JP2018100435A - Aluminum alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 6000 aluminum alloy sheet having excellent strength and bending properties.SOLUTION: An Al-Mg-Si aluminum alloy sheet contains Mg: 0.5-1.3 mass% and Si: 0.7-1.5 mass% and further contains at least one selected from Mn: 0.05-0.5 mass%, Zr: 0.04-0.20 mass%, and Cr: 0.04-0.20 mass% with the balance being Al and unavoidable impurities. The number density of transition element dispersion particles of 0.05 μm or more is 0.001/nm or less on a grain boundary, and a PFZ width of the grain boundary is 60 nm or less after an artificial aging treatment for holding the sheet for 10-30 minutes at 200-250°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aluminum alloy plate. More specifically, the present invention relates to an Al—Mg—Si based aluminum alloy plate suitable for members constituting a skeletal structure such as automobiles and railway vehicles.

  In recent years, with respect to global environmental problems caused by exhaust gas and the like, improvement in fuel consumption has been pursued by reducing the weight of the body of a transport aircraft such as an automobile. In order to meet such demands, the use of lightweight aluminum alloy materials as materials for automobiles and the like, instead of steel materials such as steel plates, is increasing.

  For example, panels such as outer panels (outer plates) and inner panels (inner plates) used in panel structures such as automobile hoods, fenders, doors, roofs, trunk grids, etc. are thin among aluminum alloy plates, and A high-strength aluminum panel plate is used, and in particular, an Al—Mg—Si based alloy plate (such as a JIS-defined 6000 based alloy plate) is applied. Aluminum alloys for outer plates and inner plates are required to have high workability, and various methods have been proposed so far to meet such demands. For example, Patent Document 1 discloses an aluminum alloy plate that has improved bending workability by controlling the cooling rate after solution treatment.

On the other hand, steel is also used as a material for frame structures (so-called white bodies) such as front pillars, center pillars, roof rails, dashboards, side members, cross members, side sills and sill inners of automobiles from the viewpoint of improving fuel efficiency. There is a need to apply an Al—Mg—Si alloy plate that is lightweight and has high strength in place of the material. In addition to having high strength as a material used for the skeleton structure of transportation equipment, development of a material excellent in bendability so as to sufficiently absorb energy at the time of collision is required.
However, the actual situation is that the development of an aluminum alloy having sufficiently excellent strength and bendability has not yet been developed as a material to be applied to the framework structure of a vehicle.

JP 2003-105473 A

  The present invention has been made to meet such demands, and an object of the present invention is to provide a 6000 series aluminum alloy plate excellent in strength and bendability.

  Aspect 1 of the present invention includes Mg: 0.5 to 1.3 mass%, Si: 0.7 to 1.5 mass%, Mn: 0.05 to 0.5 mass%, Zr: 0.04 -0.20 mass%, and Cr: further including at least one selected from 0.04-0.20 mass%, the balance being Al and inevitable impurities, and a transition of 0.05 μm or more existing on the grain boundary Al—Mg— in which the number density of element-based dispersed particles is 0.001 particles / nm or less and the PFZ width of the grain boundary after artificial aging treatment is maintained at 200 to 250 ° C. for 10 to 30 minutes is 60 nm or less. This is a Si-based aluminum alloy plate.

  Aspect 2 of the present invention is the aluminum alloy plate according to Aspect 1, further comprising Cu: more than 0 mass% and 0.5 mass% or less.

  Aspect 3 of the present invention is the aluminum alloy plate according to Aspect 1 or 2, further comprising Sc: 0.02 to 0.1% by mass.

  Aspect 4 of the present invention further includes at least one selected from Ag: 0.01 to 0.2% by mass and Sn: 0.001 to 0.1% by mass, according to any one of Aspects 1 to 3. It is an aluminum alloy plate of description.

  According to the fifth aspect of the present invention, the 0.2% proof stress after the artificial aging treatment is maintained at 200 to 250 ° C. for 10 to 30 minutes is 250 MPa or more, and the VDA bending angle is 60 ° or more. It is an aluminum alloy plate in any one of.

  According to the present invention, a 6000 series aluminum alloy plate excellent in strength and bendability can be provided.

It is a perspective view which shows the aspect of the VDA bending test which evaluates shock absorption.

