WO2012077758A1

WO2012077758A1 - Method for producing magnesium alloy rolled stock, magnesium alloy rolled stock, and press-molded body

Info

Publication number: WO2012077758A1
Application number: PCT/JP2011/078455
Authority: WO
Inventors: 新ショウ黄; 鈴木　一孝; 千野　靖正; 満坂本; 馬渕　守; 英樹森
Original assignee: 独立行政法人産業技術総合研究所; 国立大学法人京都大学; 日立金属株式会社
Priority date: 2010-12-08
Filing date: 2011-12-08
Publication date: 2012-06-14
Also published as: JP5700379B2; JPWO2012077758A1

Abstract

The present invention provides a method for producing magnesium alloy rolled stock having excellent ambient temperature moldability rivaling that of aluminum alloy rolled stock, the method for producing magnesium alloy rolled stock including: using a base material comprising, in mass percent, Al in the amount of 2.0-8.0%, and Mn in the amount 0-1.0% or less (not including 0), or also Zn in the amount of 0.2-2.0%, with the remainder being Mg and inevitable impurities; setting the surface temperature of the base material to 480-566°C less than 8 minutes in advance, and setting the surface temperature of the mill roll for rolling the base material to 50-250°C in advance; then rolling the base material to a minimum overall reduction rate of 5% or more; and annealing the base material after rolling. Further provided are magnesium alloy rolled stock and a press-molded body, the magnesium alloy rolled stock and the press-molded body produced using this method having an average grain size of less than 30μm, having a relative strength of (0002) plane rolling texture in the base material thickness center section in a normalized RD-TD plane in the (0002) pole figure of less than 5.0, and having an ambient temperature Erichsen value of at least 7.0.

Description

Magnesium alloy rolled material manufacturing method, magnesium alloy rolled material, and press-formed body

The present invention relates to a method for producing a magnesium alloy rolled material, a magnesium alloy rolled material produced using the production method, and a press-molded body obtained by press-working the rolled material.

Magnesium has the lowest density among practical structural metal materials, and its density is 1.7 g / cm ³ . Magnesium is attracting high attention as a next-generation structural lightweight material because it has the ease of recycling unique to metal materials and has abundant resources, and is used as a structural member for home appliances and transportation equipment. Has been. Currently, many magnesium products in Japan are manufactured by casting methods such as die casting. However, the current production methods using casting methods have problems such as the need for post-processing to compensate for casting defects, low yield, and problems with the strength and rigidity of members.

Generally, press molding has a high yield, and it can be said that it is an effective means of expanding demand for magnesium products because it can increase the strength and toughness of the product simultaneously with molding. If a molded body can be manufactured by press molding from a magnesium alloy rolled material manufactured using a magnesium alloy, a thin and high-strength molded body can be manufactured by an inexpensive process. Many demands can be expected for the products.

On the other hand, magnesium alloys have room temperature formability due to the fact that non-bottom slip hardly occurs at room temperature due to their crystal structure and that a strong (0002) plane texture is formed simultaneously with rolling. Very low is a problem.

At room temperature formability, that is, Erichsen value of aluminum alloy rolled material produced using aluminum alloys currently used in a wide range of fields is 8.3 (5083-0 material) when it is a 5000 series alloy, It is 9.2 (6061-T4 material) for the 6000 series alloy, and 11.0 (1100-O material) for the 1000 series alloy (Non-patent Document 1). On the other hand, the room temperature formability of the rolled magnesium alloy material, that is, the Erichsen value, is at most 2.0 to 5.0 (Non-patent Document 2).

In the future, in order to anticipate an increase in demand for rolled magnesium alloy, the magnesium alloy rolled material is given a property of room temperature formability comparable to that of aluminum alloy rolled material, that is, an Erichsen value at room temperature of at least 7.0 or more. In this technical field, there is a strong demand for the development of a new magnesium alloy rolled material manufacturing technology and products having excellent easy formability.

As a method of press-forming a magnesium alloy rolled material at room temperature, there is a method of using the magnesium alloy rolled material with the texture controlled as described above. In recent years, the present inventors have developed a magnesium alloy to which a specified amount of light rare earth elements, Zn, Mn, and Zr are added or a magnesium alloy to which specified amounts of Ca, Zn, Al, Mn, and Zr are added under specific conditions. It has been discovered that, when rolled and annealed, a pole inclined about 35 degrees in the TD direction appears in the (0002) plane texture, the formability is remarkably improved, and the Erichsen value is 8.0 or more (Patent Document 1). ). When this method is used, a magnesium alloy rolled material having room temperature formability comparable to that of an aluminum alloy can be produced.

However, in order to produce a magnesium alloy rolled material by the above-described method, it is necessary to use an expensive element such as a light rare earth element, and a Mg—Al—Zn based or Mg—Al—Mn based magnesium alloy rolled material is required. Compared with, the product cost is high. Further, the (0002) plane texture of the magnesium alloy rolled material obtained by the above-described method has a pole inclined about 35 degrees in the TD direction, that is, the direction perpendicular to the rolling direction. It is relatively difficult to deform in the direction, that is, the rolling direction. Therefore, eliminating the anisotropy of the mechanical properties has become a problem for practical use of the magnesium alloy rolled material.

As another method for modifying the texture of the rolled magnesium alloy material, a method of repeatedly bending the rolled magnesium alloy material has been proposed. This method can be applied to a Mg—Al—Zn-based magnesium alloy rolled material, and the room temperature formability can be increased to an Erichsen value of 6.5 or more, which is comparable to that of an aluminum alloy rolled material (Patent Document 2). . This technique is attracting attention as a technique for improving the room temperature formability of Mg—Al—Zn-based magnesium alloy rolled material.

However, the magnesium alloy rolled material that has been subjected to repeated bending work tends to deform in the RD direction because a pole inclined about 45 degrees in the RD direction appears in the (0002) plane texture, but in the TD direction, It is difficult to deform. Therefore, as in the case of the above-described Patent Document 1, eliminating the anisotropy of mechanical properties is a problem for practical use of the magnesium alloy rolled material manufactured by the above-described method. Moreover, in order to implement this method, it is necessary to install ancillary equipment for performing repeated bending work, which is also a barrier to the practical use of the magnesium alloy rolled material.

