JPH05195171A - Production of aluminum hard plate excellent in formability and low in earing rate - Google Patents

Abstract

PURPOSE:To produce a high-strength Al alloy hard plate excellent in deep drawability and low in earing rate by process-soaking and hot-rolling the ingot of an Al alloy of specified composition under specified conditions and then process-annealing and cold-rolling the hot-rolled alloy. CONSTITUTION:An alloy contg., by weight, 0.1-1.5% Mg, 0.1-2.0% Mn, 0.1-2.0% Fe, 0.05-0.5% Si, 0.01-0.2% Ti alone or added with 1-500ppm of B as the crystal grain refining agent and >=1 kind among 0.01-0.3% Cu, 0.01-0.5% Zn and 0.01-0.3% Cr as the strength increasing elements is directly cast into a thick plate, center of the plate is cooled at the rate of >=50 deg.C/sec. The plate is then rolled at >=30% draft, then soaked at 500-600 deg.C for 2 hr and further rolled at >=30% draft. The product is then heated to 380-600 deg.C at the rate of >=1 deg.C/sec, cooled immediately or held at that temp. for 10min and cooled at the rate of >=1 deg.C/sec, process-annealed and cold-rolled at 20-90% draft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to deep drawing cans (DR cans, DR cans).
The present invention relates to a method for producing an aluminum alloy hard plate which is suitable for deep drawing applications such as body materials for D cans, DI cans, etc., caps, condenser cases, etc. and which has high strength and which has low deep drawing ears and excellent formability. ..

[0002]

2. Description of the Related Art As an aluminum alloy for deep drawing, 1
000 series, 3000 series, 5000 series and 8000 series alloys are used depending on the application. The 1000 series alloy and the 8000 series alloy have a low ear rate but a yield strength of 100 N /
Since it is about mm ^2, it is used for applications in which strength is not so important but particularly low ear ratio is required. The 3000 series alloy has an ear ratio of 1000 series alloy and 8
Although slightly higher than 000 series alloy material, the yield strength is 200 N / mm ²
Moderate and therefore suitable for applications where strength is required. In addition, since there are many Al-Mn-based crystallizing compounds, the crystal grains become finer, so that the surface roughness after molding is small. In 5000 series alloy, the ear rate is 1000 series,
It is not so low as 8000 series and 3000 series alloys, but has a proof stress of about 250 N / mm ^2, and is therefore suitable for applications requiring strength. However, since the Mg content is large, the deep drawability is excellent, but a kagome pattern (luders) may be generated during the drawing process, which may significantly deteriorate the appearance of the can.

[0003]

As described above, various alloys have been selected and used as deep-drawing aluminum alloys according to the application, but the trend in the world is to reduce the plate thickness such as can body materials. Therefore, the aluminum alloy sheet for deep drawing has been required to have high strength to withstand the reduction in thickness. However, when the existing aluminum alloy plate is strengthened by increasing the workability, the deep-drawing ears become high and the Luders are likely to occur. Therefore, even if the strength is sufficient, it has been a practical problem in terms of ear ratio and surface condition such as Luders. The present invention solves such a problem and is excellent in deep drawability, and there is no appearance defect such as generation of Luders or skin roughness,
The object is to provide a material having a low ear rate and high strength.

[0004]

In order to achieve the above-mentioned object, the inventor has conducted diligent research on alloy composition and manufacturing conditions, and as a result, it has a yield strength and tensile strength equivalent to those of conventional 5000 series aluminum alloys. In addition, the inventors have found the conditions under which an aluminum alloy having an ear ratio as low as that of the conventional 1000 series alloy can be obtained, and the present invention has been accomplished.

That is, according to the present invention, the weight% (hereinafter the same) Mg: 0.1 to 1.5%,
Mn: 0.1-2.0%, Fe: 0.1-2.0%, S
i: 0.05 to 0.5%, Ti: 0.01 to 0.2% as a grain refiner alone or B1 to
Included with 500 ppm, and further Cu: 0.01-
0.3%, Zn: 0.01 to 0.5%, Cr: 0.01
~ 0.3%, 1 type or 2 types or more are contained, and the balance makes aluminum and an unavoidable impurity cast the aluminum alloy at a cooling rate of 50 ° C / s or more at the center of the ingot, and the rolling rate is 30% or more. Rolled at 500 ~ 6
Heat soak for 2 hours or more at 00 ℃, then roll 30%
Rolled at the above temperature and heated at a heating rate of 1 ° C / s or more for 380
Immediately after reaching a temperature of ~ 600 ° C or holding for 10 minutes or less, intermediate annealing is performed at a cooling rate of 1 ° C / s or more,
A method for producing a high-strength aluminum alloy hard plate having excellent formability and low earring rate, which is characterized by performing cold rolling at a rolling rate of 20 to 90%.