The present inventors have studied from various angles in order to realize a 6000 series aluminum alloy plate having sufficiently excellent strength and bendability as a member constituting the framework structure of a transport vehicle such as an automobile.
In the 6000 series aluminum alloy plate, when artificial aging treatment such as baking coating is performed, a precipitate-free zone (PFZ: Precipitate Free Zone) in which precipitates such as Si and Mg ₂ Si do not exist is formed in the vicinity of the grain boundary. Since PFZ has low strength and low bendability, it is known that it becomes a starting point of cracking during bending.
The present inventors have focused on the fact that the strength and bendability of an aluminum alloy can be improved by reducing the width of the PFZ that lowers the strength and bendability.
As a result of intensive studies, the present inventors reduced the PFZ width appearing in the vicinity of the grain boundary after artificial aging treatment by reducing the number density of transition element-based dispersed particles precipitated at the grain boundary of the aluminum alloy plate. As a result, it was found that an aluminum alloy plate excellent in strength and bendability can be provided.
When the transition element-based dispersed particles are present at the grain boundaries at a predetermined number density or higher, composite precipitation on the surface of the dispersed particles of Mg and Si that has diffused at the time of solution treatment cooling is promoted. The diffusion of Mg and Si atoms to the grain boundary is promoted and the concentration of Mg and Si atoms in the vicinity of the grain boundary is lowered to expand the region of the depletion layer of these elements, increasing the PFZ width and degrading the bendability. .
However, in the aluminum alloy of the present invention, composite precipitation of Mg and Si into dispersed particles can be suppressed by reducing the number density of transition element-based dispersed particles present at the grain boundaries. As a result, the depletion region of Mg and Si can be reduced, the PFZ width can be reduced, and the strength and bendability can be improved.

Below, the aluminum alloy plate which concerns on embodiment of this invention is demonstrated in detail.
The “aluminum alloy plate” as used in the embodiments of the present invention refers to aluminum after subjecting a rolled plate such as a hot rolled plate or a cold rolled plate to tempering such as solution treatment and quenching treatment. An aluminum alloy plate before an artificial aging treatment such as paint baking.

1. Organization

(1) Number density of transition element-based dispersed particles of 0.05 μm or more present on the grain boundary: 0.001 particles / nm or less The aluminum alloy plate according to the embodiment of the present invention is a transition that precipitates on the grain boundary. The number density of the element-based dispersed particles is controlled to be a predetermined value or less.

  When the number density of the transition element-based dispersed particles present on the grain boundaries is large, composite precipitation of Mg and Si that has diffused at the grain boundaries on the dispersed particles is promoted during cooling after the solution treatment in the production process. As a result, diffusion of Mg and Si from the matrix to the grain boundary is promoted, thereby reducing the concentration of Mg and Si in the vicinity of the grain boundary, expanding the Mg and Si deficient region, and increasing the PFZ width. , Strength and bendability deteriorate.

  In the aluminum alloy plate according to the embodiment of the present invention, composite precipitation of Mg and Si into dispersed particles can be suppressed by reducing the number density of transition element-based dispersed particles present on the grain boundaries. As a result, the Mg and Si deficient regions can be reduced, the PFZ width can be reduced, and the strength and bendability can be improved.

  If the number density of the transition element-based dispersed particles of 0.05 μm or more present on the grain boundary is 0.001 particles / nm or less, the effect of improving the bendability by reducing the PFZ width described above can be obtained. The number density of the transition element-based dispersed particles is preferably 0.0005 particles / nm or less.

  In the embodiment of the present invention, only the dispersed particles having a circle equivalent diameter of 0.05 μm or more are targeted as the transition element-based dispersed particles on the grain boundary defining the number density. This is because dispersed particles having a size of less than 0.05 μm have a negligible effect on the increase in the PFZ width.

  In the embodiment of the present invention, “transition element-based dispersed particles” refers to intermetallic compounds containing Mn, Cr, Zr, Fe, Cu, and the like.

(2) PFZ width of grain boundary after artificial aging treatment: 60 nm or less In the 6000 series aluminum alloy plate including the aluminum alloy plate according to the embodiment of the present invention, the grain boundary is obtained by performing artificial aging treatment such as baking coating. In the vicinity, a precipitate-free zone (PFZ: Precipitate Free Zone) in which no precipitates such as Si and Mg ₂ Si are present is formed.
As described above, the aluminum alloy plate according to the embodiment of the present invention suppresses the composite precipitation of Mg and Si into the dispersed particles by reducing the number density of the transition element-based dispersed particles existing on the grain boundaries. Therefore, the Mg and Si deficient regions can be reduced, and the PFZ width can be sufficiently reduced. As a result, an aluminum alloy plate having both excellent strength and bendability can be provided.

In the aluminum alloy according to the embodiment of the present invention, the PFZ width in the vicinity of the grain boundary is sufficiently reduced. The characteristic that the PFZ width is sufficiently reduced is that the aluminum alloy plate (that is, T4 material) according to the present invention after solution treatment is subjected to artificial aging treatment, that is, tempered to become T6 material. In particular, it can be expressed remarkably.
Therefore, in the embodiment of the present invention, artificial aging treatment is applied to the aluminum alloy plate of T4 material, and the PFZ width is measured after the artificial aging treatment, that is, the aluminum alloy plate tempered to T6 material. By doing so, an aluminum alloy plate is defined.
For example, a sufficiently reduced PFZ width can be confirmed by performing an artificial aging treatment in which an aluminum alloy plate according to an embodiment of the present invention is held at 200 to 250 ° C. for 10 to 30 minutes.

