JP5427143B2 - Aluminum alloy sheet for forming - Google Patents

Description

  The present invention relates to a high-Mg-containing Al—Mg-based alloy plate, which relates to a forming aluminum alloy plate having high formability.

  As is well known, various aluminum alloy plates have conventionally been used for each alloy for transporting machines such as automobiles, ships, airplanes or vehicles, machines, electrical products, architecture, structures, optical instruments, and components and parts of equipment. It is widely used depending on the characteristics. In many cases, these aluminum alloy plates are formed by press molding or the like, and are used as members and parts for the above-described applications. In this respect, from the viewpoint of high formability, among aluminum alloys, an Al—Mg-based alloy having an excellent balance between strength and ductility is advantageous. As this Al—Mg alloy, for example, JIS A5052, 5182 and the like are typical alloys. However, this Al—Mg alloy plate is inferior in ductility and inferior in formability as compared with a conventional cold-rolled steel plate. For this reason, conventionally, regarding the Al—Mg alloy plate, examination of component systems and optimization of manufacturing conditions have been performed.

  For example, when the Al-Mg alloy is increased in Mg content to a high Mg content exceeding 6 mass%, preferably 8 mass%, the strength ductility balance is improved. However, it is difficult to industrially manufacture such a high Mg content Al—Mg alloy plate by a normal manufacturing method in which an ingot cast by DC casting or the like is subjected to hot rolling after soaking. . The reason is that Mg is segregated in the ingot at the time of casting, and the normal hot rolling significantly reduces the ductility of the Al—Mg alloy, so that cracking is likely to occur.

  On the other hand, it is difficult to produce a high Mg content Al—Mg alloy plate by hot rolling at a low temperature while avoiding a temperature range where cracks occur. The reason is that, in such low temperature rolling, the deformation resistance of the material of the high Mg content Al—Mg alloy becomes extremely high, and the product size that can be produced is extremely limited by the current rolling mill capability. . In addition, a method of adding a third element such as Fe or Si has been proposed in order to increase the Mg content allowable amount of the high Mg Al—Mg alloy. However, when the content of these third elements is increased, a coarse intermetallic compound is easily formed, and the ductility of the aluminum alloy plate is lowered. Therefore, there is a limit to the increase in the Mg content allowable amount, and it was difficult to contain an amount of Mg exceeding 8% by mass.

For this reason, various proposals have been made to produce a high Mg content Al—Mg alloy plate by a continuous casting method such as a twin roll type.
For example, in Patent Document 1, a high Mg content Al—Mg-based alloy plate of 6 to 10% by mass is manufactured by a twin roll type continuous casting method, and the average size of the Al—Mg-based intermetallic compound is 10 μm or less. An aluminum alloy plate is described.

Moreover, in patent document 2, 2.5-8 mass% high Mg content Al-Mg type | system | group alloy board is manufactured by a continuous casting method, and the number of Al-Mg type intermetallic compounds of 10 micrometers or more is 300 pieces / mm < ² >. Hereinafter, an aluminum alloy plate for automobile body sheets having an average crystal grain size of 10 to 70 μm is described.

  Moreover, in patent document 3, 8-14 mass% high Mg content Al-Mg type | system | group alloy board was manufactured with the twin roll type continuous casting method, each Mg density | concentration measured over the board thickness direction, and these were averaged. In relation to the average Mg concentration, the maximum value of the deviation width of each Mg concentration from the average Mg concentration is 4% by mass or less in absolute value, and the average value is 0.8% by mass or less in absolute value. An aluminum alloy plate that suppresses the precipitation of Mg-based intermetallic compounds is described.

JP-A-7-252571 JP-A-8-165538 JP 2007-77485 A

  As described in Patent Documents 1 and 2, the Al—Mg-based intermetallic compound that crystallizes during casting is likely to be a starting point of fracture during press molding. Therefore, in order to improve the press formability of the high Mg-containing Al—Mg-based alloy plate, the Al—Mg-based intermetallic compound (also referred to as β phase) is made finer or less coarse. It is effective. And in patent document 1, 2, the cooling rate (casting speed) in a casting process is made quick, and the Al-Mg type | system | group intermetallic compound crystallized in the case of casting is suppressed. However, there is a problem that the higher the Mg content, the more difficult it is to reduce the β phase of the high Mg-containing Al—Mg-based alloy sheet to the extent that it does not adversely affect the press formability only by controlling the cooling rate in the casting process.

  In Patent Document 3, the degree of segregation of Mg in the thickness direction (Mg concentration distribution) is suppressed by homogenization heat treatment and final annealing conditions, and an Al—Mg-based intermetallic compound due to Mg segregation (concentration unevenness) ( (beta phase) precipitation is suppressed. However, the high Mg content Al-Mg alloy plate produced using the twin roll continuous casting method of the prior art generates Mg segregation in the plate width direction as well, thus suppressing the degree of Mg segregation in the plate thickness direction. However, there is a problem that it is difficult to reduce the β phase of the high Mg-containing Al—Mg alloy plate to such an extent that the press formability is not adversely affected.

  Therefore, in addition to or in addition to the suppression of the rate of Mg segregation in the sheet thickness direction due to the cooling rate in the casting process and the homogenization heat treatment and final annealing conditions after the casting process, a high Mg content Al- There is a demand for a technique that can reduce the β phase of the Mg-based alloy sheet to such an extent that it does not adversely affect the press formability.

  The present invention has been made to solve such problems, and the problem is to reduce the precipitation of β phase inside the high Mg-containing Al—Mg alloy plate and improve the press formability. An object of the present invention is to provide an aluminum alloy plate for forming.