[0006]

First, the reasons for limiting the alloy components in the present invention will be described. Mg: Mg is a solid solution and Mg ₂ Si, Al-Cu-M
Since it improves the strength by aging precipitation such as g, it is an essential element for obtaining tensile strength and proof stress. Also, M
g has a dislocation multiplication effect during cold rolling, and has an effect of increasing recrystallization nuclei and refining recrystallized grains. If the addition amount is less than 0.5%, the effect is small and sufficient strength cannot be obtained, and if the addition amount exceeds 1.5%, strength is easily obtained but Luders is likely to occur. Therefore, the amount of Mg is 0.1
The range is up to 1.5%. Mn: Mn also has a strengthening action by solid solution, but in the present invention, a crystallization compound produced by coexistence of Mn, Fe, and Si plays an important role. That is, in the present invention, since the casting is performed at a high cooling rate, a large amount of finely crystallized compound of about 1 μm crystallizes out. This fine crystallized substance has a function to disperse and disperse the propagation of the Luders shear band, and therefore has an effect of suppressing the generation and growth of the Luders.
It also has the effect of refining recrystallized grains and hardening the particles by dispersion, which serves to improve the strength. Addition amount is 0.1%
If it is less than 2.0%, the effect is small, and if it exceeds 2.0%, a large crystallized substance is generated to impair the formability. Therefore, the Mn content is 0.1
The range is up to 2.0%.

Fe: The addition of Fe is similar to that of Mn.
It has an effect of suppressing the generation of Luders due to the fine crystallized compound generated in the coexistence of e and Si. In particular, Fe is an indispensable element because it has a function of extracting Mn from a solid solution state to form a crystallization compound. Further, similar to Mn, it also has the effect of improving the strength by refining recrystallized grains and particle dispersion hardening. If the addition amount is less than 0.1%, the effect is small, and if it exceeds 1.8%, large crystallized substances are likely to be generated, which hinders formability. Therefore, the amount of Fe is set in the range of 0.1 to 2.0%. Since a crystallized compound is generated together with Fe, the addition amount of Fe + Mn is preferably 1.0 to 3.0%. Si: Addition of Si has an effect of age hardening by precipitation of Mg ₂ Si and strength improvement by solid solution strengthening alone, but in the present invention, Si has a function of extracting Fe and Mn from a solid solution state and has a fine crystal structure. It is an element necessary for obtaining the optimum distribution of the compound. If the addition amount is less than 0.05%, its effect will not be obtained, and if it exceeds 0.5%, the effect will be saturated, and rather excessive curing will occur and the formability will be deteriorated. Therefore, the amount of Si is set to 0.05 to 0.5%. Ti, B: Usually, in an aluminum alloy, a small amount of Ti and B is added to refine the crystal grains, and also in the present invention, a small amount of Ti and B is added. However, if less than 0.01%, the effect cannot be obtained, and
If it exceeds 2%, primary crystal TiAl ₃ crystallizes and hinders formability. Therefore, the Ti amount is set to the range of 0.01 to 0.2%. Further, when B is added together with Ti, this effect is improved. However, when B is added, if it is less than 1 ppm, it has no effect, and if it exceeds 500 ppm, coarse particles of TiB ₂ are mixed and impair the formability, so that B is 1 to 500 pp.
The range is m.

Cu, Zn, Cr: Cu is Al-Cu-M
Strength is improved by aging precipitates of g type, and Zn, C
Each r has the effect of improving strength by solid solution, so one or more of these are added. Addition amount is 0.0
If it is less than 1%, there is no effect of improving the strength, and Cu: 0.3%,
If Zn exceeds 0.5% and Cr exceeds 0.3%, the formability is deteriorated. Therefore, the addition amount of Cu is 0.01 to 0.
3%, the amount of Zn added is 0.01 to 0.5%, and the amount of Cr added is 0.01 to 0.3%. The balance of each of the above components is Al and inevitable impurities.

Next, the manufacturing method of the present invention will be described. Casting: The aluminum alloy having the above alloy components is cast under the condition that the cooling rate at the center of the ingot is 50 ° C./s or more. For example, the above condition can be satisfied by manufacturing a cast rolled plate having a plate thickness of 20 mm or less by a twin roll type continuous casting and rolling method. However, if the plate thickness is less than 2 mm, the cast structure is not completely broken and remains even after rolling to the final product plate thickness, which adversely affects. Therefore, it is desirable that the plate thickness is 2 to 20 mm. By satisfying the cooling rate condition of the present invention, it is possible to obtain a structure in which a fine crystallized compound of about 1 μm is distributed up to the center of the thickness of the ingot plate. In order to prevent the generation of Luders, it is desirable that 2000 particles / 0.2 mm ² or more of particles larger than 0.5 μm exist, and according to the casting conditions of the present invention, the distribution state of the crystallized compound is satisfied, and the generation of Luders occurs. It is effective for prevention and has the effect of improving moldability.