In recent years, as another method for modifying the texture of a magnesium alloy rolled material, the present inventors have used a plate material made of an Mg—Al—Zn based magnesium alloy up to a predetermined sample temperature, that is, 490 ° C. to 566 ° C. A method of heating in a short time, preferably less than 5 minutes, performing hot rolling at a rolling rate of 5% or more, preferably in the range of 5 to 50%, and annealing the plate material after the rolling. Proposed (Patent Document 3). The principle of this method is that the sample surface temperature at the time of rolling is raised to a high temperature of 450 ° C. or higher, and rolling is performed in a state where the activity of non-bottom sliding is activated.

Since the magnesium alloy rolled material produced by this method does not have poles greatly inclined in the TD direction or the RD direction, it has less anisotropy than the inventions described in Patent Document 1 and Patent Document 2, and (0002 ) The relative strength of the surface texture becomes lower than that of the conventional magnesium alloy rolled material, and exhibits an excellent room temperature formability equivalent to that of the aluminum alloy rolled material, that is, an Erichsen value of 7.0 or more. In addition, this technique is attracting attention as a technique that can produce a magnesium alloy rolled material with excellent formability at low cost by using existing rolling equipment without using expensive elements such as light rare earth elements.

JP 2010-013725 A JP-A-2005-298888 JP 2010-133005 A

In the invention of Patent Document 3 described above, the composition of the sample, the heating time of the sample, the heating temperature of the sample, and the total rolling rate of the sample are defined. However, the rolling process of the magnesium alloy rolled material has other important operation parameters such as the surface temperature of the rolling roll, and the resulting magnesium alloy rolled material has excellent room temperature forming due to fluctuations in various conditions other than those specified above. There is a case where it does not exhibit sex, which is a problem in practical use.

In view of the above-described problems, the present invention provides a method for producing a magnesium alloy rolled material, which can produce an Mg—Al—Mn based or Mg—Al—Zn based magnesium alloy rolled material containing a small amount of Mn with a high yield, and aluminum. Magnesium alloy rolled material produced by using the above production method, which has a room temperature formability comparable to that of a rolled alloy material and can be used in a wide range of fields such as space, aeronautical materials, electronic equipment materials, and automotive parts, and the magnesium An object of the present invention is to provide a press-formed body obtained by pressing a rolled alloy material.

As a result of intensive research and development aimed at developing a new technology capable of solving the problems in the above-described conventional technology, the present inventors have appropriately set the surface temperature of the plate material to be rolled and the temperature rising time for the surface temperature. And having the same room temperature formability as aluminum alloy rolled material by optimizing the surface temperature of the rolling roll used for rolling the plate material, and rolling the plate material and annealing the rolled plate material The inventors have found that a rolled magnesium alloy material can be produced with a high yield, and have reached the present invention.

The present invention for solving the above-described problems comprises the following technical means.
(1) By mass%, aluminum (Al) is contained in an amount of 2.0 to 8.0%, manganese (Mn) is contained in an amount of 0 to 1.0% or less (not including 0), the balance being magnesium (Mg) and inevitable After using a plate made of impurities, the surface temperature of the plate is set to 480 to 566 ° C. in advance in less than 8 minutes, and the surface temperature of the rolling roll for rolling the plate is set to 50 to 250 ° C. A method for producing a magnesium alloy rolled material, the method comprising rolling at a rolling rate of 5% or more, and annealing the plate material after rolling by the rolling.
(2) The method for producing a rolled magnesium alloy material according to (1), wherein the plate material further contains 0.2 to 2.0% by mass of zinc (Zn).
(3) The method for producing a magnesium alloy rolled material according to (1) or (2), wherein the surface temperature of the rolling roll is set to 60 to 220 ° C. in advance.
(4) The method for producing a magnesium alloy rolled material according to any one of (1) to (3), wherein the surface of the rolling roll is heated to a predetermined temperature using an external heating device.
(5) Manufacture of the magnesium alloy rolled material according to any one of (1) to (4), wherein a heat source is installed inside the rolling roll and the surface of the rolling roll is heated to a predetermined temperature. Method.
(6) The manufacturing method of the magnesium alloy rolled material according to any one of (1) to (5), wherein the plate material is rolled at a total rolling rate of 15% or more.
(7) The method for producing a magnesium alloy rolled material according to any one of (1) to (6), wherein the surface temperature of the plate material is preliminarily raised to a predetermined temperature in less than 5 minutes.
(8) A method for producing a magnesium alloy rolled material, comprising the production method according to any one of (1) to (7) as a part of a total rolling process.
(9) The manufacturing method of the magnesium alloy rolled material according to any one of (1) to (8), wherein the post-rolled plate material has a deformation structure including twins before annealing.
(10) The method for producing a magnesium alloy rolled material according to any one of (1) to (9), wherein the post-rolled sheet material has an average crystal grain size of less than 30 μm after annealing.
(11) A magnesium alloy rolled material produced by the production method according to any one of (1) to (10),
In mass%, aluminum (Al) is contained in an amount of 2.0 to 8.0%, manganese (Mn) is contained in an amount of 0 to 1.0% or less (not including 0), or zinc (Zn) is further added in an amount of 0.2. It contains ~ 2.0%, the balance is magnesium (Mg) and inevitable impurities, the average crystal grain size is less than 30μm, and the (0002) pole figure is normalized by measurement by XRD method (Schulz reflection method) The relative strength of the (0002) plane texture at the center of the thickness of the RD-TD surface is less than 5.0 (however, RD: rolling direction, TD: plate width direction), and the room temperature Erichsen value is 7.0 or more. Magnesium alloy rolled material characterized by being.
(12) A press-molded product comprising a molded product obtained by pressing the magnesium alloy rolled material according to (11) into a predetermined form.

