JP2017088906A - Aluminum alloy sheet for automobile structural member and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 6000 series aluminum alloy sheet suitable for an automobile structural member.SOLUTION: Mg amount and Si amount of an Al-Mg-Si-based aluminum alloy sheet is balanced with a specific relation, especially Cube direction is increased as an aggregate structure in a surface area of the sheet, yield ratio of the sheet is reduced, the sheet is made with high strength with 0.2% bearing force of 220 MPa, which is necessary as an automobile structural member and crushability by a VDA flexure test shown in the Figure 1 is enhanced.SELECTED DRAWING: Figure 1

Description

The present invention relates to a 6000 series aluminum alloy plate produced by ordinary rolling (ordinary method) and having excellent crushability, and relates to a method for producing the same.
The aluminum alloy sheet referred to in the present invention is a rolled sheet such as a hot-rolled sheet or a cold-rolled sheet, and after being subjected to tempering such as a solution treatment and a quenching process, the automobile structure used The material aluminum alloy plate before being formed into a member and subjected to artificial age hardening such as paint baking hardening. In the following description, aluminum is also referred to as aluminum or Al.

  In recent years, due to consideration for the global environment, social demands for reducing the weight of automobile bodies are increasing. In order to meet such demands, parts of automobile bodies such as panels (outer panels such as hoods, doors and roofs, inner panels), reinforcements such as bumper force (bumper R / F) and door beams, etc. An aluminum alloy material is applied instead of a steel material such as a steel plate.

  In order to further reduce the weight of automobile bodies, the use of aluminum alloy materials has been expanded to include members such as side members, frames, and automobile structural members such as pillars that contribute to weight reduction. It is necessary to do. However, these automotive structural members have a higher level of strength compared to the above-mentioned automotive panel materials, impact resistance in case of a vehicle collision, and protection of passengers. Characteristic) as a new characteristic.

  In this respect, an extruded profile produced by hot extrusion of a JIS or AA7000 series aluminum alloy has already been widely used as the reinforcing material of the automobile structural member. On the other hand, it is preferable that a large-sized automobile structural member such as the member, frame, pillar, or the like is made of a rolled plate such that the ingot is hot-rolled after soaking or further cold-rolled. However, the above-described 7000 series aluminum alloy has not been practically used so far because it has high strength and poor formability as a rolled sheet.

  For this reason, as an alloy for a rolled sheet manufactured by ordinary rolling (ordinary method), it is an Al—Mg—Si aluminum alloy having a lower strength and better formability than the 7000 series, and is a JIS to AA6000 series. Aluminum alloys are noted.

However, although a 6000 series aluminum alloy extruded shape has been proposed and put to practical use as the reinforcing material, there are not many proposals for rolled plates.
The extent to which a 6000 series aluminum alloy plate with improved crushability, in which the grain size and aspect ratio are controlled as the structure of the plate and the yield strength after artificial aging treatment is 230 MPa or more, is proposed in Patent Document 1 and the like It is.

On the other hand, 6000 series aluminum alloy plates are already used as large body panels (outer panels and inner panels such as hoods, fenders, doors, roofs and trunk lids) of automobiles.
For this reason, in order to combine and improve the press formability and BH property (bake hardness) required for large body panels of these automobiles, conventionally, metallurgical such as component composition, structure, or texture Many improvements have been proposed.

  For example, Patent Document 2 proposes to increase the orientation density of the Cube orientation of the texture to 20 or more in order to improve bending workability such as flat hem processing at the time of press forming as the panel material. Yes.

JP 2001-294965 A Japanese Patent No. 5148930

However, the conventional 6000 series aluminum alloy plate having an increased orientation density and average area ratio in the Cube orientation of the texture is a material for the automobile panel.
On the other hand, in the above-described automotive structural members such as members, frames, and pillars, which are used by the present invention, as described above, unlike such automotive panel uses, further enhancement of strength and crushability are newly added. It is necessary to combine various properties peculiar to this application such as press formability and corrosion resistance.

  As an example of this collapsibility, in recent years the standardization of automobile collision safety standards has been standardized by the German Automobile Manufacturers Association (VDA) for automobile structural members such as frames and pillars in Europe. Satisfying the crushability evaluated by “VDA 238-100 Plate Bending Test for Metallic Materials” (hereinafter referred to as “VDA bending test”).

  On the other hand, in order to improve the bending workability at the time of press forming in a conventional 6000 series aluminum alloy plate for an automobile panel, increasing the orientation density and the area ratio of the Cube orientation on the surface of the plate has been achieved. It is unclear whether it is effective for improving sex.

  Incidentally, the evaluation of the crushability in Patent Document 1 for the purpose of improving the crushability is performed based on the presence or absence of a crack after the 180 ° bending test. It is known that the VDA bending test as an evaluation test of the crushability of the plate has a correlation with the crushability at the time of the automobile collision. The VDA bending test that can express the superiority or inferiority of the crushability by the bending angle is a quantitative evaluation, and can express the crushability more appropriately.

  In view of such a situation, the object of the present invention is to increase the strength of a 6000 series aluminum alloy plate produced by ordinary rolling, and to provide a new crushing property, and has press formability and corrosion resistance. It is to combine various characteristics peculiar to the use of automobile structural members.

