JP4202894B2 - Mg-containing Al alloy - Google Patents

Description

  The present invention relates to an Mg-containing Al alloy having excellent formability and good surface quality after forming.

  The Mg-containing Al alloy of the present invention is excellent in moldability such as drawing workability and moldability, and is excellent in surface properties after processing. For example, a body sheet, a skeleton material, a wheel, a ship, and an electric product of an automobile. It can use suitably as materials, such as an outer plate | board.

  In the present invention, unless otherwise specified, the Mg-containing Al alloy means to include both an Al—Mg-based alloy (so-called 5000-based Al alloy) and an Al—Mg—Si-based alloy (so-called 6000-based Al alloy). is there.

  Al alloy has been attracting attention as a material that can save energy and resources due to its light weight and excellent recyclability compared to steel materials. In recent years, it has been attracting attention as a material for automobile body seats, skeleton materials, wheels, etc. It is being used. The material used for such applications is required to have properties such as strength, good moldability and weldability, and from this viewpoint, an Al alloy containing Mg is used.

  Mg-containing Al alloys can be broadly classified into Al-Mg alloys (so-called JIS standard 5000 series Al alloys) and Al-Mg-Si alloys (so-called JIS standard 6000 series Al alloys).

  Among these, the 5000 series Al alloy is an Al alloy containing Mg as an essential component, and Mg contributes to improvement in strength and press formability. Examples of the 5000 series Al alloy include JIS standard 5052 alloy, 5154 alloy, and 5454 alloy.

  On the other hand, the 6000-based Al alloy is an Al alloy containing Mg and Si as essential components, and Mg and Si contribute to improving the age hardening ability of the Al alloy. For this reason, the moldability is good due to low yield strength during press molding and bending, but heat treatment (for example, baking coating treatment) after molding improves artificial aging and yield strength, resulting in high strength. Become. In addition, since the 6000 series Al alloy has a smaller amount of alloying elements than the 5000 series Al alloy, it can be easily reused as a melting material (melting raw material) and is excellent in recyclability.

  Since these Mg-containing Al alloys are thin and high in strength, they are especially used for internal structural members of automobiles, and outer panels (outer plates) and inner parts used in panel structures such as hoods, fenders, doors, roofs and trunk lids. It is being used as a material for panels such as panels (inner plates).

  However, it is known that when the Mg-containing Al alloy is formed into a final product, surface irregularities such as stretcher strain marks and ridging marks are generated. Among them, the stretcher strain mark (hereinafter sometimes referred to as “SS mark”) is non-uniform deformation or streak-like texture unevenness caused by molding, and this is a flame-like stripe on the surface of the molded product. Since the pattern is generated, the appearance and aesthetics may be remarkably impaired and the commercial value may be lowered. This SS mark is particularly likely to occur when a 5000 series Al alloy is formed. This is because a 5000 series Al alloy has a larger amount of alloy element added than other Al alloys, and therefore, the alloy element moves by diffusion and is easily fixed to dislocations. That is, when the forming process is performed with the alloy element fixed to the dislocation, the fixed alloy element is released from the dislocation, but when this phenomenon occurs at once, the movement of the dislocation is concentrated on the same sliding surface. And slip lines are generated. This slip line becomes the SS mark.

  The ridging mark is a long streak defect generated on the surface in the rolling direction by plastic working, and is particularly likely to occur when forming a 6000 series Al alloy.

  Therefore, the present applicant has previously proposed the techniques of Patent Documents 1 to 3 for the purpose of preventing deterioration of the surface quality due to molding.

  Among these, Patent Document 1 proposes a method for producing a 5000 series Al alloy rolled plate with excellent appearance that suppresses the occurrence of SS marks by controlling the average grain size of the plate surface and inside to an appropriate range. Yes. Patent Document 2 proposes a 6000 series Al alloy for forming with improved surface properties by defining the degree of integration of the Cube orientation at the plate surface layer portion and the plate thickness ¼ portion. Further, Patent Document 3 proposes a 6000 series Al alloy plate in which the distribution density of each orientation is defined by paying attention to the crystal orientation components (Goss orientation, PP orientation, Brass orientation) of the {110} plane. It has been confirmed that the surface properties after molding are improved to some extent by these techniques. However, in recent years, with the diversification of designs, complex molding processing (for example, bending processing such as flat hemming processing or press processing such as overhang processing or deep drawing processing) has been required, and the molding processing conditions have become strict. In this case, the surface quality after the molding process may be deteriorated, and further improvement has been demanded.

On the other hand, as a technique for improving the bending workability and corrosion resistance of an Al alloy, Patent Document 4 proposes an Al alloy plate that defines the proportion of crystal grain boundaries in which the orientation difference between adjacent crystal grains is 15 ° or less. Yes. This document also describes that the occurrence of rough skin and ridging marks is prevented after molding. However, as a result of further studies by the present inventors, if the molding process conditions are made more severe and the amount of strain to be introduced is increased, the surface quality after the molding process may also deteriorate, leaving room for improvement.
Japanese Patent Laid-Open No. 10-219412 (see [Claims], [0054], etc.) JP 11-189836 A (see [Claims], [0008], [0034], etc.) Japanese Patent Laid-Open No. 11-236639 (see [Claims], [0010], [0016], etc.) JP 2003-171726 A (see [Claims], [0007], [0060], etc.)