The present invention has the following effects.
(1) A rolled magnesium alloy material having excellent formability, which is made of an Mg—Al—Mn alloy or an Mg—Al—Zn alloy containing a very small amount of Mn, can be produced.
(2) Specifically, the obtained rolled magnesium alloy material has a fine average crystal grain size, that is, less than 30 μm, and the normality of the (0002) pole figure as measured by the XRD method (Schulz reflection method). The relative strength of the (0002) plane texture in the central part of the thickness of the converted RD-TD plane is less than 5.0 and the room temperature Erichsen value is 7.0 or more, which shows excellent room temperature formability.
(3) By using the present invention, a magnesium alloy rolled material having excellent room temperature formability can be obtained without using rare earth elements that are feared of resource depletion and price increase, and using existing equipment. It can be manufactured with high process and low cost.
(4) By using the present invention, it is possible to provide a magnesium alloy rolled material that is applicable to a wide range of applications and has low mechanical property anisotropy and excellent formability.
(5) Since the magnesium alloy rolled material of the present invention is excellent in formability, the formability by press working is good, so that a press-formed product can be produced easily and easily. Manufacture of articles such as a body casing is facilitated.

The (0002) plane texture before and after annealing and the Erichsen value of the rolled AZ31B alloy produced in the example are shown. [Comparative Example 1] shows the result of the sample produced in Comparative Example 1, [ [Example 1] shows the result of the sample manufactured in Example 1, and [Comparative Example 2] shows the result of the sample manufactured in Comparative Example 2. FIG. 3 is a result of observing the structure of an RD-ND surface of the rolled AZ31B alloy manufactured in the examples by an optical microscope, and shows the structures before and after annealing. [Comparative Example 1] is Comparative Example 1 [Example 1] shows the result of the sample manufactured in Example 1, and [Comparative Example 2] shows the result of the sample manufactured in Comparative Example 2.

In the method for producing a magnesium alloy rolled material according to the present invention, particularly important technical features are that the surface temperature of the plate material to be rolled and the temperature rising time to the surface temperature are optimized and the rolling roll used for rolling the plate material is used. The purpose is to optimize the surface temperature and to roll the plate. Specifically, the surface temperature of the plate material to be rolled is previously raised to 480 to 566 ° C. for less than 8 minutes, preferably less than 5 minutes, and the surface temperature of the rolling roll used for rolling is previously set to 50 to 250. The temperature is raised to 0 ° C., preferably 60 to 220 ° C. Thus, the magnesium alloy rolling material of this invention excellent in formability can be obtained by annealing with respect to the plate material after rolling which rolled the said plate material.

In the present invention, the plate material to be rolled contains 2.0% to 8.0% aluminum (Al) and 0% to 1.0% (not including 0) manganese (Mn) in mass%. The above-mentioned plate material composed of magnesium (Mg) and unavoidable impurities is applied, but a plate material containing 0.2 to 2.0% by mass of zinc (Zn) is also applicable.

In the manufacturing method of the present invention for rolling the plate material, the structure of the post-rolled plate material before annealing shows a deformation structure including twins, and the structure of the post-annealed plate material after annealing the rolled plate material has an average crystal grain size It shows a fine structure of less than 30 μm. The post-annealed plate material having such a structure is measured by the XRD method (Schulz reflection method), and the (0002) plane texture in the central portion of the plate thickness of the normalized RD-TD surface of the (0002) pole figure is shown. It exhibits excellent room temperature formability with a relative strength of less than 5.0 and a room temperature Erichsen value of 7.0 or more, that is, the magnesium alloy rolled material of the present invention. Here, room temperature may be the same as room temperature as a commonly used term.

In addition, since the magnesium alloy rolled material of the present invention has excellent room temperature formability, it can be easily and easily pressed. Therefore, the rolled material is pressed to easily produce the press-formed body of the present invention. It is possible to provide various machined products that take advantage of the superior properties of magnesium alloys.

With regard to the above-mentioned rolled sheet and annealed sheet, the (0002) plane texture (crystal orientation distribution) is measured by X-ray diffraction (Schulz reflection method), and the X-ray diffraction strength from the (0002) plane—crystal Corresponding to the strength of the orientation of the axis − is obtained as a relative intensity value, and can be expressed, for example, in a (0002) pole figure to obtain the distribution pattern of the relative intensity value and the peak intensity value. Based on the information obtained in this way, it is possible to compare and compare the degree of randomization of the texture, that is, the degree of weakening of the anisotropy, etc. with respect to the post-rolled plate material and post-annealed plate material manufactured under various conditions. it can.

Here, “relative strength” is based on internal standards. Internal standards are all applied to the texture analysis used in the present invention. The internal standard is a technique for standardizing data using intensity data of the test sample itself. For the definition of the internal standard, see, for example, the RIGAKU X-ray Manual, Windows (registered trademark) version Cat. No. 9258J102 / P101, RINT 2000 / PC Software Positive Point Analysis (Ver.2.0) Instruction Manual Manual No. There is an explanation in MJ13203B05.

The outline of the measurement by X-ray diffraction (Schulz reflection method) will be supplemented below. The measurement is performed by adjusting a holder that can rotate the sample to be measured around the vertical axis of the sample surface, that is, the normal line and the horizontal axis, and satisfying the Bragg angle satisfying the target reflection diffraction condition, and the measurement. After fixing the sample to the Bragg angle of the pole, the holder is rotated around the vertical axis and the horizontal axis at angles α and β, respectively, and the diffraction intensity at that time is measured. The measured diffraction intensity represents the density of the pole (pole density), and if correction is required depending on the thickness of the sample, etc., it is passed through common sense correction, and the obtained pole density is plotted with respect to α angle and β angle using contour lines. By doing so, the above-described pole figure can be obtained.

The production method of the present invention and the magnesium alloy plate used for rolling in the production method will be described in more detail below.
As described above, the production method of the present invention contains 2.0 to 8.0% of aluminum (Al) and 0 to 1.0% or less (not including 0) of manganese (Mn) in mass%. Then, a plate material comprising the balance of magnesium (Mg) and inevitable impurities, or a plate material containing 0.2 to 2.0% by mass of zinc (Zn) is subjected to rolling. Among general-purpose magnesium alloys distributed in the market, AZ31B, AZ61, AZ80, AM50, AM60 etc. are mentioned as those corresponding to the chemical component. As mentioned above, magnesium has the lowest density among practical structural metal materials, has ease of recycling unique to metal materials, and has abundant resources, making it suitable as a next-generation structural lightweight material. It is.