  In order to achieve this object, the gist of the aluminum alloy plate for automobile structural members excellent in the pressure-resistant fracture resistance of the present invention is mass%, Mg: 0.3-1.0%, Si: 0.5-1 0.2% and Cu: 0.08 to 0.20%, respectively, and the Mg content [Mg] and the Si content [Si] are [Si] / [Mg] ≧ 0 .7 and 1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9%, respectively, the balance is made of Al and inevitable impurities, and the plate thickness is 2.0 mm or more. An Al—Mg—Si-based aluminum alloy plate having an average area ratio of Cube orientation of 22% or more in a surface region from the surface of the plate to a depth of 10% of the plate thickness, and a yield ratio of the plate of 0 And after the aluminum alloy sheet was subjected to artificial aging treatment at 180 ° C. for 20 minutes after stretching by 2%. As properties, a 0.2% proof stress above 220 MPa, and the bending angle at the VDA bending test is to have a crush resistance is 60 ° or more.

  Moreover, in order to achieve the said objective, the summary of the manufacturing method of the aluminum alloy plate for motor vehicle structural members excellent in the fracture resistance of this invention is the mass%, Mg: 0.3-1.0%, Si: 0.5 to 1.2% and Cu: 0.08 to 0.20%, respectively, and the Mg content [Mg] and the Si content [Si] are [Si] / Al—Mg—Si satisfying the relationship of [Mg] ≧ 0.7 and 1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9%, the balance being Al and inevitable impurities The aluminum alloy ingot is rolled after homogenization heat treatment to obtain a rolled plate having a plate thickness of 2.0 mm or more, and the solution is held for 0.1 to 30 seconds in the range of 540 to 570 ° C. with respect to this rolled plate The material temperature is 60 to 90 by performing reheating treatment within 10 minutes after completion of the quenching treatment. Cubic orientation in the surface region from the surface of the plate to a depth of 10% of the plate thickness is made as an aluminum alloy plate for automobile structural members by holding in the range of ° C for 3 to 20 hours. The average area ratio is 22% or more, the yield ratio of this plate is 0.63 or less, and the plate is stretched 2% and then subjected to artificial aging treatment at 180 ° C. for 20 minutes. The 2% proof stress is 220 MPa or more, and the bending angle in the VDA bending test is 60 ° or more.

In the present invention, on the assumption that the conventional aluminum alloy composition and manufacturing conditions are not greatly changed, the alloy composition of the 6000 series aluminum alloy sheet is specific to the balance of Mg and Si content and texture, and the use of automobile structural members. The relationship with the above characteristics was reviewed again.
As a result, it is possible to balance the contents of Mg and Si, increase the Cube orientation area ratio, etc., and further increase the strength and crushability, and then press formability and corrosion resistance. It has been found that various properties peculiar to this use can be combined.
According to the present invention, a 6000 series aluminum alloy plate suitable for automobile structural members can be obtained by a conventional method.

It is a perspective view which shows the aspect of the VDA bending test which evaluates crushability. It is the front and side view of the punch of FIG.

Hereinafter, embodiments of the present invention will be specifically described for each requirement.
As a premise thereof, the use of the Al—Mg—Si-based (hereinafter also referred to as 6000-based) aluminum alloy plate of the present invention is not the conventional automotive panel material but the automotive structural member.
For this reason, as a required characteristic of this automobile structural member (hereinafter, also simply referred to as a structural member), the above-described conventional automobile panel material has excellent crushability and can be processed into a complicated shape with a low yield ratio. It is possible to satisfy and satisfy various properties of high inter-bake strength and high intergranular corrosion resistance. Any of these characteristics is not applicable as a structural member.

More specifically, the required characteristics of these structural members have a press formability with a yield ratio of 0.63 or less, and the aluminum alloy sheet was subjected to artificial aging treatment at 180 ° C. for 20 minutes after stretching 2%. As the later characteristics, it can be defined as having a BH property of 0.2% proof stress of 220 MPa or more and a crushing property of a bending angle of 60 ° or more in the VDA bending test.
More preferably, the average area ratio of the Cube orientation of the aluminum alloy plate is 35% or more, and the aluminum alloy plate has a crushing property with a bending angle of 90 ° or more in the VDA bending test. .

  Therefore, the following description of the requirements of the present invention is intended for these structural members and is meaningful in order to satisfy and satisfy specific required characteristics.

Chemical composition (alloy) composition:
In the present invention, in order to satisfy the required characteristics of the structural member from the viewpoint of composition, the composition of the Al—Mg—Si-based (hereinafter also referred to as 6000-based) aluminum alloy plate is expressed in terms of mass%, Mg: 0.00. 3 to 1.0%, Si: 0.5 to 1.2%, Cu: 0.08 to 0.20%, respectively, and the Mg content [Mg] and the Si content [Si] satisfies [Si] / [Mg] ≧ 0.7 and 1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9%, with the balance being Al and It shall consist of inevitable impurities.

  The content range and significance of each element in the 6000 series aluminum alloy, or the allowable amount will be described below. In addition,% display of content of each element means the mass% altogether.

Mg: 0.3-1.0%
Mg, together with Si, forms a compound phase such as Mg ₂ Si during an artificial aging treatment such as a baking coating treatment, and the strength is increased by precipitation of this compound phase.
If the Mg content is too low, less than 0.3%, sufficient strength cannot be obtained.
On the other hand, if the Mg content exceeds 1.0% and is too large, a compound phase such as Mg ₂ Si crystallizes or precipitates as coarse particles during casting and solution hardening treatment, and the origin of minute fracture Work as. For this reason, the yield ratio increases and the press formability decreases due to a decrease in the fracture limit.
Therefore, the Mg content is set to 0.3 to 1.0%.