  The present invention has been made in view of such a situation, and its purpose is excellent in moldability such as drawability and moldability, and the surface after the molding process even if a severe molding process is performed. An object of the present invention is to provide an Mg-containing Al alloy having good properties (particularly, having less surface irregularities).

The Mg-containing Al alloy according to the present invention that has solved the above-mentioned problems is an Al alloy containing Mg, and the crystal plane orientation of crystal grains on the alloy surface is measured, and the plane orientation is (100) plane. When the area ratio (%) occupied by crystal grains within 10 ° from A is A and the area ratio (%) occupied by crystal grains within 20 ° from (100) plane is B, the following formula (1) and (2) The point is that the equation is satisfied.
10 ≦ B ≦ 60 (1)
A / B ≦ 0.50 (2)

  As the Mg-containing Al alloy of the present invention, when the grain size of the crystal grains on the alloy surface is measured, the area ratio occupied by the crystal grains exceeding twice the average grain size is 5.0% with respect to the whole. The following are preferred.

  The component composition of the Mg-containing Al alloy according to the present invention is not particularly limited, and may be any of an Al alloy containing Mg (5000 series Al alloy) or an Al alloy containing Mg and Si (6000 series Al alloy).

  Among these, in the case of a 5000 series Al alloy, it is preferable that Mg is contained in an amount of 2 to 8% (meaning “mass%”, the same shall apply hereinafter), and the balance is composed of Al and inevitable impurities. Fe: 1.5% or less (not including 0%), Si: 0.5% or less (not including 0%), Mn: 1% or less (not including 0%), Cr: 0.5% It is recommended to contain one or more elements selected from the group consisting of the following (not including 0%) and Zr: 0.5% or less (not including 0%).

  On the other hand, in the case of a 6000 series Al alloy, it is preferable that Mg: 0.1 to 3% and Si: 0.1 to 2.5% are contained, respectively, and the balance is composed of Al and inevitable impurities. Furthermore, Fe: 1.5% or less (not including 0%), Mn: 1% or less (not including 0%), Cr: 0.5% or less (not including 0%), and Zr: 0.5% It is recommended to contain one or more elements selected from the group consisting of the following (excluding 0%).

  In any of the above-described 5000 series Al alloy and 6000 series Al alloy, as other elements, (a) Cu: 1% or less (not including 0%) and / or Zn: 1.5% or less ( (B) Ti is preferably contained alone in combination with 0.005 to 0.2%, or B: 0.0001 to 0.05%.

  According to the present invention, the Mg-containing Al is excellent in drawing workability such as drawing workability and formability, and also has good surface properties after forming work (especially with less surface irregularities) even when subjected to severe forming work. Can provide alloys.

  As described above, in recent years, with the diversification of designs, Al alloys have been subjected to complicated forming processing. However, it has been pointed out that the surface quality after forming processing is significantly lowered when the forming processing conditions are strict. Moreover, the evaluation standard level of the surface property is considerably higher than the conventional level.

  Therefore, the present inventors have conducted research focusing on the crystal orientation (surface orientation of the surface), in particular, in order to ensure good surface quality even when molding is performed under severe conditions. The reason for paying attention to the crystal orientation is that due to the difference in crystal orientation, the introduction strain amount (crystal deformation amount) of adjacent crystal grains differs and surface irregularities are likely to occur. Then, among crystal orientations, crystal grains having (100) plane orientation [crystal grains of (100) plane] were found to be the main factors governing the occurrence of surface irregularities, and further intensive studies were conducted. As a result, the dispersion degree (degree of variation) of the (100) plane of the plate surface portion is increased [specifically, as described later, the area ratio B occupied by crystal grains within 20 ° from the (100) plane is increased. On the other hand, by reducing the area ratio A occupied by crystal grains within 10 ° from the (100) plane, it was found that the intended purpose was achieved, and the present invention was completed. Hereinafter, the present invention will be described in detail.

  In particular, in the present invention, the most important point exists in the case where the surface is controlled by the plate surface orientation [especially (100) plane] rather than being controlled by each crystal orientation unit as in the prior art. In other words, when controlling the texture as in the past to improve moldability, various properties such as moldability, bendability and corrosion resistance change depending on the orientation balance. It is necessary to divide. However, in reality, there are a wide variety of plate thicknesses and processing conditions, and it is difficult to make them in consideration of the surface properties after the forming process in actual operation.

As described above, the Mg-containing Al alloy of the present invention has an area ratio (%) occupied by crystal grains whose plane orientation is within 10 ° from the (100) plane when the plane orientation of crystal grains on the alloy surface is measured. When the area ratio (%) occupied by crystal grains within 20 ° from the A, (100) plane is B, the following formulas (1) and (2) are satisfied.
10 ≦ B ≦ 60 (1)
A / B ≦ 0.50 (2)

  Here, the texture of the Al alloy will be described. It is known that a texture such as a Cube orientation and a Goss orientation is generated in the Al alloy as shown in FIG. The formation of the texture differs depending on the processing method even if the crystal system is the same, and in the case of a rolled material, it is expressed by the rolling surface and the rolling direction. That is, as shown below, the rolling surface is represented by {xxx} and the rolling direction is represented by <ΔΔΔ>. In addition, (circle) and (triangle | delta) have shown the integer.

