JP2018184640A - High strength aluminum alloy sheet excellent in moldability, flexure processability and shape freezing property, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 3000 series aluminum alloy sheet having applicability to a body sheet for automobile outer sheet and excellent in moldability, flexure processability and shape freezing property.SOLUTION: A sheet has a component composition containing Si:0.70 to 0.95 mass%, Fe:0.10 to 0.85 mass%, Mn:0.40 to 1.80 mass%, Mg:0.25 to 0.35 mass% Ti:0.005 to 0.10 mass% and the balance Al with inevitable impurities, tensile strength of 190 MPa or more, 0.2% baring force of less than 155 MPa, elongation value of 15% or more and 0.2% bearing force after conducting an aging treatment at 170°C×20 min. after 2% prestrain induction of 160 MPa or more.SELECTED DRAWING: None

Description

  The present invention relates to a 3000 series aluminum alloy plate excellent in formability, bending workability and shape freezing property, which is used for a body panel for an automobile outer plate.

  In order to apply an aluminum alloy plate as a body sheet for automobiles, it is necessary to form it into a desired shape with a press mold, and a 5000 series aluminum alloy plate excellent in press formability with controlled texture is developed. It has been. The 5000 series aluminum alloy plate has been conventionally used as a body sheet material for automobiles because it has excellent strength and deep drawability by solid solution strengthening in which Mg is dissolved in a matrix.

  For example, Patent Document 1 is an Al—Mg-based alloy plate that contains 2 wt% ≦ Mg ≦ 6 wt% of Mg, and sums at least one selected from Fe, Mn, Cr, Zr, and Cu. 0.03 wt% or more (when Cu is selected, 0.2 wt% or more as Cu), and the content of each element is Fe ≦ 0.2 wt%, Mn ≦ 0.6 wt%, Cr ≦ 0 .3 wt%, Zr ≦ 0.3 wt%, Cu ≦ 1.0%, the balance being Al and inevitable impurities, the ratio of the volume fraction of the CUBE orientation to the volume fraction of the S orientation (S / Developed an Al-Mg alloy plate with excellent deep drawability, which has a texture with a Cube) of 1 or more, a GOSS orientation of 5% or less, and a crystal grain size in the range of 20 to 100 μm. Has been.

  Furthermore, since body sheets for automobiles are baked and coated after press molding, they are required to be excellent in so-called bake hardness. For this reason, a 6000 series aluminum alloy plate excellent in so-called press formability and low-temperature bake hardenability, which has been pre-aged after solution treatment, has also been developed.

For example, Patent Document 2 discloses an aluminum alloy plate which has been subjected to an aging treatment, in terms of weight% (hereinafter the same), Mg: 0.15 to 2.0%, Si: 0.2 to 2.0%, and An Al-Mg-Si aluminum alloy sheet excellent in press formability and bake hardenability characterized by containing Sn: 0.03 to 0.3% and the balance being made of Al and inevitable impurities is described. ing.
According to Patent Document 2, an aluminum alloy plate in which at least one of press formability and low-temperature bake hardenability is further improved can be provided.

  By the way, the body sheet for automobiles needs to be subjected to a hem bending process in order to crimp and integrate the outer panel and the inner panel. However, since the 6000 series aluminum alloy plate is inferior to the 5000 series aluminum alloy plate in so-called bending workability, it is necessary to prevent microcracking and rough skin after bending. Especially in bending, there are many cases in which defects such as microcracks, which are thought to be caused by the formation of high-density shear bands, are often seen, and it is also an issue to appropriately control the quantitative ratio of various intermetallic compounds. . In addition, there is a need to suppress the spring back after press molding in a demand for thinner and higher strength.

For example, Patent Document 3 contains Si: 0.4 to 1.5% (mass%, hereinafter the same), Mg: 0.2 to 1.2%, and Fe contained as impurities is 1.0%. A T4 tempered material of a molten aluminum alloy sheet having a composition comprising the balance Al and inevitable impurities, and coexisting with an Mg ₂ Si compound among the Al—Fe—Si based compounds present in the sheet An Al—Mg—Si alloy plate material excellent in bending workability is described, characterized in that the quantitative ratio of the Al—Fe—Si compound is 50% or less.
According to Patent Document 3, it is possible to provide an Al—Mg—Si based alloy sheet material that suppresses the occurrence of cracking in bending after pressing and is excellent in bending workability after pressing that can be applied as an automobile outer plate. It is said that.

Patent Document 4 contains 1.0 to 2.0% by mass of Fe and further 2.0% by mass or less of Mn, the balance is made of aluminum and inevitable impurities, and Ti as the inevitable impurities is 0.00. Excellent in formability characterized by having a component composition limited to 01% by mass or less, an average crystal grain size of 20 μm or less, and a structure in which the area ratio of {110} -oriented crystals is adjusted to 25% or more Aluminum alloy sheets are described.
According to Patent Document 4, by semi-continuous casting (DC casting) with electromagnetic stirring, an elongation of 35% or more, an average r value of 0.85 or more, a bulge height of 33 mm or more, and 2. It is said that all of the limit drawing ratios of 17 or more can be achieved.