Si: 0.5-1.2%
Si, together with Mg, forms a compound phase such as Mg ₂ Si during artificial aging treatment such as baking coating treatment, and the compound phase precipitates to increase the strength.
If the Si content is too low, less than 0.5%, sufficient strength cannot be obtained.
On the other hand, if the Si content exceeds 1.2% and the compound phase such as Mg ₂ Si is crystallized or precipitated as coarse particles during casting and solution hardening, the origin of minute fracture Work as. For this reason, the yield ratio increases and the press formability decreases due to a decrease in the fracture limit.
Therefore, the Si content is 0.5 to 1.2%.

Mg content [Mg] and Si content [Si]
The content of Mg and the content of Si, in addition to the above-mentioned respective contents, are important in order to improve press formability and crushability in terms of composition.
In this regard, the Mg content [Mg] and the Si content [Si] are [Si] / [Mg] ≧ 0.7 and 1.4% ≦ 1.3 [Mg] + The relationship of [Si] ≦ 1.9% is satisfied.

[Si] / [Mg] ≧ 0.7
The higher the Si content and the lower the Mg content, the higher the work hardening ability, the lower the yield ratio, and the higher the press formability due to the solid solution strengthening due to the solid solution of Si in the matrix. To do.
When [Si] / [Mg] is less than 0.7, sufficient work hardening ability cannot be obtained, and the yield ratio increases, so that press formability is lowered.
Accordingly, [Si] / [Mg] is set to 0.7 or more. In addition, if [Si] / [Mg] is 1.8 or more, the yield ratio is further reduced and press formability is improved. Preferably, [Si] / [Mg] is 1.8 or more. .

1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9%
Si and Mg form a β ″ phase that becomes a strengthening phase after baking hard (artificial age hardening treatment), and this compound phase precipitates to increase the strength.
However, if it contains too much Mg or Si, the compound phase such as Mg ₂ Si crystallizes or precipitates as coarse particles during casting and solution hardening treatment, and acts as a starting point for minute fractures. Decrease greatly. These crystallization states or precipitation states depend on the contents of Si and Mg.
If 1.3 [Mg + [Si] is less than 1.4%, sufficient BH properties (bake strength after baking) cannot be obtained.
On the other hand, if 1.3 [Mg] + [Si] exceeds 1.9%, it crystallizes or precipitates as coarse grains during casting and quenching, and the crushability is significantly reduced.
Therefore, 1.3 [Mg] (= 1.3 × meaning Mg content) + [Si] (meaning Si content) is in the range of 1.4 to 1.9%, preferably 1.6 to The range is 1.9%.

Cu: 0.08 to 0.20%
Cu dissolves in the matrix and improves the work hardening ability by solid solution strengthening, reduces the yield ratio, and improves the press formability.
However, if the Cu content exceeds 0.20%, Cu solute-deficient layer PFZ is formed in the vicinity of the grain boundary along with aging precipitation, and in the corrosive environment, the layer that is lower in potential than the inside of the grain is formed. It dissolves selectively and the intergranular corrosion resistance deteriorates.
On the other hand, if the Cu content is less than 0.08%, sufficient work hardening ability cannot be obtained, and the yield ratio cannot be reduced, and the press formability is lowered.
Therefore, the Cu content is in the range of 0.08 to 0.20%.

Other Elements In the present invention, other elements are basically impurities, and the following upper limit is set as an allowable amount when contained from a melting raw material of an ingot such as scrap. The following upper limit regulations include 0%.
Mn: 1.0% or less, Fe: 0.5% or less, Cr: 0.3% or less, Zr: 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zn: 0.5% or less, Ag: 0.1% or less, Sn: 0.15% or less.

BH property (bake hard property, artificial age hardening):
In order to have the necessary strength and rigidity as an automotive structural member, an aluminum alloy plate is subjected to artificial age hardening treatment (hereinafter simply referred to as aging) under specific conditions at 180 ° C. for 20 minutes after stretching 2% for reproducibility. BH property is defined after the processing.
As an automobile structural member, the higher the BH property, the better. However, in the present invention, a material having a BH property of 0.2 MPa proof stress of 220 MPa or more is regarded as acceptable.

Yield ratio:
A low yield ratio indicates a low yield strength for tensile strength. The higher the tensile strength with respect to the proof stress, the higher the breaking limit, and the lower the proof strength with respect to the tensile strength, the smaller the springback amount and the better the press formability. Therefore, in order to have press formability that can be processed into a complicated structural member shape, the yield ratio is set to 0.63 or less.

Thickness:
The thickness of the aluminum alloy plate is required to be 2.0 mm or more in order to have the necessary strength and rigidity as an automobile structural member. The upper limit of the plate thickness is not particularly defined, but is about 4.0 mm in consideration of the limit of forming process such as press forming and the range of weight increase that does not impair the lightening effect from the steel plate as a comparative material. From this preferable thickness range (2.0 to 4.0 mm), a hot rolled sheet or a cold rolled sheet is appropriately selected.

