JP2005256053A - Aluminum alloy sheet having excellent bending workability and press formability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg-Si-based Al alloy sheet which has excellent bending workability, such as hem processing, and press formability, and has other characteristics required at the time of panel formation, such as low-temperature aging hardenability, in combination. <P>SOLUTION: The Al-Mg-Si-based aluminum alloy sheet controlled in cube orientation distribution density and anisotropy of an (r) value is formed of such a structure that the cube orientation distribution density of the aluminum alloy sheet ranges from 10 to 30 and that Δr ranges from 0.2 to 1.4. The aluminum alloy sheet is thereby provided with the bending workability and the press formability or is provided with the other characteristics required at the time of panel formation in combination as well. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is excellent in bending workability such as hem processing even when room temperature aging has progressed after manufacturing the plate, and is excellent in other properties required for forming panels such as press formability and low temperature aging hardening ability. The present invention relates to an Al-Mg-Si aluminum alloy plate (hereinafter, aluminum is also simply referred to as Al).

  Conventionally, Al-Mg-based AA to JIS with excellent processability (hereinafter simply referred to as formability) for automobiles, ships, vehicles and other transport equipment, home appliances, buildings, and structural members and parts. 5000 series (satisfying the standard) specified in the standard, Al-Mg-Si series AA to JIS 6000 series (hereinafter simply referred to as 5000 series to 6000 series) with excellent formability and bake hardenability Alloy materials (a general term for each aluminum alloy wrought material such as a rolled plate material, an extruded shape material, and a forged material) are used.

  In recent years, with respect to global environmental problems caused by exhaust gas and the like, improvement in fuel efficiency has been pursued by reducing the weight of the body of a transport aircraft such as an automobile. For this reason, in particular, the application of lighter Al alloy materials instead of steel materials that have been used in the past is increasing for automobile bodies.

  Among these Al alloy materials, panels such as the outer panel (outer plate) and inner panel (inner plate) of panel structures such as automobile hoods, fenders, doors, roofs, and trunk lids are thin and high-strength Al. As an alloy plate, use of an excess Si type 6000 series Al alloy plate has been studied.

  This excess Si type 6000 series Al alloy sheet is basically an Al—Mg—Si series aluminum alloy sheet containing Si and Mg as essential elements and having a Si / Mg mass ratio of 1 or more. And since this excess Si type 6000 series Al alloy plate has excellent age-hardening ability, it secures formability by reducing the yield strength during press molding and bending processing, and paint baking treatment of the panel after molding etc. It is age-hardened by heating at the time of relatively low-temperature artificial aging treatment to improve proof stress, and has age-hardening ability that can secure the required strength.

  Further, these excess Si type 6000 series Al alloy plates have a relatively small amount of alloy elements as compared with other 5000 series Al alloys having a large amount of alloy such as Mg. For this reason, when the scraps of these 6000 series Al alloy sheets are reused as an Al alloy melting material (melting raw material), the original 6000 series Al alloy ingot is easily obtained and the recyclability is also excellent.

  On the other hand, in the outer panel of the automobile, etc., an Al alloy plate is formed by press forming such as overhanging, drawing or trim to form an outer panel, and then the edge of the outer panel is bent (folded 180 degrees) to join the edge of the inner panel. A severe bending process called a hem (other name for hemming) process is performed in combination.

  However, in flat hem processing of Al alloy outer panels, compared to conventional flat hem processing of steel plate panels, the edge of the flat hem formed (hem portion, bent portion) has rough skin, minute cracks, Defects such as relatively large cracks are likely to occur. And when these defects arise, application as an outer panel becomes impossible.

  In contrast to the flat hem processing of such an Al alloy outer panel, it has been conventionally possible to prevent the occurrence of defects at the edge curved portion on the flat hem processing process side or the material side of the Al alloy plate, and to perform flat hem processing or bending processing. Various techniques for improving the performance have been proposed.

  Among them, it has been proposed to control the cube orientation distribution density in the texture in order to improve the bending workability such as flat hem of a 6000 series Al alloy plate containing excess Si type. These account for the proportion of crystal grain boundaries where the orientation difference between adjacent crystal grains is 15 ° or less or 20% or more, or the grain boundary length where the orientation difference between adjacent crystal grains is 20 ° or less is 20%. This is the above (see Patent Documents 1 and 2).

In a conventional manufacturing method, the crystal grain structure of a 6000 series Al alloy sheet is usually isotropic. On the other hand, the above-mentioned technique is a method in which specific crystal orientations are extremely accumulated to reduce the accumulation of dislocations at the grain boundaries during bending and / or grain boundary precipitation is suppressed due to grain boundary energy reduction. It is intended to improve severe bending workability by flat hem (hemming) processing, which is peculiar to outer panels of automobiles, etc., by suppressing boundary cracking.
JP 2003-171726 A JP2003-166029

  It is generally considered that cube orientations are accumulated as a technique for obtaining a structure defined by the above technique with a 6000 series Al alloy plate. However, when the proportion of crystal grains having a cube orientation is increased, a strong anisotropy occurs in material characteristics due to the anisotropy of the crystal orientation itself.

  When the material properties have strong anisotropy, bending workability such as flat hem processing is improved, but press formability such as bulging to the outer panel is lowered. That is, both bending workability and press formability cannot be improved. In the above prior art, the press formability is evaluated by an Erichsen test etc., and the press formability is also good. However, such an evaluation method using small test pieces is not sufficient as an evaluation of the formability of an actual 6000 series Al alloy plate on an outer panel or the like. There are many cases where the results of both do not correspond, for example, a problem occurs during overhang forming.

