JP6760000B2 - Magnesium alloy plate material - Google Patents

Description

The present invention relates to a magnesium alloy plate material.

In general, a magnesium alloy plate has a hexagonal crystal structure (hcp structure), and its (0002) plane is parallel to the plate surface, so that it is poor in plastic workability at room temperature. In Patent Documents 1 and 2, a magnesium alloy containing various additive elements in a predetermined amount is subjected to rolling treatment and heat treatment under predetermined conditions, and the crystal orientation of the (0002) plane is set in the plate width direction with respect to the plate surface. A magnesium alloy plate material having improved plastic workability at room temperature is disclosed by inclining it by 30 ° (FIG. 1 (d), FIG. 2 (b), (d), and FIG. 3 (c) of Patent Document 1). ), (F), FIGS. 1 (2), (3) of Patent Document 2.

Japanese Unexamined Patent Publication No. 2010-013725 Japanese Unexamined Patent Publication No. 2012-122102

It is desired to develop a magnesium alloy plate material that has both plastic workability and strength at room temperature. The magnesium alloy plates of Patent Documents 1 and 2 have low strength. In particular, since the crystal orientation of the (0002) plane is inclined by 30 ° in the plate width direction with respect to the plate surface, the anisotropy of the crystal orientation and the strength and elongation is large, and the strength in the plate width direction is low.

Therefore, one of the purposes is to provide a magnesium alloy plate material having excellent plastic workability at room temperature and also having excellent strength.

The magnesium alloy plate material according to the present disclosure is
A magnesium alloy plate made of a magnesium-based alloy
The magnesium-based alloy is
Ca is 0.05% by mass or more and 0.3% by mass or less, rare earth element is 0.05% by mass or more and 0.5% by mass or less, and Zn is 0.5% by mass or more and 6.2% by mass or less. And the composition that the balance is Mg and unavoidable impurities, including
When the average crystal grain size is 15 μm or less and the pole figure of the (0002) plane is taken by the EBSD method, the crystal orientation of the (0002) plane is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and its extreme density. It comprises a tissue having three or more peaks of 2.5 or more.

The magnesium alloy plate material is excellent in plastic workability at room temperature and also in strength.

Sample No. It is a pole figure of the (0002) plane by the EBSD method of 1-1.

<< Explanation of Embodiments of the Present Invention >>
First, the contents of the embodiments of the present invention will be listed and described.

(1) The magnesium alloy plate material according to one aspect of the present invention is
A magnesium alloy plate made of a magnesium-based alloy
The magnesium-based alloy is
Ca is 0.05% by mass or more and 0.3% by mass or less, rare earth element is 0.05% by mass or more and 0.5% by mass or less, and Zn is 0.5% by mass or more and 6.2% by mass or less. And the composition that the balance is Mg and unavoidable impurities, including
When the average crystal grain size is 15 μm or less and the pole figure of the (0002) plane is taken by the EBSD method, the crystal orientation of the (0002) plane is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and its extreme density. It comprises a tissue having three or more peaks of 2.5 or more.

According to the above configuration, it is excellent in plastic workability at room temperature and also in strength. The crystal orientation of the (0002) plane is in various directions because the crystal grain size is small and there are three or more peaks in which the inclination angle of the crystal orientation of the (0002) plane with respect to the plate surface is 10 ° or more and 70 ° or less. Since it is inclined to, the crystal orientation, strength, and elongation anisotropy are small, and it is easy to combine plastic workability and strength at room temperature. Details of each additive element will be described later.

(2) As one form of the magnesium alloy plate material, Ca is replaced with one of 0.1% by mass or more and 0.65% by mass or less of Sr or 0.15% by mass or more and 1.0% by mass or less of Ba. To do.

According to the above configuration, as in the case of containing Ca, it is excellent in plastic workability at room temperature and also in strength.

(3) As one form of the magnesium alloy plate material, at least one of Sr of 0.1% by mass or more and 0.65% by mass or less and Ba of 0.15% by mass or more and 1.0% by mass or less is contained. Can be mentioned.

According to the above configuration, it is easy to further improve the plastic workability and strength at room temperature.

(4) As one form of the magnesium alloy plate material, the structure further has a peak in which the inclination angle of the crystal orientation of the (0002) plane with respect to the plate surface is less than 10 ° and the extreme density is 2.5 or more. At least one is included.