Area ratio of Cube orientation:
In the present invention, in order to improve the crushability (crush resistance, crushing characteristics) of the plate, the area ratio of the Cube orientation in an arbitrary surface region from the surface of the plate to a depth of 10% of the plate thickness is 22% or more. And
Here, the “surface of the plate” in the present invention means the surface of a natural oxide film (thickness of several tens to several hundreds nm) formed on (surface) the aluminum alloy matrix.
In the surface area from the surface of this plate to the depth of 10% of the plate thickness in the plate thickness (depth) direction, when the layer containing the Cube orientation exists in the vicinity of the surface of the plate thickness, the area ratio of the Cube orientation Is higher, the formation of shear bands on the outer side of the bend is suppressed, and the crushability of the plate is improved.
Since the standard of the thickness of the outer bending layer that has a significant influence on the crushability is about 10% of the plate thickness, an area where the area ratio of the Cube orientation is high is within the range of 10% of the plate thickness from the surface of the plate. Arbitrary area (range).

If the Cube orientation area ratio of the surface region is smaller than 22%, the crushability is significantly deteriorated.
Therefore, the Cube orientation area ratio of this surface region is set to 22% or more, and if the Cube orientation area ratio is more than 35%, the crushability is excellent. Preferably, the Cube orientation area ratio of this surface region is 35% or more. And

Measurement of area ratio of Cube orientation:
The average area ratio of the Cube orientation of the crystal grains of these plates was taken from an arbitrary depth position in the surface region (range) from the surface of the plate to the depth of 10% of the plate thickness in the depth direction. As an observation surface extending in parallel with the rolling surface (rolling surface) of the measurement sample (three pieces) in plan view of the plate (measurement sample), the surface region from the surface of the plate to a depth of 10% of the plate thickness Of these, polishing is performed by mechanical polishing or buffing so that an observation surface at an arbitrary depth position appears.

About the test piece obtained in this way, using SEM-EBSD, the measurement range of a rectangular region in which the length of the side in the rolling direction of the plate is 1000 μm × the length of the side in the plate width direction is 320 μm on the observation surface In contrast, the electron beam is irradiated at a pitch of 5 μm.
As the SEM apparatus, for example, SEM (JEOLJSM5410) manufactured by JEOL Ltd., EBSD measurement / analysis system manufactured by TSL: OIM (Orientation Imaging Macrograph, analysis software name “OIM Analysis”) is used, and each crystal grain has a Cube orientation. It is determined whether or not (within 15 ° from the ideal orientation), and the area of each crystal orientation in the measurement visual field is obtained.
This measurement is performed, for example, by scanning an electron beam at a step interval of 5 μm, and the crystal orientation of each measurement point is measured and analyzed in combination with the measurement point position data. Measure orientation.
And the average area ratio (%) with respect to the area (320,000 micrometers ² ) of the said measurement range which is a measurement total area of the crystal grain which has Cube orientation per sample is measured, and also it averages by the number of the measured samples 3 pieces Turn into.

The SEM-EBSD (EBSP) method is a general-purpose field-emission scanning electron microscope (FESEM) equipped with an EBSD (Electron Back Scattering (Scattered) Diffraction Pattern) system. This is a crystal orientation analysis method.
More specifically, in the preparation of the observation sample of SEM-EBSD, the observation sample (cross-sectional structure) is further mechanically polished into a mirror surface. Then, it is set in a lens barrel of FESEM, and an electron beam is irradiated onto the mirror-finished surface of the sample to project EBSD (EBSP) on the screen. This is taken with a high-sensitivity camera and captured as an image on a computer. In the computer, the orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. The calculated crystal orientation is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, crystal orientation data of tens of thousands to hundreds of thousands of points in the cross section of the plate can be obtained at the end of measurement.
For this reason, there is an advantage that the observation field is wide, and the distribution state, the average crystal grain size, the standard deviation of the average crystal grain size, or the information of orientation analysis can be obtained within a few hours for a large number of crystal grains. Therefore, it is optimal when accurately measuring the texture such as the area ratio of the Cube orientation as in the present invention.

In the case of an aluminum alloy plate, a texture composed of many orientation factors (crystal grains having these orientations) shown below is usually formed, and there are crystal planes corresponding to them. In general, the texture in an aluminum alloy rolled recrystallized plate is mainly composed of a Cube orientation, a Goss orientation, a Brass orientation, an S orientation, and a Copper orientation. In the case of a texture of a sheet material by rolling, these texture expressions are expressed by a rolling surface and a rolling direction, the rolling surface is expressed by {hkl}, and the rolling direction is expressed by <uvw>. Based on this expression, each direction is expressed as follows.
Cube orientation {001} <100>
Goss orientation {011} <100>
Brass orientation (B orientation) {011} <211>
Cu orientation (Copper orientation) {112} <111>
S orientation {123} <634>

Crushability:
Crushability is the property that when a shocking load such as a car crash is applied, the structural member does not crack or collapse in the initial stage or on the way of deformation (or even if it occurs) and deforms to the end. In addition, a member having good crushability is bent and deformed into a bellows shape without cracking or crushing (or even if it occurs).
In the present invention, the crushability is evaluated as acceptable for a vehicle structural member having a crushing property of a bending angle of 60 ° or more in the VDA bending test. The larger the bending angle, the higher the crushability, and 90 ° or more is more preferable. On the other hand, if the bending angle is less than 60 °, it cannot be used for automobile structural members.