  This is due to the fact that press molding conditions and flat hem processing conditions for actual outer panels and the like tend to become increasingly severe and difficult in recent years. The outer panel shape formed by overhanging tends to be complicated, such as the overhang height and the overhang area being increased, and the shape has a curved portion with stretched flange deformation. For this reason, molding defects such as cracks and rough skin are more likely to occur.

  Thus, improvement of press formability and hemmability is a technical problem that contradicts each other, and it is difficult to achieve both. For example, when flat hem workability is improved by reducing the proof strength of an Al alloy plate, problems such as reduced press formability and insufficient proof strength after artificial age hardening at low temperatures occur. For this reason, it is possible to achieve both press formability and flat hemmability characteristics at the same time, even with various techniques for controlling crystallized matter and precipitates that have been proposed in the past and techniques for adding a large amount of Cu and the like. This is a very difficult technical issue.

  The present invention has been made by paying attention to such circumstances, and its purpose is excellent in bending workability such as hem processing and press formability, and is required for paneling such as low-temperature age-hardening ability. The aim is to provide an Al-Mg-Si Al alloy sheet having other characteristics.

In order to achieve this object, the gist of the aluminum alloy sheet of the present invention is an Al-Mg-Si aluminum alloy sheet in which the cube orientation distribution density and the anisotropy of the r value are controlled. The cube orientation distribution density by the crystal orientation distribution function analysis in the 1/4 depth part of the plate thickness from the surface is in the range of 10-30, and the r value r in the direction parallel to the rolling direction of this aluminum alloy plate ₀ is the index indicating the perpendicular direction of r value r ₉₀ to the rolling direction, the direction of 45 degrees r value r ₄₅ to the rolling direction, the anisotropy of r ₄₅ for r ₀ and r ₉₀ (r ₀ + r ₉₀ −2 × r ₄₅ ) / 2 is in the range of 0.2 to 1.4.

  The Al alloy sheet referred to in the present invention refers to a sheet (rolled sheet) aged at room temperature after being subjected to a tempering treatment after cold rolling. Therefore, each of the above requirements is not immediately after the tempering treatment (immediately after the plate production), but any period from the tempering treatment (after the plate production) to the press molding or bending (for example, one month or more after the plate production). This refers to the state of an Al alloy plate sufficiently aged at room temperature. In addition, the tempering treatment referred to here mainly refers to solution treatment and quenching treatment, but various tempering treatments such as a subsequent arbitrary heat treatment, for example, a pre-aging treatment described later, and an aging treatment further applied as necessary. Indicates that includes.

  The following description will be focused on an excess Si type 6000 series Al alloy plate. In the present invention, Al—Mg—Si to 6000 series Al alloy plates other than the excess Si type are not as severe as the problem, but can be included in the scope of the present invention. Similarly, the following description of bending workability will be made mainly on hem processing such as flat hem. However, if the hem workability is good, other hat-type bends that have the same processing (deformation) mechanism are used. Bending workability such as processing and 90 degree bending is also improved. Therefore, the present invention can be applied to bending processing other than hem processing and can be included in the scope of the present invention.

  According to the present invention, it is preferable that the room temperature aging itself of the excess Si type 6000 series Al alloy plate is suppressed, but even if it is aged at room temperature after the production of the Al alloy plate, the press formability and bending of flat hem, etc. An excess Si type 6000 series Al alloy plate excellent in processing can be obtained.

  For this purpose, the inventors have reexamined the relationship between press formability and hem workability and the crystal grain structure (anisotropy of material properties) having the cube orientation of the excess Si-type 6000 series Al alloy plate. . As a result, the higher the material property anisotropy, the better the bending of flat hem, etc. It was found that it improved rapidly. They have also found that slightly increasing the anisotropy of the material properties does not adversely affect press formability such as stretch forming.

  In other words, the conventional texture control focusing on the cube orientation did not realize this fact, and accumulated the cube orientation too much to improve the bending process such as flat hem (too much anisotropy). For this reason, press formability such as stretch forming has been reduced.

  In the present invention, based on this knowledge, the control range of the cube orientation (anisotropic) of the crystal grain structure is made lower to improve the bending process of flat hem and the like and to reduce the press formability such as stretch forming. I won't let you. Then, the degree of cube orientation (anisotropic) of the grain structure is defined by the cube orientation distribution density by the crystal orientation distribution function analysis.

  On the other hand, in order to further improve press formability such as stretch forming, it is necessary to suppress wrinkles during stretch forming. In an excess Si type 6000 series Al alloy plate having anisotropy as in the present invention, since the amount of material inflow in the directions of 0 °, 45 °, and 90 ° of the formed plate is different, from the early stage of overhang forming “Wrinkles” are likely to occur. And the more anisotropic, the deeper the wrinkle tends to be, and in order to suppress this wrinkle, it is necessary to take measures such as increasing the wrinkle pressing force during pressing (pressing the plate against the mold). It becomes. However, if the wrinkle holding force is too strong, a new problem arises that cracks are likely to occur during press molding.

Therefore, in the present invention, in order to suppress the occurrence of the “wrinkles” in press forming and further improve press formability, the r value r _{90 in the} direction perpendicular to the rolling direction and the direction parallel to the rolling direction The difference of the r value r _{45 in} the 45 degree direction with respect to the rolling direction with respect to the r value r ₀ of the rolling direction, in other words, the anisotropy of the r value r _{45 in} the 45 degree direction with respect to the rolling direction (the r of the r ₄₅ Control anisotropy with respect to ₉₀ and r ₀ .