Furthermore, in Patent Document 5, Mn: 1.0 to 1.6% by mass, Fe: 0.1 to 0.8% by mass, Si: 0.5 to 1.0% by mass, Ti: 0.005 to 0.10% by mass, Mg as an impurity is regulated to less than 0.10% by mass, the remainder has a component composition consisting of Al and inevitable impurities, and the metallographic structure has a circle equivalent diameter of 1 μm or more. The area ratio of the two-phase particles is 1.5 to 3.5%, the average crystal grain size is 20 to 50 μm, the area ratio of {100} oriented crystals parallel to the plate surface and {123} < It exhibits a recrystallized texture with an AR {100} / AR {123} <634> ratio, which is a ratio to the area ratio of the 634> orientation crystal, of 4.8 or more, and has a tensile strength of 155 MPa or more and a 0.2% proof stress. Excellent bending workability and shape freezing characteristics, characterized by 100 MPa or less and elongation of 26% or more It describes a high-strength aluminum alloy plate was.
According to Patent Document 5, it has high strength that can be applied to a body sheet for automobiles, adjusts the recrystallized texture obtained by annealing the rolled texture, and has formability, particularly bending workability and shape. It is said that a 3000 series aluminum alloy plate excellent in freezing can be provided.

In addition, Patent Document 6 includes Si: 0.5 to 1.4 mass%, Fe: 0.3 to 1.1 mass%, Cu: 0.1 to 0.3 mass%, and Mg: 0.03. -0.6 mass%, Mn: 0.7-1.4 mass%, Ti: 0.01-0.1 mass%, and the balance: Al and impurities, Zn as impurities is 1.0 mass% Less than 0.1% by mass of Cr as an impurity, 0.1% by mass or less of Ni as an impurity, tensile strength of over 180 MPa, 0.2% proof stress of less than 140 MPa, and elongation Describes an aluminum alloy plate characterized by being a cold-rolled annealed material having a value of 23% or more and an average grain size of recrystallized grains of less than 30 μm.
According to Patent Document 6, a large amount of secondary alloy ingot containing Mn and Fe can be blended at the time of casting of the original slab, it is excellent in recyclability, and formability and shape freezing property applicable to automobile body sheets and the like. It is said that it can provide an aluminum alloy plate that is superior to the above.

Japanese Patent No. 4339869 JP-A-6-340940 JP 2006-241548 A JP 2010-121164 A International Publication No. 2015/155911 JP2015-96650A

  Certainly, 5000 series and 6000 series aluminum alloy plates are excellent in formability and have characteristics as body sheets for automobiles. However, in an aluminum alloy plate containing Mg as an essential element, the oxide film produced on the surface is relatively thick, and surface treatment such as pickling may be required before press molding. Furthermore, a surface pattern such as a stretcher / strain mark or ridging may occur during press molding. Further, there is a concern that the mechanical properties of the 6000 series aluminum alloy plate may change over time due to natural aging after the final plate is manufactured.

  Patent Document 4 describes 3000 series and 8000 series aluminum alloy plates that do not contain Mg as an essential element. However, after both faces of the obtained ingot are chamfered, homogenized heat treatment, rolling process is performed. It was necessary to perform final annealing, and the number of processes was large and the cost was high.

  Furthermore, although Patent Document 5 describes that a 3000 series aluminum alloy plate in which the Mg content is regulated can be provided by a manufacturing method with a small number of steps, in order to increase the shape freezing property at the time of press forming, 0. The 2% yield strength is regulated to 100 MPa or less, and there is a concern that the yield strength is insufficient after press molding and baking.

  In addition, Patent Document 6 describes that a 3000 series aluminum alloy plate containing Mg can be provided by a manufacturing method with a small number of steps. However, in order to increase the shape freezing property during press molding, The% yield strength is regulated to less than 140 MPa, and there is a concern that the yield strength is insufficient after press molding-baking coating.

  From the above, it is necessary to develop a high-strength aluminum alloy plate that contains Mg as an essential element and has excellent formability and bending workability. In addition, when used as a body sheet for an automobile outer plate, it is natural that it has formability, particularly excellent bending workability, and further suppresses temporal changes in mechanical properties after manufacturing the final plate, It is also necessary to suppress spring back after press molding. Therefore, it is desired to develop a high-strength 3000 series aluminum alloy plate excellent in formability, bending workability, and shape freezing property, in which a change in mechanical properties after manufacturing the final plate is suppressed.