This bending test for evaluating the crushability is carried out as a VDA bending test in accordance with “VDA 238-100 Plate Bending Test for Metallic Materials” in the standards of the German Automobile Manufacturers Association (VDA).
This test method is shown in perspective view in FIG. 1 and in front and side views of the punch used in FIG.
First, a plate-shaped test piece is placed on two rolls arranged parallel to each other with a roll gap, as shown by dotted lines in FIG.
Specifically, the plate-shaped test piece is placed at the center of the roll gap so that the rolling direction and the extending direction of the plate-shaped pushing and bending jig arranged vertically are perpendicular to each other. It is placed horizontally and equally on the left and right on the two rolls so that the central part is located.
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, when the load F from the upper bending jig is maximized (just before the bending tip at the center of the plate test piece breaks), the angle of the bending outside of the center of the plate test piece is the bending angle. The degree of crushability is evaluated by measuring as (°) and the bending angle. The larger the bending angle, the more the plate-shaped test piece is not crushed in the middle, the bending deformation is continued, and the crushability is higher.

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 the two roll diameters D are respectively 30 mm and the roll gap L were 2.0 times the plate-shaped test piece plate thickness (in the examples described later, 2.0 mm of the cold-rolled plate thickness 2.5 mm, 5 mm). 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. 2, the punch, which is a plate-like pushing and bending jig, has a tip of the lower thin plate-like (thickness 2 mm) blade that presses against the center portion of the plate-like test piece. The taper shape has a sharp radius r of 0.2 mmφ.

Production method:
Next, a method for producing the aluminum alloy plate of the present invention will be described below. The aluminum alloy sheet of the present invention is a conventional process or a known process, and the aluminum alloy ingot having the above-mentioned 6000 series component composition is subjected to homogenization heat treatment after casting, and then subjected to hot rolling and cold rolling to obtain a predetermined process. It is manufactured by being subjected to a tempering treatment such as solution hardening and quenching.

  However, in these manufacturing processes, in order to obtain a texture defined by the present invention, as described later, the rolling rate condition of the cold rolling is in a preferred range, the pre-aging treatment conditions after solution treatment and quenching treatment, The preferable range.

(Dissolution, casting cooling rate)
First, in the melting and casting process, an ordinary molten casting method such as a continuous casting method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten aluminum alloy adjusted to be dissolved within the above-mentioned 6000 series component composition range. Cast.

(Homogenization heat treatment)
Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling. This homogenization heat treatment (uniform heat treatment) is important for sufficiently dissolving Si and Mg in addition to the normal purpose of homogenizing the structure (eliminating segregation in crystal grains in the ingot structure). It is. The conditions are not particularly limited as long as the object is achieved, and normal one-stage or one-stage processing may be performed.

  The homogenization heat treatment temperature is appropriately selected from the range of 500 ° C. or more and 560 ° C. or less, and the homogenization (retention) time is 1 hour or more. If this homogenization temperature is low, segregation within the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that the crushability may be lowered.

(Hot rolling)
After performing this homogenization heat treatment, hot rolling is performed to produce a hot rolled sheet. Hot rolling is composed of an ingot (slab) rough rolling process and a finish rolling process according to the thickness of the rolled sheet. In these rough rolling process and finish rolling process, a reverse or tandem rolling mill is appropriately used.
The hot-rolled sheet retains the hot-rolled processed structure, and the degree of accumulation of the Cube orientation increases, and the average area ratio of the Cube orientation in the surface region from the surface of this plate to a depth of 10% of the plate thickness is It becomes preferable 35% or more, and the crushability is remarkably improved. Therefore, it is good also as a product board of the final board thickness of 2.0 mm or more with a hot-rolled sheet, without performing cold rolling with respect to a hot-rolled sheet.

(Cold rolling)
When the hot-rolled sheet is cold-rolled to have a desired thickness, the hot-rolled processed structure remains, the degree of accumulation of the Cube orientation is increased, and 10% of the sheet thickness is increased from the surface of the sheet. In order to increase the average area ratio of the Cube orientation in the surface region up to the depth to 22% or more, preferably 35% or more, it is preferable to set the cold rolling rate to 70% or less and the smallest possible rolling rate.
When the rolling rate of the cold rolling is higher than 70%, a uniform strain is introduced in the thickness direction after the cold rolling, resulting in uniform fine and equiaxed grains during the solution heat treatment, but other than the Cube orientation. As the area ratio of the crystal orientation increases, the Cube orientation area ratio of the surface region from the plate surface to a depth of 10% of the plate thickness inevitably becomes smaller than 22%, and the crushability may be deteriorated. .
In this respect, the rolling rate of cold rolling is preferably as small as less than 5%. When the rolling ratio of the cold rolling is less than 5%, almost no strain is introduced by the cold rolling, and as in the hot-rolled sheet, the structure as hot-rolled remains and the degree of accumulation of the Cube orientation is increased. The Cube orientation area ratio in the surface region from the plate surface to a depth of 10% of the plate thickness becomes 35% or more, and the crushability is remarkably improved. Therefore, the rolling rate of cold rolling is preferably less than 5%.
In addition, you may perform intermediate annealing suitably between cold rolling passes.

(Solution and quenching)
After the cold rolling, solution treatment and subsequent quenching to room temperature are performed. For this solution hardening treatment, a normal continuous heat treatment line may be used. However, in order to obtain a sufficient solid solution amount of each element such as Mg and Si, quenching is performed after holding at a solution treatment temperature (attainment temperature) of 540 ° C. or more and 570 ° C. or less for 0.1 second to 60 seconds. It is preferable to carry out the treatment continuously.
When the solution temperature is lower than 540 ° C., sufficient solid solubility of Mg and Si is not ensured, and sufficient post-baking strength may not be obtained. On the other hand, when the solution temperature exceeds 570 ° C., it is close to the melting point and may be melted during the solution treatment. If the retention time for solution treatment is longer than 60 seconds, the initial strength is high and the yield ratio may increase. Accordingly, the solution temperature is preferably 540 ° C. to 570 ° C., and the solution retention time is preferably 0.1 to 60 seconds.