Specifically, the difference between the r ₉₀ and the r value r _{45 in} the direction of 45 degrees relative to the rolling direction of the sheet, with respect to the average value of r ₉₀ and the r value r _{0 in the} direction parallel to the rolling direction of the sheet, r The difference of the r value in the excess Si type 6000 series Al alloy sheet, with (r ₀ + r ₉₀ −2 × r ₄₅ ) / 2 in the range of 0.2 to 1.4, which is an anisotropy index of ₄₅ to r ₉₀ and r ₀ Control the direction. This anisotropy control of the r value is common with the above-mentioned cube orientation control in terms of controlling the anisotropy of the crystal grain structure of the plate, and of course improves the bending workability such as flat hem processing.

  In the present invention, even if the excess Si type 6000 series Al alloy plate is aged at room temperature after production by giving such controlled cube orientation and r value anisotropy to the excess Si type 6000 series Al alloy plate. Both the stretch formability and flat hem workability are improved. It should be noted that this press formability and flat hem processing can further improve other press formability such as drawing and other hem processing such as roped hem.

Hereinafter, embodiments of the Al alloy plate of the present invention will be specifically described.
First, the structural requirements of the Al alloy sheet of the present invention will be described.
(Cube orientation distribution density)
In the present invention, as described above, in order to improve the flat hem workability of the Al alloy plate and not reduce the press formability such as the overhang forming, in the portion having a depth of 1/4 of the plate thickness from the surface of the Al alloy plate. The cube orientation distribution density by the crystal orientation distribution function analysis is set in the range of 10-30.

  If the cube orientation distribution density is less than 10, the flat hem workability of the Al alloy plate is not improved. On the other hand, when the cube orientation distribution density exceeds 30, press formability such as stretch forming is lowered.

  In the present invention, when defining the cube orientation distribution density, the cube orientation distribution density is defined by a crystal orientation distribution function analysis (hereinafter referred to as ODF analysis), which is more accurate in measuring the crystal texture.

  The cube orientation distribution density by ODF analysis can express a wide range quantitatively because the cube orientation is expressed by the ratio (dimensionalless) from the random orientation (non-oriented Al powder sample of the standard sample). For this reason, there is no tendency like the cube orientation measurement by the integrated intensity, and the cube orientation distribution can be measured more accurately. On the other hand, in the measurement of the Cube orientation using other integral intensities, the difference between the samples tends to be very small at a high integral intensity ratio because of the ratio calculation. Also, since the rotational orientation in the plane (100 planes) cannot be separated, there is a tendency that only pure cube orientation cannot be extracted.

  The cube orientation distribution density measured by ODF analysis from the Al alloy plate surface to a depth of 1/4 of the plate thickness can be measured, for example, by Rigaku Corporation's X-ray diffractometer [Model “Rigaku RAD-rX” (Ru-200B )] Is used to grind from the surface of the Al alloy plate to a depth of 1/4 of the plate thickness and measure this portion. The above X-ray diffractometer can perform ODF analysis with an incomplete pole figure. In other words, incomplete pole figures of {100} plane and {111} plane are created by Schluz's reflection method, ODF analysis is performed by applying Bunge's iterative series expansion method (positivity method), and cube orientation distribution density Can be requested.

  Regarding the relationship between the bending direction of the plate (plate after press molding) and the cube orientation (distribution direction) in flat hem processing, make sure that the plate's cube orientation is parallel to the bending direction of the plate (bending of the plate). When bending is performed (with the processing direction parallel or perpendicular to the rolling direction of the blank), the cube orientation during deformation becomes stable, and good flat hem workability is obtained. Even if the cube orientation of the plate is rotated 90 degrees, it has the same structure, so there is no distinction between 0 degrees and 90 degrees. For this reason, even if the bending direction of the plate is parallel or perpendicular to the rolling direction of the material plate, the cube orientation becomes the same structure, and good flat hem workability is obtained. However, depending on the relationship between the bending direction of the plate other than the above two directions and the cube orientation (distribution direction) of the plate, such as the rolling direction of the material plate is 45 degrees with the bending direction of the plate, the cube orientation is deformed. There is a possibility that the crystal orientation is randomized and the flat hem workability is inferior, and the bending direction of the plate in the flat hem processing is preferably the above two directions.

(r-value anisotropy)
In the present invention, in order to improve bending workability such as flat hem processing of Al alloy sheet and press formability such as stretch forming, r value r parallel to the rolling direction of Al alloy sheet is further provided. ₀ is the index indicating the perpendicular direction of r value r ₉₀ to the rolling direction, the direction of 45 degrees r value r ₄₅ to the rolling direction, the anisotropy of r ₄₅ for r ₀ and r ₉₀ (r ₀ + r ₉₀ −2 × r ₄₅ ) / 2 [hereinafter also referred to as Δr] is in the range of 0.2 to 1.4.

  If the above Δr is less than 0.2, the mechanical properties of each of the parallel, 45 ° and 90 ° directions of the plate in the rolling direction of the plate are made as uniform as possible. And the cube orientation distribution density cannot be 10 or more. Therefore, there is no effect of improving the bending workability when aged at room temperature after manufacturing the plate.

  On the other hand, when Δr exceeds 1.4, anisotropy increases due to accumulation of cube orientation, and bending work such as flat hem improves. However, since the cube orientation is accumulated too much (anisotropy is increased too much), the material inflow in the directions of 0 °, 45 ° and 90 ° of the press-molded plate is greatly different. As a result, “wrinkles” are likely to occur from an early stage in press molding. And in order to suppress this wrinkle, it is necessary to press-mold with a wrinkle pressing force stronger than usual, and cracks due to this strong wrinkle pressing force tend to occur on the contrary.