Based on such an expression method, each direction is expressed as follows. For more details, see “Cross Texture” written by Shinichi Nagashima (published by Maruzen Co., Ltd.) and the Light Metal Society of Japan, “Light Metal” Commentary Vol.43 (1993) P.285-293.
Cube orientation: {001} <100>
CR orientation: {001} <520>
RW orientation: {001} <110> [Cube orientation in which the (100) plane rotates the plate surface]
Goss orientation: {011} <100>
Brass orientation: {011} <211>
S direction: {123} <634>
Cu orientation: {112} <111>
(Or D direction: {4 4 11} <11 11 8>)
SB orientation: {681} <112>

  As for the recrystallized texture, it is also known that the Cube orientation is formed and a recrystallized orientation close to the Brass orientation, Cu orientation, and S orientation is formed.

  Of these, in the present invention, the above formulas (1) and (2) are defined as orientation references having the (100) plane. Here, the orientation having the (100) plane includes the Cube orientation, the RW orientation, and the CR orientation, as shown in FIG. These are based on the reason that, unlike other crystal orientations, distortion is less likely to occur during molding and deformation is difficult. The Cube orientation is a main orientation of the recrystallized texture of aluminum as is generally known, and is one of the main crystal orientations in Al-Mg alloys and Al-Mg-Si alloys. Yes, RW orientation and CR orientation other than Cube orientation are also processed from various directions with respect to the rolling direction of the plate in actual forming processing (for example, press processing or drawing processing). Because it is necessary to control.

  In the present invention, it is important to shift the crystal orientation of the (100) plane, which is difficult to be strained during molding, from the ideal crystal plane [that is, (100) plane]. From this point of view, according to the present invention, as defined in (1) above, when the plate surface orientation of all crystal grains on the alloy surface is measured, the area ratio occupied by crystal grains whose plate surface orientation is within 20 ° from the (100) plane. B was determined to be 10 to 60% with respect to the whole. If the area ratio is less than 10%, the strain introduced into the surface portion becomes too large, resulting in defects, and the surface properties after molding are reduced. Preferably it is 15% or more. On the other hand, if the area ratio becomes too high, distortion is difficult to be introduced at the time of molding, and an internal defect is generated because the molding process or drawing process is obstructed, resulting in poor surface properties. From this point of view, the area ratio should be kept below 60%. More preferably, it is 55% or less.

  Further, in the present invention, as defined in (2) above, the area ratio occupied by crystal grains whose plate orientation is within 10 ° from the (100) plane is A, and the area ratio occupied by crystal grains within 20 ° from the (100) plane is When A is B, A / B is 0.50 or less.

  Here, A / B of 0.50 or less means that the degree of dispersion (degree of deviation) from the ideal crystal plane [that is, (100) plane] becomes large when the (100) plane is used as a reference. The difference in strain between adjacent crystal grains can be alleviated and the surface unevenness can be reduced. When A / B exceeds 0.50, the area ratio of A increases. That is, there are many crystal grains having ideal crystal planes or crystal grains whose deviation from the ideal crystal plane is within 10 °, and the amount of strain introduced into each crystal grain during molding cannot be made uniform. The difference in the amount of strain introduced into the crystal grains becomes large, and irregularities are generated on the surface portion. Preferably, the A / B is 0.48 or less.

  Next, a method for measuring the plate orientation of crystal grains on the alloy surface will be described.

  First, in the present invention, the alloy surface refers to a surface at a position where the depth from the outermost surface of the alloy is D / 4, where D is the plate thickness. Then, the sample surface taken from the position of D / 4 is mechanically polished, then buffed, and then electrolytically polished to obtain a plate surface orientation measuring test piece.

  The plate surface orientation of the crystal grains in the test piece is measured using SEM-EBSP (also referred to as Electron Back Scattering Pattern (EBSD)). In the examples described later, SEM (JEOL JSM 5410) manufactured by JEOL Ltd. is used as the SEM device, EBSP: TSL (OIM) is used as the EBSP measurement / analysis system, the measurement area is 1000 μm × 1000 μm, and the measurement step interval is 3 μm or less.

  The plate plane orientation is measured for each crystal grain observed in the measurement region, and the area ratio B occupied by the crystal grains whose deviation from the (100) plane is within 20 ° with respect to all the crystal grains and the (100) plane The area ratio A / B is calculated by calculating the area ratio A occupied by the crystal grains having a deviation of 10 ° or less with respect to all the crystal grains.

  Furthermore, in the present invention, when the grain sizes of all the crystal grains existing on the alloy surface (specifically, the crystal grains observed in the measurement region) are measured, the crystal grains exceeding twice the average grain size. The area ratio occupied by is preferably 5.0% or less with respect to the whole. When the surface of the Mg-containing Al alloy is observed, crystal grains of various sizes are observed. However, if extremely coarse crystal grains are present, non-uniform deformation occurs near the coarse crystal grains, and after forming Cause unevenness of the tissue surface. Therefore, it is preferable that the distribution of the crystal grain size is uniform. From this viewpoint, the area ratio occupied by the crystal grains exceeding twice the average crystal grain size is set to 5.0% or less based on the whole. More preferably, it is 4.5% or less.

  Here, the average crystal grain size is obtained by measuring the maximum diameter of each crystal grain observed in a predetermined measurement region using the SEM-EBSP and calculating the average value of the obtained results.

  The requirements regarding the crystal orientation that characterize the present invention have been described above. Next, the component composition of the Al alloy targeted in the present invention [Al alloy containing Mg (5000 series Al alloy) or Al alloy containing Mg and Si (6000 series Al alloy)] will be described.