  The quenching process that follows the solution treatment is performed in order to ensure a cooling rate such that Mg-Si-based precipitates are generated during cooling and the solid solution Mg amount and the solid solution Si amount do not decrease. Water cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion are selected and used.

(Reheating treatment: preliminary aging treatment)
After such solution treatment, after quenching and cooling to room temperature (after completion of quenching), perform reheating treatment and keep the material temperature in the range of 60 to 90 ° C. for 3 to 20 hours. Is preferred.
If the room temperature holding time until the start of reheating treatment (heating start) is too long, Si-rich Mg-Si clusters are generated due to room temperature aging, and Mg-Si clusters with a good balance between Mg and Si are increased. Since it becomes difficult to perform, the BH property may be lowered. Accordingly, the shorter the room temperature holding time is better, the solution treatment and quenching treatment and the reheating treatment may be continued so that there is almost no time difference, and the lower limit time is not particularly set.

In the reheating treatment, by holding at 60 to 90 ° C. for 3 to 20 hours, the Mg—Si cluster having a good balance between Mg and Si is formed, and the BH property is improved.
When the reheat treatment temperature is less than 60 ° C. or the holding time is less than 3 hours, it is difficult to increase the Mg—Si cluster having a good balance between Mg and Si, as in the case where the reheat treatment is not performed. Therefore, the yield strength (BH property) after baking coating tends to be low.
On the other hand, when the reheating treatment temperature exceeds 90 ° C. or the holding time exceeds 20 hours, the initial strength is high and the yield ratio may increase.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  Mechanical properties such as yield ratio, strength, etc. after BH with respect to the texture of the 6000 series aluminum alloy cold-rolled sheet of each component composition shown in Table 1 with various production conditions changed as shown in Table 2 The intergranular corrosion resistance was evaluated as the crushability evaluated in the VDA bending test and the corrosion resistance necessary as a structural member. These results are also shown in Table 2.

An aluminum alloy having the chemical composition shown in Table 1 is melt cast, and the resulting ingot is homogenized under conditions of 540 ° C. × 4 hours, followed by hot rolling at 260 ° C. to 350 ° C. as it is. Went. Next, it cold-rolled by each rolling rate shown in Table 2 so that the final board thickness might be set to 2.5 mm, and it was set as the cold rolled sheet.
Thereafter, this cold-rolled sheet is heated at a heating rate of 100 ° C./min or more, and after the solution treatment at each temperature and each holding time shown in Table 2, the solution hardening and quenching treatment is continued until it is immersed in water to room temperature. I went. Then, what performed a reheating process reheated to each temperature range shown in Table 2, made the time hold | maintained at 60 degreeC or more into the conditions shown in Table 2, and it stood to cool to room temperature after that.

  Samples are taken from this aluminum alloy plate, and the texture and yield ratio of the surface region of the cross section are measured. Further, mechanical properties and crushability after BH, and the resistance usually required for automobile structural members are obtained. Intergranular corrosion was investigated.

Average area ratio of Cube orientation:
The area ratio (%) of the Cube orientation is mechanically polished with respect to the cross section perpendicular to the plate width direction of the test material after the reheating treatment, and after electrolytic polishing, the plate width surface in the surface region is measured by SEM-EBSD method. The crystal orientation in the normal direction was measured.
The crystal orientation deviation within ± 5 ° was defined as belonging to the same crystal orientation. Table 2 shows the average area ratio of the Cube orientation in the surface region from the plate surface to a depth of 10% of the plate thickness.

Mechanical properties:
The mechanical properties were obtained by carrying out a tensile test under the following conditions.
The yield ratio was determined for the test material after 6 months (after aging at room temperature) after the reheating treatment, and as a structural member, the yield ratio was 0.63 or less, 0.60 or less was even better. 64 or more was regarded as defective.
The yield strength after BH was also measured at 180 ° C. after applying a pre-strain of 2% simulating press forming of a plate to a test material 6 months after the reheating treatment (after aging at room temperature) using a tensile tester. The proof stress of an artificially aged product (AB material) was measured under the heat treatment conditions for 1 minute. And for structural members, it was evaluated that 220 MPa or more passed and 230 MPa was even better.

  In the tensile test, No. 5 test pieces (25 mm × 50 mmGL × plate thickness) of JISZ2201 were sampled from the respective test materials and subjected to a tensile test at room temperature. The tensile direction of the test piece at this time was the direction perpendicular to the rolling direction. The tensile speed was 5 mm / min up to 0.2% proof stress and 20 mm / min after proof stress. The N number for the measurement of mechanical properties was 5, and each was calculated as an average value.

Crushability:
Crushability is determined by artificial aging under conditions of heat treatment at 180 ° C. for 20 minutes after applying a pre-strain of 2% to the specimen after 6 months (after room temperature aging) after the reheating treatment. This was used as a measurement target of the VDA bending test.

