JP4534573B2 - Al-Mg alloy plate excellent in high-temperature high-speed formability and manufacturing method thereof - Google Patents

Description

  The present invention relates to an Al—Mg alloy plate excellent in high-temperature high-speed formability and a method for producing the same.

  Al—Mg alloys are proposed as processed and formed materials such as automobile plate materials because they are light and have excellent strength and corrosion resistance. However, since the elongation at room temperature is low, there is a problem that it cannot be formed into a complicated shape by cold working. For this reason, an Al-Mg superplastic alloy is developed that suppresses recrystallization during hot working and refines the crystal grains, for example, causes an elongation of several hundred percent in a high temperature range of 500 to 550 ° C. It is applied to various uses.

A conventional Al-Mg superplastic alloy exhibits superplasticity at a slow molding speed (strain rate) of 10 ⁻⁴ to 10 ⁻³ / sec, and takes a long time, so that it is applied to normal press molding. Is not practical because of low productivity.

  Therefore, an aluminum alloy plate capable of obtaining sufficient elongation even at a high speed forming of 100 times or more of the conventional method such as a strain rate of 0.1 / sec or more in a high temperature region where hot working is performed, and capable of suppressing cavity generation during forming. Has been developed.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 10-259441), Mg: 3.0 to 8.0% (% by weight, hereinafter the same), Cu: 0.21 to 0.50%, Ti: 0.001 to 0.1% is contained, Fe as impurities is limited to 0.06% or less, Si is limited to 0.06% or less, the balance is composed of Al and impurities, and the average crystal grain size is 20 to 200 μm. An aluminum alloy plate having excellent high-speed superplastic formability and having few cavities after forming has been proposed.

  However, in the above prior art, in order to achieve good high-temperature high-speed formability in the final product plate, large slab casting by semi-continuous casting, face grinding, homogenization treatment, hot rolling, cold rolling In other words, there is a problem in that the cost is high because many processes such as intermediate annealing, final rolling, and final annealing are required.

Furthermore, since the cooling rate during casting of a large slab is as slow as 1 to tens of degrees centigrade / sec, the crystallized material such as Al—Fe—Si and Al ₆ Mn becomes coarser to several tens μm or more and is homogenized. In the final product plate after the processes such as hot rolling, cold rolling, annealing, etc., coarse crystallized material of 10 μm or more still remains, and the crystallized material and the matrix are formed during high temperature forming. Cavities are likely to occur due to peeling at the interface. As a countermeasure, a method of suppressing the content of Fe and Si to 0.1% or less is adopted. However, since it is necessary to use expensive high-purity metal, the cost is inevitably increased. There was no problem.
Japanese Patent Laid-Open No. 10-259441 (Claims)

  The present invention provides an aluminum alloy plate that eliminates the above-described conventional problems, improves high-temperature high-speed formability, and reduces cavities after forming, and a method for manufacturing the same, without the need to use high-purity metal that increases costs. With the goal.

In order to achieve the above object, according to the present invention,
% By mass
Mg: 2.0-8.0%,
Si: 0.06 to 0.2%,
Fe: 0.1 to 0.5%,
Mn: 0.1 to 0.5%, and the balance Al and inevitable impurities,
An aluminum alloy plate having excellent high-temperature high-speed formability and having few cavities after forming, wherein the density of an intermetallic compound having an equivalent circle diameter of 1 to 5 μm is 5000 / mm ² or more and an average crystal grain size is 20 μm or less. Provided.

In order to achieve the above object, according to the present invention, there is further provided a method for producing an aluminum alloy plate of the present invention, comprising:
Preparing a molten alloy having the composition of the aluminum alloy sheet of the present invention;
The alloy melt is cast by a twin belt casting machine at a cooling rate of 20 ° C. to 150 ° C./sec during casting to form a slab having a thickness of 5 to 15 mm,
Continue to wind the slab as a coil,
The slab unrolled from the coil is cold-rolled at a cold rolling rate of 70 to 96%,
The obtained cold-rolled sheet is annealed to 420 to 500 ° C. at a temperature rising rate of 5 ° C./sec or more,
There is provided a method for producing an aluminum alloy plate which is excellent in high-temperature high-speed formability and has few cavities after forming.