  In order to solve the above-mentioned problem, a forming aluminum alloy plate according to the present invention is a forming aluminum alloy plate containing Mg: 6.0 to 15.0 mass%, with the balance being Al and impurities, In a square region having one side of the total plate width set on the surface of the forming aluminum alloy plate, at a plurality of plate width direction measurement points set at predetermined intervals in the plate width direction and the plate length direction. The Mg concentration is measured, and the average value of those Mg concentrations is defined as the plate width direction average Mg concentration (Co). At the measurement points in the plate width direction, a plurality of thicknesses set over the entire plate thickness at predetermined intervals in the plate thickness direction. When the Mg concentration is measured at the measurement point in the plate thickness direction, and the average value thereof is defined as the plate thickness direction average Mg concentration (Ci), the plate thickness direction average Mg concentration (Ci) and the plate width direction average Mg concentration (Co) Defined by the difference (Ci-Co) The absolute value of the frequency Mg segregation ratio (X) is the maximum value of 0.5 wt% or less, and the average value thereof is equal to or less than 0.1 wt%.

  According to the said structure, the area | region Mg segregation degree (X) defined by the difference of the board thickness direction average Mg density | concentration (Ci) and board width direction average Mg density | concentration (Co) of an aluminum alloy plate for shaping | molding is below predetermined value. By being the maximum value and the average value, the segregation of Mg in the entire thickness of the forming aluminum alloy plate, that is, in both the plate thickness direction and the plate width direction is suppressed. Precipitation of the β phase is reduced, and uneven deformation during molding and strain concentration due to nonuniform deformation are suppressed.

  In the forming aluminum alloy sheet according to the present invention, in the calculation of the region Mg segregation degree (X) in addition to the region Mg segregation degree (X), at least one of the measurement points in the plate width direction, the plate thickness direction When the Mg concentration measured over the whole plate thickness at a predetermined interval is defined as the plate thickness direction Mg concentration (Ct), the difference between the plate thickness direction Mg concentration (Ct) and the plate thickness direction average Mg concentration (Ci) (Ct The absolute value of the thickness direction Mg segregation degree (Y) defined by -Ci) is preferably 4% by mass or less and the average value of 0.8% by mass or less.

  According to the said structure, in addition to the said area | region Mg segregation degree (X), the board defined by the difference of the board thickness direction Mg density | concentration (Ct) and board thickness direction average Mg density | concentration (Ci) of the aluminum alloy plate for shaping | molding Since the thickness direction Mg segregation degree (Y) is a maximum value and an average value below a predetermined value, the segregation of Mg is further suppressed, so that the precipitation of β phase inside the forming aluminum alloy plate is further reduced. At the same time, non-uniform deformation during molding and strain concentration due to non-uniform deformation are further suppressed.

In the aluminum alloy sheet for forming according to the present invention, the Mg content is preferably more than 8% by mass and 14% by mass or less.
According to the said structure, by prescribing | regulating Mg content to a predetermined range, while the intensity | strength and ductility of an aluminum alloy plate for shaping | molding improve, precipitation of (beta) phase inside the aluminum alloy plate for shaping | molding is reduced.

  In the aluminum alloy sheet for molding according to the present invention, the impurities are Fe: 1.0 mass% or less, Si: 0.5 mass% or less, Ti: 0.1 mass% or less, B: 0.05 mass% or less. Mn: 0.3% by mass or less, Cr: 0.3% by mass or less, Zr: 0.3% by mass or less, V: 0.3% by mass or less, Cu: 1.0% by mass or less, Zn: 1. It is preferable that it is at least one element of 0% by mass or less.

  According to the above configuration, by regulating the content of Fe and Si as impurities, an Al—Mg-based intermetallic compound composed of Al—Mg— (Fe, Si) or the like inside the forming aluminum alloy plate, Precipitation of intermetallic compounds other than Al—Mg based materials such as Al—Fe and Al—Si is suppressed, and fracture toughness and press formability are improved. Moreover, press formability is not inhibited by regulating the contents of Ti, B, Mn, Cr, Zr, V, Cu, and Zn as impurities.

  In the aluminum alloy sheet for forming according to the present invention, formation of β phase is reduced by suppressing the segregation of Mg, and excellent press formability can be obtained. Further, the aluminum alloy sheet for forming is restricted to a narrower Mg content, or in addition to Mg, at least one element of Fe, Si, Ti, B, Mn, Cr, Zr, V, Cu, Zn Is contained as an impurity, and the press formability is further improved by regulating the content thereof.

The some measurement point of Mg density | concentration used when calculating the Mg segregation degree of the aluminum alloy plate for shaping | molding which concerns on this invention is shown, (a) is a top view, (b) is the AA line cross section of (a). FIG. It is sectional drawing which shows typically the structure of the thin plate continuous casting apparatus used in the case of manufacture of the aluminum alloy plate for shaping | molding which concerns on this invention. It is sectional drawing which shows typically the structure of the thin plate continuous casting apparatus used in the case of manufacture of the aluminum alloy plate for shaping | molding which concerns on this invention. It is a graph which shows the calculation result of the area | region Mg segregation degree in the aluminum alloy plate for shaping | molding which satisfies the requirements of this invention. It is a graph which shows the calculation result of the area | region Mg segregation degree in the aluminum alloy plate for shaping | molding which does not satisfy the requirements of this invention. It is a graph which shows the calculation result of the sheet thickness direction Mg segregation degree in the aluminum alloy plate for shaping | molding which satisfy | fills the requirements of this invention. It is a graph which shows the calculation result of the sheet thickness direction Mg segregation degree in the aluminum alloy plate for shaping | molding which does not satisfy the requirements of this invention.