  Among these, in the case of a 5000 series Al alloy (Al-Mg series Al alloy), it is preferable to contain 2 to 8% of Mg. Mg is an element that enhances strength and formability by solid solution strengthening, and exerts its effect even when added in a small amount. However, when it is contained at 2% or more, press formability is particularly good. More preferably, it is 2.5% or more, and further preferably 3% or more. On the other hand, the upper limit of the Mg content is not particularly limited as long as it is within a range that can maintain high yield strength (preferably high yield strength and good press formability), but if the content is too high, hot workability deteriorates. Since the production tends to be difficult, it is preferably 8% or less. More preferably, it is 7% or less, more preferably 6% or less, and particularly preferably 5.5% or less.

In the case of a 6000 series Al alloy (Al-Mg-Si series Al alloy), it is preferable to contain Mg: 0.1-3% and Si: 0.1-2.5%, respectively. By containing Mg and Si together and maintaining at an appropriate temperature after the solution treatment, an aggregate of Mg ₂ Si structure called GP zone and an intermediate phase in which this aggregate is further developed are generated. Artificial age hardening. Therefore, it becomes an Al alloy plate with high yield strength (that is, yield strength after artificial age hardening). Even if Mg and Si are added in a small amount, the effect is exhibited. However, in order to ensure the artificial age-hardening ability, Mg is contained in the range of 0.1 to 3% and Si in the range of 0.1 to 2.5%, respectively. It is preferable. A more preferable lower limit of the Mg content is 0.3% and an upper limit is 2%, and a more preferable lower limit is 0.4% and an upper limit is 1.5%. On the other hand, the more preferable lower limit of the Si content is 0.3% and the upper limit is 1.5%, and the more preferable lower limit is 0.4% and the upper limit is 1.2%.

  The ratio of Si to Mg (Si / Mg) is not particularly limited, but is preferably 1.0 or more and 10 or less, and more preferably 1.5 or more and 6 or less in terms of mass ratio.

  Any of the above Mg-containing Al alloys may contain other elements in addition to these essential components, and the balance is Al and inevitable impurities. When other elements to be described later are contained, the Al content is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Further, the purity of Al is preferably high, and the recyclability after using the Mg-containing Al alloy can be enhanced by using high-purity Al as a base material.

  Here, the other elements include (1) an element that refines crystal grains (for example, Fe, Si, Mn, Cr, Zr, Ti, V, etc.), and (2) an element that increases the age hardening rate (for example, , Cu, Zn, etc.), (3) elements that refine the ingot structure (for example, Ti, B, etc.) are preferably used. These elements may be contained alone or in combination of two or more selected arbitrarily. Hereinafter, the effects and contents of the element additions (1) to (3) will be described.

  (1) As an element for refining crystal grains (for example, Fe, Si, Mn, Cr, Zr, Ti, V, etc.), in the case of a 5000 series Al alloy, in addition to Mg, Fe: 1.5% or less (Not including 0%), Si: not more than 0.5% (not including 0%), Mn: not more than 1% (not including 0%), Cr: not more than 0.5% (not including 0%), and Zr: 0.5 It is preferable to contain one or more elements selected from the group consisting of% or less (not including 0%). In the case of a 6000 series Al alloy, in addition to the above Mg and Si, Fe: 1.5% or less (not including 0%), Mn: 1% or less (not including 0%), Cr: 0.5% or less It is preferable to contain one or more elements selected from the group consisting of (not including 0%) and Zr: 0.5% or less (not including 0%).

  As described above, Fe, Si, Mn, Cr, and Zr are all elements that refine crystal grains, and contribute to improvement of mechanical properties (for example, strength, ductility, toughness, curability, and the like).

In particular, Fe and Si are usually mixed as inevitable impurities in the Al alloy. In the Al alloy, an Al—Fe system [for example, Al _m Fe (where m is an integer of 3 to 6) or Al ₆ ( Fe, Mn), Al ₁₂ (Fe, Mn) ₃ Cu ₁₂ , Al ₇ Cu ₂ Fe, etc.], Al—Fe—Si system [eg, α-AlFeSi, β-AlFeSi, etc.], Al—Mn—Fe—Si Various intermetallic compounds of the system (for example, crystallized substances and precipitates) are formed, and the effect of promoting the refinement of crystal grains and improving the workability and the like. Further, the texture can be controlled by adding Fe or Si.

  Among these, Fe contributes to the promotion of refinement of crystal grains and the improvement of formability by appropriately distributing intermetallic compounds. In order to effectively exhibit such an effect of adding Fe, the content is preferably 0.01% or more, more preferably 0.05% or more, and further preferably 0.1% or more. However, if the Fe content is too large, coarse crystals are formed and the workability is deteriorated, so the upper limit is preferably made 1.5%. More preferably, it is 1% or less, More preferably, it is 0.6% or less.

  In particular, in the case of a 5000 series Al alloy, formability is improved by containing Si instead of Fe or in combination with Fe. However, in the case of 5000 series Al alloy, when Si content exceeds 3%, addition of Si exceeding 0.5% causes age hardening by Si addition in addition to solid solution strengthening by the original Mg addition, Since Si becomes too hard and the moldability is hindered, the Si content should be suppressed to 0.5% or less. More preferably, it is 0.45% or less, More preferably, it is 0.4% or less.

  In addition, Mn, Cr, Zr, Ti, and V are elements that promote the refinement of crystal grains and act to improve workability and surface properties. However, if the content is too large, a coarse compound is formed in the Al alloy, and this compound serves as a starting point of fracture, which not only promotes surface irregularities, but also deteriorates workability. The preferred contents of these elements are as follows.