The aluminum alloy sheet of the present invention has high-temperature high-speed formability by refining crystal grains without the need for high-purity bare metal by uniformly dispersing fine intermetallic compounds with a specified range of chemical composition and microstructure. Increased and reduced the cavity after molding.
Further, the production method of the present invention secures a high cooling rate during casting by twin belt casting, regulates the cold rolling rate in cold rolling, and limits the annealing conditions after cold rolling. A uniform fine dispersion of the compound and a refinement of the crystal grain were realized.
By using the aluminum alloy plate of the present invention, a high-quality molded product can be obtained, the molding time is shortened, and the productivity is improved.

  The reason why the chemical composition of the alloy is limited in the present invention will be described. In the present specification, “%” representing the chemical composition means “% by mass” unless otherwise specified.

[Mg: 2.0-8.0%]
Mg is an element that increases the strength, and in order to exhibit this effect, the Mg content needs to be 2.0% or more. However, if the Mg content exceeds 8.0%, the castability of the thin slab decreases. Therefore, the Mg content is limited to 2.0 to 8.0%. When emphasizing castability, it is preferable to further limit the upper limit of the Mg content to 6.0% or less.

[Si: 0.06 to 0.2%]
Si is crystallized as fine grains of Al-Fe-Si-based or Mg 2 _Si intermetallic compound, such as during casting and functions as a nucleation site for recrystallization during annealing after cold rolling. Therefore, the larger the number of particles of these intermetallic compounds, the more recrystallized nuclei that are generated. As a result, a large number of fine recrystallized grains are formed. In addition, the fine particles of the intermetallic compound pin the grain boundaries of the recrystallized grains that are generated, suppress the growth due to the coalescence of the crystal grains, and keep the finest crystal grains stable. In order to develop these effects, the Si content needs to be 0.06% or more. However, if the Si content exceeds 0.2%, the tendency for the intermetallic compound to crystallize to become coarse increases, and the generation of cavities is promoted during high-temperature deformation. Therefore, the Si content is limited to 0.06 to 0.2%. A preferable range is 0.07 to 0.15%.
In general, Si is an object to be excluded as an impurity element as in the case of Fe described below. However, in the present invention, an appropriate amount of Si is present on the contrary in order to refine the recrystallized grains as described above. Therefore, high-purity bullion is not required, and the associated cost increase does not occur.

[Fe: 0.1-0.5%]
Fe crystallizes as fine particles of an intermetallic compound such as Al—Fe—Si during casting and functions as a nucleation site for recrystallization during annealing after cold rolling. Therefore, the larger the number of particles of these intermetallic compounds, the more recrystallized nuclei that are generated. As a result, a large number of fine recrystallized grains are formed. In addition, the fine particles of the intermetallic compound pin the grain boundaries of the recrystallized grains that are generated, suppress the growth due to the coalescence of the crystal grains, and keep the finest crystal grains stable. In order to exhibit this effect, the Fe content needs to be 0.1% or more. However, if the Fe content exceeds 0.5%, the tendency for the intermetallic compound to crystallize to become coarse increases, and the generation of cavities is promoted during high-temperature deformation. Therefore, the Fe content is limited to 0.1 to 0.5%. A preferable range is 0.1 to 0.3%.
In general, Fe is an object to be excluded as an impurity element as in the case of Si. However, in the present invention, an appropriate amount of Si is conversely present in order to refine the recrystallized grains as described above. Therefore, high-purity bullion is not required, and the associated cost increase does not occur.

[Mn: 0.1 to 0.5%]
Mn is an element that refines the recrystallized grains. In order to exhibit this effect, the Mn content needs to be 0.1% or more. However, if the Mn content exceeds 0.5%, a coarse Al— (Fe · Mn) —Si system is formed, and the generation of cavities is promoted during high temperature deformation. Therefore, the Mn content is limited to 0.1 to 0.5%. In particular, when emphasis is placed on preventing the generation of cavities, it is preferable to further limit the upper limit of the Mn content to 0.3%.