As described above, the aluminum alloy plate according to the embodiment of the present invention can remarkably exhibit a sufficiently reduced PFZ width by performing the artificial aging treatment. In the aluminum alloy plate according to the embodiment of the present invention, the PFZ width of the grain boundary after the artificial aging treatment is 60 nm or less, preferably 40 nm or less.
If the PFZ width after the artificial aging treatment is in such a range, when the aluminum alloy plate according to the embodiment of the present invention is used as a member for a skeleton structure such as a vehicle, excellent impact resistance characteristics are exhibited. be able to.

  The number density of the transition element-based dispersed particles of 0.05 μm or more present on the grain boundary and the PFZ width of the grain boundary can be measured as follows using a transmission electron microscope (TEM), for example.

  The number density of the transition element-based dispersed particles of 0.05 μm or more present on the grain boundary is, for example, randomly sampled at five locations from an aluminum alloy plate tempered into a T4 material after solution treatment, After preparing the specimen for TEM observation so that the thickness center part becomes the observation surface, the incident direction of the electron beam is adjusted so as to be parallel to the (100) plane, and the magnification is 100,000 times or more for each sample. Three fields of view of the grain boundary region are taken. For each field of view, the precipitates on the grain boundaries were analyzed by energy dispersive X-ray analysis (EDX), and Mg-Si-based precipitates, Mg-Si-Cu-based precipitates, and Si precipitates were removed. Elemental precipitates are identified, and among them, the number of precipitates corresponding to a circle equivalent diameter of 0.05 μm or more is counted and calculated as a number density (number / nm) per grain boundary length. And it can measure by calculating the average value of the number density in three visual fields of each sample, and calculating | requiring the average value in five places of samples.

  As for the PFZ width, for example, five samples were prepared from an aluminum alloy plate after artificial aging treatment, that is, tempered to T6 material, by the same method as the TEM observation after the solution treatment described above, and the incidence of the electron beam Adjust so that the direction is parallel to the (100) plane. Then, at a magnification of 100,000 times or more, three fields of the grain boundary region are observed for each sample, and the PFZ width of the portion having the widest PFZ is measured in each field of view. And the PFZ width | variety of an aluminum alloy plate can be measured by calculating | requiring the average value of PFZ width | variety of 15 places in total.

  In addition, PFZ is a TEM photograph that is formed by an interface between a crystal grain precipitation region (a dark color region in a TEM photo) and a precipitation thin region (a light color region in a TEM photo) and a grain boundary. It is an enclosed area. The PFZ width is a distance between a crystal grain boundary and an interface between a crystal grain precipitation region and a precipitation thin region in a TEM photograph.

2. Chemical composition:
Next, the composition of the aluminum alloy plate according to the embodiment of the present invention will be described. The aluminum alloy plate according to the embodiment of the present invention is made of a 6000 series aluminum alloy, and the component composition only needs to have a normal chemical composition as a 6000 series aluminum alloy.

(1) Si: 0.7% by mass or more and 1.5% by mass or less Si, together with Mg, is an element that contributes to solid solution strengthening. In addition, during the artificial aging treatment such as paint baking treatment, it forms an aging precipitate that contributes to strength improvement, exhibits age hardening ability, and is an indispensable element for obtaining the strength (proof strength) required for automobile structural materials It is.
Also, by adding more than a predetermined amount, the thickness of the Si atom concentration-deficient layer formed by diffusing into the grain boundary during solution cooling is reduced, the PFZ width is reduced, and the bendability is improved. Can do.

If the Si content is less than 0.7% by mass, the strength is insufficient. Therefore, the Si content is 0.7% by mass or more, preferably 0.8% by mass or more.
On the other hand, when Si content exceeds 1.5 mass%, a coarse compound will be formed and ductility will be deteriorated. Therefore, the Si content is 1.5% by mass or less, preferably 1.4% by mass or less.

(2) Mg: 0.5% by mass or more and 1.3% by mass or less Mg, together with Si, is an element that contributes to solid solution strengthening. In addition, during artificial aging treatment such as paint baking treatment, it forms an aging precipitate that contributes to strength improvement together with Si, exhibits age hardening ability, and is an essential element for obtaining the necessary proof strength as a structural material for automobiles It is. Also, by adding more than a predetermined amount, the thickness of the Mg atom concentration-deficient layer formed by diffusing to the grain boundary during solution cooling is reduced, the PFZ width is reduced, and the bendability is improved. Can do.

If the Mg content is less than 0.5% by mass, the strength is insufficient. Therefore, Mg content is 0.5 mass% or more, and 0.6 mass% or more is preferable.
On the other hand, if the Mg content exceeds 1.3% by mass, a shear band is easily formed during cold rolling, which causes cracks during rolling. Therefore, the Mg content is 1.3% by mass or less, preferably 1.2% by mass or less.