Each specimen was stretched 2% in a direction perpendicular to the rolling direction, and cut into square test pieces having a plate thickness of 2.5 mm, a width b of 60 mm, and a length l of 60 mm.
Using this test piece, a three-point bending test was performed in which the bending line was parallel to the rolling direction in accordance with VDA238-100. The test speed until the load reached 30 N was 10 mm / min, and the test speed thereafter was 20 mm / min. The bending process is set to stop when the maximum load is reduced by 60 N due to the occurrence of cracks or the reduction of the plate thickness.
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.
And, for the structural member, the maximum bending angle of the plate-shaped test piece after this bending test (when the load F from the push-bending jig is maximized = just before the bending tip of the center portion of the plate-shaped test piece breaks) When the bending angle was 90 ° or more, it was evaluated as “以上”, when it was 60 ° or more, “good”, and less than 60 ° was evaluated as “poor”.

Intergranular corrosion resistance:
The intergranular corrosion resistance evaluation test was based on ISO11846 Method B.
The test material was artificially subjected to heat treatment at 180 ° C. for 20 minutes after 2% pre-strain was applied to the test material after 6 months (after room temperature aging) after the reheating treatment. In order to remove the surface film, the film was aged and immersed in 5% NaOH (60 ° C.) for 1 minute, washed with water, immersed in 70% HNO ₃ for 1 minute, washed again with water, and dried at room temperature.
An aqueous solution containing HCl and NaCl (containing 30 g / L of NaCl and 10 ± 1 ml / L of 36% concentrated hydrochloric acid) was used as the corrosive solution, and the corrosive solution was 5 ml per 1 cm ² of the surface area of the material at 25 ° C. for 24 hours. It was immersed in the liquid. Next, the corrosion products were removed by immersion in 70% HNO ₃ and brushing with a plastic brush, washed with water, and dried at room temperature.
Three sites where corrosion was judged to be deep by the depth of focus method were selected, and each site was embedded in a cross-section, and the depth of intergranular corrosion at each cross-section was measured with an optical microscope.
The three specimens taken from three arbitrary locations on the plate were used, and the maximum intergranular corrosion depth was less than 300 μm among the three specimens measured for structural members. Those with a value of ○ were accepted with a circle, and those with 300 μm or more were rejected with a ×.

As is clear from Tables 1 and 2, each of the inventive examples is within the composition range of the aluminum alloy of the present invention, and is manufactured within the range of the preferred conditions described above.
As a result, as shown in Table 2 above, Invention Example No. 1 to 11, the average area ratio of the Cube orientation in the surface region from the surface of this plate to the depth of 10% of the plate thickness is 22% or more, the yield ratio is 0.63 or less, and the aluminum alloy As a characteristic after the artificial aging treatment at 180 ° C. for 20 minutes after stretching 2% of the plate, it has a 0.2% proof stress of 220 MPa or more, and has a crushing property with a bending angle of 60 ° or more in the VDA bending test. doing.

Among these, in particular, Invention Example No. In Nos. 1 and 2, the Cube area ratio in the surface region from the plate surface to a depth of 10% of the plate thickness was 35% or more, and thus further excellent crushability was exhibited.
In addition, Invention Example No. 3 is that the Mg content [Mg] and the Si content [Si] are further [Si] / [Mg] ≧ 1.8 and 1.6% ≦ 1.3 [Mg]. In order to satisfy the relationship of + [Si] ≦ 1.9%, an excellent yield ratio and post-BH yield strength were exhibited.

  On the other hand, as shown in Table 1, each comparative example is manufactured by deviating from the above-mentioned range of preferable hot rolling conditions although the alloy composition is out of the scope of the present invention or the alloy composition is within the scope of the present invention. ing. As a result, as shown in Table 2, the average area ratio and yield ratio of the Cube orientation do not satisfy the requirements, and the strength and crushability after BH, or intergranular corrosion properties are inferior.

Comparative Example No. Nos. 12 to 23 have an alloy composition outside the scope of the invention.
Comparative Example No. 12 and 13 are alloy numbers 6 and 7 in Table 1, and the Mg content is less than the lower limit (Comparative Example No. 12 is less than the lower limit of 1.3 [Mg] + [Si]). Post-proof strength is inferior.
Comparative Example No. 14 is Alloy No. 8 in Table 1, and since the Mg content exceeds the upper limit value, the yield ratio exceeds 0.63. Moreover, since 1.3 [Mg] + [Si] exceeds the upper limit of the present invention, the crushability is inferior.
Comparative Example No. 15 is the alloy number 9 of Table 1, and since 1.3 [Mg] + [Si] exceeds the upper limit, the crushability is inferior.
Comparative Example No. No. 16 is alloy number 10 of Table 1, and since the Si content is less than the lower limit, the post-BH yield strength is inferior. Further, since [Si] / [Mg] is less than the lower limit value, the yield ratio exceeds 0.63.
Comparative Example No. 17 is Alloy No. 11 in Table 1, and since the Si content exceeds the upper limit, the yield ratio exceeds 0.63. Moreover, since 1.3 [Mg] + [Si] exceeds the upper limit, the crushability is inferior.
Comparative Example No. 18 is alloy number 12 of Table 1, and since 1.3 [Mg] + [Si] exceeds the upper limit, the crushability is inferior.
Comparative Example No. 19 is alloy number 13 of Table 1, and since Cu is less than a lower limit, the yield ratio exceeds 0.63. Moreover, the yield strength after baking is also inferior.
Comparative Example No. 20 is alloy number 14 of Table 1, and since Cu has exceeded the upper limit, intergranular corrosion property is inferior.
Comparative Example No. 21 is Alloy No. 15 in Table 1, and the yield ratio exceeds 0.63 because the Mg content is less than the lower limit and [Si] / [Mg] is less than the lower limit of the present invention. Moreover, since 1.3 [Mg] + [Si] is less than the lower limit of the present invention, the yield strength after BH is inferior.
Comparative Example No. No. 22 is alloy number 16 in Table 1, and 1.3 [Mg] + [Si] is less than the lower limit value, so the post-BH yield strength is inferior.
Comparative Example No. 23 is alloy number 17 of Table 1, and since 1.3 [Mg] + [Si] exceeds the upper limit, the crushability is inferior.