[Cu of optional components: 0.1 to 0.5%]
In the present invention, Cu can be added in the range of 0.1 to 0.5% in order to improve the strength of the aluminum alloy plate. In order to obtain a strengthening effect, the Cu addition amount needs to be 0.1% or more. However, when Cu addition amount exceeds 0.5%, castability will fall. When emphasizing castability, it is preferable to further limit the upper limit of the Cu addition amount to 0.3% or less.

[Zr and Cr as optional components: 0.1 to 0.4%]
In the present invention, at least one of Zr and Cr can be added in the range of 0.1 to 0.4% in order to assist the refinement of recrystallized grains. Zr and Cr are elements that refine the recrystallized grains. In order to exhibit this effect, it is necessary that the addition amount of both Zr and Cr be 0.1% or more. However, if the amount of addition exceeds 0.4%, a coarse intermetallic compound is formed during casting, and the generation of cavities is promoted during high-temperature deformation. In particular, when emphasis is placed on preventing the generation of cavities, it is preferable to further limit the upper limit of the addition amount to 0.2% or less.

[Other elements]
In the present invention, Ti can be added in the range of 0.001 to 0.15% in order to refine the cast structure. In order to exhibit this effect, it is necessary to make Ti addition amount 0.001% or more. However, when the Ti addition amount exceeds 0.15%, a coarse compound such as TiAl ₃ is generated, the moldability at high temperature is lowered, and the generation of cavities is promoted. A preferable range is 0.006 to 0.10%.

Next, the reason why the structure of the alloy plate is limited in the present invention will be described.
[The density of an intermetallic compound having an equivalent circle diameter of 1 to 5 μm is 5000 / mm ² or more]
The present invention uses fine intermetallic compound particles as (1) recrystallization nucleation sites and (2) grain boundary pinning means of recrystallized grains, and fine recrystallized grains are obtained by annealing after cold rolling. Generate. The fine-grained structure thus obtained exhibits high ductility during high-temperature high-speed deformation, thereby increasing high-temperature high-speed moldability.

In order to obtain the above effect, an intermetallic compound having an equivalent circle diameter of 1 to 5 μm needs to be present at a density of 5000 / mm ² or more. As already described, intermetallic compounds such as Al— (Fe · Mn) —Si, Mg ₂ Si, Al ₆ Mn, etc. crystallize out as the intermetallic compound. In order for these intermetallic compounds to exhibit the effects (1) and (2) above, the equivalent circle diameter needs to be 1 to 5 μm. If the equivalent circle diameter is less than 1 μm, the particles are too small to achieve the effects (1) and (2). Conversely, if it exceeds 5 μm, cavities are likely to occur during high-temperature high-speed molding, and the strength and ductility after molding are reduced.
The intermetallic compound in the above size range needs to be present at a density of 5000 / mm ² or more. If the density is less than 5000 / mm ² , the recrystallized grain size during annealing exceeds 20 μm, and the elongation during high-temperature deformation is reduced.

[Average crystal grain size of 20 μm or less]
The alloy plate of the present invention has an average crystal grain size of 20 μm or less. When the average crystal grain size exceeds 20 μm, the elongation at high temperature deformation decreases.

The reason why the conditions of the production method of the present invention are limited will be described.
[Casting 5-15mm thick slab by twin belt casting and winding coil]
In the double belt casting method, molten metal is poured from one end into a gap between a pair of water-cooled rotating belts facing up and down, and the molten metal is solidified by cooling from the belt surface to form a slab, and the formed slab is used as the other end of the belt gap. It is a continuous casting method that is drawn out from a coil and wound into a coil.

  In the present invention, the thickness of the slab cast by this twin belt casting method is 5 to 15 mm. If the thickness is within this range, a large solidification rate can be ensured even in the central portion of the plate thickness, so that it is easy to form a uniform cast structure. This makes it easy to control the average grain size of the recrystallized grains in the final product plate to 20 μm or less. The above slab thickness range is also appropriate from the aspect of twin belt casting. That is, if the slab thickness is less than 5 mm, the amount of aluminum alloy passing through the casting machine per unit time becomes too small, and twin belt casting itself becomes difficult. When the slab thickness exceeds 15 mm, it becomes difficult to wind it as a coil.