(3) Mn: selected from 0.05 mass% to 0.5 mass%, Zr: 0.04 mass% to 0.20 mass% and Cr: 0.04 mass% to 0.20 mass% One or more types of Mn, Zr, and Cr exist as dispersed particles, contribute to refinement of crystal grains, and improve formability. If the amount of these elements added is too small, the number density of the dispersed particles decreases, and the increase in yield strength during stretching decreases, which may decrease the strength after baking. On the other hand, when there is too much content of these elements, a coarse compound may be formed and ductility may be deteriorated.
Therefore, the Mn content is 0.05% by mass to 0.5% by mass, the Zr content is 0.04% by mass to 0.20% by mass, and the Cr content is 0.04% by mass to 0%. 20% by mass or less.
Mn, Zr, and Cr may contain only 1 type and may contain it in combination of 2 or more type.

(4) Balance In one preferred embodiment, the balance is Al and inevitable impurities. As inevitable impurities, it is assumed that trace elements such as Ti, B, Fe, Zn, V, Na, Ca, In, Be, and Sr, which are brought in depending on the situation of raw materials, materials, manufacturing equipment, and the like, are mixed.

  The aluminum alloy plate according to the embodiment of the present invention is not limited to the composition described above. As long as the characteristics of the aluminum alloy plate according to the embodiment of the present invention can be maintained, other elements may be further included as necessary. Other elements that can be selectively contained as described above are exemplified below.

(5) Cu: more than 0% by mass and 0.5% by mass or less Cu has an effect of accelerating age hardening of the final product in addition to contributing to improvement of strength by solid solution strengthening. In order to obtain such an effect of Cu, it is preferable to include more than 0% by mass. On the other hand, when there is too much content of Cu, there exists a possibility that corrosion resistance may deteriorate, and it is unpreferable. Therefore, the Cu content is preferably 0.5% by mass or less.

(6) Sc: 0.02% by mass or more and 0.1% by mass or less Sc exists as dispersed particles, contributes to refinement of crystal grains, and improves moldability. If the amount added is too small, the number density of the dispersed particles is lowered, and the amount of increase in yield strength during stretching is reduced, which may reduce the strength after baking. On the other hand, when there is too much content, there exists a possibility that a coarse compound may be formed and ductility may be deteriorated.
Therefore, the preferable content of Sc is 0.02% by mass or more and 0.1% by mass or less.

(7) One or more types selected from Ag: 0.01% by mass to 0.2% by mass and Sn: 0.001% by mass to 0.1% by mass Ag is a molding process into a structural material Aging precipitates that contribute to strength improvement by the subsequent artificial aging heat treatment have the effect of precipitating closely and finely and promoting high strength. In addition, Sn has the effect of suppressing the cluster formation at room temperature by adding, and maintaining the excellent formability of the plate after solution treatment and quenching treatment for a long time, and then baking coating. Improves the strength of artificial aging heat treatment.
If the added amount of these elements is too small, the above-described effects cannot be obtained. On the other hand, if the addition amount is too large, Ag may rather reduce various properties such as rollability and weldability, saturate the strength improvement effect, and may only be expensive. The effect is saturated, and on the contrary, hot brittleness may occur, and hot workability (hot ductility) may be significantly deteriorated.
Therefore, the preferable content of Ag is 0.01% by mass or more and 0.2% by mass or less, and the preferable content of Sn is 0.001% by mass or more and 0.1% by mass or less.
Ag and Sn may contain only 1 type and may contain it in combination of 2 or more type.

3. Mechanical properties As described above, the aluminum alloy plate according to the embodiment of the present invention has excellent strength and at the same time excellent bending properties because the PFZ width that reduces strength and bendability is reduced. Can do. Therefore, when the aluminum alloy plate according to the embodiment of the present invention is applied to a skeleton structure of a transport machine such as an automobile, excellent energy absorption characteristics can be exhibited at the time of a vehicle collision.
The excellent strength and bendability of the aluminum alloy plate according to the embodiment of the present invention can be obtained by performing artificial aging treatment on the aluminum alloy plate according to the present invention and tempering it to become a T6 material. It can be remarkably expressed. For example, excellent mechanical properties can be confirmed by subjecting the aluminum alloy plate according to the embodiment of the present invention to an artificial aging treatment under conditions of holding at 200 to 250 ° C. for 10 to 30 minutes.

(1) Strength The aluminum alloy plate according to the embodiment of the present invention has a 0.2% proof stress of 250 MPa or more measured by a tensile test after artificial aging treatment, that is, after tempering a T6 material. In a preferred form, it is 270 MPa or more. Thereby, sufficient strength can be secured.

(2) Bendability The bendability indicating the energy absorption characteristic at the time of collision can be measured, for example, by performing a VDA bending test based on the VDA standard “VDA238-100 Plate bending test for metallic materials” defined by the German Automobile Manufacturers Association. It can be evaluated by a bending angle (in this specification, sometimes referred to as a VDA bending angle) (°).
The aluminum alloy plate according to the embodiment of the present invention has a bending angle measured by a VDA test bending test after artificial aging treatment, that is, after tempering to T6 material, is preferably 60 ° or more. In the embodiment, the angle is 70 ° or more. Thereby, sufficiently excellent energy absorption characteristics can be secured.