Comparative Example No. 24 to 35, alloy numbers 1 and 2 in Table 1, and the alloy composition is within the scope of the invention, but the production method is out of the preferred range.
Comparative Example No. Nos. 24 and 25 are inferior in crushability because the rolling ratio of the cold rolling is too high and the Cube average area ratio of the surface area of the plate is less than 22%.
Comparative Example No. Since No. 26 does not perform a reheating process, the post-baking yield strength is inferior.
Comparative Example No. 27 and 28 are inferior in post-baking proof stress because no reheating treatment is performed. Moreover, since the rolling rate of cold rolling was too high and the Cube average area ratio of the surface area of the plate was less than 22%, the crushability was inferior.
Comparative Example No. No. 29 is inferior in yield strength after BH because the solution temperature is less than the preferred lower limit.
Comparative Example No. No. 30, because the solution retention time exceeds the preferred upper limit, so the yield ratio exceeds 0.63.
Comparative Example No. No. 31 has poor post-BH yield strength because the time required for reheating exceeds 10 minutes.
Comparative Example No. No. 32 is inferior in yield strength after BH because the reheating temperature is less than the preferred lower limit.
Comparative Example No. In No. 33, since the reheating temperature exceeds the preferable upper limit value, the yield ratio exceeds 0.63.
Comparative Example No. No. 34 is inferior in post-BH yield strength because the retention time of 60 ° C. or higher is less than the preferred lower limit after reheating.
Comparative Example No. No. 35 has a retention ratio of 60 ° C. or higher after the reheating exceeds the preferable upper limit value, so the yield ratio exceeds 0.63.

  Therefore, the results of the above examples support the significance of satisfying all the compositions and structures defined in the present invention for automobile structural members.

  According to the present invention, a 6000 series aluminum alloy sheet produced by ordinary rolling is used for automobile structural members such as pressurization and corrosion resistance after increasing strength and providing new crushability. Can have various characteristics peculiar to. For this reason, application of a 6000 series aluminum alloy plate can be expanded as an automobile structural member.

Claims (4)

  In mass%, Mg: 0.3-1.0%, Si: 0.5-1.2%, Cu: 0.08-0.20%, respectively, and the content of Mg [Mg] And the Si content [Si] is as follows: [Si] / [Mg] ≧ 0.7 and 1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9% Each is an Al—Mg—Si based aluminum alloy plate, the balance of which is made of Al and inevitable impurities, and the plate thickness is 2.0 mm or more, from the surface of this plate to a depth of 10% of the plate thickness. After the average area ratio of Cube orientation in the surface region is 22% or more and the yield ratio of this plate is 0.63 or less, the aluminum alloy plate is subjected to artificial aging treatment at 180 ° C. for 20 minutes after stretching by 2%. As characteristics, the 0.2% proof stress is 220 MPa or more, and the bending angle in the VDA bending test is 60 ° or more. Automobile structural member for an aluminum alloy sheet and having a to crushing.   The Mg content [Mg] and the Si content [Si] of the aluminum alloy plate are further set to [Si] / [Mg] ≧ 1.8 and 1.6% ≦ 1.3 [ The aluminum alloy plate for automotive structural members according to claim 1, wherein the relationship of Mg] + [Si] ≤1.9% is satisfied.   3. The automobile according to claim 1, wherein the aluminum alloy plate has a crushing property in which an average area ratio of the Cube orientation is 35% or more and a bending angle in the VDA bending test is 90 ° or more. Aluminum alloy plate for structural members. In mass%, Mg: 0.3-1.0%, Si: 0.5-1.2%, Cu: 0.08-0.20%, respectively, and the content of Mg [Mg] And the Si content [Si] is as follows: [Si] / [Mg] ≧ 0.7 and 1.4% ≦ 1.3 [Mg] + [Si] ≦ 1.9% An Al—Mg—Si-based aluminum alloy ingot consisting of Al and inevitable impurities in the balance is rolled after homogenization heat treatment to obtain a rolled plate having a plate thickness of 2.0 mm or more. The solution treatment and the quenching treatment, which are held in the range of 540 to 570 ° C. for 0.1 to 30 seconds, are continuously performed, and within 10 minutes after the quenching treatment is completed, the reheating treatment is performed and the material temperature is 60. Hold for 3 to 20 hours in the range of ~ 90 ° C to make an aluminum alloy plate for automobile structural members. As the structure and characteristics of this plate, this plate The average area ratio of the Cube orientation in the surface region from the surface of the sheet to a depth of 10% of the plate thickness is set to 22% or more, and the yield ratio of the plate is set to 0.63 or less. After being subjected to an artificial aging treatment at 180 ° C. for 20 minutes, the 0.2% proof stress is 220 MPa or more, and the bending angle in the VDA bending test is 60 ° or more. A method for producing an aluminum alloy plate for an automotive structural member.