Here, the r value itself of the plate is widely used for evaluation of press formability. The r value is defined as the ratio ε _{w /} ε _t of the strain in the plate width direction (ε _w ) and the strain in the plate thickness direction (ε _t ). Therefore, this r value can be calculated by log (W ₀ / W) / log (W ₀ l / l ₀ W) in the tensile test. Where, W ₀ : width before tensile deformation (mm), W: width after tensile deformation (mm), l ₀ : length before tensile deformation (mm), l: length after tensile deformation (mm) is there.

(Relationship between cube orientation distribution density and r-value anisotropy)
Figure 1 shows the relationship between the above-mentioned cube orientation distribution density and r-value anisotropy and the bending workability. In FIG. 1, the horizontal axis is cube orientation distribution density (0 to 150), the left vertical axis is hemmability (9-step evaluation in 0.5 increments from 0.0 to 4.0: the evaluation method will be described later in the examples), right The vertical axis of is an index (r ₀ + r ₉₀ −2 × r ₄₅ ) / 2 indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ (0.0 to 1.6).

In FIG. 1, the hatched range is the range of the present invention, the cube orientation distribution density is in the range of 10 to 30, and Δr (r ₀ + r ₉₀ −2 × r ₄₅ ) / 2 is 0.2 to The range is 1.4.

  In Fig. 1, curve A shows the relationship between flat hem workability and cube orientation distribution density, and extrapolated flat hem workability data for each excess Si type 6000 series Al alloy sheet produced by changing the cube orientation distribution density. Is. Curve B shows the relationship between flat hem workability and Δr, and is an extrapolation of flat hem workability data of each excess Si type 6000 series Al alloy plate produced by changing Δr. Here, the curve A rises to the right, and it can be seen that the flat hem workability improves as the cube orientation distribution density increases. On the other hand, curve B has a downward slope, and it can be seen that the flat heme workability decreases as Δr increases.

  As shown in Fig. 1, just by slightly increasing the cube orientation distribution density in the range of 10 to 30, the bending workability of flat hem and the like is drastically improved from 4.0 to 3.5 or more. And if it is this range, it will not have a bad influence on press moldability, such as overhang forming. On the other hand, when the cube orientation distribution density exceeds 30, bending workability such as flat hem is improved from 2.0 to 0.5 or more, but press formability such as stretch forming is remarkably lowered.

  Further, as shown in FIG. 1, by making Δr in the range of 0.2 to 1.4, bending workability such as flat hem can be set to 0.5 to 3.5. In Fig. 1, the one with a cube orientation distribution density of less than 10 and Δr of 1.5 or less is an Al alloy plate having isotropicity by a conventional method, and the 4.0 level where bending workability such as flat hem is remarkably inferior. Become.

(Average crystal grain size)
In defining these crystal grain structures, as a premise, it is preferable that the average crystal grain size of the Al alloy plate is refined to 50 μm or less. By making the crystal grain size fine or small within this range, flat hem workability and press formability are ensured or improved. When the crystal grain size exceeds 50μm and becomes coarse, press formability such as flat hem workability and overhang deteriorates significantly, and defects such as cracks in the hem part and defects such as cracks and rough surfaces during press molding occur. Is likely to occur.

  The crystal grain size referred to here is the maximum diameter of crystal grains in the longitudinal (L) direction of the plate. The crystal grain size is measured by a line intercept method in the L direction by observing the surface of the Al alloy plate that has been mechanically polished by 0.05 to 0.1 mm and then electrolytically etched using an optical microscope. 1 The measurement line length is 0.95mm, and the total measurement line length is 0.95 x 15mm by observing a total of 5 fields with 3 lines per field.

(Chemical composition)
Next, an embodiment of the chemical composition of the Al alloy sheet of the present invention will be described below.
The basic composition of the Al alloy plate of the present invention is Al-Mg-Si (6000) in order to ensure various characteristics such as formability, strength, weldability, corrosion resistance, etc. required for the above-mentioned structure and the outer panel. System) Al alloy. If it is not within the range of the Al-Mg-Si (6000 series) Al alloy, the specified range and structure of the r value specified in the present invention will not be achieved, and the above characteristics will not be exhibited.

  In addition, in order to ensure the above required characteristics, Si: 0.4 to 1.3%, Mg: 0.2 to 1.2%, Mn: 0.01 to 0.65%, Cu: 0.001 to 1.0%, and Si / Mg in mass ratio It is preferable to use an excess Si type Al—Mg—Si-based Al alloy of 1 or more. In order to ensure the definition and various characteristics of the structure, more strictly, the remainder other than the specified components is preferably Al and inevitable impurities. In the present invention, the percentage display of the chemical component composition means the mass%, including the percentage display in the above claims.

  In addition to the above alloy elements, other alloy elements such as Cr, Zr, Ti, B, Fe, Zn, Ni, and V are basically impurity elements. However, from the viewpoint of recycling, not only high-purity Al ingots but also 6000 series alloys and other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting raw materials as melting materials. In the case of melting, these other alloy elements are necessarily included. Accordingly, the present invention allows these other alloy elements to be contained within a range not impairing the intended effect of the present invention.

The preferable content range and significance of each element, or the allowable amount will be described below. Si: 0.4 to 1.3%.
Si forms a compound phase such as GP zone together with Mg at the time of artificial aging treatment at low temperature and short time, such as solid solution strengthening and paint baking treatment, and exhibits age-hardening ability. It is an essential element for obtaining the required strength. Therefore, in the 6000 series Al alloy plate, it is the most important element for combining various properties such as press formability and hem workability.

  In addition, the proof stress at the time of artificial aging treatment at the low temperature and short time (paint baking treatment after forming on a plate, as an evaluation test, 160 ° C. × 20 minutes low temperature aging treatment after applying 2% stretch) is 170 MPa or more, In order to exhibit excellent low-temperature age-hardening ability, it is preferable to have an excess Si type 6000-based Al alloy composition in which Si / Mg is 1.0 or more by mass and Si is excessively contained with respect to Mg.