4). Manufacturing Method Next, a manufacturing method of the aluminum alloy plate according to the embodiment of the present invention will be described.
As described above, in the aluminum alloy plate according to the embodiment of the present invention, the number density of the transition element-based dispersed particles existing on the crystal grain boundary is sufficiently reduced. Precipitation of ₂ Si and the like can be suppressed, and the PFZ width can be sufficiently reduced.
As can be seen from the description of the manufacturing process below, such characteristics are, among other things, by strictly controlling the heating rate in the homogenization heat treatment, and further by controlling the solution treatment temperature and the cooling rate during cooling. It can be achieved.
Hereinafter, each step will be described.
(1) Melting and Casting First, in the melting and casting process, the Al alloy molten metal whose melting is adjusted within the above-mentioned 6000 series component standard range is used for normal melting such as continuous casting rolling method and semi-continuous casting method (DC casting method). An aluminum alloy ingot (slab) is cast by appropriately selecting a casting method.

(2) Homogenization heat treatment Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment.
The homogenizing heat treatment is performed at a homogenizing temperature (holding temperature) of 450 ° C. or higher and lower than the melting point. By this homogenization heat treatment (uniform heat treatment), the homogenization of the structure, that is, the segregation in the crystal grains in the ingot structure can be eliminated. If the homogenization temperature is less than 450 ° C., segregation in the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that the bendability is lowered.

  In the embodiment of the present invention, by controlling the heating temperature raising condition during the homogenization heat treatment, the PFZ width of the finally obtained aluminum alloy plate can be reduced and the bendability can be improved. Specifically, the heating temperature raising condition is controlled as follows.

(200 ° C to 450 ° C: 80 ° C / hour or more)
In the embodiment of the present invention, the temperature of the aluminum alloy ingot is increased from 200 ° C. to 450 ° C. at an average heating rate of 80 ° C./hour or more. Preferably, the average heating rate in the temperature range from 200 ° C. to 450 ° C. is preferably 90 ° C./hour or more, more preferably 100 ° C./hour or more.

When the average heating rate in the temperature range is less than 80 ° C./hour, the transition element-based dispersed particles are excessively precipitated at the crystal grain boundaries, and Mg that has diffused at the grain boundaries during cooling in the subsequent solution treatment step and Si promotes the composite precipitation on the surface of the dispersed particles, and as a result, the diffusion of Mg and Si from the matrix is promoted, so that the atomic concentrations of Mg and Si in the vicinity of the grain boundaries are lowered. For this reason, the region of the Mg and Si element depletion layer in the vicinity of the crystal grain boundary expands, the PFZ width increases, and the bendability decreases.
When the average heating rate in the temperature range is 80 ° C./hour or more, excessive precipitation of transition element-based dispersed particles at the grain boundary can be suppressed, and the above-described combined precipitation of Mg and Si can be suppressed. Therefore, the PFZ width can be reduced and the bendability can be improved.

(450 ° C to homogenization temperature: 40 ° C / hour or less)
When the average heating rate in the temperature range from 450 ° C. to the homogenization temperature exceeds 40 ° C./hour, the transition element-based dispersed particles deposited on the grain boundaries cannot be coarsened, and dispersion on the grain boundaries is not possible. The number density of particles increases, and the PFZ width after artificial aging increases. Therefore, the temperature range from 450 ° C. to the homogenization temperature is increased at an average heating rate of 40 ° C./hour or less. By raising the temperature range at an average heating rate of 40 ° C./hour or less, the transition element-based dispersed particles precipitated at the grain boundaries are further coarsened, and the reduction of the number density of the dispersed particles on the grain boundaries is promoted. And the PFZ width after artificial aging can be reduced.

(Retention time after reaching homogenization temperature: 4 hours or more)
The aluminum alloy ingot is heated at the above average heating rate, and after reaching a homogenization temperature lower than the melting point, it is preferably maintained at the homogenization temperature for 4 hours or more. As a result, the transition element-based dispersed particles precipitated at the grain boundaries can be further coarsened and the number density can be reduced.

  The above-described homogenization heat treatment step may be performed under any one of the soaking conditions, the soaking conditions, the soaking conditions, or the two-stage soaking conditions. Two-stage soaking conditions are preferable, and one-time soaking conditions are more preferable.

  Under the one-time soaking condition, after the holding at the homogenization temperature, the hot rolling is started by cooling to the hot rolling start temperature or holding at or near the hot rolling start temperature. The second soaking condition means that after the first soaking, the steel sheet is once cooled to a temperature of 200 ° C. or less including room temperature, reheated, and maintained at that temperature for a certain time, and then hot rolling is started. On the other hand, the two-stage soaking condition is to cool after the first soaking, but not to 200 ° C. or less, after stopping the cooling at a higher temperature and maintaining at that temperature, Hot rolling is started after reheating to the same temperature or higher temperature.

  Regardless of the conditions, the first temperature increase of the homogenization heat treatment (that is, the temperature increase in the first soaking condition, the first temperature increase in the second soaking condition, or the temperature increase in the two-stage soaking condition) In this case, by controlling the average heating rate from 200 ° C. to 450 ° C. to 80 ° C./hour or more, excessive precipitation of transition element-based dispersed particles at the grain boundary can be suppressed, and the finally obtained aluminum alloy The PFZ width of the plate can be reduced and the bendability can be improved.