  Mn: The effect is exhibited by addition of a small amount, but is preferably 0.02% or more, more preferably 0.06% or more. On the other hand, the preferable upper limit of Mn is 1%, and the more preferable upper limit is 0.5%.

  Cr: The effect is exhibited by addition of a small amount, but is preferably 0.01% or more, more preferably 0.05% or more. On the other hand, the preferable upper limit of Cr is 0.5%, the more preferable upper limit is 0.3%, and the further preferable upper limit is 0.2%.

  Zr: The effect is exhibited by addition of a small amount, but is preferably 0.01% or more, more preferably 0.05% or more. On the other hand, the preferable upper limit of Zr is 0.5%, the more preferable upper limit is 0.3%, and the more preferable upper limit is 0.2%.

  Ti: The effect is exhibited by addition of a small amount, but is preferably 0.005% or more, more preferably 0.01% or more. On the other hand, the preferable upper limit of Ti is 0.2%, the more preferable upper limit is 0.15%, and the further preferable upper limit is 0.1%.

  (2) As an element (for example, Cu or Zn) that increases the age hardening rate, Cu: 1.0% or less (not including 0%) and / or Zn: 1.5% or less (not including 0%) It is preferable to do.

  Cu and Zn are both elements that increase the age hardening rate, and exert their effects when added in a small amount. However, if the content is too large, a coarse compound is formed and bending workability deteriorates in particular. In particular, when the Cu content is too large, the corrosion resistance is also deteriorated. Preferred amounts when these elements are added are as follows.

  Cu: The effect is exhibited by addition of a small amount, but it is preferably at least 0.1%, more preferably at least 0.2%. On the other hand, the preferable upper limit of Cu is 1%, and the more preferable upper limit is 0.6%.

  Zn: The effect is exhibited when added in a small amount, but it is preferably at least 0.1%, more preferably at least 0.2%. On the other hand, the preferable upper limit of Zn is 1.5%, the more preferable upper limit is 1.0%, and the more preferable upper limit is 0.6%.

  In addition, when using together Cu and Zn, it is preferable to set it as 1.5% or less in total, More preferably, it is 1.4% or less.

  (3) As an element for refining the ingot structure (for example, Ti, B, etc.), Ti may be further contained alone by 0.005 to 0.20%, or B may be contained in combination with 0.0001 to 0.05%. preferable.

  Among these, in order to exhibit the effect of adding Ti effectively, the lower limit is made 0.005%. However, if the content is too large, a coarse Al—Ti intermetallic compound is crystallized to hinder improvement in formability, so the upper limit is preferably made 0.2%. More preferably, it is 0.15% or less.

  B, like Ti, is an element for refining the ingot crystal grains, but the effect cannot be obtained by adding B alone, and the desired effect is exhibited only when used together with Ti. In order to effectively exhibit the effect of addition of B by using such Ti together, it is preferable to add B in an amount of 0.0001% or more. However, if the B content is too large, a coarse Ti—B intermetallic compound is formed and the workability is deteriorated, so the upper limit is preferably made 0.05%.

  Next, a method for efficiently producing the Mg-containing Al alloy according to the present invention will be described.

  As described above, in the present invention, it is important to appropriately control (disperse) the plane orientation of crystal grains on the alloy surface in relation to the (100) plane. In order to produce such an Mg-containing Al alloy, it is important to appropriately control the conditions for introducing strain into the surface, especially during hot rolling, and the structure and texture formed thereby. In particular, the tension during hot finish rolling was found to be an important factor.

  That is, the Al alloy is generally manufactured through steps of homogenization heat treatment (soaking), hot rolling (hot rough rolling and hot finish rolling), cold rolling, and final annealing. The specific conditions of each manufacturing process vary depending on the amount of alloy elements, etc., and the plane orientation of the crystal grains obtained thereby changes, so that the desired Al alloy can be obtained, so that the overall conditions in the series of manufacturing processes Should be set appropriately. Hereinafter, preferable ranges in each step will be described.

  First, homogenization heat treatment is performed on an ingot such as a slab obtained by a semi-continuous casting method (DC casting method: Direct Chill) (soaking step). By performing the homogenization heat treatment, the amount of Mg dissolved in the Al matrix increases, and the texture of the hot-rolled sheet can be controlled. The conditions of the soaking process vary depending on the type of alloy and the like, and in the case of an Al—Mg alloy (5000 series Al alloy), it is preferable that the soaking temperature is about 400 to 550 ° C. and the holding time is about 1 to 20 hours. . However, when heated for a long time, other alloy elements such as Mn and Fe-based precipitates are generated, and a desired textured form cannot be obtained by hot-rolled sheets.

On the other hand, in the case of an Al—Mg—Si-based alloy (6000-based Al alloy), it is preferable that the soaking temperature is 500 ° C. or higher and the holding time is 4 hours or longer. This is because, by increasing the heat treatment time, the above-described Mg ₂ Si and Si crystallized substances and Si precipitates can be dissolved. However, when transition elements such as Fe and Mn are added to the alloy, a coarse precipitate is formed when heated for more than 20 hours.

  Next, hot rough rolling is performed on the ingot subjected to the homogenization heat treatment. The starting temperature of the hot rough rolling is preferably about 400 to 560 ° C. When the temperature is lower than 400 ° C., rolling is performed without generating sufficient recrystallization during hot rolling, so that the balance of the texture is lost. On the other hand, when the temperature exceeds 560 ° C, the surface of the hot-rolled sheet is oxidized or seized, and the recrystallized grains are coarsened, which tends to cause deterioration of surface properties, deterioration of formability, and rough skin after forming. is there. The end temperature of hot rough rolling may be about 350 to 470 ° C.