An embodiment of an aluminum alloy sheet for forming according to the present invention will be described in detail.
The forming aluminum alloy plate according to the present invention (hereinafter referred to as an aluminum alloy plate) is made of an aluminum alloy containing a high content of Mg, and is defined by a plate width direction average Mg concentration Co and a plate thickness direction average Mg concentration Ci. The region Mg segregation degree X is restricted to a predetermined value or less.

First, regarding the chemical component composition of the aluminum alloy plate, the significance of each alloy element and the reason for limiting the numerical value will be described.
The aluminum alloy plate is composed of an aluminum alloy containing Mg: 6.0 to 15.0% by mass and the balance being Al and impurities, that is, a high Mg-containing Al—Mg alloy. In addition, the aluminum alloy plate includes, as elements other than Mg, Fe: 1.0 mass% or less, Si: 0.5 mass% or less, Ti: 0.1 mass% or less, B: 0.05 mass% or less, Mn : 0.3 mass% or less, Cr: 0.3 mass% or less, Zr: 0.3 mass% or less, V: 0.3 mass% or less, Cu: 1.0 mass% or less, Zn: 1.0% It is preferably composed of a high Mg-containing Al—Mg-based alloy containing at least one element having a mass or less as an impurity.

(Mg)
Mg is an important alloy element that increases the strength and ductility of the Al alloy sheet. When the Mg content is less than 6.0% by mass, the strength and ductility are insufficient, the characteristics of the high Mg-containing Al—Mg alloy are not obtained, and the press formability is insufficient. On the other hand, if the Mg content exceeds 15.0% by mass, the segregation of Mg in the aluminum alloy plate, that is, the degree of Mg segregation in the region can be regulated within a predetermined range even if the manufacturing method and conditions are controlled. It becomes difficult. As a result, the precipitation of β phase on the aluminum alloy plate increases, and the press formability is remarkably lowered. In addition, the work hardening amount is increased and the cold rollability is also lowered. Therefore, Mg content is 6.0-15.0 mass%, Preferably it exceeds 8 mass% and is 14 mass% or less.

(Fe, Si)
Fe and Si are elements that should be regulated to the smallest possible amount. Fe and Si are precipitated as an Al—Mg-based intermetallic compound composed of Al—Mg— (Fe, Si) or an intermetallic compound other than Al—Mg based such as Al—Fe or Al—Si. When the Fe content exceeds 1.0% by mass, or when the Si content exceeds 0.5% by mass, the amount of precipitation of these intermetallic compounds becomes excessive, and fracture toughness and formability are reduced. It greatly inhibits. As a result, press formability is significantly reduced. Therefore, the Fe content is 1.0% by mass or less, preferably 0.5% by mass or less, and the Si content is 0.5% by mass or less, preferably 0.3% by mass or less.

(Ti, B, Mn, Cr, Zr, V, Cu, Zn)
Ti and B have a refinement effect on the cast plate (ingot) structure, and Mn, Cr, Zr, and V have a refinement effect on the rolled plate structure. Cu and Zn also have an effect of improving strength. For this reason, it may be intentionally included with the aim of these effects, and it is allowed to contain one or more of these elements within a range that does not impair the press formability that is a characteristic of the alloy plate of the present invention. These allowable amounts are Ti: 0.1 mass% or less, B: 0.05 mass% or less, Mn: 0.3 mass% or less, Cr: 0.3 mass% or less, Zr: 0.3 mass% or less V: 0.3% by mass or less, Cu: 1.0% by mass or less, and Zn: 1.0% by mass or less are preferable.

  Next, with regard to the plate width direction average Mg concentration Co, the plate thickness direction average Mg concentration Ci, and the region Mg segregation degree X defined by the plate width direction average Mg concentration Co and the plate thickness direction average Mg concentration Ci of the aluminum alloy plate This will be described in detail with reference to FIG.

(Average Mg concentration in the plate width direction: Co)
As shown in FIG. 1 (a), the plate width direction average Mg concentration Co is a square region having one side of the total plate width W set on the surface of the aluminum alloy plate, that is, the total plate width W and its In a region surrounded by a plate length L having the same length as the total plate width W, a plurality of plate width direction measurements set at a predetermined interval a in the plate width direction and at a predetermined interval b in the plate length direction The Mg concentration on the surface of the aluminum alloy plate is measured at the point Px, and the Mg concentration is averaged, that is, the average value of the measured Mg concentration. And this plate width direction average Mg density | concentration Co becomes a parameter | index of the degree of Mg segregation in the plate width direction in the surface of an aluminum alloy plate. In addition, the Mg concentration is measured by using an EPMA (electron probe microanalyzer) capable of line analysis and scanning in the plate width direction of the aluminum alloy plate.

  In addition, in order to obtain reproducibility of the degree of Mg segregation in the plate width direction of the aluminum alloy plate, a square region with one side of the entire plate width W is set on the surface of the aluminum alloy plate, and aluminum in the region is formed. It is necessary to measure the Mg concentration on the surface of the alloy plate. The number (points) of the plate width direction measurement points Px set in the region is 5 points or more without including the plate end in the plate width direction and 25 points or more in total in the plate length direction. preferable. Then, the interval a in the plate width direction and the interval b in the plate length direction are set so that the number of measurement points Px in the plate width direction is 25 or more. Further, the interval b in the plate length direction is preferably set to 0.5 to 2 times the interval a in the plate width direction.

(Thickness direction average Mg concentration: Ci)
As shown in FIG. 1B, the plate thickness direction average Mg concentration Ci is calculated at a predetermined interval c in the plate thickness direction at all measurement points of the plurality of plate width direction measurement points Px set in the region. The Mg concentration at the plate depth position (synonymous with the plate thickness direction Mg concentration Ct to be described later) is measured at a plurality of plate thickness direction measurement points Py set over the plate thickness T, and those Mg concentrations are averaged. That is, the average value of the measured Mg concentration. The plate thickness direction average Mg concentration Ci is an index of the degree of Mg segregation in the plate thickness direction (plate depth direction) of the aluminum alloy plate. The Mg concentration is measured using EPMA in the same manner as described above to scan the cross section in the plate width direction in the plate thickness direction and measure the Mg concentration at each thickness position in the range of the total plate thickness T.