  When the Si content is less than 0.4%, the age-hardening ability and further various properties such as press formability and hemmability required for each application cannot be obtained. On the other hand, when Si exceeds 1.3%, heme workability and bending workability are significantly impaired. Furthermore, weldability is significantly impaired. Therefore, Si is preferably in the range of 0.4 to 1.3%. In the outer plate, hem workability is particularly emphasized, so that the Si content is 0.6 to 1.0% in order to further improve flat hem workability without degrading other properties such as press formability. The lower range is preferable.

Mg: 0.2-1.2%.
Mg forms a compound phase such as GP zone together with Si during solid tempering and artificial aging treatment such as paint baking treatment, to show age hardening ability and to obtain the required strength of 170 MPa or more as a plate Is an essential element.

  If the Mg content is less than 0.2% (mass%, the same applies hereinafter), the absolute amount is insufficient, so that the compound phase cannot be formed during the artificial aging treatment, and the age hardening ability cannot be exhibited. For this reason, the said required intensity | strength required as a board cannot be obtained.

  On the other hand, if the Mg content exceeds 1.2%, moldability such as press formability and bending workability (hem workability) is remarkably impaired. Therefore, the Mg content is in the range of 0.2 to 1.2% and Si / Mg is 1.0 or more. In order to further improve the flat heme workability, when the Si content is set to a lower range of 0.6 to 1.0%, in order to obtain an excess Si type 6000 series Al alloy composition correspondingly, Further, the Mg content is preferably set to a low range of 0.2 to 0.8%.

Cu: 0.001 to 1.0%
Cu has the effect of promoting precipitation of a compound phase such as a GP zone in the crystal grains of the Al alloy material structure under the conditions of artificial aging treatment at a relatively low temperature and short time of the present invention. Moreover, Cu dissolved in the aging treatment state also has an effect of improving formability. This effect is not obtained when the Cu content is less than 0.001%. On the other hand, if it exceeds 1.0%, the stress corrosion cracking resistance, the thread rust resistance of the corrosion resistance after coating, and the weldability are significantly deteriorated. For this reason, in the case of plate applications such as for automobile outer panels, the amount is preferably 0.1% or less where the expression of yarn rust resistance becomes significant.

Mn: 0.01 to 0.65%
Mn produces dispersed particles (dispersed phase) during the homogenization heat treatment, and these dispersed particles have the effect of preventing grain boundary movement after recrystallization, so that fine crystal grains can be obtained. . As described above, the press formability and hem workability of the Al alloy plate of the present invention improve as the crystal grains of the Al alloy structure become finer. In this respect, when the Mn content is less than 0.01%, these effects are not obtained.

  On the other hand, if the Mn content increases, coarse Al-Fe-Si- (Mn, Cr, Zr) -based intermetallic compounds and crystal precipitates are likely to be generated during melting and casting, which is likely to be the starting point of fracture. This causes a decrease in the mechanical properties of the Al alloy sheet. In particular, in flat hem processing where the processing conditions are severe due to the complicated shape and thinning, or the existence of a gap between the inner plate end and the inner edge of the outer plate edge, the Mn content is 0.25%. If it exceeds the range, hemmability will be reduced. For this reason, Mn is set in the range of 0.01 to 0.65%, and more preferably in the range of 0.01 to 0.25% in the flat hem processing in which the processing conditions are severe.

Cr, Zr.
Similar to Mn, these Cr and Zr transition elements have the effect of producing dispersed particles (dispersed phase) during homogenization heat treatment and obtaining fine crystal grains. However, if Cr and Zr are contained in an amount exceeding 0.15%, the hemmability is lowered in flat hem processing in which the processing conditions are severe. Therefore, the Cr and Zr contents are preferably regulated to 0.15% or less.

Ti, B.
When Ti and B are contained in amounts exceeding Ti: 0.1% and B: 300 ppm, coarse crystallized substances are formed and formability is lowered. However, Ti and B are contained in a very small amount, and have the effect of reducing the crystal grains of the ingot and improving the press formability. Therefore, the content of Ti: 0.1% or less and B: 300ppm or less is allowed.

Fe.
Fe mixed in from the melting raw material and contained as impurities produces crystallized products such as Al ₇ Cu ₂ Fe, Al ₁₂ (Fe, Mn) ₃ Cu ₂ , and (Fe, Mn) Al ₆ . These crystallized substances serve as nuclei of recrystallized grains, and when Fe is contained in an amount of 0.08% or more, the crystal grains are prevented from coarsening and the crystal grains are reduced to a fine grain of 50 μm or less. However, on the other hand, these crystallized materials significantly deteriorate the fracture toughness and fatigue characteristics, and further, the flat hem workability and press formability in which the processing conditions are severe. These deterioration characteristics become significant when the Fe content exceeds 0.50%. For this reason, the content of Fe when contained is preferably 0.08 to 0.50%.

Zn.
When Zn exceeds 0.5%, the corrosion resistance is remarkably lowered. Therefore, the Zn content is preferably 0.5% or less.

(Molding)
The hemming targeted by the Al alloy sheet of the present invention is particularly intended for flat hemming. Explaining a specific flat hem processing method, through a down flange process of bending the edge of the outer plate to an angle close to 90 ° with a tool such as a punch, and a prehem process of bending the edge of the outer plate further inward to about 135 °, The end portion of the inner plate is accommodated (inserted) in the bent portion of the outer plate, and the edge of the outer plate is further bent inward to an angle of 180 ° with a tool to form a flat hem. In this flat hem, the inner plate and the 180-degree bent portion of the outer plate are joined and brought into close contact with each other to have a flat bent portion shape.