  After the hot rough rolling described above, hot finish rolling is performed. As described above, in the present invention, it is extremely important to control the tension during the hot finish rolling within an appropriate range.

  That is, hot finish rolling will be described. In the case of Al alloy, it is usually performed by a tandem rolling mill equipped with a stand of about 3 to 6 stages, and finished into a rolled plate having a desired size. As a result of investigations by the present inventors, it has been clarified that the tension between the stands in the hot finish rolling affects the strain state of the surface layer portion, and the degree of dispersion from the (100) plane of the finally obtained Al alloy sheet. It turns out that you decide. Therefore, it has become clear that in order to produce an Mg-containing Al alloy that satisfies the requirements defined in the present invention, the average value of the tension between all the stands should be in the range of 3 to 20 MPa.

  Here, the average value of the tension between all the stands is calculated as follows. For example, when hot finish rolling is performed by a tandem rolling mill equipped with a four-stage stand, the tension between the first stand and the second stand is σ1, the tension between the second stand and the third stand is σ2, If the tension between the third stand and the fourth stand is expressed as σ3, there are three places between the stands, so the average value of the tension between all the stands can be calculated as (σ1 + σ2 + σ3) / 3.

  Incidentally, conventionally, the tension between the stands is not controlled under the general Al alloy operating conditions, or even if it is controlled, it exceeds 20 MPa, and is generally about 25 to 36 MPa. The reason why the tension between the stands exceeds 20 MPa is that there is a merit that rolling meandering and coil winding failure (such as generation of scratches) can be suppressed. However, as described above, from the viewpoint of improving the surface quality after the molding process, it is important to make the tension between the stands slightly smaller than before. In other words, if the average value of tension between all stands exceeds 20 MPa, the equivalent strain due to rolling increases near the surface layer, and then cold rolling (may be annealed after hot rolling depending on the required properties) When intermediate annealing is performed in the middle of cold rolling and then final annealing is performed, the recrystallization texture has a higher degree of accumulation of crystal grains having a (100) plane. That is, the value of A / B exceeds 0.50, and the degree of dispersion on the (100) plane becomes small. More preferably, the average value of the tension between all the stands is adjusted to 18 MPa or less.

  However, if the average value of the tension is less than 3 MPa, the generation of the (100) plane on the surface portion of the plate surface is insufficient, and the formability tends to be hindered. On the other hand, if the tension is too small, it is likely to cause rolling defects and poor prospects, rolling plate meandering, coil winding defects (scratches), etc. during hot finishing with multiple tandem rollings and coil windings. The problem is likely to occur. More preferably, the average value of the tension is adjusted to 5 MPa or more.

  The tension between the stands is controlled mainly by adjusting the rolling reduction rate at each stand or adjusting the rotation speed of the roll. Specifically, although it depends on the thickness of the product plate and hot-rolled plate, the reduction ratio in each stand is adjusted to a range of about 20 to 60%, or the first half stands (for example, the first stand and the second stand). Is adjusted by adjusting the rotation speed of the roll in the range of 20 to 150 m / min and adjusting the rotation speed of the roll in the latter half stand (for example, the third and subsequent stands) to the range of 100 to 400 m / min. .

  Other conditions other than the tension between stands in hot finish rolling are as follows: Hot finish rolling finish temperature: 230 to 360 ° C (depending on the lower process), total processing rate: about 60 to 95%, final rolling final processing rate : About 20 to 50%, final rolling final rolling speed: about 200 to 400 m / min is preferable. Of these, the finish temperature of the hot finish rolling may be suitably set within a suitable range depending on the product sheet thickness, the cold rolling rate, and the presence or absence of intermediate annealing. Overall, the desired crystal orientation can be obtained by appropriately combining these conditions.

  After hot finish rolling as described above, each step of cold rolling and final annealing is performed.

  Of these, in cold rolling, the cold rolling rate is preferably suppressed to 80% or less so that the final thickness is about 0.5 to 10 mm. In addition, when the final annealing is held for a long time, the crystal grains grow and the balance of the texture is lost, and coarse crystal grains are generated, resulting in rough skin after forming. 300 to 450 ° C. and 2 to 10 hours are recommended. In the case of rapid thermal annealing with a 5000 or 6000 series Al alloy, it is recommended that the temperature is 500 to 580 ° C. and within 3 minutes. Note that slow heating annealing means that the coil is inserted into the furnace as it is, and the temperature is increased by heating and annealing, and rapid heating annealing means that the coil is wound and heated to increase the temperature and annealing. is doing.

  After the hot rolling, before the cold rolling (that is, to the non-uniform structure generated during the hot rolling), annealing may be performed to recrystallize, or the intermediate annealing may be performed during the cold rolling. May be performed. In the present invention, this annealing and intermediate annealing are particularly referred to as an intermediate process, and an Al alloy having a more excellent surface property can be obtained by the intermediate process. Since the temperature in each step of cold rolling and final annealing differs depending on whether or not annealing is performed after hot rolling and when intermediate annealing is performed in the middle of cold rolling. It is preferable to set the temperature appropriately and appropriately according to the thickness and desired characteristics.