  The present invention has been devised to solve such a problem, has high strength applicable to a body sheet for an automobile outer plate, and changes with time in mechanical properties after the production of the final plate. An object of the present invention is to provide a high-strength 3000 series aluminum alloy plate excellent in formability, bending workability and shape freezing property.

  In order to achieve the object, the high-strength aluminum alloy plate excellent in bending workability of the present invention is Si: 0.70 to 0.95 mass%, Fe: 0.10 to 0.85 mass%, Mn: Contains 0.40 to 1.80% by mass, Mg: 0.25 to 0.35% by mass, Ti: 0.005 to 0.10% by mass, with the balance being Al and inevitable impurities. The tensile strength is 190 MPa or more, the 0.2% proof stress is less than 155 MPa, the elongation value is 15% or more, and 0.2% after applying aging treatment at 170 ° C. for 20 minutes after introducing 2% pre-strain. Yield strength is 160 MPa or more. Furthermore, the 0.2% proof stress is preferably 140 MPa to less than 155 MPa.

  The manufacturing method of the aluminum alloy plate excellent in formability, bending workability and shape freezing property of the present invention is as follows: Si: 0.70 to 0.95 mass%, Fe: 0.10 to 0.85 mass%, Mn: It contains 0.40 to 1.80 mass%, Mg: 0.25 to 0.35 mass%, Ti: 0.005 to 0.10 mass%, and the balance is composed of Al and inevitable impurities. A slab having a thickness of 2 to 15 mm is continuously cast from a molten aluminum alloy using a thin slab continuous casting machine, and the slab is directly wound on a roll without hot rolling, and a final cold rolling ratio of 70 to 95% is achieved. It is characterized in that it is cold-rolled and held in a continuous annealing furnace at a holding temperature of 450 to 570 ° C. for 10 to 60 seconds for rapid cooling, natural aging, and artificial aging treatment. Furthermore, it is preferable that the artificial aging treatment is a treatment of holding for 1 to 48 hours at a holding temperature of 160 to 270 ° C. in a heating furnace.

The aluminum alloy plate of the present invention has high strength and is excellent in formability, bending workability and shape freezing property. A 3000 series alloy melt containing Mg is continuously cast by a thin slab continuous caster and wound directly on a roll, and cold rolled to the final thickness without homogenization or intermediate annealing. The Mn solid solution amount can be kept high. In addition, since a 3000 series alloy cold-rolled material containing Mg is rapidly heated and rapidly cooled by a continuous annealing furnace, and then subjected to natural aging, an artificial aging treatment is performed to produce a final plate. The strength can be increased by aging precipitation of Mg ₂ Si. In particular, since it has been subjected to artificial aging treatment, the change with time of mechanical properties after the production of the final plate is reduced, so that stable bending workability and press formability can be imparted.
Therefore, according to the present invention, a high-strength aluminum alloy plate excellent in formability, bending workability, and shape freezing property applicable to a body panel for an automobile outer plate can be provided at a low price.

Even if the conventional 3000 series aluminum alloy plate has high strength, there are many cases where defects such as microcracking and rough appearance occur especially in bending. For this reason, it is necessary to appropriately adjust the size of the intermetallic compound by appropriately controlling the cooling rate during slab casting. Moreover, the 3000 series aluminum alloy plate may have a low strength depending on its component composition or manufacturing process, and there is also a problem that the yield strength after press molding-baking coating is insufficient.
Therefore, a material having high strength and excellent formability, bending workability, and shape freezing property is required as a material to be used.

  As described above, in order to suppress the spring back after press molding, for example, after regulating the content of Mg, the slab cooling rate at the time of casting is increased by a thin slab continuous casting machine, and the intermetallic compound There is also a method to devise the casting process such as controlling the size. However, if the content of Mg in the 3000 series aluminum alloy plate is regulated, the proof stress after press forming-baking coating tends to decrease. Therefore, in order to improve the yield strength after press molding-baking coating, it is necessary to contain an appropriate amount of Mg.

On the other hand, in the 3000 series aluminum alloy plate containing Mg, although the strength is high, depending on its component composition and plate making conditions, Mg ₂ Si and the like are precipitated by natural aging after the final plate production, There is concern that the mechanical properties change over time. As described above, in the 3000 series aluminum alloy plate containing Mg, it is necessary to provide a stable bending workability and press formability by reducing a change in mechanical properties with time after the final plate is manufactured.
The inventors of the present invention have intensively studied to obtain an aluminum alloy plate excellent in formability, bending workability and shape freezing property through investigation of a 3000 series aluminum alloy plate containing Mg, and have reached the present invention.
The contents will be described below.