  Further, in order to obtain reproducibility of the degree of segregation of Mg in the thickness direction of the aluminum alloy plate, the interval c in the thickness direction is preferably set to 0.2 mm or less. The first measurement point of the plate thickness direction measurement point Py is the already measured plate width direction measurement point Px.

(Region Mg segregation degree: X)
The region Mg segregation degree X is defined by the difference (Ci-Co) between the plate thickness direction average Mg concentration (Ci) and the plate width direction average Mg concentration (Co). It is an index of the degree of Mg segregation in both the plate thickness direction and the plate width direction. And in the aluminum alloy plate which concerns on this invention, the absolute value of the area | region Mg segregation degree X is 0.5 mass% or less in the maximum value, and is 0.1 mass% or less in the average value. The sheet width direction average Mg concentration Co, the sheet thickness direction average Mg concentration Ci, and the region Mg segregation degree X are the chemical composition of the aluminum alloy sheet, the manufacturing conditions described later, specifically the cooling conditions during casting, the casting It is controlled by the plate thickness or the amount of face cutting, the homogenization heat treatment condition, and the final annealing condition.

  When the maximum value or average value of the region Mg segregation degree X becomes larger on the plus side, the β phase due to Mg segregation tends to precipitate. For this reason, the β phase that is the starting point of fracture increases, the strength and elongation decrease, and the moldability decreases. In addition, when the maximum value or the average value of the region Mg segregation degree X is increased to the minus side, there are many portions where the Mg concentration is significantly reduced, and thus such Mg concentration is greatly increased. In the lower part, the strength is lowered. For this reason, at the time of tensile deformation in molding, non-uniform deformation occurs in which only the portion where the Mg concentration becomes low is preferentially deformed. For this reason, the distortion at the time of shaping | molding will concentrate partially, especially elongation will fall and a moldability will fall.

  Therefore, when the maximum value of the region Mg segregation degree X exceeds 0.5 mass% in absolute value, or the average value exceeds 0.1 mass% in absolute value, that is, any one of the above requirements is satisfied. When not satisfy | filling or when not satisfy | filling both requirements, the moldability in an aluminum alloy plate will fall.

  In the aluminum alloy plate according to the present invention, in addition to the region Mg segregation degree X, the plate thickness direction Mg segregation degree Y defined by the plate thickness direction Mg concentration Ct and the plate thickness direction average Mg concentration Ci is restricted to a predetermined value or less. It is preferable that

(Thickness direction Mg concentration: Ct, thickness direction average Mg concentration: Ci)
The plate thickness direction Mg concentration Ct is the Mg concentration measured at the plurality of plate thickness direction measurement points Py described in FIG. 1B as described above, and the plate thickness direction average Mg concentration Ci is measured. It is the average value of Mg concentration Ct in the thickness direction.

  However, the plate thickness direction Mg concentration Ct and the plate thickness direction average Mg concentration Ci are the plate thickness directions measured at least one of the plate width direction measurement points Px of the region when calculating the region Mg segregation degree X. Mg concentration at And what was measured at one point of the plate width direction measurement point Px of the plate width center part is preferable, and what is measured at three points in the vicinity of the plate width center part and both ends of the plate width is further averaged. preferable.

(Thickness direction Mg segregation degree Y)
The sheet thickness direction Mg segregation degree Y is defined by the difference (Ct−Ci) between the sheet thickness direction Mg concentration (Ct) and the sheet thickness direction average Mg concentration (Ci). This is an index of the degree of Mg segregation, and in combination with the region Mg segregation degree X, the degree of Mg segregation of the entire aluminum alloy plate is well reproduced. And in the aluminum alloy plate which concerns on this invention, it is preferable that the absolute value of sheet thickness direction Mg segregation degree Y is 4 mass% or less in the maximum value, and is 0.8 mass% or less in the average value. . The plate thickness direction Mg concentration Ct, the plate thickness direction average Mg concentration Ci, and the plate thickness direction Mg segregation degree Y are the chemical composition of the aluminum alloy plate, the manufacturing conditions described later, specifically, the cooling conditions during casting, It is controlled by the cast plate thickness or the amount of face cutting, the homogenization heat treatment condition, and the final annealing condition.

  When the maximum value or average value of the Mg segregation degree Y in the plate thickness direction becomes larger on the plus side, the β phase due to Mg segregation is likely to precipitate. For this reason, the β phase that is the starting point of fracture increases, the strength and elongation decrease, and the moldability decreases. Further, when the maximum value or average value of the Mg segregation degree Y in the plate thickness direction becomes larger on the minus side, there are many portions where the Mg concentration is significantly lowered, and thus such Mg concentration The strength is lowered in the portion where the temperature is significantly lowered. For this reason, at the time of tensile deformation in molding, non-uniform deformation occurs in which only the portion where the Mg concentration becomes low is preferentially deformed. For this reason, the distortion at the time of shaping | molding will concentrate partially, especially elongation will fall and a moldability will fall.

  Therefore, when the maximum value of the thickness direction Mg segregation degree Y exceeds 4 mass% in absolute value, or the average value exceeds 0.8 mass% in absolute value, that is, any one of the above requirements is satisfied. When not satisfy | filling or when not satisfy | filling both requirements, the moldability in an aluminum alloy plate will fall.