  First, when (a) the cold work rate is high (for example, about 50 to 75%), (b) the cold work rate is low (for example, less than 50%), and after the hot rolling, annealing is performed before cold rolling. When performing intermediate annealing during cold rolling or (c) final annealing immediately after hot rolling (without annealing or intermediate annealing), set to a relatively low temperature side of about 230 to 300 ° C It is preferable.

  On the other hand, (a) when the cold working rate is low and annealing is performed before cold rolling after hot rolling, or when intermediate annealing is not performed during the cold rolling, or (b) as hot rolled sheet In the case of manufacturing at a relatively high temperature, it is preferable that the temperature is set at a relatively high temperature of about 290 to 370 ° C.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

  An Mg-containing Al alloy having the composition shown in Table 1 below was melted, and an ingot having a thickness of 600 mm and a width of 1500 mm was obtained by a DC casting method. Ingot types A to D shown in Table 1 below are 5000 series Al alloys, and ingot types E to G are 6000 series Al alloys.

  After subjecting the resulting ingot to homogenization heat treatment, the Mg-containing Al alloy sheet is subjected to hot rough rolling, hot finish rolling (intermediate process if necessary), cold rolling, and final annealing. Obtained. Table 2 shows the conditions for some of these processes. Hereinafter, conditions of each process will be described according to the manufacturing process.

  First, the homogenization heat treatment was performed at 480 to 520 ° C. for 4 to 10 hours for Nos. 1 to 11 in Table 2, and at 540 ° C. for 4 hours for Nos. 12 to 18.

  In the hot rough rolling, the start temperature is 450 to 535 ° C., the end temperature is 350 to 450 ° C., and the thickness of the rough rolled steel sheet after the rough rolling is 30 to 35 mm.

  The conditions for hot finish rolling (end temperature, average of tension between stands, plate thickness after hot rolling) are as shown in Table 2 below. Here, the average of the tension between the stands shown in Table 2 was calculated according to the procedure described above. Note that the final rolling final speed was 150 to 250 m / min, the final rolling speed was reduced for the thick plate, and the final rolling speed was increased for the thin plate. The rolling reduction in the final finishing pass was 20 to 35%. The number of stands used in the hot finish rolling in the examples is four.

  In addition, the intermediate process shown in Table 2 is that (a) annealing after hot rolling and before cold rolling, or (b) following (a) performing intermediate annealing in the middle of cold rolling. The annealing temperature (the annealing temperature and time for b) is shown in the table. In the table, “heating gradually heating” means a heat treatment performed by inserting the coil as it is into the furnace and starting the heating, and the heating rate at this time varies depending on the size of the coil, but is approximately 20 ~ 200 ° C / h. In the table, “no sluggishness” indicates that no intermediate process is performed.

  Next, the final cold rolling rate in cold rolling was set to 38 to 80%, and cold rolled steel plates having the thicknesses shown in Table 2 were obtained. Here, the final cold rolling rate refers to the rolling reduction from the intermediate annealing to the final thickness when intermediate annealing is performed during the cold rolling process, and corresponds to the cold rolling rate when intermediate annealing is not performed.

  Thereafter, the final annealing is performed, but specific conditions (heating rate, annealing temperature, holding time) are as shown in Table 2. However, “heating rate: rapid 30000” in the table indicates that rapid heating was performed at a temperature increase rate of 30000 ° C./h, and the temperature was increased while winding the coil. On the other hand, “heating rate: 40 ° C./h” means that the coil is inserted into the furnace as a coil and heated up.

  Next, for the Mg-containing Al alloy obtained through the above steps, the crystal plane orientation of crystal grains on the alloy surface and the grain diameters of all crystal grains existing on the alloy surface were measured according to the measurement method described above. For the crystal grains whose plate surface orientation was measured, the area ratio A (area%) of the crystal grains within 10 ° from the (100) plane occupying the measurement region and the area ratio B (area%) of the crystal grains within 20 °, respectively. Calculated. The A / B value was determined from the calculated A and B values. Moreover, the average value of the measured crystal grain diameter was calculated, and this was made into the average crystal grain diameter. Furthermore, the area ratio (area%) that the crystal grains exceeding twice the average crystal grain diameter occupy in the measurement region was calculated. The results are shown in Table 3 below.

  Table 4 below shows more detailed data on Nos. 1, 2, 5, and 6 among Nos. 1 to 18 shown in Table 3 above. Also, for Nos. 1, 2, 5, and 6, photographs of the (100) plane crystal grain distribution observed on the alloy surface color-coded by crystal orientation by image analysis are shown as (a) in FIGS. . 2 to 5, the crystal grains within 10 ° from the (100) plane are shown as “dark”, and the crystal grains within 10 ° and over 20 ° from the (100) plane are shown as being thinly colored. Accordingly, the area occupied by crystal grains whose plate plane orientation is within 10 ° from the (100) plane is the total area (x) of the crystal grains colored “dark” in the figure, and the plane plane orientation is (100) plane. The area occupied by the crystal grains within 20 ° from the total area (x) of the “dark” colored crystal grains and the total area (y) of the “lightly” colored crystal grains in the figure (x + y) ). And the ratio of the total area (x) to the area of the measurement region (measurement region: 1000 μm × 1000 μm) is the area ratio A (area%) occupied by crystal grains whose plate plane orientation is within 10 ° from the (100) plane, The ratio of the area (x + y) to the area of the measurement region (measurement region: 1000 μm × 1000 μm) is defined as the area ratio B (area%) occupied by crystal grains whose plate plane orientation is within 20 ° from the (100) plane.