First, the action of each element contained in the 3000 series aluminum alloy plate of the present invention, the appropriate content, etc. will be described.
[Si: 0.70 to 0.95 mass%]
Although Si depends on the cooling rate at the time of ingot casting, fine intermetallic compounds such as Al- (Fe · Mn) -Si are crystallized, and some of them are solid-solved in the matrix. Increase strength. In the artificial aging treatment, Mg ₂ Si precipitates uniformly and finely with fine clusters precipitated in the matrix by natural aging as nuclei, so that Si is an essential element.
When the Si content is less than 0.70% by mass, the size and number of intermetallic compounds such as Al— (Fe · Mn) —Si are reduced, and the precipitation amount of Mg ₂ Si is further reduced. This is not preferable because the strength of the film cannot be obtained. When the Si content exceeds 0.95% by mass, the strength of the aluminum alloy plate is increased, but the shape freezing property and the bending workability are lowered, which is not preferable.
Therefore, the Si content is in the range of 0.70 to 0.95 mass%. A more preferable Si content is in the range of 0.75 to 0.95 mass%. A more preferable Si content is in the range of 0.80 to 0.95 mass%.

[Fe: 0.10 to 0.85 mass%]
Although Fe depends on the cooling rate at the time of slab casting, it is an essential element because it crystallizes fine intermetallic compounds such as Al- (Fe · Mn) -Si and increases the proof stress of the aluminum alloy sheet. .
If the Fe content is less than 0.10% by mass, the cost of the bullion increases, which is not preferable. When the Fe content exceeds 0.85% by mass, the size and number of intermetallic compounds such as Al— (Fe · Mn) —Si increase, and the shape freezing property and bending workability deteriorate. Absent.
Therefore, the Fe content is in the range of 0.10 to 0.85 mass%. A more preferable Fe content is in the range of 0.10 to 0.80 mass%. A more preferable Fe content is in the range of 0.15 to 0.80 mass%.

[Mn: 0.40 to 1.80 mass%]
Mn is an element that increases the proof stress of the aluminum alloy plate, and a part of the element is an essential element because it promotes solid solution strengthening by solid solution in the matrix. Further, Mn is an element constituting a fine intermetallic compound such as Al- (Fe.Mn) -Si during casting within the range of the alloy composition of the present invention, and is further dissolved in the matrix during solution treatment. Mn that has been deposited also precipitates as a fine intermetallic compound, increasing the yield strength.
If the Mn content exceeds 1.80% by mass, the shape freezing property decreases, which is not preferable. Further, if the Mn content is less than 0.40 mass%, the strength of the aluminum alloy plate becomes too low, which is not preferable.
Therefore, the preferable Mn content is in the range of 0.40 to 1.80% by mass. A more preferable Mn content is in the range of 0.40 to 1.70% by mass. A more preferable Mn content is in the range of 0.40 to 1.60% by mass.

[Mg: 0.25 to 0.35 mass%]
Mg dissolves in the matrix to promote solid solution strengthening and enhances the yield strength of the aluminum alloy plate. In the artificial aging process, Mg ₂ Si precipitates uniformly and finely with fine clusters precipitated in the matrix by natural aging as nuclei, and is an essential element.
If the Mg content exceeds 0.35% by mass, the shape freezing property and the bending workability deteriorate, which is not preferable. Further, if the Mg content is less than 0.25% by mass, the strength of the aluminum alloy plate becomes too low, which is not preferable.
Therefore, the preferable Mg content is in the range of 0.25 to 0.35 mass%. A more preferable Mg content is in the range of 0.25 to 0.33 mass%. A more preferable Mg content is in the range of 0.27 to 0.33 mass%.

[Ti: 0.005 to 0.10% by mass]
Ti is an essential element because it acts as a grain refiner during ingot casting and can prevent casting cracks. Of course, Ti may be added alone, but by coexisting with B, a more powerful grain refinement effect can be expected, so addition with a rod hardener such as Al-5% Ti-1% B There may be.
If the Ti content is less than 0.005% by mass, the effect of miniaturization at the time of ingot casting is insufficient, which may cause casting cracks, which is not preferable. If the Ti content exceeds 0.10% by mass, a coarse intermetallic compound such as TiAl ₃ may crystallize during ingot casting, which may reduce press formability and bending workability in the final plate. It is not preferable.
Therefore, the Ti content is in the range of 0.005 to 0.10% by mass. A more preferable Ti content is in the range of 0.005 to 0.07 mass%. A more preferable Ti content is in the range of 0.01 to 0.05% by mass.
In addition, about Ti content, although the more preferable range is prescribed | regulated by reducing both a lower limit and an upper limit with respect to a preferable range, the more preferable range is independent about each of a lower limit and an upper limit. It is not necessary to apply both at the same time.

[Cu: less than 0.05% by mass]
In the present invention, Cu is an unavoidable impurity. In the present invention, if the Cu content is in the range of less than 0.05% by mass, the shape freezing property and the bending workability are not significantly lowered. However, when the Cu content is 0.05% by mass or more, shape freezing property and bending workability are remarkably lowered. Therefore, the preferable Cu content is set to a range of less than 0.05% by mass. A more preferable Cu content is in the range of less than 0.03% by mass. A more preferable Cu content is in the range of less than 0.02% by mass.