The aluminum alloy plate according to the present invention preferably has an average crystal grain size of 100 μm or less on the surface thereof.
(Average crystal grain size)
By reducing the average crystal grain size of the aluminum alloy plate surface to 100 μm or less, the press formability is improved. When the average crystal grain size exceeds 100 μm and becomes coarse, the press formability tends to decrease, and defects such as cracks and rough skin during molding tend to occur. On the other hand, even if the average crystal grain size is too small, an SS (stretcher strain) mark peculiar to a 5000 series aluminum alloy plate is generated during press molding. From this viewpoint, the average crystal grain size is 20 μm or more. It is preferable to do.

  The crystal grain size referred to in the present invention is the maximum diameter of crystal grains in the plate length (L) direction. The crystal grain size is measured by a line intercept method in the L direction by observing the electrolytically etched surface using a 100 × optical microscope after mechanically polishing the aluminum alloy plate by 0.05 to 0.1 mm. The length of one measurement line is 0.95 mm, and the total measurement line length is 0.95 × 15 mm by observing a total of five fields with three lines per field.

Next, a method for manufacturing the above-described aluminum alloy plate will be described.
The aluminum alloy sheet of the present invention is manufactured by performing a melting casting process, a homogenizing heat treatment process, a cold rolling process, and a final annealing process. Hereinafter, each step will be described.

<Melting casting process>
The melt casting process is a process of melting a high Mg content Al—Mg alloy having the above-described chemical composition and manufacturing a cast plate from the molten metal using a thin plate continuous casting method. As the thin plate continuous casting method, a graphite fixed mold type continuous casting method is preferable.

  The graphite fixed mold type continuous casting method is performed using a thin plate continuous casting apparatus 10 as shown in FIG. 2, and the molten metal 2 stored in the holding furnace 1 is transferred from the casting port 1a to the continuous mold 3 (graphite fixed mold 4). In this method, the molten metal 2 is solidified by the graphite fixing mold 4 while cooling the graphite fixing mold 4 by the water-cooling jacket 5 to form a cast sheet 6 having a thin plate thickness. The produced cast plate 6 is carried out to the next process by the roll 7. In this method, since the cooling rate is higher than that in the DC casting method, a fine cast structure is obtained, and the press formability is improved. Since a sheet having a relatively thin thickness of about 5 mm can be obtained, steps such as hot rough rolling and hot finish rolling after casting, which have been performed with a conventional DC ingot (thickness 200 to 600 mm), can be omitted. .

(Cooling rate)
In the graphite fixed mold type continuous casting method, if the thickness of the cast plate 6 is in the range of 5 to 20 mm, the cooling rate in casting is 15 ° C./s. When the cooling rate is slow, the degree of Mg segregation increases, and the Mg segregation degree (the above-mentioned region Mg segregation degree X and sheet thickness direction Mg segregation degree Y, hereinafter referred to as Mg segregation degree) is within the scope of the present invention. It may be difficult to suppress the precipitation of the β phase, and the precipitation of β phase due to this may not be suppressed. Further, the β phase as a whole tends to become coarse or precipitate in large quantities. As a result, there is a high possibility that the press formability is significantly lowered.

In addition, since this cooling rate is difficult to measure directly, a method known from the dendrite arm spacing (Dendrite secondary branch interval: DAS) of the cast cast plate 6 (for example, Light Metal Society, 8.20, 1988). Published in “Methods of measuring aluminum dendrite arm spacing and cooling rate”). That is, the average interval d between adjacent dendrite secondary arms (secondary branches) in the cast structure of the cast plate 6 is measured by the intersection method (number of fields of view of 3 or more, number of intersections of 10 or more). Using d, the following equation is obtained: d = 62 × C− ^0.337 (where d: dendrite secondary arm interval mm, C: cooling rate ° ^C./s ). Therefore, it can be said that this cooling rate is a solidification rate.

(Pouring temperature)
In the graphite fixed mold type continuous casting method, the pouring temperature when the molten metal 2 is poured into the graphite fixed mold 4 is in the range of liquidus temperature + 50 ° C. to liquidus temperature + 250 ° C., preferably the liquidus temperature + 100 ° C. to liquidus temperature + 150 ° C. When the pouring temperature is lower than the liquidus temperature + 50 ° C., the molten metal is solidified in the mold, and the cast plate breaks easily. When the pouring temperature exceeds the liquidus temperature + 250 ° C., the cooling rate during casting becomes slow, the degree of Mg segregation increases, and it becomes difficult to suppress the degree of Mg segregation within the scope of the present invention. Therefore, it is not possible to suppress the precipitation of β phase and the decrease in formability caused by this.

(Drawing method)
In the graphite fixed mold type continuous casting method, in order to stabilize the casting, the roll 7 for feeding the casting plate 6 in the casting direction is periodically rotated in the direction opposite to the casting direction to retract the casting plate 6. The backward stroke length is in the range of 0.5 to 5 mm, preferably 1 to 3 mm. Further, if a holding time of 1 s or less is added before the retreat, the castability becomes more stable.

  When the retreat stroke length exceeds 5 mm, the segregation layer having a high Mg concentration generated on the surface of the cast plate 6 penetrates into the plate during retreat, and breaks because a cast plate crack occurs at that site. On the other hand, when the retreat stroke length is less than 0.5 mm, the solid-liquid coexisting part is not compressed, and the cast plate 6 breaks in the solid-liquid coexisting part region that is easily broken. Therefore, the reverse stroke length is in the range of 0.5 to 5 mm.

(Average casting speed)
In the graphite fixed mold type continuous casting method, when the molten metal 2 is cast with the graphite fixed mold 4, the average casting speed is in the range of 100 to 500 mm / min, preferably 250 to 350 mm / min. When the average casting speed is less than 100 mm / min, the molten metal 2 rapidly solidifies in the vicinity of the casting port 1a, so that when the roll 7 is pulled out, the drawing resistance at that portion increases. 6 is easy to break. When the average casting speed exceeds 500 mm / min, a molten metal leak due to insufficient cooling occurs near the cast plate outlet 4a.