Aluminum (Al) is preferably 2.0 to 8.0%, and manganese (Mn) is preferably 0 to 1.0% or less (excluding 0). When Al is contained in this range, significant solid solution strengthening is achieved, and when Al and Mn are contained in this range, an Al—Mn intermetallic compound is precipitated inside the Mg alloy, which is suitable as an alloy. This is because it is possible to have a high strength. If the Al content exceeds 8.0%, the hot workability decreases, and if it is less than 2.0%, it is difficult to provide a suitable strength, so this should be avoided. Further, if the content of Mn exceeds 1.0%, the intermetallic compound is coarsened and the strength tends to be lowered, so this should be avoided.

Furthermore, it can contain 0.2 to 2.0% by mass of zinc (Zn). This is because, if Zn is further contained in the range, it can contribute to improvement of mechanical properties such as strength as in the case of Al. Note that if the Zn content exceeds 2.0%, the hot workability deteriorates and should be avoided.

As a result of attempting detailed and systematic experiments using the above-described magnesium alloy plate, the present inventors have determined that the plate material to be rolled has a surface temperature of 480 to 566 ° C. for less than 8 minutes in advance. More preferably, the temperature is raised in less than 5 minutes, and the surface temperature of the rolling roll used for rolling is raised to 50 to 250 ° C., more preferably 60 to 220 ° C., and then rolling. By annealing the plate material, the deformation structure including twins formed in the plate material after rolling before annealing was weakened by the (0002) plane texture accompanying recrystallization during annealing, and excellent after annealing. It was found that room temperature formability was developed.

In the present invention, the surface temperature of the plate material used for rolling is preliminarily raised to 480 to 566 ° C. in less than 8 minutes because the plate material itself has a temperature range of 450 ° C. or higher where the non-bottom slide can slide at the moment of rolling. This is to keep non-bottom dislocations at the grain boundaries of the deformed structure. The lower limit of the surface temperature of the plate material to be preliminarily raised is defined as 480 ° C. or higher because the surface temperature of the plate material is lowered by the contact with the rolling roll during rolling. This is because the surface temperature of the plate material should be increased by an amount corresponding to the temperature drop. The reason why the upper limit value is set to 566 ° C. or less is that when the plate material is heated to a temperature exceeding the upper limit value, the plate material ignites and easily burns.

Although Patent Document 3 stipulates that the surface temperature of the plate material used for rolling is raised to 490 to 566 ° C., the present invention specifies that the surface temperature of the plate material used for rolling is raised to 480 to 566 ° C. did. Both have a temperature difference of 10 ° C. at the lower limit. This is because, in the present invention, by optimizing the relationship between the surface temperature of the plate material to be rolled and the surface temperature of the rolling roll, even when the lower limit is lowered by 10 ° C., This is because it can be maintained in the temperature range of 450 ° C. or higher, and rolling can be performed under conditions in which non-bottom sliding is active.

Further, in the present invention, in order to make the structure of the plate material after rolling into a structure in which abnormal grain growth is suppressed, in raising the surface temperature of the plate material before rolling, in as short a time as possible, preferably less than 8 minutes, Preferably, the temperature is raised to a target temperature in less than 5 minutes. Thereby, it is possible to prevent the growth of abnormal grains in the structure of the plate material during the temperature rise. As a method for raising the surface temperature of the plate material used for rolling in a short time, for example, a simple method in which the temperature of the heating furnace used for raising the temperature is set high or a rapid heating method, that is, electric heating or infrared heating. There is a way to use. It should be noted that when the temperature of the plate material is increased, it will be dissolved if it exceeds the solidus temperature of 566 ° C., so this temperature should not be exceeded.

As well as the surface temperature of the plate material used for rolling described above, the surface temperature of the rolling roll used for rolling, which greatly affects the temperature state of the plate material during rolling, is important. In the present invention, the surface temperature of the rolling roll is set to 50 to 250 ° C. in advance. As described above, this is to maintain the sheet material at the moment of rolling in a temperature range of 450 ° C. or higher where the non-bottom slide slides, and the relationship with the surface temperature of the sheet material used for rolling, and the rolling roll The surface temperature of the rolling roll used for rolling was defined as an appropriate range in consideration of the surface state that does not cause rough surface.

If the surface temperature of the rolling roll is set to less than 50 ° C., even if the surface temperature of the plate material used for rolling is raised to 480-566 ° C. in a short time, the surface of the plate material is brought into contact with the rolling roll during rolling. The temperature drops to a temperature lower than 450 ° C. For this reason, under this condition, the activity of non-bottom slip decreases during rolling, and as a result, the activity of non-bottom dislocations is suppressed, and the bottom dislocations accumulate at the grain boundaries and twin interfaces, High-density non-bottom dislocations are less likely to accumulate at grain boundaries and twin interfaces, and during annealing, approximate recrystallization behavior appears in the plate after warm rolling, resulting in a different orientation from the base metal. The generation of recrystallized grains becomes insufficient.

Also, if the surface temperature of the rolling roll is set to a temperature exceeding 250 ° C., recrystallization occurs during rolling, and it becomes difficult to accumulate high-density non-bottom dislocations at grain boundaries and twin interfaces. That is, under this condition, static recrystallization cannot be caused in the annealing process after rolling, it becomes difficult to generate recrystallized grains having an orientation different from that of the base material, and the surface of the rolling roll Rough skin and fine cracks occur, and in some cases, there is an increased possibility of serious problems such as surface peeling.

As a method of raising the temperature of the surface of the rolling roll, there is a method of using an external heating device such as a hot air dryer, a gas burner, a resistance furnace or the like disposed in the immediate vicinity of the rolling roll. In addition, there is a method in which a SiC hot spring or a heating fluid is disposed as a heat source inside the rolling roll and the temperature is raised not only on the surface of the rolling roll, but can be selected according to manufacturing conditions.