  However, since the Al alloy sheet of the present invention is excellent in flat hem workability, which is a severe condition, the condition is one step looser than that, such as a rope hem having a rope-like cross-sectional shape in which the bent portion swells in an arc shape. Naturally, it is excellent in workability. In addition, the other work-type (deformation) mechanisms, such as the above-mentioned hat-shaped bending and 90-degree bending, and other bending workability, or in general, V-bending, U-bending, end bending, wave bending, tensile bending, etc. It is also excellent in bending workability called Therefore, the present invention is also intended for hem processing such as other rope hems, and also for bending processing other than hem processing.

  It should be noted that hem processing such as flat hem is performed on all four sides of the Al alloy plate of the present invention, or only on the selected side (side edge portion), and the hem processing is performed on the outer side. Whether the end shape of the plate is a linear shape, an arc shape, or a complicated shape having corners is appropriately selected according to the design of the member such as the outer plate.

  The Al alloy sheet of the present invention is also intended for press forming such as the above-described overhanging as well as hem workability. In press molding, in particular, the above-described shape of the outer plate or the like is applied to overhanging when the size is increased and complicated. However, these excellent stretch-formability means that the processing conditions are relatively gentle and that other drawability is excellent. Therefore, the Al alloy sheet of the present invention is also intended for particularly stretch forming and other press forming that can be represented by stretch forming.

(Production method)
The manufacturing method of the above Al alloy plate of the present invention will be described.
In order to obtain the structure having the cube orientation distribution density and r-value anisotropy of the present invention for the 6000 series Al alloy sheet, in addition to the above component composition, the processing rate in the following cold rolling To control. In this respect, a normal Al alloy plate obtained by a conventional method basically has neither cube orientation distribution density nor r-value anisotropy as in the present invention, and cannot be obtained.

  In order to obtain a structure having cube orientation distribution density and r-value anisotropy of the present invention, cold rolling is performed at a high reduction ratio of 70% or more. By increasing the reduction ratio in cold rolling, sufficient strain energy can be accumulated in the cold rolled sheet. As a result, a structure having the cube orientation distribution density and the anisotropy of the r value can be obtained by tempering treatment including annealing and solution treatment described later. If the rolling reduction in cold rolling is low, it will not be different from ordinary materials, and the structure cannot be accumulated by the tempering treatment described later. On the other hand, even if the reduction ratio in cold rolling is increased to 80% or more, the cube orientation distribution density and the r-value anisotropy become excessive, and the press formability is reduced to the following. Therefore, the rolling reduction in cold rolling is preferably 70 to 80%.

  Other process conditions can be used in a conventional manner, but there are also preferable conditions for improving the flat hem workability and other characteristics of the outer plate and the like, which will be described below.

  First, in the melting and casting process, an Al alloy molten metal adjusted to be within the component specification range of the present invention is appropriately selected from ordinary melting and casting methods such as a continuous casting rolling method and a semi-continuous casting method (DC casting method). Cast.

  Next, the Al alloy ingot is subjected to a homogenization heat treatment, followed by hot rolling and cold rolling at the high reduction rate, and processing into a plate shape such as a coil shape or a plate shape. At that time, after the hot rolling, annealing prior to the cold rolling can be performed to control the direction in which the cubes are not accumulated (the direction in which the cube orientation distribution density is reduced).

  The processed Al alloy plate is first subjected to solution treatment and quenching treatment as a tempering treatment. The solution treatment and quenching treatment are important steps for sufficiently depositing the compound phase such as the GP zone in the grains by an artificial age hardening treatment such as a subsequent paint bake hardening treatment. The solution treatment conditions for producing this effect are preferably performed in a temperature range of 500 to 560 ° C.

  Conventionally, in the case of a plate for which flat hemmability is particularly important, or in the case of the severe flat hemming condition, the solution treatment temperature is set to a lower temperature side of 500 to 530 ° C. However, in the present invention, as described above, the hem workability such as flat hem and the press formability are particularly excellent even if the 0.2% proof stress of the Al alloy plate is not as low as 140 MPa or less as in the prior art.

  For this reason, the solution treatment temperature is set on the high temperature side in the range of 530 to 560 ° C, and the 0.2% proof stress of the Al alloy plate is set to a high strength exceeding 140 MPa. It is preferable that a compound phase such as a zone is sufficiently precipitated in the grains, and a high-strength plate exceeding 170 MPa is obtained even in the low-temperature and short-time artificial age hardening treatment in the coating process after molding.

  In quenching after the solution treatment, the cooling rate is preferably 50 ° C./min or higher. When the cooling rate is slow at less than 50 ° C./min, the strength after quenching is low, the age hardening ability is insufficient, and the high proof stress of 170 MPa or more cannot be ensured by the artificial aging treatment at a low temperature for a short time.

  In addition, Si, MgSi and the like are likely to precipitate on the grain boundaries, which is likely to be the starting point of cracks during press molding and flat hem processing, and these moldability is reduced. In order to ensure this cooling rate, the quenching process may be air cooling such as a fan, but there is a high possibility that the cooling rate will be slow, and it is preferable to perform the quenching process by selecting from water cooling means such as mist, spray, and immersion.

  In the present invention, as described above, room temperature aging itself is allowed, but room temperature aging may be suppressed. That is, after the solution hardening treatment, a preliminary aging treatment may be performed to suppress the formation of clusters that cause room temperature aging and promote the precipitation of the GP zone. This preliminary aging treatment is preferably held in a temperature range of 50 to 100 ° C., preferably 60 to 90 ° C., for a required time of 1 to 24 hours. The cooling rate after the pre-aging treatment is preferably 1 ° C./hr or less.