(Cast plate thickness)
In the graphite fixed mold type continuous casting method, the thickness of the cast plate 6 to be continuously cast is set to a range of 5 to 20 mm. When the plate thickness is less than 5 mm, the molten metal 2 rapidly solidifies in the vicinity of the casting port 1a, so that when the roll 7 is pulled out, the drawing resistance at that portion increases, so the cast plate 6 breaks. easy. When the plate thickness exceeds 20 mm, the cooling rate of casting is remarkably slow, the degree of Mg segregation is increased, and it becomes difficult to suppress the Mg segregation degree within the scope of the present invention, and the β phase resulting therefrom There is a possibility that it is not possible to suppress the precipitation of. Further, the β phase as a whole tends to become coarse or precipitate in large quantities. As a result, there is a high possibility that the press formability is significantly lowered.

(Chamfering process)
In the graphite fixed mold type continuous casting method, Mg segregation is likely to occur on the surface of the cast plate 6. Therefore, it is preferable to perform a chamfering process in which a predetermined amount of both sides of the produced cast plate 6 is cut. The degree of Mg segregation can be suppressed within the scope of the present invention by removing the Mg segregation portions on both sides of the plate by chamfering. Since the depth of the Mg segregation part corresponds to the reverse stroke length, the amount of chamfering is the reverse stroke length of the above-described drawing method.

  In the above, the thin plate continuous casting method has been described by taking the graphite fixed mold type continuous casting method as an example. However, if the Mg segregation degree of the aluminum alloy plate can be suppressed within the scope of the present invention, it is limited to this method. is not. For example, a twin roll type continuous casting method may be used.

  The twin roll type continuous casting method is performed using a thin plate continuous casting apparatus 100 as shown in FIG. 3, and between a pair of rotating water-cooled copper molds (double rolls 500), from the hot water supply nozzle 400 of the holding furnace 200 to the molten metal 300. Is poured and solidified, and between the twin rolls 500, it is reduced immediately after solidification and rapidly cooled to obtain a cast plate 600 having a thin plate thickness. As this twin roll type continuous casting method, the Hunter method, the 3C method and the like are known. In this method, a sheet having a relatively thin plate thickness of 1 to 13 mm can be obtained. Therefore, hot rough rolling, hot finish rolling, etc. after casting performed in a conventional DC ingot (thickness 200 to 600 mm), etc. This step can be omitted.

<Homogenization heat treatment process>
The homogeneous heat treatment step is a step of performing a predetermined homogenization heat treatment on the cast plate 6 produced in the above step. The homogenization heat treatment is performed for a necessary time at a temperature of 400 ° C. or higher and a liquidus temperature or lower. This heat treatment time is approximately 1 second (1 s) or less when the homogenized heat treatment is performed on the cast plate 6 by the thin plate continuous casting method using a continuous heat treatment furnace. By this homogenization heat treatment, the degree of Mg segregation is reduced, and the degree of Mg segregation can be suppressed within the scope of the present invention.

  In the homogenization heat treatment, there is a possibility that an Al—Mg-based intermetallic compound (β phase) is generated when the heating rate and the cooling rate are low in the course of both the heating and cooling of the cast plate 6. There is enough. In particular, the temperature range in which the β phase is likely to be generated is a range in which the temperature at the center of the cast plate is 200 to 400 ° C. when the temperature is raised and a homogenization heat treatment temperature to 100 ° C. when the temperature is cooled. For this reason, when performing such a homogenization heat treatment, in order to suppress the generation of the β phase, the temperature at the center of the cast plate is in the range of 200 to 400 ° C. during the heating to the homogenization heat treatment temperature. It is preferable to set the average temperature rising rate of 5 ° C./s or more. In cooling from the homogenization heat treatment temperature, the average cooling rate in the range from the homogenization heat treatment temperature to 100 ° C is preferably 5 ° C / s or more.

<Cold rolling process>
The cold rolling process is a process in which the cast plate 6 that has been subjected to the homogenization heat treatment is cold-rolled to a thickness of the product plate, for example, 0.1 to 13 mm, and the cast structure is processed into a texture by cold rolling. The Therefore, when the plate thickness of the cast plate 6 to be cold-rolled is thick, it is preferable that intermediate annealing is performed in the middle of cold rolling so that the cold rolling rate in the final cold rolling is 60% or less. The degree of work organization in cold rolling depends on the cold rolling rate of cold rolling, and the cast structure may remain due to the texture control. It is allowed as long as it does not inhibit.

<Final annealing process>
The final annealing step is a step of performing a predetermined final annealing on the cold-rolled sheet produced in the above step. In the final annealing step, the cold rolled sheet is finally annealed at 400 ° C. to the liquidus temperature (° C.). By this final annealing, the degree of Mg segregation is reduced, the degree of Mg segregation can be suppressed within the scope of the present invention, and the precipitation of β phase and the press formability due to this can be suppressed.

  When the final annealing temperature is less than 400 ° C., there is a high possibility that the solution effect will not be obtained, and there is no effect of reducing the degree of Mg segregation. For this reason, the final annealing temperature is preferably 450 ° C. or higher. Furthermore, after this final annealing, it is necessary to cool at a temperature range of 500 to 300 ° C. at an average cooling rate as fast as possible of 10 ° C./s or more. If the average cooling rate after the final annealing is slow and less than 10 ° C./s, the degree of segregation of Mg becomes larger in the cooling process, and the degree of Mg segregation cannot be suppressed within the scope of the present invention. There is a possibility that the β phase precipitation and the press formability due to this cannot be suppressed. The average cooling rate is preferably 15 ° C./s or more.