(3) Hot rolling Hot rolling is comprised of an ingot (slab) rough rolling step and a finish rolling step in accordance with the thickness of the rolled sheet. In the rough rolling process and the finish rolling process, a reverse or tandem rolling mill is appropriately used.

  When the hot rolling start (that is, rough rolling start) temperature exceeds the solidus temperature, burning (that is, partial melting of the ingot) occurs, so that hot rolling itself may be difficult. Moreover, if the hot rolling start temperature is less than 350 ° C., the load during hot rolling becomes too high, and the hot rolling itself may be difficult. Therefore, the hot rolling (rough rolling) start temperature is preferably 350 ° C. to the solidus temperature, more preferably 400 ° C. to the solidus temperature.

(4) Hot rolling annealing treatment Before performing cold rolling described later, the hot rolled sheet may be annealed (roughened) as necessary. By annealing the hot-rolled sheet, properties such as formability can be further improved by refining the crystal grains and optimizing the texture.

(5) Cold rolling In cold rolling, the obtained hot-rolled sheet is rolled to produce a cold-rolled sheet (including a coil) having a desired final thickness. In order to make the crystal grains finer, the cold rolling rate is preferably 40% or more, and intermediate annealing may be performed between cold rolling passes for the same purpose as the annealing step described above.

(6) Solution treatment and quenching treatment (solution treatment temperature: 500 ° C. or higher)
The obtained cold-rolled sheet is subjected to a solution treatment and a quenching treatment to room temperature. By this solution treatment, Mg and Si can be sufficiently dissolved, and the strength can be improved. When the solution treatment temperature (holding temperature) is less than 500 ° C., each element of Mg and Si cannot be sufficiently dissolved, and high strength cannot be obtained. Accordingly, the solution treatment temperature (holding temperature) is 500 ° C. or higher, preferably 550 ° C. or higher.

(Average cooling rate of 500 to 300 ° C .: 50 ° C./second or more)
As described above, in the method for producing an aluminum alloy plate according to the embodiment of the present invention, in the homogenization heat treatment step, the temperature range of 200 to 450 ° C. is increased at a large average heating rate of 80 ° C./second or more, and The temperature range from 450 ° C. to the homogenization temperature is increased at an average heating rate of 40 ° C./hour or less. As a result, the number density of the transition element-based dispersed particles existing on the crystal grain boundaries of the cold-rolled sheet is sufficiently reduced by performing the solution treatment.

  In the method for producing an aluminum alloy plate according to the embodiment of the present invention, a solution treatment is performed on the cold-rolled plate as described above, and the average cooling rate after holding at the solution treatment temperature is strictly controlled. As a result, the number density of the transition element-based dispersed particles present on the crystal grain boundaries of the finally obtained aluminum alloy plate can be sufficiently reduced, the PFZ width can be reduced, and the bendability can be improved.

  Specifically, in the manufacturing method according to the embodiment of the present invention, after the solution treatment, a temperature range of 500 to 300 ° C. is cooled at an average cooling rate of 50 ° C./second or more. By cooling at such a large average cooling rate, grain boundary diffusion of Mg and Si during cooling can be suppressed. As a result, composite precipitation of Mg and Si on the surface of the transition element-based dispersed particles precipitated at the grain boundaries can be suppressed, so that a deficient layer of Mg atoms and Si atoms is formed in the vicinity of the grain boundaries. Can be suppressed. Therefore, when an aluminum alloy plate according to an embodiment of the present invention is subjected to artificial aging treatment and tempered to a T6 material, the PFZ width of the grain boundary can be reduced to 60 nm or less, and excellent strength and bendability can be obtained. It can be demonstrated.

  In order to ensure such an average cooling rate of 50 ° C./second or higher in the quenching treatment, air cooling using a fan and water cooling means such as mist, spray, and immersion may be appropriately selected and used.

(7) Pre-aging treatment In the manufacturing method according to this embodiment, in order to further improve the age-hardening property in the artificial age-hardening treatment such as the baking coating process, the pre-aging treatment may be performed after the quenching treatment as necessary. Good. The preliminary aging treatment is preferably held in the temperature range of 60 to 150 ° C, preferably in the temperature range of 70 to 120 ° C for 1 to 24 hours. The cooling rate after the preliminary aging treatment is preferably 1 ° C./hour or less.