Actually, rolling was performed using a sample in which the surface temperature of the rolling roll was set to 30 ° C., which is less than 50 ° C., and the surface temperature of the plate material was previously increased to the above temperature range. The result is shown in FIG. 2 as a result of [Comparative Example 1] described later. A deformed structure containing twins was confirmed in the structure of the sample before annealing. For this reason, although the texture strength accompanying annealing is somewhat weakened, it is insufficient, and an Erichsen value of 7.0 or more, which is excellent at room temperature as well as a rolled aluminum alloy material, could not be expressed.

In addition, when rolling was performed using a sample in which the surface temperature of the rolling roll was set to 300 ° C. exceeding 250 ° C. and the surface temperature of the plate material was preliminarily raised to the above temperature range, the result of [Comparative Example 2] described later As shown in FIG. 2, a deformed structure including twins was not confirmed in the structure of the sample before annealing. This suggests that recrystallization occurred in the sample during rolling, indicating that the dislocation density decreased with rearrangement of dislocations. Regarding the dislocation density, as shown in FIG. 2, the surface temperature of the rolling roll was set to 30 ° C., which will be described later, [Comparative Example 1] described later, and 90 ° C. [Example 1], and 300 ° C. [Comparative Example 2] is compared, and in [Comparative Example 1] and [Example 1], a deformed structure containing twins remains, and it is considered that the dislocation density inside the sample is higher than that of [Comparative Example 2]. be able to.

Regarding the deformation structure, Li et al. (Non-patent Document 3) and Barnett et al. (Non-Patent Document 4) have found that a deformed structure containing twins is formed in the Mg alloy structure subjected to cold rolling, and the sample is annealed. It is reported that recrystallized grains are generated with twins as nuclei. These findings suggest that the deformed structure becomes a nucleus for generating recrystallized grains.

As described above, using the plate material made of the magnesium alloy, the surface temperature of the rolling roll used for rolling is set to 50 to 250 ° C., and the surface temperature of the plate material used for rolling is raised to the above-described temperature in advance. When rolling is performed, the sheet material can be maintained in a temperature range of 450 ° C. or higher where non-bottom sliding can be active during rolling, so that non-bottom dislocations are accumulated at the grain boundaries or twin interfaces at high density during rolling. An organization can be formed. And also from the knowledge regarding the deformation | transformation structure | tissue mentioned above, when the board | plate material after the rolling is annealed, it can be anticipated that the recrystallized nucleus which absorbed the high-density non-bottom dislocation was generated. Note that the surface temperature of the rolling roll should be 60 to 220 ° C. in consideration of the relationship with the surface temperature of the plate material to be heated in advance, so that the surface condition of the plate material and the rolling roll during rolling is more stable. desirable.

For example, when high-density dislocations are accumulated at grain boundaries and twin interfaces in a plate after rolling, static recrystallization occurs with annealing (Non-patent Document 5). Also, in general, when the surface temperature of the plate material used for rolling is raised to a room temperature of 30 ° C. to 200 ° C. and rolled, the criticality of the column surface <a> slip and the conical surface <c + a> slip (non-bottom slip) Since the decomposition shear stress (CRSS) is sufficiently larger than the CRSS of the bottom surface <a> slip, the non-bottom slip can hardly be activated. However, when the surface temperature of the plate is rolled at 450 ° C. or higher, the non-bottom slip CRSS is almost the same value as the bottom <a> slip CRSS, so the non-bottom slip is active. (Patent Document 3). Therefore, when rolling is performed with the surface temperature of the plate material raised to 450 ° C. or higher, non-bottom slip is active in the deformed rolling grains. Will accumulate at grain boundaries and twin interfaces.

Unlike the present invention, in warm rolling in which a plate material is rolled at a surface temperature of 150 to 300 ° C. during rolling, it is generally considered that high-density bottom dislocations are accumulated at grain boundaries or twin interfaces. Thus, recrystallized grains having the same orientation as the base material are often generated at the grain boundaries or twin interfaces where high-density bottom dislocations are accumulated during annealing. Compared to this, when recrystallized nuclei that absorbed high-density non-bottom dislocations were generated as described above, the recrystallized nuclei showed a grain boundary tilt angle different from the recrystallized nuclei that absorbed many bottom dislocations, As a result, many recrystallized grains having different orientations from the base material are generated.

In the case of hot rolling in which rolling is performed while holding the plate material in a temperature range of 450 ° C. or higher during rolling, the activity of non-bottom sliding occurs actively along with bottom sliding during rolling, and conventional warm rolling The accumulation of non-bottom dislocations that could not be obtained in the case occurs at grain boundaries or twin interfaces. A plate material in which non-bottom dislocations are accumulated at a high density can accumulate different types of dislocations at grain boundaries from a plate material obtained by warm rolling in which bottom dislocations are accumulated at a high density. For this reason, if the plate material after rolling is annealed, nucleation behavior different from that in the case of warm rolling occurs, or crystal rotation different from that in the case of warm rolling occurs immediately after nucleation, and the orientation is different from that of the base material. Crystal grains are formed, and as a result, a random texture is formed.

As described above, at the grain boundaries or twin interfaces that absorb non-bottom dislocations at high density, different types of dislocations accumulate at the grain boundaries or twin interfaces that absorb bottom dislocations at high density. Thus, recrystallized grains having a completely different orientation from the parent phase are formed. Therefore, the decrease in the texture strength accompanying annealing observed in [Example 1] described later is based on the grain boundary or twin interface where high-density non-bottom dislocations are accumulated accompanying annealing. Can be considered as a result of the formation of recrystallized grains with different orientations.

In the present invention, during annealing, in order to weaken the texture strength of the sheet material after rolling, sufficient plastic deformation is imparted during the above-described rolling, and the deformation structure containing twins or the inside of the sheet material after rolling, It is necessary to accumulate high density dislocations. Therefore, in the rolling described above, it is necessary to perform a rolling process of at least a total rolling rate of 5% or more, preferably 15% or more.