  As the preliminary aging treatment, the quenching end temperature after the solution treatment is increased to 50 to 100 ° C., and then immediately reheated or kept as it is. Alternatively, it is immediately reheated to 50 to 100 ° C. after quenching to room temperature after solution treatment.

  Further, in the case of continuous solution quenching, the quenching process is completed within the temperature range of the preliminary aging, and the coil is wound around a coil at the same high temperature. In addition, you may reheat before winding up to a coil, and you may heat-retain after winding. Moreover, after the quenching process to room temperature, it may be reheated to the above temperature range and wound at a high temperature.

  Furthermore, in order to suppress aging at room temperature, a GP zone may be generated by performing sub-aging treatment at a relatively low temperature without time delay after the preliminary aging treatment. When the time delay is present, room temperature aging (natural aging) occurs with time even after the preliminary aging treatment, and after this room temperature aging occurs, the effect of the sub-aging treatment is hardly exhibited.

  In order to obtain these effects, in the composition range of the Al alloy material, the aging treatment temperature is set to a sub-aging treatment range of 80 to 120 ° C., and the aging treatment time is set to a necessary time, preferably 1 to 24 hours, From this range, it is preferable to select a temperature and a time at which an aging treatment effect is obtained according to the composition. The cooling rate after the sub-aging treatment is preferably 1 ° C./hr or less. If the aging treatment temperature is less than 80 ° C. and the holding time is too short, the GP zone cannot be generated. For this reason, the room temperature aging inhibitory effect and the low temperature age hardening ability cannot be obtained. On the other hand, when the temperature exceeds 120 ° C, it is not much different from the normal aging treatment, the β "phase is precipitated and aging progresses too much, and the strength becomes too high. This is the same even if the aging treatment holding time is too long. The preliminary aging treatment temperature may be set as high as the aging treatment described later, or a heat treatment combined with or continuous with the aging treatment.

  In addition to this, it is of course possible to further increase the strength by performing aging treatment or stabilization treatment at a higher temperature according to the application or required characteristics.

  Next, examples of the present invention will be described. In order to control the anisotropy of material properties for each 6000 series compositional range Al alloy plate shown in Table 1, as shown in Table 2, the presence or absence of annealing after hot rolling and the reduction rate of cold rolling Various changes were made to produce 1.0 mm thick Al alloy plates, and the press formability and hem workability were evaluated.

  The presence or absence of annealing after hot rolling and the production conditions of the Al alloy sheet other than the cold rolling reduction ratio are almost the same except for the thickness of the hot rolled sheet for changing the rolling reduction ratio of the following cold rolling. Performed under conditions. In other words, 400mm-thick ingots of each composition range shown in Table 1 were melted by DC casting method and then subjected to homogenization heat treatment at 540 ° C x 4 hours to a thickness of 2.3-8mmt at an end temperature of 300 ° C. Were hot rolled with various changes. In order to control cube orientation distribution density and r-value anisotropy, this hot-rolled sheet was selectively subjected to batch annealing at 350 ° C for 5 hours, and then the rolling reduction was further reduced to a thickness of 1.0 mm. Was subjected to cold rolling.

  Next, these cold-rolled sheets were tempered under the following conditions. The cold-rolled plate was put into an air furnace maintained at 570 ° C., and when the plate reached a solution treatment temperature of 550 ° C. (holding time 0 second), a process of quenching in hot water at 70 ° C. was performed. The cooling rate during the quenching process is 200 ° C / second, the quenching end temperature (quenching temperature) is 70 ° C in common, and pre-aging treatment is held at this temperature for 2 hours after quenching (cooling rate 0.6 ° C after holding) (Slow cooling at / hr).

  Assuming and taking into account that Al alloy sheets aged sufficiently at room temperature after tempering are press-formed and hemmed, the tempered Al alloy sheets are treated for 4 months (120 days) after tempering. Were allowed to age at room temperature.

Cut out the required number of test plates and specimens from these Al alloy plates after aging at room temperature, and tensile strength (σ _B ) and proof stress (σ _0.2 ) and elongation (%) of each test plate parallel to the rolling direction. Then, r values in the respective directions of the r ₉₀ , r ₄₅ , and r ₀ were measured. The Δr was determined. These results are shown in Table 2. As a result of measuring the crystal grain size of the test plates after aging at room temperature by the above-described method, all the crystal grain sizes were 50 μm or less in both the inventive examples and the comparative examples.

  The tensile test was performed according to JIS Z 2201 and the shape of the test piece was a JIS No. 5 test piece. The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke.

  Further, the test plate after the room temperature aging was subjected to a molding test by simulating that the Al alloy plate aged at room temperature was subjected to press molding or hem processing as an automobile panel. More specifically, a stretch forming test and a flat hem processing test after the stretch forming were performed to evaluate the formability. These results are also shown in Table 2.

  The conditions of the stretch forming test were that a plurality of 1000 mm square test plates (blanks) were cut out from the test plate after aging at room temperature and stretched using a die with a bead by a mechanical press. The shape of the molded product was a hat type with a square tube-like overhang part with a side of 500 mm at the center and a height of 50 mm, and flat flanges around the four sides of the overhang part. .

  The overhang forming test was performed three times under the same conditions as the wrinkle holding force of 490 kN, the lubricating oil as a general rust preventive oil, and the forming speed as 20 mm / min. The evaluation was performed separately for the corner crack and the flange (end) crack, and the corner crack of the molded hat mold plate did not occur three times. Things were evaluated as x.