Rolling / soaking: If the rolling ratio of 30% or more is not applied, it is not uniformly performed during recrystallization by soaking and coarsens, and the grain boundaries thereof adversely affect the final product. The rolling before the soaking is a necessary process for lowering the ear ratio, but there are some points that are not clear about the mechanism, but the following two approaches can be considered. 1.
The recrystallized grains formed up to the lower limit of the soaking temperature, 500 ° C., have a Cube orientation of a component that lowers the ear ratio and an R orientation that raises the ear ratio. In order to take in the crystal grains having the R orientation (preferred growth), the crystal grains having the Cube orientation increase after soaking. The crystal grains having the Cube orientation remain even during the subsequent cold rolling, and Cu during the intermediate annealing after the cold rolling is performed.
The low ear process is established because it can be a recrystallized nucleus of be direction. When the casting structure composed of coarse crystal grains is soaked during soaking, the Cube orientation does not form even when the lower limit of the soaking temperature of 500 ° C. is reached, so that the subsequent Cube orientation growth in the high temperature region Impossible. Recrystallize Cu
A cold rolling rate of 30% or more is required to generate the be direction. 2. When strain is applied by cold rolling after casting, supersaturated solid solution transition elements such as Mn can be easily finely dispersed (dispersed) at a temperature lower than 300 ° C when the heating rate is slow like soaking (about 35 ° C / h). ), A fine precipitate easily forms a solid solution in the subsequent heating state at 500 ° C. or higher, and the precipitate-free zone (hereinafter referred to as PFZ) becomes wide. When soaking in the as-cast state, there is no strain, so the amount of precipitation during the temperature rise process is small, and supersaturated solid solution transition elements such as Mn precipitate only when the diffusion rate in the high temperature region is higher than 500 ° C. In order to start the process, it is not as fine as the precipitate that precipitates at a low temperature, the precipitation proceeds due to soaking, and the disappearance of the precipitate due to the equilibrium reaction is not easy. The smaller the PFZ, the preferential growth of the Cube orientation is promoted by annealing such as CAL. As for the soaking temperature, if many Al-Mn-based precipitates of 0.5 μm or less are present, pinning of dislocations will occur during molding, which will cause the generation of Luders. It is necessary to hold the above to reduce the amount of the Al-Mn-based precipitates of 0.5 μm or less.
The higher the holding temperature, the better, but if the temperature is higher than 620 ° C, eutectic melting will occur and the temperature cannot be raised above this. It should be noted that it is preferable from the viewpoint of manufacturability and the appearance of the product to remove the surface layer in order to remove the surface oxide between the end of soaking and the final plate thickness. The method may be mechanical removal or etching with caustic liquid or the like. Rolling: A rolling rate of 30% or more is required in order to uniformly cause recrystallization and refine crystal grains.

Intermediate annealing: The intermediate annealing conditions are a heating rate of 1 ° C./s or more and an ultimate temperature of 380 ° C. or more and a cooling rate of 1 ° C./s or more. As a result, solid solution of metal elements such as Mg, Si, and Cu is promoted, and age hardening is performed in the final annealing or final baking coating treatment to improve the strength. Furthermore, 1
By heating to the recrystallization temperature at a heating rate of not less than ° C / s, preferential generation and growth of Cube-oriented recrystallized grains are promoted, which is effective in reducing the ear rate. If the heating rate is less than 1 ° C./s, the progress of recrystallization is pinned by the compound that precipitates during heating, and the preferential growth of the Cube orientation is hindered, resulting in a random orientation.
The ears are raised by 5 °. The longer the holding time is, the more solid solution of the alloying elements progresses, which is advantageous for increasing the strength.
Holding for more than a minute only increases the annealing cost and is less effective for the time, and it is difficult to hold for a long time in an annealing furnace such as the current CAL (continuous annealing furnace). Further, if the heating rate and the reached temperature satisfy the above conditions, recrystallization proceeds during the temperature rise, and therefore cooling can be started immediately after reaching the predetermined temperature, which is sufficiently effective. Therefore, the holding time was set immediately after reaching the predetermined temperature or within 10 minutes. If the ultimate temperature is set to be higher than 600 ° C, the temperature distribution may be varied to cause local eutectic melting. Therefore, the ultimate temperature is set to 380 to 600 ° C.

Cold rolling: If the rolling ratio of the cold rolling after the intermediate annealing is less than 20%, the desired strength cannot be obtained, and if it exceeds 90%, 45 ° ears are highly generated. Therefore, the rolling rate of the final cold rolling is set to 20 to 90%.