[Other inevitable impurities]
Inevitable impurities are uncontrolled elements that are inevitably mixed in from raw metal, return material, etc., and their allowable contents are, for example, less than 0.20 mass% of Cr and 0.20 mass% of Zn Less than 0.10% by mass of Ni, less than 0.05% by mass in total of Ga and V, and less than 0.02% by mass for Pb, Bi, Sn, Na, Ca and Sr, It is less than 05 mass%, and even if it contains an element outside the control within this range, the effect of the present invention is not hindered.

By the way, when the 3000 series aluminum alloy plate is applied to an automobile body sheet or the like, not only has the high strength and excellent press formability and bending workability, but also suppresses the spring back after press forming. It is necessary to keep the proof stress low. Moreover, it is necessary to increase the yield strength after press molding and baking. When the strength of a press-formed product is high, the degree of freedom in designing an automobile body panel increases.
The strength of the material can be known from the tensile strength at the time of the tensile test, the moldability can be known from the elongation value at the tensile test, and the shape freezing property can be known from the proof stress at the tensile test. In addition, by simulating the proof stress after press forming-baking coating, press the baked coating press by measuring 0.2% proof strength after aging treatment at 170 ° C for 20 minutes after introducing 2% pre-strain. You can know the yield strength of the molded product.
The details will be given in the description of Examples below. As a 3000 series aluminum alloy plate of the present invention applied to a body sheet for an automobile outer plate, the tensile strength is 190 MPa or more, 0. 2% proof stress is less than 155 MPa, elongation value is 15% or more, and 0.2% proof stress after aging treatment at 170 ° C. for 20 minutes after introduction of 2% pre-strain is 160 MPa or more. Is preferred. Furthermore, the 0.2% proof stress is preferably 140 MPa to less than 155 MPa. If the 0.2% proof stress is 140 MPa or more, scratches are unlikely to occur during conveyance of the final plate.

  Further, details will be given in the description of Examples below, and in any case, it has the above specific component composition, and has a tensile strength of 190 MPa or more, a 0.2% proof stress of less than 155 MPa, and an elongation value of 15% or more. In addition, the present invention exhibits a formability, bending workability and shape freezing property according to the present invention in which 0.2% proof stress after aging treatment at 170 ° C. for 20 minutes after introduction of 2% pre-strain exhibits a value of 160 MPa or more. It becomes a high-strength aluminum alloy plate excellent in.

Next, an example of a method for manufacturing the aluminum alloy plate for press forming as described above will be briefly introduced.
[Dissolution / Smelting]
When the raw material is charged into the melting furnace and the predetermined melting temperature is reached, the flux is appropriately charged and stirred, and after degassing in the furnace using a lance, etc., if necessary, hold it quietly. Separate the cocoon from the surface of the melt.
In this melting / melting process, it is important to add raw materials such as a master alloy again because it is a predetermined alloy component. However, a sufficient sedation time is required until the flux and soot float and separate from the molten aluminum alloy to the molten metal surface. It is extremely important to take The sedation time is usually preferably 30 minutes or longer.

In some cases, the molten aluminum alloy melted in the melting furnace may be cast after it is once transferred to the holding furnace, but may be cast directly from the melting furnace. A more desirable sedation time is 45 minutes or more.
If necessary, in-line degassing or filtering may be performed.
In-line degassing is mainly of a type in which an inert gas or the like is blown into a molten aluminum from a rotating rotor, and hydrogen gas in the molten metal is diffused and removed in bubbles of the inert gas. When nitrogen gas is used as the inert gas, it is important to control the dew point to, for example, −60 ° C. or lower. The amount of hydrogen gas in the ingot is preferably reduced to 0.20 cc / 100 g or less.

  When there is a large amount of hydrogen gas in the ingot, porosity may occur in the final solidified part of the ingot. Therefore, the reduction rate per pass in the cold rolling process is regulated to, for example, 20% or more to reduce the porosity. It is preferable to crush. Also, the hydrogen gas that is supersaturated in the ingot is dependent on the heat treatment conditions of the cold-rolled coil. In some cases, blowholes are generated. For this reason, the more preferable amount of hydrogen gas in the ingot is 0.15 cc / 100 g or less.

[Thin slab continuous casting]
Thin slab continuous casters include both twin belt casters and twin roll casters.
The twin-belt casting machine includes a pair of rotating belt portions which are provided with endless belts and are opposed to each other, a cavity formed between the pair of rotating belt portions, and a cooling means provided inside the rotating belt portion. The molten metal is supplied into the cavity through a nozzle made of a refractory, and a thin slab is continuously cast.
The twin roll casting machine includes a pair of rotating roll portions that are provided with endless rolls so as to face each other, a cavity formed between the pair of rotating roll portions, and a cooling means provided inside the rotating roll portion. The molten metal is supplied into the cavity through a nozzle made of a refractory, and a thin slab is continuously cast.