Next, examples of the present invention will be described.
The Al—Mg-based alloys (Examples A to E, Comparative Examples F and G) having various chemical composition shown in Table 1 were melted by the above-described graphite fixed mold type continuous casting method and twin roll type continuous casting method. Each sheet was cast under the conditions shown in 2. Each cast plate was selectively subjected to chamfering treatment and homogenization heat treatment under the conditions shown in Table 2, and then cold-rolled to a plate thickness of 1.0 mm or a plate thickness of 11.0 mm without hot rolling. Rolled. In addition, the intermediate annealing during these cold rolling was not performed. Next, these cold-rolled sheets were subjected to final annealing in a continuous annealing furnace under the temperature and cooling conditions shown in Table 2 (the holding time at the annealing temperature was 1 second or less), and an aluminum alloy sheet for forming (Example No. .1 to 5, Comparative Example Nos. 6 to 20). Here, the forming aluminum alloy plate (Comparative Example No. 6) was manufactured by a manufacturing method using a twin-roll continuous casting method described in Patent Document 3.

Further, in the graphite fixed mold type continuous casting method, the retreat stroke length was 3 mm, the average casting speed was 300 mm / min, the casting temperature (the pouring temperature): the liquidus temperature + 140 ° C. In the twin roll type continuous casting method, the peripheral speed of the twin roll was 70 m / min, the pouring temperature when pouring the molten metal into the twin roll was the liquidus temperature + 20 ° C., and the twin roll surface was not lubricated. .
Thermodynamic calculation software Thermo-Calc Ver.R (Al-DATA Ver.6) was used to calculate the liquidus temperature of each alloy.

About the obtained aluminum alloy plate for shaping | molding (Example No. 1-5, comparative example No. 6-22), area | region Mg segregation degree X and plate thickness direction Mg segregation degree Y of each alloy plate were calculated in the following procedure, and evaluated. The results are shown in Table 2.
In addition, Example No. The calculation result of the region Mg segregation degree X in FIG. The calculation result of the region Mg segregation degree X of 6 is shown in FIG. And the calculation result of the sheet thickness direction Mg segregation degree Y of Example 1 is shown in FIG. FIG. 7 shows the calculation results of the thickness segregation degree Y of 16 in the plate thickness direction.

(Calculation and evaluation of region Mg segregation degree X)
A square region having a side length of 100 mm is set on the surface of the forming aluminum alloy plate, and the plate width direction within the region is 16.6 mm apart (interval a) at 5 points without including the plate end, the plate length. A total of 25 plate width direction measurement points Px (Nos. 1 to 25) of 5 points were set at 25 mm intervals (interval b) in the direction (see FIG. 1A). Then, the Mg concentration on the surface of the aluminum alloy plate at each measurement point was measured, and the average value of the Mg concentration at each measurement point was calculated to obtain the average Mg concentration Co in the plate width direction.

  Next, at each measurement point of the plate width direction measurement points Px (No. 1 to 25), a plurality of plate thickness direction measurement points Py were set at intervals of 0.01 mm (interval c) in the plate thickness direction (FIG. 1 ( b)). Then, the Mg concentration of the aluminum alloy plate at each measurement point (predetermined plate thickness position (predetermined depth position)) is measured, the average value of the Mg concentration at each measurement point is calculated, and the plate thickness direction average Mg concentration Ci It was.

  Then, the plate thickness direction average Mg concentration Ci and the plate width direction average Mg concentration Co at each measurement point of the plate width direction measurement point Px (No. 1 to 25) are defined by the difference (Ci-Co) between the two. Region Mg segregation degree X was calculated (see FIGS. 4 and 5). For measurement of Mg concentration, EPMA (JEOL X-ray microanalyzer: JXA-8800RL) was used.

  The evaluation of the region Mg segregation degree X is satisfied (◯) when the absolute value of the maximum value is 0.5% by mass or less, unsatisfactory (×) when the absolute value exceeds 0.5% by mass, and the absolute value of the average value Satisfactory (O) when the value was 0.1% by mass or less, and unsatisfactory (x) when the value exceeded 0.1% by mass.

(Calculation and evaluation of sheet thickness direction Mg segregation degree Y)
One point (No. 13) is selected from the plate width direction measurement points (No. 1 to 25), and the plate thickness direction (a plurality of plate thickness direction measurement points Py) measured at the measurement point is selected. The Mg concentration was defined as the Mg concentration Ct in the thickness direction. And the plate thickness direction Mg segregation degree Y defined by the difference (Ct-Ci) of both was computed using the plate thickness direction average Mg density | concentration Ci calculated above as those average values. When the plate thickness direction measurement point Py is 0.01 mm or 1.0 mm, it is the surface of the alloy plate (see FIGS. 6 and 7).

  The evaluation of the thickness direction Mg segregation degree Y is satisfied when the absolute value of the maximum value is 4% by mass or less (O), and is unsatisfactory (X) when the absolute value exceeds 4% by mass, and the absolute value of the average value is Satisfied (◯) when 0.8% by mass or less, and unsatisfactory (x) when exceeding 0.8% by mass.

  Moreover, about the obtained aluminum alloy plate for shaping | molding (Example No. 1-5, Comparative Examples 6-22), the average crystal grain size of each alloy plate was measured in accordance with the measuring method described above.

(Average crystal grain size)
Example No. 1-5, comparative example No.1. The average crystal grain sizes of 6 to 10, 12 to 17, and 19 to 22 were in the range of 30 to 60 μm. Comparative Example No. The average crystal grain sizes of 11 and 18 exceeded 100 μm.