[Cooling rate during casting 20 to 150 ° C / sec]
In the manufacturing method of the present invention, a slab having a thickness of 5 to 15 mm is cast by twin belt casting. At that time, in order to crystallize the intermetallic compound having an equivalent circle diameter of 1 to 5 μm defined in the alloy of the present invention at a density of 5000 pieces / mm ² or more, the cooling rate at the slab thickness ¼ at the time of casting is set. 20 to 150 ° C./sec. In the aluminum alloy of the present invention, an intermetallic compound such as Al— (Fe · Mn) —Si or Mg ₂ Si crystallizes during casting. When the cooling rate is less than 20 ° C./sec, these intermetallic compounds are coarsened and increase in excess of 5 μm. Conversely, when the cooling rate exceeds 150 ° C./sec, the intermetallic compounds are refined. Since the density of intermetallic compounds with an equivalent circle diameter of 1 to 5 μm is less than 5000 / mm ^{2 in} both cases, the number of recrystallization nuclei decreases during the final annealing (CAL). The recrystallized grains become coarse.

[Cold rolling at a cold rolling rate of 70 to 96%]
The deposition of dislocations generated by plastic working by cold rolling around crystallized substances is essential for forming a fine recrystallized structure during the final annealing. If the cold rolling rate is less than 70%, the accumulation of dislocations becomes insufficient and a fine recrystallized structure cannot be obtained. When the cold rolling rate exceeds 96%, ear cracks occur during cold rolling, making it difficult to perform cold rolling.

[Annealing is performed at a temperature rising rate of 5 ° C./sec or more to 420 to 500 ° C.]
In the present invention, the above annealing is performed as the final annealing after cold rolling. This is generally performed by continuous annealing, but it is not necessary to limit to this.
The annealing temperature of final annealing shall be 420-500 degreeC. If it is lower than 420 ° C., the energy required for recrystallization is insufficient, so that recrystallization becomes insufficient and a fine recrystallized structure cannot be obtained. However, if it exceeds 500 ° C., the recrystallized grain size exceeds 20 μm, and a fine recrystallized structure cannot be obtained.

  The rate of temperature rise to the annealing temperature is 5 ° C / sec or more. When the temperature is raised slowly at a rate of less than 5 ° C./sec, the recrystallized grains become coarse and a fine recrystallized structure cannot be obtained.

  Finally, the forming process of the aluminum alloy plate of the present invention is preferably performed at a temperature of 400 to 550 ° C. If the molding temperature is less than 400 ° C., sufficient elongation cannot be obtained. When the forming temperature exceeds 550 ° C., the crystal grains become coarse, and within the range of the present invention, local melting occurs in the alloy having a high Mg composition, and the elongation decreases. The strain rate during molding is preferably 0.1 / sec or more. If the strain rate is less than 0.1 / sec, the crystal grains become coarse during the forming process, resulting in a decrease in elongation.

  A molten aluminum alloy having the composition shown in Table 1 was cast by a twin belt casting method to obtain a slab having a thickness of 7 to 9 mm. Each slab was cold-rolled to a thickness of 1 mm, annealed at 450 ° C., cut out a test piece defined in JIS H7501, and measured the elongation after a tensile test. Furthermore, after polishing the cross section of the broken sample, the cavity area ratio (cavity ratio) was measured with an image analyzer. The manufacturing process and characteristics are shown in Table 2.

As is clear from the alloy composition of Table 1, for the plate (invention product, sample numbers 1 to 7) obtained by cold rolling a thin slab cast by a twin belt type casting machine, Fe 0.1% or more, Despite being 0.06% or more of Si, the density of the intermetallic compound having an equivalent circle diameter of 1 to 5 μm in the final plate was 5000 / mm ² or more and the crystal grain size was 20 μm or less. For this reason, the elongation at a tensile temperature of 500 ° C. was good at 200% or more, and the cavity ratio after high-temperature tension was also good at 1% or less within the range of 0.15 to 0.27%.

About the plate (Comparative example, sample number 8) which cold-rolled the thin slab cast by the twin roll caster, the cooling rate at the time of casting is relatively high at 300 ° C./sec. Therefore, the equivalent circle diameter is less than 1 μm. Since a lot of very fine crystallized substances were generated, the density of the intermetallic compound having an equivalent circle diameter of 1 to 5 μm in the final plate was less than 5000 / mm ² , and the crystal grain size was larger than 20 μm and became coarse. For this reason, the cavity ratio after high-temperature tension was 0.12%, which was relatively low and good, but the elongation at a tensile temperature of 500 ° C. was inferior at 80%.

