intermediate annealing is performed. The effect of refining the recrystallized grains in the softened intermediate material cannot be sufficiently obtained, and the strength and formability of the final sheet cannot be sufficiently improved. On the other hand, if the Mn content exceeds 1.8%, the Al-Fe-Mn-based crystallized product may become coarse and inhibit the formability. Therefore, the amount of Mn is 1.
0% to 1.8%.

Fe: Fe is an element inevitably contained as an impurity in a normal aluminum alloy. F
If e exceeds 0.20%, the number of crystallized Al-Fe-Mn-based compounds increases, the amount of Mn solid solution decreases, the strength cannot be improved, and the formability is impaired. % Or less. Also, Mn + F
If e exceeds 1.8%, an Al-Mn-based giant intermetallic compound is formed, which significantly impairs the formability. Therefore, Mn + Fe was made 1.8% or less.

[0012] In addition to the above elements, it is basically sufficient to use unavoidable impurities other than Al and Fe.

In addition, Cr 0.15 for improving strength
% Or less, V0.15% or less, and Zr 0.15% or less.

The inevitable impurities other than Fe include:
Si, Zn, Cu and the like may be contained, but if the content of Si is 0.4% or less, the content of Zn is 0.5% or less, and the content of Cu is 0.3% or less, the effect of the present invention is not impaired. Absent.

In a general aluminum alloy,
In order to refine the ingot crystal structure, a small amount of Ti
Alternatively, a small amount of Ti may be added in combination with a small amount of B or C. In the case of the present invention, these may be added as needed. However, the amount of Ti when adding Ti alone is 0.20% or less, the amount of Ti when adding Ti and B in combination is 0.10% or less, B is 0.05% or less, and Ti and C Is added in a combined amount of 0.10
% Or less, and the C content is preferably 0.05% or less,
If it is within these ranges, the effect of the present invention is not particularly impaired. In order to prevent oxidation of the molten metal during casting, Be
May be added in an amount of 0.01% or less.

In the aluminum alloy hard plate according to the first aspect of the present invention, not only the component composition is regulated as described above, but also the precipitation state of the Al ₆ Mn precipitate is important. That is, the object of the present invention is to improve the SCC resistance, to have a high strength even after baking, and to improve the formability. For that purpose, in the state of the final hard plate, the particle size is 1 μm.
It is necessary that 1000 or more Al ₆ Mn precipitates are dispersed per 0.1 mm ² . The Al ₆ Mn precipitate that satisfies this state of precipitation is refined by refining the recrystallized grains in the intermediate material after hot rolling or softening during the intermediate annealing, so that the final hard plate is subjected to a paint baking treatment (270 ° C.).
(× 20 seconds), yield strength is 280N / mm ² With the above, high strength is obtained, and the moldability such as drawability and overhang is excellent.

If the distribution of Al ₆ Mn precipitates does not satisfy this state of precipitation, the recrystallized structure of the intermediate material after hot rolling or softening after intermediate annealing becomes a mixed grain of grains and layers, and the final Anisotropy occurs in the strength of the hard plate after the paint baking treatment, and the formability deteriorates.

Here, in order to make the recrystallized structure finer in the intermediate material after hot rolling or after intermediate annealing, the recrystallization after hot rolling or the state immediately before the recrystallization treatment in intermediate annealing is performed. As described above, Al ₆ M of 1 μm or more
It is necessary that at least 1000 n precipitates exist per 0.1 mm ² , but if the Al ₆ Mn precipitates satisfy the above conditions in the state of the final hard plate, the Since the condition is satisfied even in the state immediately before the recrystallization treatment by self-recrystallization or intermediate annealing, in the invention of claim 1, the above condition is defined as the final hard plate.

Next, a method of manufacturing the above-described aluminum alloy plate, that is, a manufacturing method of the second aspect of the present invention will be described.

First, an alloy having the composition described above is cast. The casting method itself is not particularly limited.
The casting temperature (the temperature immediately above the spout) is set to 680 ° C.
D when the casting speed in the steady state was 40 mm / min or more
It is cast by a C casting method (semi-continuous casting method) or the like.

The obtained ingot is subjected to a homogenization treatment (soaking heat treatment). This soaking is an important step not only to make the ingot structure uniform, but also to precipitate Al ₆ Mn. That is, in the present invention, a high-temperature and long-time soaking treatment is performed to precipitate 1000 μm or more of Al ₆ Mn precipitates having a size of 1 μm or more per 0.1 mm ^2. By refining the recrystallized grains in the intermediate material, the required strength and good formability after painting and baking of the final hard plate can be obtained. Here, if the soaking temperature is less than 500 ° C. or the soaking time is less than 1 hour, A
l ₆ Mn precipitates of precipitation is insufficient, whereas the soaking temperature will occur local melting if exceeds the 600 ° C., also if soaking time exceeds 48 hours, the effect of Al ₆ Mn deposition is saturated A problem arises in terms of economic efficiency, and furthermore, the oxidation of the surface proceeds to deteriorate the surface quality. Therefore, the soaking conditions must be in the range of 500 to 600 ° C. × 1 to 48 hours. The Al ₆ Mn precipitate deposited by such a soaking process does not dissolve in the matrix in the subsequent process, and since it is originally fine, it is crushed by processing and becomes smaller in diameter. little, therefore per 0.1 mm ² of 1μm or more Al ₆ Mn precipitates in the soaking step also 10
If more than 00 are precipitated, Al ₆ Mn can be obtained even during recrystallization treatment of the intermediate material after hot rolling or intermediate annealing.
The precipitate can satisfy the same conditions.