  Furthermore, about the obtained aluminum alloy plate for shaping | molding (Example No. 1-5, comparative example No. 6-22), the press formability of each alloy plate was evaluated in the following procedure. The results are shown in Table 2.

(Evaluation of press formability)
A tensile test is performed using a test piece taken from the alloy plate, the tensile strength (TS: MPa), the total elongation (EL:%) are measured, and the strength ductility balance value defined by (TS) × (EL) The press formability was evaluated. When the strength ductility balance value was 11000 or more, it was judged as acceptable (◯), and when it was less than 11,000, it was judged as unacceptable (x).

  In addition, the specimens are collected from any five locations with a distance of 100 mm or more in the longitudinal direction of the alloy plate, and the (TS) value and (EL) value are average values of the measured values of the five specimens. Was used. Furthermore, the tensile test was performed in accordance with JISZ2201, and the shape of the test piece was performed with a JIS No. 5 test piece so that the longitudinal direction of the test piece coincided with the rolling direction of the alloy plate. The crosshead speed was 5 mm / min, and the test was performed at a constant speed until the test piece broke.

表１、２の結果から、本発明の要件を満足する実施例Ｎｏ．１〜５は、本発明の要件を満足しない比較例Ｎｏ.６〜２２に比べて、プレス成形性において優れていた。

From the results of Tables 1 and 2, Example No. satisfying the requirements of the present invention. 1-5 were excellent in press moldability compared with comparative example No. 6-22 which does not satisfy the requirements of this invention.

  Specifically, Comparative Example No. 6 is an alloy plate described in Patent Document 3, but the Mg segregation degree (region Mg segregation degree) cannot be suppressed within the scope of the present invention, so press formability. It was inferior to. In Comparative Examples Nos. 7 and 14, the Mg segregation degree can be suppressed within the range of the present invention, but since the Mg content is below the lower limit, the strength ductility balance is low and the press formability is poor. It was. In Comparative Examples No. 8 and 15, since the Mg content exceeded the upper limit, the degree of Mg segregation was large and the press formability was poor. Comparative Example No. Since 9, 10, 16, and 17 were not subjected to homogenization heat treatment, the degree of Mg segregation was large and the press formability was poor. Since Comparative Example No. 11 and 18 had a slow cooling rate during casting, the degree of Mg segregation was large and the press formability was poor. In Comparative Examples No. 12 and 19, since the final annealing temperature was low, the Mg segregation degree was large and the press formability was poor. In Comparative Examples 13 and 20, the cooling rate during the final annealing was slow, so the degree of Mg segregation was large and the press formability was poor. Although the comparative example 21 performed the face-cutting process which cuts the plate | board both surfaces of the cast board produced by the twin roll type continuous casting method 1.75mm, Mg segregation degree (area | region Mg segregation degree) can be suppressed in the range of this invention. Therefore, the press formability was inferior. Since the comparative example 22 did not chamfer both sides of the cast plate produced by the graphite fixed mold type continuous casting method, the degree of Mg segregation was large and the press formability was poor.

a, b, c interval L plate length W plate width T plate thickness Px plate width direction measurement point Py plate thickness direction measurement point 1 holding furnace 1a casting port 2 molten metal 3 continuous casting mold 4 graphite fixed mold 4a casting plate outlet 5 Water-cooled jacket 6 Cast plate 7 Roll 10 Thin plate continuous casting device 100 Thin plate continuous casting device 200 Holding furnace 300 Molten metal 400 Hot water supply nozzle 500 Twin roll 600 Cast plate

Claims (4)

Mg: 6.0-15.0% by mass, and the balance is a forming aluminum alloy plate made of Al and impurities,
In a square region having one side of the total plate width set on the surface of the forming aluminum alloy plate, at a plurality of plate width direction measurement points set at predetermined intervals in the plate width direction and the plate length direction. Mg concentration is measured, and the average value of those Mg concentrations is the average Mg concentration in the plate width direction (Co),
At the measurement points in the plate width direction, the Mg concentration is measured at a plurality of plate thickness direction measurement points set over the entire plate thickness at a predetermined interval in the plate thickness direction, and the average value thereof is calculated as the plate thickness direction average Mg concentration (Ci )
The absolute value of the region Mg segregation degree (X) defined by the difference (Ci-Co) between the plate thickness direction average Mg concentration (Ci) and the plate width direction average Mg concentration (Co) is 0.5. An aluminum alloy sheet for forming, characterized by having a mass% or less and an average value of 0.1 mass% or less. In addition to the region Mg segregation degree (X),
In calculating the region Mg segregation degree (X), at least one of the measurement points in the plate width direction, the Mg concentration measured over the entire plate thickness at a predetermined interval in the plate thickness direction is the Mg concentration in the plate thickness direction (Ct). When
The absolute value of the thickness direction Mg segregation degree (Y) defined by the difference (Ct−Ci) between the thickness direction Mg concentration (Ct) and the thickness direction average Mg concentration (Ci) is 4 masses. %, And the average value is 0.8 mass% or less, The aluminum alloy sheet for shaping | molding of Claim 1 characterized by the above-mentioned.   The forming aluminum alloy sheet according to claim 1 or 2, wherein the Mg content is more than 8 mass% and not more than 14 mass%.   The impurities are Fe: 1.0 mass% or less, Si: 0.5 mass% or less, Ti: 0.1 mass% or less, B: 0.05 mass% or less, Mn: 0.3 mass% or less, Cr : 0.3% by mass or less, Zr: 0.3% by mass or less, V: 0.3% by mass or less, Cu: 1.0% by mass or less, Zn: 1.0% by mass or less The aluminum alloy sheet for forming according to any one of claims 1 to 3, wherein the aluminum alloy sheet for forming is formed.

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