  In addition, the maximum height (mm) of the generated `` wrinkle '' was measured regardless of cracking during this stretch forming, and the average of the wrinkle height during the three moldings was 1.0 mm or less. Was evaluated as ◯, when exceeding 1.0 mm and not more than 2.0 mm, Δ and when exceeding 2.0 mm as ×.

  Next, the flat hem processing test was as follows. The press-molded Al alloy plate was simulated to be hemmed as an outer plate, and the entire surface of one end of the flat flange portion of the plate was flat-hemmed under the following conditions.

  First, the flat hemming allowance of the Al alloy plate (distance from the end folded inside the plate after the hemming to the end of the bent portion) is set to 12 mm, and the down flange process is simulated to simulate the edge of the Al alloy plate. Was bent to a 90 degree angle. At this time, the 90 ° bending radius of the Al alloy plate was set to 0.8. Next, by simulating the prehem process, the edge of the Al alloy plate was further bent inward to an angle of 135 °.

  After that, simulating stricter flat hemming conditions, the inner plate was not inserted into the bent portion of the Al alloy plate, but the bent portion was further bent 180 degrees inward, and flat hem processing was performed to adhere to the plate surface. .

  Then, the surface state of the flat hem, such as rough skin, minute cracks, and large cracks, was visually observed. Evaluation is as follows: 0.0: Surface condition is good with no rough skin or minute cracks, 1.0: Some rough skin occurs partially, 2.0: Although rough skin occurs entirely, including fine ones This is performed at each stage of 3.0: No cracks are generated, 3.0: Small cracks are partially generated, and 4.0: Relatively large cracks are generated. A total of 9 grades were added. In this evaluation, it is judged that hemmability is good or can be used for hem processing by changing hem processing conditions, etc., up to 3.5 stages, and 4.0 stage cannot be used for hem processing even if hem processing conditions are changed.

Furthermore, in order to investigate low-temperature age-hardening ability (paint bake hardenability), a test plate was collected from the press-formed Al alloy plate and subjected to artificial age-hardening treatment at a low temperature of 160 ° C for 20 minutes, The tensile strength (ABσ _B ) parallel to the rolling direction (of the original Al alloy plate) (ABσ _B ) and the proof stress (ABσ _0.2 ) of each test plate after the treatment were measured. These results are also shown in Table 2.

  As is apparent from Tables 1 and 2, Invention Examples 1 to 7 in the alloy composition range of the present invention, the cube orientation distribution density is in the range of 10 to 30, and Δr is in the range of 0.2 to 1.4. After aging at room temperature for the above 4 months (120 days), the yield strength is higher than immediately after tempering, and flat hem processing is possible even under conditions that are disadvantageous to moldability and age hardening, Since there is no generation of cracks and the amount of wrinkles generated is small, it has excellent stretch formability and also has excellent artificial age hardening ability.

  Moreover, the test conditions and evaluation of the press formability and flat hem workability lead to the evaluation of actual severe processing conditions such as automobile outer plates. Therefore, Invention Examples 1 to 7 have both the above press formability and flat hemmability, and the amount of wrinkles generated even when the overhang height, the overhang area, etc. are increased by press forming such as overhang forming. It shows that it has less stretchability and is excellent in formability and can be applied to actual automobile outer plates.

  On the other hand, Comparative Examples 8, 9, 11, and 13 can be said to be plates produced by a conventional method, and are conventional equivalent materials having almost no r value anisotropy. Therefore, despite the same alloy composition corresponding to each of the invention examples, the cube orientation distribution density is less than 10 and Δr is about 0.1, which is a result that deviates slightly from the scope of the present invention. For this reason, Comparative Examples 8, 9, 11, and 13 are significantly inferior in flat hem processability to the inventive examples.

  Further, Comparative Examples 10, 12, and 14 are cases where the material properties have strong anisotropy, the cube orientation distribution density exceeds 30, and Δr exceeds 1.4, which is a result that deviates from the scope of the present invention. It has become. As a result, the flat hem workability is superior to that of the invention example, but the stretch forming is remarkably reduced.

  According to the present invention, an Al-Mg-Si-based Al alloy sheet that has excellent bending workability such as hem processing and press formability, and also has other characteristics required for forming a panel such as low-temperature age-hardening ability. Can be provided. Therefore, it has a great industrial value in that the Al alloy plate can be expanded to plate applications.

FIG. 5 is an explanatory diagram showing the relationship between cube orientation distribution density and r-value anisotropy and bending workability in an Al alloy plate.

Claims (4)

An Al-Mg-Si aluminum alloy plate with controlled cube orientation distribution density and r-value anisotropy, and crystal orientation distribution function analysis at 1/4 depth from the surface of the aluminum alloy plate The cube orientation distribution density by the range of 10 to 30, and the aluminum alloy plate, r value r _{0 in the} direction parallel to the rolling direction, r value r _{90 in the} direction perpendicular to the rolling direction, (R ₀ + r ₉₀ −2 × r ₄₅ ) / 2 is an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ , with an r value r _{45 in the} direction of 45 degrees with respect to the rolling direction. An aluminum alloy plate excellent in bending workability and press formability, characterized by being in the range.   The aluminum alloy plate contains Si: 0.4 to 1.3%, Mg: 0.2 to 1.2%, Mn: 0.01 to 0.65%, Cu: 0.001 to 1.0%, and Si / Mg is 1 or more by mass, and the balance The aluminum alloy sheet excellent in bending workability and press formability according to claim 1, comprising a composition in which is Al and inevitable impurities.   The aluminum alloy plate excellent in bending workability and press formability according to claim 1 or 2, wherein the aluminum alloy plate is hemmed after stretch forming. The aluminum alloy plate according to any one of claims 1 to 3, wherein the aluminum alloy plate is for an automobile outer panel.

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