In order to minimize the abnormal grain growth of the crystal grains in the plate after rolling, it is effective to reduce as much as possible the opportunity to expose the plate used for rolling to a high temperature from before the rolling to during rolling. For example, up to a predetermined thickness, cold rolling or warm rolling or hot rolling by raising the surface temperature to a low temperature side close to 480 ° C., the present invention is applied only to final rolling. By rolling, abnormal grain growth of crystal grains in the plate after rolling can be minimized.

In the present invention, the texture strength is weakened by utilizing a deformed structure and high-density dislocations including twins accumulated in the post-rolled sheet material after the rolling described above. It is necessary to perform annealing, that is, complete annealing on the above-described rolled plate material. Specifically, it is preferable to perform heat treatment at 300 to 450 ° C. for 10 minutes or more. It should be noted that when the heat treatment is performed at a temperature exceeding 450 ° C., abnormal grain growth may occur.

As described above, based on the knowledge obtained from the series of research and development by the present inventors, aluminum (Al) is 2.0 to 8.0% and manganese (Mn) is 0 to 1.0% or less (0% by mass). Or a plate material containing 0.2 to 2.0% zinc (Zn) and the balance being magnesium (Mg) and inevitable impurities, and the surface temperature of the plate material is set to 8 minutes in advance. Less than 5 minutes, preferably less than 5 minutes, and after the surface temperature of the rolling roll for rolling the sheet material is set to 50 to 250 ° C., preferably 60 to 220 ° C., the sheet material is at least fully rolled. By rolling at a rate of 5% or more, preferably 15% or more, and annealing the plate after rolling by the rolling, the plate has a fine structure, that is, an average crystal grain size of less than 30 μm, and a (0002) plane texture The relative intensity of A plate is less than can be manufactured at low cost, and high yield process.

The plate material made of the magnesium alloy thus obtained has excellent formability at room temperature of 30 ° C., having a formability comparable to that of a rolled aluminum alloy, that is, having a room temperature Erichsen value of at least 7.0 or more. It becomes the magnesium alloy rolled material of the present invention. Here, the Erichsen value was adopted as an index representing the formability of the magnesium alloy rolled material. The Erichsen test for obtaining the Erichsen value is intended to be a test according to JIS-B7729 and JIS-Z2274.

Further, the magnesium alloy rolled material of the present invention is measured by the XRD method (Schulz reflection method), and the (0002) plane texture relative to the (0002) pole figure normalized RD-TD surface central portion is measured. It has a (0002) plane texture whose strength is less than 5.0 (however, RD: rolling direction, TD: sheet width direction). Actually, as will be described later as [Comparative Example 1], even if the relative strength shows a value of less than 5.0, due to special events such as microcracks, excellent room temperature moldability, A room temperature Erichsen value of less than 7.0 may not develop. However, a magnesium alloy rolled material having excellent room temperature formability, that is, a room temperature Erichsen value of 7.0 or more, exhibits a value with a relative strength of the (0002) plane texture of less than 5.0.

In addition, the relative strength of the (0002) plane texture of the surface layer portion and the central portion of the magnesium alloy rolled material shows different values, and generally a strong relative strength is measured at the surface layer portion. Therefore, in the present invention, as described above, the peak intensity detected when the (0002) plane texture of the RD-TD plane is measured in the central portion, which is the region where the relative intensity is the weakest, is (0002). The relative strength of the surface texture was adopted.

Next, the present invention will be specifically described based on Examples and Comparative Examples (Examples 1 to 16, Comparative Examples 1 to 3). In addition, this invention is not limited at all by these Examples.

[Examples 1 and 2] and [Comparative Examples 1 and 2]
In [Example 1], [Example 2], [Comparative Example 1], and [Comparative Example 2], in order to produce AZ31B, which is a sample for evaluation, an AZ31B alloy; Mg-2.7% Al-0.8% Zn-0.4% Mn was used as a test material. The shape of the sample before rolling was 80 × 110 × 5.0 mm ³ . Rolling was performed using a two-stage rolling mill having a rolling roll diameter of 160 mm and a rolling roll width of 250 mm, and setting the surface temperature of the rolling roll to a predetermined temperature range from room temperature to 300 ° C. . The rotation speed of the rolling roll was 10 m / min.

The rolling conditions of each sample are as shown in Table 1. The sample was put into a muffle furnace previously maintained at 470 ° C., and when the surface temperature reached 450 ° C. lower than 480 ° C., the sample was taken out and rolled at a rolling rate of 21% per pass. A total of 6 rollings were performed on the same rolling schedule, and a sample having an initial thickness of 5.0 mm was rolled to 1.26 mm. The rolling so far is rolling step 1 shown in Table 1.

Next, the sample is put into a muffle furnace previously maintained at 560 ° C., and when the surface temperature reaches 525 ° C. within the range of 480 to 566 ° C. defined in the present invention, the sample is taken out immediately, Rolling was performed at a rolling rate of 21% by pass to obtain a plate material having a thickness of 1.0 mm. This rolling is rolling step 2 shown in Table 1. The total rolling ratio in rolling in which the surface temperature of the sample falls within the range of 480 to 566 ° C. defined in the present invention is 21%.

In the rolling steps 1 and 2 described above, the total rolling rate by 7-pass rolling performed with the sample surface temperature set at 470 ° C. or higher is 80%. In rolling steps 1 and 2, for each rolling pass, the sample was subjected to reverse rolling by rotating 180 ° about ND. Moreover, after the rolling step 2, that is, after the final rolling, the plate material was annealed under the conditions of 350 ° C. and a keeping time of 60 minutes.

[Examples 3 to 9]
In [Example 3] to [Example 9], in order to manufacture AZ61 which is a sample for evaluation, AZ61 alloy; the composition is mass%, Mg-5.9% Al-0.5% Zn-0.3% Mn was used as a test material. The shape of the sample before rolling was 80 × 140 × 2.0 mm ³ . For rolling, a two-stage rolling mill having a rolling roll diameter of 160 mm and a rolling roll width of 250 mm was used, and rolling was performed after setting the surface temperature of the rolling roll to a predetermined temperature of 60 to 210 ° C. . The rolling roll rotation speed was 10 m / min.