[Slab thickness 2-15mm]
The thin slab continuous casting machine can continuously cast a thin slab having a thickness of 2 to 15 mm. If the slab thickness is less than 2 mm, even if casting is possible, it will be difficult to achieve a final rolling rate of 70 to 95%, which will be described later, depending on the thickness of the final plate. When the slab thickness exceeds 15 mm, it is difficult to wind the slab directly on a roll. In this slab thickness range, the cooling rate of the slab is about 40 to 1000 ° C./second in the vicinity of the slab thickness ¼, and the intermetallic compound such as Al— (Fe · Mn) —Si is fine. Crystallized out.

(Cold rolling)
A slab is continuously cast using a thin slab continuous casting machine, and the slab is directly wound on a roll without being hot-rolled, and then cold-rolled. For this reason, the chamfering process, the homogenization process, and the hot rolling process required for the slab (ingot) manufactured by the conventional semi-continuous casting can be omitted. The roll directly wound with the thin slab is passed through a cold rolling machine and usually subjected to several passes of cold rolling. At this time, since work hardening occurs due to plastic strain introduced by cold rolling, an intermediate annealing process may be performed in a batch furnace at a holding temperature of 300 to 400 ° C. for 1 to 8 hours as necessary.

[Final cold rolling rate 70-95%]
After cold rolling with a final cold rolling rate of 70 to 95%, solution treatment is performed. When the final cold rolling rate is within this range, the average crystal grain size after the solution treatment can be set to 20 to 50 μm, and the appearance skin after press molding can be finished beautifully. Therefore, it is possible to obtain recrystallized grains adjusted to 20 to 50 μm in the solution treatment process by keeping processing costs low and accumulating dislocations by adding processing while securing the solid solution amount of the transition metal element. It becomes possible. If the final cold rolling rate is less than 70%, the amount of work strain accumulated during cold rolling is too small, and 20 to 50 μm recrystallized grains cannot be obtained by solution treatment. When the final cold rolling rate exceeds 95%, the amount of processing strain accumulated during cold rolling is too large, the work hardening is severe, the edge cracks at the edges, and rolling becomes difficult. Therefore, a preferable final cold rolling rate is in the range of 70 to 95%. A more preferable final cold rolling rate is in the range of 75 to 95%. A more preferable final cold rolling rate is in the range of 75 to 90%.

[Solution treatment]
The solution treatment is preferably a solution treatment in which a continuous annealing furnace is held at a holding temperature of 450 ° C. to 570 ° C. for 10 to 60 seconds and then rapidly cooled. As means for rapidly cooling, air cooling by air injection or water cooling by mist injection is desirable. Mn dissolved in the matrix by the solution treatment is absorbed by the intermetallic compound that has been finely crystallized, thereby promoting recrystallization and increasing elongation.
If the holding temperature is less than 450 ° C., it is difficult to obtain a recrystallized structure. When the holding temperature exceeds 570 ° C., the thermal strain becomes severe, and burning may occur depending on the alloy composition. If the holding time is less than 10 seconds, the solid temperature of the coil does not reach a predetermined temperature, and the solution treatment may be insufficient. If the holding time exceeds 60 seconds, the process takes too much time and productivity is lowered.

[Natural aging]
In the production method of the present invention, it is essential that after solution treatment, natural aging is performed, and artificial aging treatment is further performed to obtain a final plate. Due to the natural aging after the solution treatment, fine clusters that can become precipitation nuclei such as Mg ₂ Si are uniformly formed in the matrix. Natural aging may be allowed to stand at room temperature for several hours to six months, but the quality of keeping the coil storage temperature appropriately, for example, regulating the holding time to 16 to 48 hours, etc. Administratively desirable.

[Artificial aging treatment]
The artificial aging treatment is preferably performed by inserting the coil into a heating furnace, and is held at a holding temperature of 160 to 270 ° C. for 1 to 48 hours. When the holding temperature is less than 160 ° C., the bending workability of the final plate is lowered, and it is difficult to obtain predetermined mechanical characteristics, which is not preferable. When the holding temperature exceeds 270 ° C., the strength of the final plate is lowered, and it becomes difficult to obtain predetermined mechanical characteristics, which is not preferable. If the holding time is less than 1 hour, the treatment may be terminated while the coil body temperature is not uniform, which is not preferable. When the holding time exceeds 48 hours, productivity is lowered, which is not preferable.

  By going through the continuous casting process, cold rolling process, solution treatment, natural aging and artificial aging treatment as described above, it is possible to obtain a high-strength aluminum alloy plate excellent in formability, bending workability and shape freezing property. it can.