After the homogenization treatment, hot rolling is performed. The hot rolling start temperature may be the same as that of a conventional Al-Mg alloy, and is usually 400 to 550 ° C. In performing the hot rolling, after soaking, the steel sheet may be cooled once and then reheated to 400 to 550 ° C, or may be heated from 400 to 550 ° C without reheating after soaking. Rolling may be performed.

After the completion of hot rolling, 1. With the hot rolled sheet as it is Alternatively, perform intermediate annealing after hot rolling,
3. Alternatively, in one of the states of performing moderate cold rolling after hot rolling and then performing intermediate annealing, cold rolling of 60% or more is finally performed to obtain a hard plate.

In the case where the hot-rolled sheet is left as it is before the final cold rolling, it is preferable that the sheet is self-recrystallized by winding it as a coil at a high temperature. It is more preferable that after hot rolling, moderate cold rolling is performed, then intermediate annealing is performed, and complete fine recrystallization is performed. When performing the intermediate annealing, any of a normal continuous annealing method and a batch annealing method may be used, but the continuous annealing method is preferable in terms of recrystallization grain refinement and productivity. In the case of the continuous annealing method, the heating rate is 1
C./sec., Maintained within a temperature range of 450 to 600.degree. C. for 120 seconds or less, a temperature lowering rate of 1.degree. C./sec., And in the case of a batch annealing method, a temperature increasing rate of 20.degree. C./hour, a temperature range of 300 to 450.degree. In general, the temperature is maintained for 1 to 10 hours and the temperature is lowered at a rate of 20 ° C./hour.

In the final cold rolling, 60% or more is required to obtain a required strength after baking. The hard plate obtained by this cold rolling may be used as it is for applications such as can lids, but in order to further suppress the decrease in strength after baking, the final thickness of about 30 minutes to 10 hours at 100 to 200 ° C. Heat treatment may be performed. The baking treatment of the can lid is generally performed at 180 to 400 ° C. for about 5 to 1800 seconds. As described above, the example of the can lid has been described. However, the hard plate of the present invention is suitably applied to other uses such as blinds, which require SCC resistance, strength, and formability even after heat treatment such as paint baking. Is done.

[0026]

EXAMPLE For the alloys indicated by the alloy symbols A to C in Table 1, the casting temperature (the temperature immediately above the spout) was 705 ° C. and the casting speed was 60 by the DC casting method (semi-continuous casting method) according to a conventional method.
Cast at a rate of mm / min, thickness 460mm, width 1200mm, length 3
A 000 mm ingot was obtained. With respect to the obtained ingot, manufacturing conditions No. 1 to No. Under various conditions as shown in FIG. 6, a soaking treatment (homogenization treatment), preheating before hot rolling, and hot rolling were performed to obtain a rolled plate having a thickness of 2.0 to 4.0 mm. Thereafter, cold rolling and intermediate annealing were appropriately performed to obtain a final hard plate having a thickness of 0.3 mm. Although not shown in the table, the manufacturing conditions No. Sample No. 3 had a temperature of 320 ° C. immediately before coil winding after hot rolling, and it was recrystallized by self annealing when examined before final cold rolling.

Immediately after the soaking treatment, the number of Al ₆ Mn precipitates of 1 μm or more per 0.1 mm ² was examined, and the results are also shown in Table 2.

Further, the final hard plate is subjected to a heat treatment at 270 ° C. for 20 seconds using an oil bath as a heat treatment corresponding to the coating baking, and the plate after the heat treatment contains 0.1 mm of Al ₆ Mn precipitate of 1 μm or more. The number per unit ² and the strength anisotropy, which is the difference between the L-direction proof stress and the 45-degree proof stress in the L-direction proof stress by the tensile test, were examined. If the strength anisotropy is large, sufficient roundness cannot be obtained when punching the outer shape of the lid, or sufficient roundness cannot be obtained in the rivet part when forming a rivet part by attaching a tab to the lid. Or, if pressure is applied after attaching the lid to the can body, buckling may occur from the 45 ° direction. Further, a plate having a die diameter of 32.84 mm and a punch diameter of 32.0 mm was subjected to a heat-treated plate corresponding to the above-mentioned paint baking.
mm and blank diameter of 58.0 mm,
The Erichsen value was determined by the SZ 2247 Erichsen test A method. The results are shown in Table 3. Further SC resistance
Regarding the C property, the sheet subjected to the heat treatment corresponding to the above-mentioned paint baking was subjected to a heat treatment at 120 ° C. × 7 days corresponding to the change of Mg ₂ Al ₃ for about 10 years.
Examination was carried out under severe conditions with increased C sensitivity. In this SCC test, stress is applied by uniaxial tension in an NaCl aqueous solution, and a DC current of 5 mA / cm ² is applied to the test piece in order to evaluate SCC resistance in a relatively short time. , That is, by a uniaxial tension method with an electric current. The added stress was set to 80% of the proof stress of each material after performing the process of increasing the SCC sensitivity, and the rupture life of the test piece was examined. The SCC property was evaluated. These results are also shown in Table 3.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