The rolling conditions of each sample are as shown in Table 1. The sample was put in a muffle furnace previously maintained at 540 ° C. or 500 ° C., and the sample was taken out when the surface temperature reached 505 ° C. or 480 ° C. and rolled at a rolling rate of 26% per pass. On the same rolling schedule, a total of 3 times of rolling was performed, the sample with an initial thickness of 2.0 mm was rolled, and a plate material with a thickness of 0.8 mm was obtained. This rolling is rolling step 1 shown in Table 1. The total rolling ratio in rolling in which the surface temperature of the sample falls within the range of 480 to 566 ° C. defined in the present invention is 59.5%. In this rolling step 1, rolling was performed by reverse rolling in which the sample was rotated 180 ° about ND for each rolling pass. In addition, after the rolling step 1, that is, after the final rolling, the plate material was annealed under conditions of 350 ° C. and a keeping time of 60 minutes.

[Comparative Example 3] and [Example 10] to [Example 16]
In [Comparative Example 3] and [Example 10] to [Example 16], in order to manufacture AM60 which is a sample for evaluation, AM60 alloy; the composition is Mg-6.2% by mass%. Al-0.4% Mn was used as a test material. The sample shape before rolling was 80 × 140 × 2.0 mm ³ . The rolling was performed using a two-stage rolling mill having a rolling roll diameter of 160 mm and a rolling roll width of 250 mm, and setting the surface temperature of the rolling roll to a predetermined temperature range of room temperature to 210 ° C. . The rolling roll rotation speed was 10 m / min.

The rolling conditions of each sample are as shown in Table 1. The sample was put into a muffle furnace in which the furnace temperature was previously maintained at 500 ° C., and when the surface temperature reached 480 ° C., which is the lower limit of the range of 480 to 566 ° C. defined in the present invention, the sample was taken out immediately. Rolling was performed at a rolling rate of 26% per pass. A total of two rollings were performed on the same rolling schedule, and a sample having an initial thickness of 2.0 mm was rolled to 1.1 mm. The rolling so far is rolling step 1 shown in Table 1.

Next, the sample is put into a muffle furnace previously maintained at 575 ° C. or 555 ° C., and when the surface temperature reaches 545 ° C. or 520 ° C. which falls within the range of 480 to 566 ° C. defined in the present invention, the sample is Was immediately rolled at a rolling rate of 27% in one pass to obtain a plate material having a thickness of 0.8 mm. This rolling is rolling step 2 shown in Table 1. The total rolling ratio in rolling in which the surface temperature of the sample falls within the range of 480 to 566 ° C. defined in the present invention is 27%.

In the rolling steps 1 and 2 described above, the total rolling rate by three-pass rolling performed with the sample surface temperature set to 470 ° C. or higher is 60%. In rolling steps 1 and 2, for each rolling pass, the sample was subjected to reverse rolling by rotating 180 ° about ND. Moreover, after the rolling step 2, that is, after the final rolling, the plate material was annealed under the conditions of 350 ° C. and a keeping time of 60 minutes.

In order to evaluate the room temperature formability of the plate material manufactured as described above, that is, a magnesium alloy rolled material, an Erichsen test was conducted. The Eriksen test was conducted according to JIS-B7729 and JIS-Z2247. The blank shape is φ60 mm for convenience of the plate material shape, the thickness is 1 mm or 0.8 mm, the mold temperature (sample temperature) is 30 ° C., the molding speed is 5 mm / min, and the wrinkle holding force is 10 kN. Graphite grease was used as the lubricant.

The (0002) plane texture of the magnesium alloy rolled material was measured by the XRD method (Schulz reflection method), and the relative strength of the (0002) plane texture normalized using the internal standard was determined. The texture strength of the normalized (0002) plane was determined. In the measurement, a φ34 mm disk was cut out from each rolled magnesium alloy sample, and the RD-TD surface was ground to a thickness of 0.4 mm to 0.5 mm, and then # 2400 SiC abrasive paper was used. Then, the surface was polished to obtain a measurement sample.

Further, the structure of the RD-ND plane of each of the rolled magnesium alloy materials was observed with an optical microscope, and by a section method (refer to literature: AW Thompson: Metallography, Vol. 28 (1972), p. 366). The average crystal grain size was calculated. A value obtained by multiplying the obtained average intercept length by a factor of 1.74 was defined as an average crystal grain size.

Table 2 shows the room temperature Erichsen value, texture strength, and average crystal grain size of each measurement sample. In Table 2, [Comparative Example 1], [Comparative Example 2], [Example 1], and [Example 2] are the results of the AZ31B alloy.
In [Comparative Example 1] in which the surface temperature of the rolling roll was set to 30 ° C. at normal temperature and [Comparative Example 2] set to 300 ° C., the texture strength was not significantly weakened, and the Erichsen value of less than 7.0 Met. On the other hand, in [Example 1] in which the roll surface temperature was set to 90 ° C. and [Example 2] in which the roll temperature was set to 150 ° C., the texture strength was significantly weakened, and the Erichsen value was 7.0 or more. It was. In addition, as an average crystal grain diameter, all had fine crystal grains of less than 30 μm.

Further, the influence of the surface temperature of the rolling roll, which is particularly important in the present invention, will be described using [Example 1], [Comparative Example 1], and [Comparative Example 2] which are changed only to the surface temperature of the rolling roll.
FIG. 1 shows a pole figure, a peak intensity value, and a room temperature Erichsen value, which are relative intensity distributions of the (0002) plane texture before and after annealing for each sample. All samples were rolled after the surface temperature of the sample was heated to 525 ° C. in about 2 minutes in the final rolling.

When attention is paid to the (0002) plane texture before annealing, the texture strength indicating the degree of orientation of the (0002) plane is around 6.0 for any sample. From the viewpoint of the texture strength, each sample I could not find any difference. On the other hand, paying attention to the (0002) plane texture after annealing, it was confirmed that there was a difference in the change in texture strength with the difference in the surface temperature of the rolling roll.