[Production of thin slab continuous casting simulation material]
5 kg of ingots having a component composition of 21 levels were each inserted into a # 20 crucible, and the crucible was heated in a small electric furnace to melt the ingot. Next, a lance was inserted into the molten metal, and N ₂ gas was blown in at a flow rate of 1.0 L / min for 5 minutes for degassing treatment. Thereafter, sedation for 30 minutes was performed, and the soot that floated on the surface of the molten metal was removed with a stirring rod. Next, the crucible was taken out from the small electric furnace, and the molten metal was poured into a water-cooled mold having an internal size of 200 × 200 × 16 mm to produce a thin slab. Examples 1 to 8 and Comparative Examples 1 to 13 were prepared from the molten metal in each crucible. Each specimen was obtained. The disk samples of these test materials were subjected to composition analysis by emission spectroscopic analysis. The results are shown in Tables 1 and 2. After chamfering both sides of this thin slab by 3 mm to obtain a thickness of 10 mm, cold rolling was performed without applying homogenization treatment and hot rolling to obtain a cold rolled material having a plate thickness of 1.0 mm. . In addition, the intermediate annealing process is not performed during the cold rolling process. The final cold rolling rate in this case was 90%.

  Next, these cold-rolled materials (test materials) were each cut into a predetermined size and then inserted into a salt bath, and 530 ° C. × 15 seconds (Examples 1 to 6, Comparative Examples 1 to 10, 12). 13) or 565 ° C. × 15 seconds (Examples 7 and 8 and Comparative Example 11), and the sample material was quickly taken out from the salt bath, cooled with water, and subjected to a solution treatment. Thereafter, natural aging was performed at room temperature for 24 hours. These were inserted into an annealer and subjected to artificial aging treatment at 200 ° C. for 36 hours to obtain a final plate.

  Furthermore, these final plates were simulated by press molding-baking coating, introduced with 2% pre-strain using a tensile testing machine, and further inserted into an annealer and subjected to aging treatment at 170 ° C. for 20 minutes. Thus, an aging treatment material was introduced after the introduction of pre-strain.

  Next, various properties were measured and evaluated for each specimen (the final plate and the pre-strained aging treatment material) thus obtained.

[Measurement of various properties by tensile test]
The characteristics of each of the obtained test materials (final plate, pre-strained aging-treated material) were evaluated based on the tensile strength, 0.2% proof stress, and elongation value (%) of the tensile test.
Specifically, a JIS No. 5 test piece was sampled from the obtained specimen so that the tensile direction was parallel to the rolling direction, and a tensile test was performed according to JISZ2241, and a tensile strength of 0. 2% yield strength and elongation (elongation at break) were determined. These tensile tests were performed three times for each specimen (n = 3), and the average value was calculated.
The final plate having a tensile strength of 190 MPa or more was evaluated as good strength evaluation (◯), and the final plate having a tensile strength of less than 190 MPa was determined as poor strength evaluation (x). The final plate having a 0.2% yield strength of less than 155 MPa was evaluated as good shape freezing evaluation (◯), and the final plate having a yield strength of 155 MPa or higher was evaluated as poor shape freezing evaluation (×). The final plate having an elongation value of 15% or more was defined as good formability evaluation (◯), and the final plate having an elongation value of less than 15% was defined as poor moldability evaluation (x). In addition, the pre-strained aging treatment material having a 0.2% proof stress of 160 MPa or more was evaluated as good (O), and the pre-strained aging material after less than 160 MPa was evaluated as a poor molded product strength evaluation ( X). These evaluation results are shown in Tables 3 and 4.

[Evaluation of bending workability by bending test]
As a test piece for a bending test, a test piece having a size of 25 mm × 50 mm was taken with the 0 ° direction (L direction) as a longitudinal direction with respect to the rolling direction of the final plate. The bending test was performed by compressing the test pieces until they were in close contact with each other after bending from 40 ° to 60 ° in a state where the direction of 90 ° with respect to the longitudinal direction of the test pieces was pressed against a punch having a punch diameter of 1 mm. Evaluation of bending workability was performed by ranking from 0 to 4 points from no crack / wrinkle to breakage according to the surface state of the bent part after contact bending. The final plate that was 0 to 1 point was evaluated as good (◯) for bending workability evaluation, and the final plate that was 2 to 4 points was evaluated as poor bending workability evaluation (×). In addition, these bending tests were performed 3 times (n = 3) for each specimen, and the average value was calculated. These evaluation results are shown in Tables 3 and 4.