(8) Pre-strain treatment In the method for producing an aluminum alloy plate according to the present embodiment, if necessary, after the solution treatment and quenching treatment described above, or when performing a pre-aging treatment, cooling is completed after the pre-aging treatment. After 6 hours or more have passed, a strain of about 5 to 20% may be applied to the cold-rolled sheet. Thereby, dislocations are introduced into the cold rolled sheet. Clusters exist after 6 hours or more have elapsed after quenching or preliminary aging. Therefore, during the subsequent artificial aging treatment or baking coating treatment, the cluster becomes an obstacle to the movement accompanying the recovery of the dislocation, and the dislocation is hardly recovered. As a result, not only the conventional precipitation strengthening but also the dislocation strengthening can increase the strength after the artificial aging treatment or baking coating treatment. Furthermore, by introducing strain, Mg and Si are preferentially precipitated in dislocations existing in the PFZ at grain boundaries during baking coating or artificial aging treatment, and as a result, the PFZ width can be further reduced. And the bendability can be further improved.

  In the pre-strain processing step, any method of adding strain to the cold-rolled sheet may be used. For example, the strain may be applied by a tensile test, cold rolling, a leveler, or the like.

  If it is those skilled in the art who contacted the manufacturing method of the aluminum alloy plate which concerns on embodiment of this invention demonstrated above, the aluminum alloy plate which concerns on this invention by the manufacturing method different from the manufacturing method mentioned above by trial and error can be obtained. There is a possibility.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can be implemented with modifications within a range that can be adapted to the above-described gist, which are all included in the technical scope of the present invention. Is done.

1. Preparation of test piece An aluminum alloy ingot having the composition shown in Table 1 was melted by a DC casting method.
In Tables 1 to 3, underlined numerical values indicate that they are out of the scope of the present invention.

Subsequently, the obtained ingot was subjected to homogenization heat treatment and hot rolling under the conditions shown in Table 2 to obtain a hot-press plate of 3 to 25 mm. This hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet having a thickness of 2.0 mm. The obtained cold-rolled sheet was subjected to a solution treatment under the conditions shown in Table 2, and then subjected to a preliminary aging treatment at 100 ° C. for 8 hours to obtain an aluminum alloy sheet tempered into a T4 material. In the solution treatment, the holding time at the ultimate temperature was 30 minutes. About the predetermined | prescribed sample, the pre-strain process was further performed on the conditions shown in Table 2 by the tension test. In addition, the average heating rate of the homogenization heat treatment described in Table 2 indicates the average heating rate at the first temperature increase in the test piece in which the soaking pattern is a soaking condition twice.
Subsequently, all the test pieces were subjected to artificial aging treatment under the conditions shown in Table 2 to obtain an aluminum alloy plate tempered into a T6 material.

2. Observation of structure In the following manner, the number density of 0.05 μm or more transition element-based dispersed particles existing on the grain boundary and the PFZ width of the grain boundary were measured. These results are shown in Table 3.

(Number density of dispersed particles)
The number density of the transition element-based dispersed particles of 0.05 μm or more present on the grain boundaries was measured by TEM observation on the T4 material before the artificial aging treatment. Specifically, five points were sampled from the test piece of T4 material, and the test piece was adjusted so that TEM observation was possible at the center of the plate thickness. The incident direction of the electron beam was adjusted to be parallel to the (100) plane, and the grain boundary region was photographed in three fields for each sample at a magnification of 100,000 or more. In each field of view, the precipitate on the grain boundary is analyzed by energy dispersive X-ray analysis (EDX), and the transition element system excluding the Mg-Si-based precipitate, Mg-Si-Cu-based precipitate, and Si precipitate The number of precipitates corresponding to a circle equivalent diameter of 0.05 μm or more was counted and calculated as the number density per grain boundary length (pieces / nm). The average value of the number density in three fields of each sample is calculated, the average value in five samples is obtained, and the number density of 0.05 μm or more transition element-based dispersed particles present on the grain boundary of the test piece did. In Table 3, it was shown as “number density of grain boundary precipitates”.

(PFZ width of grain boundary)
The PFZ width of the grain boundary was measured by TEM observation on the T6 material after the artificial aging treatment. Specifically, five points were sampled from the test piece of T6 material, and the test piece was adjusted so that TEM observation was possible at the center of the plate thickness. Then, the incident direction of the electron beam was adjusted to be parallel to the (100) plane. Then, at a magnification of 100,000 times or more, three fields of the grain boundary region were observed for each sample, and the PFZ width at the widest PFZ width was measured in each field of view. And the average value of PFZ width | variety of 15 places in total was calculated | required, and it was set as the PFZ width | variety of the grain boundary of the test piece. In Table 3, it is shown as “PFZ width”.

3. Mechanical properties Mechanical properties were measured as follows. These results are shown in Table 3.

(Strength)
The strength was evaluated by performing a tensile test on the T6 material after the artificial aging treatment and measuring a 0.2% yield strength (MPa). The tensile test was processed into a JIS No. 5 test piece so that the tensile direction was perpendicular to the rolling direction, and the test piece was broken at a distance of 50 mm and a tensile rate of 5 mm / min based on JIS Z 2241 (2011 revised version). At a constant speed until.
In the present invention, the case where the 0.2% proof stress is 250 MPa or more is regarded as acceptable.