In the texture strength of [Comparative Example 1] where the surface temperature of the rolling roll was kept at room temperature, it decreased to 3.6 after annealing, and in the texture strength of [Example 1] which was previously set to 90 ° C., after annealing. It decreased to 2.8. However, in the sample of [Comparative Example 2] in which the surface temperature of the rolling roll was set to 300 ° C. in advance, no weakening of the texture strength accompanying annealing could be confirmed.

The room temperature Erichsen value of each sample was 6.7 in [Comparative Example 1] in which the surface temperature of the rolling roll was kept at room temperature, and 8.8 in [Example 1], which was 90 ° C. in advance. Yes, it was 4.0 in [Comparative Example 2] at 300 ° C. in advance. Therefore, from this result, it was confirmed that the room temperature formability of the sample, that is, the magnesium alloy rolled material, was improved according to the weakening of the texture strength generated during annealing.

From the above, even if the rolling is carried out after raising the surface temperature of the plate material to be rolled up to 450 ° C. or higher, which is the temperature at which non-bottom slip is active, the surface temperature of the rolling roll. If it is not optimized, it is confirmed that even if annealing is performed on the plate material after rolling, the strength of the texture does not weaken, and the magnesium alloy rolled material after annealing does not exhibit excellent room temperature formability. It was.

In Table 2, [Example 3] to [Example 9] are the results of evaluation using AZ61 alloy in the same manner as described above. The texture strengths of [Example 3] to [Example 9] in which the surface temperature of the rolling roll was 60 to 210 ° C. showed a marked weakening, had fine crystal grains of less than 30 μm, and 7.0 The above Eriksen value was obtained.

In Table 2, [Comparative Example 3] and [Example 10] to [Example 16] are the results of evaluation using the AM60 alloy in the same manner as described above. In [Comparative Example 3] in which the surface temperature of the rolling roll was 30 ° C., which was normal temperature, the Erichsen value was less than 7.0. On the other hand, the textures of [Example 10] to [Example 16] in which the surface temperature of the rolling roll was 60 to 210 ° C. showed marked weakening and had fine crystal grains of less than 30 μm. The Eriksen value was 0 or more.

As described above in detail, the present invention relates to a method for producing a magnesium alloy rolled material, a magnesium alloy rolled material, and a press-formed body. By the present invention, a rare earth element that is feared of resource depletion and price increase is used. Without using existing rolling equipment, the anisotropy and formability are improved at the same time, and the average crystal grain size has a fine structure of less than 30 μm, and the strength of the (0002) plane texture is less than 5.0. A cold-formability comparable to that of a rolled aluminum alloy, that is, an excellent cold-formability of Mg—Al—Mn or Mg—Al—Zn containing a small amount of Mn, having an Erichsen value of at least 7.0 or more. A magnesium alloy rolled material and a press-molded body using the same can be easily and inexpensively manufactured. According to the present invention, for example, a magnesium alloy rolled material that can be used in a wide range of fields such as space / aeronautical materials / electronic equipment materials, automobile members, etc., as well as home appliances such as digital cameras, notebook computers, and PDAs, and the like are used. A press-molded body can be provided at a low cost.

Claims

In mass%, aluminum (Al) is contained in 2.0 to 8.0%, manganese (Mn) is contained in 0 to 1.0% or less (not including 0), and the balance is composed of magnesium (Mg) and inevitable impurities. After using the plate material, the surface temperature of the plate material is set to 480 to 566 ° C. in advance in less than 8 minutes, and the surface temperature of the rolling roll for rolling the plate material is set to 50 to 250 ° C., the plate material is set to at least a total rolling rate of 5 A method for producing a magnesium alloy rolled material, comprising rolling at a rate of at least% and annealing the rolled plate after rolling.
The method for producing a magnesium alloy rolled material according to claim 1, wherein the plate material further contains 0.2 to 2.0 mass% of zinc (Zn).
The method for producing a magnesium alloy rolled material according to claim 1 or 2, wherein the surface temperature of the rolling roll is set to 60 to 220 ° C in advance.
The method for producing a rolled magnesium alloy material according to any one of claims 1 to 3, wherein the surface of the rolling roll is heated to a predetermined temperature using an external heating device.
The method for producing a magnesium alloy rolled material according to any one of claims 1 to 4, wherein a heat source is installed inside the rolling roll and the surface of the rolling roll is heated to a predetermined temperature.
The method for producing a magnesium alloy rolled material according to any one of claims 1 to 5, wherein the plate material is rolled at a total rolling rate of 15% or more.
The method for producing a rolled magnesium alloy material according to any one of claims 1 to 6, wherein the surface temperature of the plate material is raised in advance in less than 5 minutes to a predetermined temperature.
A manufacturing method of a magnesium alloy rolled material, characterized in that the manufacturing method according to any one of claims 1 to 7 is included in a part of the entire rolling process.
The method for producing a magnesium alloy rolled material according to any one of claims 1 to 8, wherein the post-rolled sheet material has a deformation structure including twins before annealing.
The method for producing a magnesium alloy rolled material according to any one of claims 1 to 9, wherein the post-rolled plate material has an average crystal grain size of less than 30 µm after annealing.
A magnesium alloy rolled material produced by the production method according to any one of claims 1 to 10,
In mass%, aluminum (Al) is contained in an amount of 2.0 to 8.0%, manganese (Mn) is contained in an amount of 0 to 1.0% or less (not including 0), or zinc (Zn) is further added in an amount of 0.2. It contains ~ 2.0%, the balance is magnesium (Mg) and inevitable impurities, the average crystal grain size is less than 30μm, and the (0002) pole figure is normalized by measurement by XRD method (Schulz reflection method) The relative strength of the (0002) plane texture at the center of the thickness of the RD-TD surface is less than 5.0 (however, RD: rolling direction, TD: plate width direction), and the room temperature Erichsen value is 7.0 or more. Magnesium alloy rolled material characterized by being.
A press-molded product comprising a molded product obtained by pressing the magnesium alloy rolled material according to claim 11 into a predetermined form.