In the above embodiment, the manufacturing conditions No. 5
Is an example manufactured by applying a conventional general manufacturing process using an alloy with an alloy code B corresponding to 5182 alloy, which is a high-strength can lid material that has been widely used in the past. Further, the manufacturing conditions No. No. 6 is an example manufactured by applying a conventional general manufacturing process of 5182 alloy using an alloy having an alloy code C corresponding to 5454 alloy which is known not to cause SCC even under severe conditions. is there. Therefore, the manufacturing conditions No. 51 obtained by 5
No. 82 alloy equivalent material was used as a standard for strength and formability. 6 was evaluated as a standard for SCC resistance.

Manufacturing conditions No. 1 to No. Material No. 3 is one in which both the component composition and the production process satisfy the conditions specified in the present invention. As compared with the conventional example of the 5182-equivalent alloy of No. 5, the L-direction proof stress, strength anisotropy, ear ratio, strength such as Erichsen value, and mechanical properties were equal or better. On the other hand, anti-SCC
The properties are shown in Production Condition No. SCC rupture life is the same as that of the comparative example of the alloy 5454 equivalent to No. 6, and the ductile fracture of the dimple fracture surface is equivalent to that of the comparative example even in the observation of the fracture surface.
Was not going to happen.

On the other hand, the manufacturing condition No. As for the material No. 4, although the alloy A within the component composition range specified in the present invention is used,
This is a comparative example in which the homogenization treatment temperature is lower than the lower limit specified in the present invention. In this case, since the homogenization treatment temperature is low, an Al ₆ Mn precipitate having a size of 1 μm or more cannot be obtained,
Intermediate annealing caused a delay in recrystallization, resulting in a layered and granular mixed grain structure, resulting in deterioration in strength anisotropy, ear ratio, Erichsen value, and the like. On the other hand, since the SCC resistance is within the component composition range defined in the present invention, the production conditions No. 1-3
And 6 were equivalent to the 5454 equivalent alloy.

[0035]

As is evident from the above-described embodiments, according to the present invention, it has been known that the stress corrosion cracking resistance is good.
It is superior to that of 454 alloy and has no risk of stress corrosion cracking even under severe use environment.
It is possible to obtain an aluminum alloy hard plate having high strength comparable to that of the two alloys, small strength anisotropy, and good formability.

Therefore, by using the aluminum alloy hard plate according to the present invention for a can lid material which is required to have stress corrosion cracking resistance for beer or carbonated beverage having a high internal pressure, the thickness can be reduced as compared with the conventional one. It is possible to reduce the weight of the can and the material cost. The aluminum alloy hard plate of the present invention can of course be used for blind materials other than the can lid. Further, the intermediate material that has been subjected to the intermediate annealing can be used for a vehicle body (inner and outer), a suspension member, and the like.

Claims (2)

(57) [Claims] 1. It contains 2.0 to 3.5% of Mg (% by weight, the same applies hereinafter) and 1.0% to 1.8% of Mn, and regulates Fe as an impurity to 0.20% or less. 1.8
% Or less, the balance being Al and inevitable impurities, and the number of Al ₆ Mn precipitate particles having a particle size of 1 μm or more is 1000 or more per 0.1 mm ² , and 270 ° C. ×
Strength of 280 N / mm ² after baking treatment for 20 seconds A high-strength aluminum alloy hard plate excellent in stress corrosion cracking resistance, characterized in that: 2. Mg 2.0-3.5%, Mn 1.0%-
An alloy containing 1.8%, Fe as an impurity is controlled to 0.20% or less, Mn + Fe is 1.8% or less, and the balance consists of Al and unavoidable impurities.
It is cast at a casting speed of 40 mm / min or more at a temperature of 80 ° C. or more, and the obtained ingot is cast at a temperature in the range of 500 to 600 ° C. for 1 to 48 hours.
Al ₆ M with a particle size of 1 μm or more
More than 1000 n-particles are precipitated per 0.1 mm ² , and then hot-rolled, and then cold-rolled and intermediate-annealed as necessary to obtain the required final sheet thickness. %. A method for producing a high-strength aluminum alloy hard plate excellent in stress corrosion cracking resistance, characterized by performing cold rolling of at least 30%.