(Bendability)
The bendability is determined by performing a VDA bending test based on the VDA standard “VDA238-100 Plate bending test for metallic materials” stipulated by the German Automobile Manufacturers Association for the T6 material after artificial aging treatment. °). This test method is shown in perspective view in FIG.
First, the plate-like test piece of the T6 material is placed on two rolls arranged parallel to each other with a roll gap, as shown by dotted lines in FIG. . Specifically, the roll gap is set so that the rolling direction of the plate-shaped test piece of the T6 material and the extending direction of the plate-shaped pushing and bending jig arranged vertically upright are perpendicular to each other. It is placed on two rolls horizontally and equally in length so that the central part is located in the center. Then, the pressing and bending jig is pressed against the center of the plate-shaped test piece from above to apply a load, and the plate-shaped test piece is bent toward the narrow roll gap (bending) to bend and deform. The center part of the plate-shaped test piece is pushed into the narrow roll gap.

  At this time, the angle of the bending outside of the center part of the plate-like test piece when the load F from the pushing bending jig from the maximum is measured as a bending angle (°), and the magnitude of the bending angle. Evaluate the shock absorption. It can be said that as the bending angle is larger, the plate-shaped test piece is not crushed in the middle, the bending deformation is continued, the shock absorption (crushing property) is higher, and the bending property is better.

As test conditions for this VDA bending test, the symbols shown in FIG. 1 are used to indicate that the plate-shaped test piece has a square shape of width b: 60 mm × length l: 60 mm, and each of the two roll diameters D is 30 mm. The roll gap L was 4 mm, which is 2.0 times the plate thickness of the plate-shaped test piece. s is the depth of intrusion into the roll gap at the center of the plate-like test piece when the load F is maximum. In addition, as shown in FIG. 1, the plate-like pushing / bending jig presses against the center portion of the plate-like test piece so that the lower end side has a radius of 0.2 mmφ at the tip (lower end). It has a sharp tapered shape. In each example, the above bending test was carried out by three plate-like test pieces (three times), and the average value of the bending angles (°) was adopted.
In the present invention, the case where the VDA bending angle is 60 ° or more is regarded as acceptable.

4). Summary As shown in Tables 1 to 3, the test piece No. Examples 1 to 9 are examples that satisfy all the requirements (composition, production conditions, and structure) defined in the present invention. All of these samples achieved a 0.2% proof stress of 250 MPa or more and a VDA bending angle of 60 ° or more.

  In contrast, no. In No. 10, since the average heating rate in the temperature range of 200 to 450 ° C. in the homogenization heat treatment was small, excessively dispersed particles were precipitated on the grain boundaries, and the PFZ width was increased. As a result, the bendability was insufficient.

No. 11 is an example with a large average heating rate in the temperature range of 450 degreeC-homogenization temperature. As a result, the number density of dispersed particles on the grain boundary increased and the PFZ width increased. As a result, the bendability was insufficient.

  No. No. 12 is an example in which the average heating rate in the temperature range of 200 to 450 ° C. of the homogenization heat treatment is small and the average heating rate from 450 ° C. to the homogenization temperature is large. Therefore, the dispersed particles are excessively precipitated on the grain boundary, the PFZ width is increased, and the bendability is insufficient.

  No. 13 is an example in which the average heating rate in the temperature range of 200 to 450 ° C. of the homogenization heat treatment is small and the average heating rate from 450 ° C. to the homogenization temperature is large. Therefore, the number density of dispersed particles on the grain boundary increased, the PFZ width increased, and the bendability was insufficient.

  No. 14 is an example in which the holding temperature of the solution treatment is low. Therefore, the dispersed particles are excessively precipitated on the grain boundary, the PFZ width is increased, and the strength is insufficient.

  No. No. 15 had a low Mg content, so the PFZ width increased and the strength was insufficient.

  No. No. 16 had a low Si content, so the PFZ width increased and the strength was insufficient.

Claims (5)

Mg: 0.5 to 1.3% by mass,
Si: 0.7-1.5 mass%
Including
Mn: 0.05 to 0.5% by mass,
Zr: 0.04 to 0.20 mass%, and Cr: 0.04 to 0.20 mass%
Further including at least one selected from
The balance is Al and inevitable impurities,
The number density of the transition element-based dispersed particles of 0.05 μm or more present on the grain boundary is 0.001 piece / nm or less,
An Al—Mg—Si-based aluminum alloy plate having a PFZ width of 60 nm or less at a grain boundary after artificial aging treatment that is maintained at 200 to 250 ° C. for 10 to 30 minutes. The aluminum alloy plate according to claim 1, further comprising Cu: more than 0% by mass and 0.5% by mass or less. Sc: 0.02-0.1% by mass
The aluminum alloy plate according to claim 1 or 2, further comprising: Ag: 0.01-0.2% by mass, and Sn: 0.001-0.1% by mass
The aluminum alloy plate according to any one of claims 1 to 3, further comprising one or more selected from the group consisting of:   The aluminum according to any one of claims 1 to 4, wherein the 0.2% proof stress after artificial aging treatment at 200 to 250 ° C for 10 to 30 minutes is 250 MPa or more, and the VDA bending angle is 60 ° or more. Alloy plate.

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