According to the above configuration, since the (0002) plane has crystals along or substantially along the plate surface, it is easy to secure the strength in the plate surface of the magnesium alloy plate material.

(5) One form of the magnesium alloy plate material further includes Mn of 0.1% by mass or more and 0.8% by mass or less.

When the Mn content is 0.1% by mass or more, the corrosion resistance can be easily improved. In addition, it contributes to the miniaturization of crystal grain size. When the Mn content is 0.8% by mass or less, the Mn content is not excessively large, the crystal grain size is unlikely to be coarse, and the formation of intermetallic compounds is easily suppressed. Therefore, the machine for magnesium alloy plates. It is easy to suppress the deterioration of the target characteristics.

(6) One form of the magnesium alloy plate material is that the 0.2% proof stress in the plate width direction is 95 MPa or more.

According to the above configuration, the 0.2% proof stress in the plate width direction is large, and the strength in the plate width direction is excellent.

(7) As one form of the magnesium alloy plate material, an Eriksen value of 8.0 mm or more can be mentioned.

According to the above configuration, the Eriksen value is large and the magnesium alloy plate material is excellent in plastic workability.

(8) One form of the magnesium alloy plate material is that the breaking elongation in the plate width direction is 28% or more.

According to the above configuration, the breaking elongation in the plate width direction is large, and the ductility in the plate width direction is excellent.

(9) One form of the magnesium alloy plate material is that the tensile strength in the plate width direction is 200 MPa or more.

According to the above configuration, the tensile strength in the plate width direction and the 0.2% proof stress are large, and the strength in the plate width direction is excellent.

<< Details of Embodiments of the present invention >>
Details of the embodiments of the present invention will be described below.

[Magnesium alloy plate material]
The magnesium alloy plate material according to the embodiment is made of a magnesium-based alloy, and will be described in detail in the method for producing a magnesium alloy plate material described later, but is a plate material obtained by heat-treating a rolled plate material obtained by rolling a cast plate material. One of the features of this magnesium alloy plate material is that it has a composition containing a specific amount of a specific additive element and a structure having a specific crystal plane having a specific orientation while satisfying a specific average crystal grain size. is there. The details will be described below.

[composition]
The magnesium-based alloy has a composition in which at least one of Ca (calcium) and RE (rare earth element) and Zn (zinc) are contained as additive elements in a specific amount, and the balance is Mg and unavoidable impurities. This composition may replace all of Ca with either Sr (strontium) or Ba (barium), or may contain at least one of Sr and Ba in addition to Ca. This composition may further contain Mn (manganese).

The specific composition of the magnesium-based alloy is Mg-Zn-Ca-based alloy, Mg-Zn-RE-based alloy, Mg-Zn-Ca-RE-based alloy, Mg-Zn-RE-Mn-based alloy, Mg-Zn- Sr-based alloy, Mg-Zn-Ba-based alloy, Mg-Zn-Sr-RE-based alloy, Mg-Zn-Ba-RE-based alloy, Mg-Zn-Ca-Sr-based alloy, Mg-Zn-Ca-Ba-based Alloys, Mg-Zn-Ca-Sr-Ba alloys, Mg-Zn-Ca-Sr-RE alloys, Mg-Zn-Ca-Ba-RE alloys, Mg-Zn-Ca-Sr-Ba-RE alloys Examples include alloys.

(Zn)
Zn improves mechanical properties such as strength, elongation at break, and tensile strength. The Zn content may be 0.5% by mass or more and 6.2% by mass or less. When the Zn content is 0.5% by mass or more, the mechanical properties can be easily improved. When the Zn content is 6.2% by mass or less, the formation of intermetallic compounds is easily suppressed, and the deterioration of plastic workability at room temperature (20 ° C. ± 15 ° C.) and the deterioration of mechanical properties are suppressed. easy.

In the case of Mg-Zn-Ca alloy, Mg-Zn-RE alloy, Mg-Zn-Sr alloy, and Mg-Zn-Ba alloy, the Zn content is 0.5% by mass or more and 6.2. It is preferably 1% by mass or less, and particularly preferably 1.5% by mass or more and 4.0% by mass or less.
In the case of Mg-Zn-Ca-RE alloy, Mg-Zn-RE-Mn alloy, Mg-Zn-Sr-RE alloy, and Mg-Zn-Ba-RE alloy, the Zn content is 0. It is preferably 5.5% by mass or more and 5.0% by mass or less, and particularly preferably 1.0% by mass or more and 3.5% by mass or less.