  Moreover, the relationship (distribution state) between the crystal grain size and the area ratio is shown as (b) in FIGS. 2 to 5 for the (100) plane crystal grains observed on the alloy surface.

  Next, for the Mg-containing Al alloy thus obtained, the surface quality after forming was evaluated by the surface roughness after the tensile test and the surface properties after drawing.

  First, a tensile test was performed at room temperature (20 ° C.) using a JIS standard Z2201 No. 5 test piece [parallel length gauge length (GL): 25 mm × plate thickness: 50 mm], and the surface of the test piece after the test. The roughness of the unevenness was measured. The specimen used for the tensile test was taken from the Mg-containing Al alloy so that the longitudinal direction of the specimen was perpendicular to the rolling direction. Therefore, the tensile direction is also perpendicular to the rolling direction. The tensile test was performed according to a metal material tensile test method defined in JIS standard Z2241 (1980). Here, the tensile speed was 5 mm / min up to 0.2% proof stress, and 20 mm / min after 0.2% proof stress.

  The tensile deformation was performed under two conditions of 15% stretch (strength) or 20% stretch (strength).

  Tensile tests are usually performed at a strength of about 15%, but in the present invention, in order to simulate molding under more severe conditions, in addition to the usual 15% stretch, a tensile test is also performed with 20% stretch showing severe molding conditions. It is up to you. In the present invention, the roughness of the surface after the tensile test with 20% stretch has reached the acceptance criteria, and the acceptance criteria is the surface roughness roughness for both 15% stretch and 20% stretch. Is 15 μm or less.

  A roughness meter was used for the measurement of the roughness of the unevenness, and the unevenness of the alloy surface was measured over about 20 mm along the longitudinal direction of the tensile test piece. The number of measurement locations was three, and the distance between the maximum depth (valley) and the maximum height (peak) at each measurement location was calculated, and the average of the three locations was defined as surface roughness.

  A specific example of the measurement result of the surface roughness is described with reference to FIG. FIG. 6 is a schematic diagram showing the result of measuring the roughness of the alloy surface, where a is the measurement length (about 20 mm), b is the maximum depth (valley), and c is the maximum height (peak). ing. Actual measurement data is as indicated by a solid line in the figure. In the present invention, a curve (indicated by a dotted line in the figure) obtained by averaging the solid line data is obtained, and a distance d between the maximum depth b and the maximum height c is obtained. Was calculated. This was similarly calculated for a total of three places, and the average was defined as the surface roughness of the alloy of the present invention.

In addition, the surface property (roughness) after the drawing was subjected to a drawing deformation test according to an Erichsen test method defined in JIS standard Z2247 using a disk-shaped test piece cut out with a diameter of 100 mm. Specifically, a 50% diluted solution of Gastrol No. 700 was used as a lubricating oil, and the one formed into a cup shape with an Erichsen tester was used as a test piece for measuring surface properties. Detailed processing conditions of the drawing deformation test are as follows. Punch diameter: 50 mm diameter, the punch shoulder R: 4.5 mm, dice diameter: φ65.1mm, R of the die-side shoulder portion: 14 mm, blank holding ^{pressure: 4903MPa (500kgf / mm 2)} , drawing ratio: 2 (diaphragm Rate: 50%). Next, the surface after the drawing deformation test was visually observed and evaluated according to the following criteria.
<Evaluation criteria>
◎: No rough skin ○: Mild rough skin △: Rough skin ×: Strong rough skin

  These evaluation results are summarized in Table 5.

  As is clear from Tables 3 and 5, No.1 to 4, No.8 to 10, and Nos. 12 to 15 that satisfy the requirements specified in the present invention are not only 15% stretched but also after 20% stretched. But the surface quality is good.

  On the other hand, No.5-7, No.11, No.16-18 are examples in which any requirement defined in the present invention is outside the scope of the present invention, and the surface quality after 20% stretching is degraded. . In particular, No.6 and No.16 have good surface quality after 15% stretching, but the surface quality after 20% stretching deteriorates, indicating that they are not suitable for use under severe molding conditions. .

It is a schematic diagram for demonstrating the texture of Al alloy. This is a drawing-substituting photograph in which the surface of No. 1 was photographed with an electron microscope and analyzed. This is a drawing-substituting photograph in which the surface of No. 2 was photographed with an electron microscope and analyzed. It is a drawing substitute photograph in which the surface of No. 5 was photographed with an electron microscope and image analysis was performed. It is a drawing-substituting photograph in which the surface of No. 6 was photographed with an electron microscope and subjected to image analysis. It is a schematic diagram which shows the alloy surface unevenness | corrugation roughness measuring method in this invention.

Claims (2)

6000 series Al alloy plate containing Mg,
The thickness of the Al alloy plate is 0.5 to 10 mm,
The crystal plane orientation of the crystal grains on the surface of the alloy plate is measured, and the area ratio (%) occupied by the crystal grains whose plane orientation is within 10 ° from the (100) plane is A, and the crystal grains within 20 ° from the (100) plane When the area ratio (%) occupied by is B,
A 6000-based Mg-containing Al alloy plate characterized by satisfying the following formulas (1) and (2):
26 ≦ B ≦ 44 (1)
0.30 ≦ A / B ≦ 0.46 (2)   The area ratio occupied by crystal grains exceeding twice the average crystal grain size when the grain size of crystal grains on the alloy plate surface is measured is 5.0% or less of the whole. Mg-containing Al alloy plate.

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