A normal slab cast by a DC casting machine is soaked, hot-rolled to a thickness of 7 mm, and then cold-rolled (Comparative Example, Sample No. 9) has a relatively low cooling rate of 5 ° C./sec during casting. Due to the slowness, a crystallized product having an equivalent circle diameter exceeding 5 μm is generated, so that the density of the intermetallic compound having an equivalent circle diameter of 1 to 5 μm in the final plate is less than 5000 / mm ² and slightly larger than the crystal grain size of 20 μm. It became. For this reason, the cavity ratio after high-temperature tension was as poor as 1.5%, and the elongation at a tensile temperature of 500 ° C. was as poor as 160%.

A thin slab cast by a twin-belt casting machine is cold-rolled to a thickness of 2 mm, subjected to intermediate annealing at 350 ° C., and then cold-rolled to 1 mm (Comparative Example, Sample No. 10). Although the density of the intermetallic compound having an equivalent circle diameter of 1 to 5 μm is 5000 / mm ² or more, the cold rolling rate before final annealing is low at less than 70%, so that the crystal grain size is slightly larger than 20 μm. The elongation at a tensile temperature of 500 ° C. was inferior to less than 200%.

For a plate obtained by cold rolling a thin slab cast by a twin belt type casting machine (Comparative Example, Sample No. 11), the density of an intermetallic compound having an equivalent circle diameter of 1 to 5 μm in the final plate is 5000 / mm ² or more, The crystal grain size was 20 μm or less. However, since the tensile temperature in the tensile test was relatively low at 350 ° C., the elongation was inferior to less than 200%.

For a plate obtained by cold rolling a thin slab cast by a twin belt type casting machine (comparative example, sample number 12), the density of an intermetallic compound having a circle-equivalent diameter of 1 to 5 μm in the final plate is 5000 / mm ² or more, The crystal grain size was 20 μm or less. However, since the tensile rate in the tensile test was relatively slow at 0.01 / sec, the cavity ratio after high-temperature tension was also inferior at 1.8%, and the elongation at a tensile temperature of 500 ° C. was inferior at less than 200%.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in high temperature high speed moldability, and provides the aluminum alloy plate with few cavities after shaping | molding, and its manufacturing method.

Claims (4)

% By mass
Mg: 2.0-8.0%,
Si: 0.07 to 0.15 %,
Fe: 0.1 to 0.15 %,
Mn: 0.1 to 0.5%
Consisting of the balance Al and inevitable impurities,
Circle equivalent diameter density of 1~5μm intermetallic compounds 6145-7501 pieces / mm ^2, Ri mean grain size 10 [mu] m der less,
The elongation at the time of tensile deformation at a strain rate of 0.1 to 1.0 / sec in the temperature range of 400 to 550 ° C. is 200% or more, and the cavity ratio in the cross section after fracture due to the tensile deformation is 0.27%. Is
An aluminum alloy plate having excellent high-temperature and high-speed formability and having few cavities after forming.   The aluminum alloy plate according to claim 1, further comprising Cu: 0.1 to 0.5 mass%.   The aluminum alloy plate according to claim 1 or 2, further comprising at least one of Zr: 0.1 to 0.4 mass% and Cr: 0.1 to 0.4 mass%. A method for producing an aluminum alloy plate according to any one of claims 1 to 3 ,
A molten alloy having a composition according to any one of claims 1 to 3 is prepared,
The alloy melt is cast by a twin belt casting machine at a cooling rate of 20 to 150 ° C./sec during casting to form a slab having a thickness of 7 to 9 mm.
Continue to wind the slab as a coil,
The slab unrolled from the coil is cold-rolled at a cold rolling rate of 70 to 96%,
The obtained cold-rolled sheet is annealed to 420 to 500 ° C. at a temperature rising rate of 5 ° C./sec or more,
A method for producing an aluminum alloy plate that is excellent in high-temperature high-speed forming and has few cavities after forming.