By the above manufacturing process, a metal structure having a low ear rate and less likely to cause Luders can be obtained. After the cold rolling, a final annealing may be performed as necessary as a softening treatment for enhancing the aging property or adjusting the strength. In that case, annealing is performed at a temperature of 100 to 250 ° C for 30 minutes or more. Is desirable.

[0014]

EXAMPLES Examples of the present invention will be described below. An aluminum alloy having the chemical composition shown in Table 1 was cast, rolled and heat-treated by the manufacturing method shown in Table 2 to prepare a sample.

[0015]

[Table 1]

[0016]

[Table 2]

1 to 3 are conventional examples used for deep drawing applications, 8 is an example of the invention, and 4 to 7 are comparative examples in which the manufacturing method of the invention alloy is changed. Here, the cooling rate of DC (DC casting) is about 10 ° C./s, and the cooling rate of SC (continuous casting and rolling) is about 150 ° C./s. The SC material is continuously cast to a plate thickness of 7 mm (cold rolling in the invention example), and after soaking, it is immersed in 60% 10% caustic soda solution for 45 seconds, washed with water, desmutted, washed with water, and dried. did. Intermediate annealing The batch annealing was performed at 330 or 350 ° C. for 2 hours. The temperature rising / cooling rate at this time was about 35 ° C./h.
On the other hand, continuous annealing (CAL annealing) was performed at 500 ° C. for 0 s (no holding). The heating / cooling rate at this time is approximately 20 ° C /
It was s. The baking was performed by holding it in an oil bath.

The obtained sample was examined for tensile strength, proof stress, elongation, ear ratio, LDR, crystal grain size, skin roughness, and generation of Luders. Ear rate is 5 using a punch with 32 shoulders 4R
The measurement was performed by deep-drawing an 8 circle with a clearance of 30%. Further, the LDR was measured by using a punch having 32 shoulders and 2R with a clearance of 30% and a change of the circle diameter, and was obtained as a limit drawing ratio = circle diameter / 32. The rough skin was evaluated by visually squeezing it in a cup, and ◯ was evaluated as good, Δ was intermediate, and × was bad. In addition, Luders was ranked in a cup and visually evaluated for rank. O was none, Δ was small, and X was defective. The results are shown in Table 3. Here, the unit of tensile strength and proof stress is N / mm ²
Is.

[0019]

[Table 3]

No. 1 is a conventional example made of a 1000-series alloy, and although the ear rate is low, the strength is low and rough skin is noticeable. No. 2 is a conventional example made of a 3000 series alloy, and is inferior to the invention example in all points except for the determination of Luders. No. 3 is a conventional example made of a 5000-series alloy and has high strength but is inferior in terms of ear ratio and Luders. No. 8 is an example of the invention, and the tensile strength is large and the elongation is good and the ear rate is low. Nos. 4 to 7 are comparative examples in which the manufacturing conditions were changed by using an alloy having the same composition as the invention example. No4 is 3000 series alloy,
DC casting material Inferior in strength and ear ratio to the invention examples. No. 5: 3000 series alloy, continuously cast rolled material without soaking. Compared with the invention examples, the strength is higher, but the ear rate, Luders,
Inferior in LDR. No. 6: 3000 series alloy, continuous casting and rolling material, intermediate batch annealed material Inferior in strength, ear rate, and LDR to the invention examples. No. 7: 3000 series alloy, continuously cast rolled material, which is inferior in ear ratio as compared with the invention example of unrolled material before soaking.

[0021]

As described above in detail, according to the present invention, it is possible to obtain an aluminum alloy hard plate which is excellent in deep drawability even if the strength is increased, has no appearance defects such as generation of Luders and rough skin, and has a low ear rate. , Can fully meet the needs for thinning and contribute to the expansion of the market.

Claims (1)

[Claims] 1. Weight% (hereinafter the same) Mg: 0.1
1.5%, Mn: 0.1 to 2.0%, Fe: 0.1
2.0%, Si: 0.05 to 0.5%, Ti: 0.01 to 0.2% as a grain refiner alone or together with B to 500 ppm, and further C
u: 0.01 to 0.3%, Zn: 0.01 to 0.5%,
Cr: An aluminum alloy containing one or more of 0.01 to 0.3% and the balance of aluminum and unavoidable impurities, and a cooling rate of 5 at the center of the ingot.
Casting at 0 ° C / s or more, rolling at a rolling rate of 30% or more, then soaking at 500 to 600 ° C for 2 hours or more, then rolling at a rolling rate of 30% or more, heating at 1 ° C / s or more. Immediately after reaching the temperature of 380 to 600 ° C by heating at a speed or 10
A high strength with excellent formability and a low ear rate, which is characterized by performing intermediate annealing in which the material is held for less than 1 minute and then cooled at a cooling rate of 1 ° C./s or more, and then cold-rolled at a rolling rate of 20 to 90%. Manufacturing method of aluminum alloy hard plate.