(Ca)
Ca promotes the inclination of the (0002) plane with respect to the plate surface (plane orthogonal to the plate thickness direction) and improves the mechanical properties. The Ca content is 0.05% by mass or more and 0.3% by mass or less. When the Ca content is 0.05% by mass or more, the mechanical properties can be easily improved. In addition, it also contributes to improving the flame retardancy of the molten metal. When the Ca content is 0.3% by mass or less, the formation of intermetallic compounds can be easily suppressed, and the deterioration of plastic workability at room temperature and the deterioration of mechanical properties can be easily suppressed.

In the case of the Mg-Zn-Ca based alloy, the Ca content is preferably 0.05% by mass or more and 0.3% by mass or less, and particularly preferably 0.1% by mass or more and 0.2% by mass or less.
In the case of the Mg-Zn-Ca-RE alloy, the Ca content is preferably 0.05% by mass or more and 0.2% by mass or less, and particularly preferably 0.08% by mass or more and 0.15% by mass or less.

(Sr)
Sr promotes the inclination of the (0002) plane with respect to the plate surface and improves the mechanical properties. The content of Sr is 0.1% by mass or more and 0.65% by mass or less. When the content of Sr is 0.1% by mass or more, the mechanical properties can be easily improved. When the Sr content is 0.65% by mass or less, the formation of intermetallic compounds is easily suppressed, and the deterioration of plastic workability at room temperature and the deterioration of mechanical properties are easily suppressed.

In the case of the Mg-Zn-Sr alloy, the Sr content is preferably 0.1% by mass or more and 0.65% by mass or less, and particularly preferably 0.22% by mass or more and 0.45% by mass or less.
In the case of the Mg-Zn-Sr-RE alloy, the Sr content is preferably 0.1% by mass or more and 0.45% by mass or less, and particularly preferably 0.17% by mass or more and 0.33% by mass or less.

(Ba)
Ba promotes the inclination of the (0002) plane with respect to the plate surface and improves the mechanical properties. The content of Ba is 0.15% by mass or more and 1.0% by mass or less. When the Ba content is 0.15% by mass or more, the mechanical properties can be easily improved. When the Ba content is 1.0% by mass or more, it is easy to suppress the formation of intermetallic compounds, and it is easy to suppress the deterioration of plastic workability at room temperature and the deterioration of mechanical properties.

In the case of the Mg—Zn—Ba based alloy, the content of Ba is preferably 0.15% by mass or more and 1.0% by mass or less, and particularly preferably 0.35% by mass or more and 0.7% by mass or less.
In the case of the Mg-Zn-Ba-RE alloy, the Ba content is preferably 0.15% by mass or more and 0.7% by mass or less, and particularly preferably 0.27% by mass or more and 0.52% by mass or less.

(RE)
RE promotes the inclination of the (0002) plane with respect to the plate surface, and improves the mechanical properties by grain refinement. RE is at least one rare earth element selected from the elements of Group 3 of the periodic table, that is, scandium (Sc), yttrium (Y), lanthanoid, and actinide, and is an alloy containing a plurality of rare earth elements. Including misch metal. The content of RE is 0.05% by mass or more and 0.5% by mass or less. When the RE content is 0.05% by mass or more, the mechanical properties can be easily improved. When the RE content is 0.5% by mass or less, the formation of intermetallic compounds is easily suppressed, and the deterioration of plastic workability at room temperature and the deterioration of mechanical properties are easily suppressed.

In the case of the Mg-Zn-RE alloy, the RE content is preferably 0.05% by mass or more and 0.5% by mass or less, and particularly preferably 0.15% by mass or more and 0.35% by mass or less.
In the case of Mg-Zn-Ca-RE alloy, Mg-Zn-RE-Mn alloy, Mg-Zn-Sr-RE alloy, and Mg-Zn-Ba-RE alloy, the RE content is 0. It is preferably 0.05% by mass or more and 0.4% by mass or less, and particularly preferably 0.1% by mass or more and 0.3% by mass or less.