[Evaluation results of characteristics of each specimen]
Examples 1 to 8 in Table 3 showing the property evaluation results of the test materials are within the composition range of the present invention. The tensile strength of the final plate, the 0.2% proof stress of the final plate, the elongation value of the final plate, The 0.2% proof stress of the aging treatment material after the introduction of pre-strain and the bending workability of the final plate all satisfied the standard values. Specifically, final plate tensile strength: 190 MPa or more, final plate 0.2% proof stress: less than 155 MPa, final plate elongation value: 15% or more, 0.2% proof strength of pre-strained aging treatment : 160 MPa or more, bending workability of final plate: 0 to 1 standard value was satisfied. That is, Examples 1 to 8 had good strength evaluation, good shape freezeability evaluation, good moldability evaluation, good molded product strength evaluation, and good bending workability evaluation.

On the other hand, Comparative Examples 1 to 13 in Table 4 showing the property evaluation results of the test materials are outside the composition range of the present invention, and the tensile strength of the final plate, 0.2% proof stress of the final plate, At least one of the elongation value, the 0.2% proof stress of the pre-strained aging treated material, and the bending workability of the final plate did not satisfy the standard value.
In Comparative Example 1, since the Si, Mn, and Mg contents were too low, the final plate had poor strength evaluation and the molded product had poor strength evaluation. In Comparative Example 2, since the Si and Cu contents were too high, the shape freezeability evaluation failure and the bending workability evaluation failure were found. In Comparative Example 3, since the Si and Cu contents were too high, the shape freezeability evaluation failure and the bending workability evaluation failure were poor. In Comparative Example 4, since the Fe and Cu contents were too high, the shape freezeability evaluation failure, the formability evaluation failure, and the bending workability evaluation failure were found. In Comparative Example 5, since the Fe and Cu contents were too high, the shape freezeability evaluation failure and the bending workability evaluation failure were found. In Comparative Example 6, since the Cu content was too high, the shape freezeability evaluation failure, the formability evaluation failure, and the bending workability evaluation failure were found. In Comparative Example 7, the Cu content was too high, resulting in poor shape freezing evaluation and poor bending workability evaluation. In Comparative Example 8, since the Cu content was too high and the Mg content was too low, the strength evaluation of the final plate was poor, the strength evaluation of the molded product was poor, and the bending workability was poor. In Comparative Example 9, since the Cu and Mg contents were too high, the shape freezeability evaluation failure, the formability evaluation failure, and the bending workability evaluation failure were found. Since the comparative example 10 had too high Cu content, it was a shape freezing evaluation defect and a bending workability evaluation defect. Since the comparative example 11 had too high Mn content, it was a bending workability evaluation defect. In Comparative Example 12, since the Mg content was too low, the final plate had poor strength evaluation and the molded product had poor strength evaluation. In Comparative Example 13, since the Si content was too low, the final plate had poor strength evaluation and the molded product had poor strength evaluation.

  From the above, having the above specific component composition, tensile strength is 190 MPa or more, 0.2% proof stress is less than 155 MPa, elongation value is 15% or more, and 170 ° C. × 20 after introduction of 2% pre-strain. It can be seen that a sheet having a 0.2% proof stress of 160 MPa or more after aging treatment for minutes is a high-strength aluminum alloy plate excellent in formability, bending workability and shape freezing property.

Claims (4)

  Si: 0.70 to 0.95 mass%, Fe: 0.10 to 0.85 mass%, Mn: 0.40 to 1.80 mass%, Mg: 0.25 to 0.35 mass%, Ti: It contains 0.005 to 0.10% by mass, and the balance is composed of Al and inevitable impurities. The tensile strength is 190 MPa or more, the 0.2% proof stress is less than 155 MPa, and the elongation value is 15% or more. And, after introducing 2% pre-strain, after aging treatment at 170 ° C for 20 minutes, 0.2% proof stress is 160MPa or more, high strength excellent in formability, bending workability and shape freezing property Aluminum alloy plate.   The high-strength aluminum alloy sheet excellent in formability, bending workability, and shape freezing property according to claim 1, wherein the 0.2% proof stress is 140 MPa to less than 155 MPa.   Si: 0.70 to 0.95 mass%, Fe: 0.10 to 0.85 mass%, Mn: 0.40 to 1.80 mass%, Mg: 0.25 to 0.35 mass%, Ti: A slab having a thickness of 2 to 15 mm is continuously cast by using a thin slab continuous casting machine with a molten aluminum alloy containing 0.005 to 0.10% by mass and the balance being Al and inevitable impurities. The slab is directly wound on a roll without hot rolling, subjected to cold rolling with a final cold rolling rate of 70 to 95%, and held in a continuous annealing furnace at a holding temperature of 450 to 570 ° C. for 10 to 60 seconds for rapid cooling. And a method for producing a high-strength aluminum alloy plate excellent in formability, bending workability and shape freezing property, characterized by performing natural aging and performing artificial aging treatment.   The high-strength aluminum alloy excellent in formability, bending workability, and shape freezing property according to claim 3, wherein the artificial aging treatment is a treatment of holding in a heating furnace at a holding temperature of 160 to 270 ° C for 1 to 48 hours. A manufacturing method of a board.