(Mn)
Mn improves corrosion resistance. The Mn content is preferably 0.1% by mass or more and 0.8% by mass or less. When the Mn content is 0.1% by mass or more, the corrosion resistance can be easily improved. In addition, it contributes to the miniaturization of crystal grain size. When the Mn content is 0.8% by mass or less, the crystal grain size is unlikely to be coarse, and the formation of intermetallic compounds is easily suppressed. Therefore, the plastic workability at room temperature is lowered and the mechanical properties are reduced. It is easy to suppress the decrease of. The Mn content is further preferably 0.2% by mass or more and 0.6% by mass or less, and particularly preferably 0.25% by mass or more and 0.5% by mass or less.

The composition of the magnesium-based alloy can be confirmed, for example, by performing component analysis by ICP emission spectroscopy (ICP-OES), electron beam microanalyzer (EPMA), or the like.

[Organization]
The magnesium-based alloy has a structure in which the average crystal grain size is small, the crystal orientation of the (0002) plane satisfies a specific angle with respect to the plate surface, and the extreme density has a specific number of peaks satisfying a specific numerical value. The average crystal grain size is measured as follows. Insert the measurement sample into a scanning electron microscope (SEM), put it in a vacuum state, and take one or more observation fields (surface or cross section of magnesium alloy plate) of 150 μm × 500 μm under the conditions of room temperature and acceleration voltage of 15 kV. , EBSD (Electron Back-Scatter Diffraction) method is used to color-code (map) each crystal grain in each crystal orientation for the entire observation field. Image analysis is performed on the obtained mapping image using OIM (Orientation Imaging Microcopy) 6.2.0 manufactured by TSL Solutions Co., Ltd. At this time, the area of each particle is obtained by performing image analysis using data points having a confidence coefficient (Confidence Index: CI value) of 0.1 or more in the above analysis software, and the average value of the diameters of circles equal to each area. Is the average crystal grain size. The crystal orientation of the (0002) plane and its extreme density can be obtained by taking a pole figure of the (0002) plane by the EBSD method.

(Average crystal grain size)
The average crystal grain size is 15 μm or less. When the average crystal grain size is 15 μm or less, the plastic workability and strength at room temperature are excellent. The smaller the average crystal grain size, the more preferable.

In the case of the Mg—Zn—Ca based alloy, the average crystal grain size is preferably 15 μm or less, and particularly preferably 12 μm or less.
In the case of the Mg-Zn-RE alloy and the Mg-Zn-Ca-RE alloy, the average crystal grain size is preferably 12 μm or less, and particularly preferably 8 μm or less.
In the case of the Mg-Zn-RE-Mn alloy, the average crystal grain size is preferably 10 μm or less, particularly preferably 7 μm or less.
The lower limit of the average crystal grain size is practically about 4 μm.

(Crystal face)
In the structure of the magnesium-based alloy, the crystal orientation of the (0002) plane is inclined at an angle of 10 ° or more and 70 ° or less with respect to the plate surface, and there are three or more peaks having an extreme density of 2.5 or more. Since the crystal orientation of the (0002) plane is inclined in various directions by the presence of three or more peaks having an inclination angle of the crystal orientation of the (0002) plane with respect to the plate surface of 10 ° or more and 70 ° or less, the crystal The anisotropy of orientation, strength and elongation is small, and it is easy to combine plastic workability and strength at room temperature. Examples of the inclination direction of the crystal orientation of the plane (0002) with respect to the plate surface include a rolling direction and a direction between the plate width direction and the rolling direction, in addition to the plate width direction. Since the rolled plate material is generally a long material, when the plate material is viewed in a plan view, the longitudinal direction thereof is the rolling direction and the lateral direction is the plate width direction. In other words, the rolling direction is the direction in which the plate advances during rolling, and the plate width direction is a direction orthogonal to the rolling direction and along the plane direction of the plate (direction along the axial direction of the rolling roll).

The inclination angle can be further set to 15 ° or more and 60 ° or less, and particularly 25 ° or more and 55 ° or less. The extreme density can be 3.0 or more, further 3.5 or more, 4.0 or more, and particularly 4.5 or more and 5.0 or more. It is preferable that four or more peaks having an extreme density of 2.5 or more are present. For example, it is preferable that three or more peaks having an extreme density of 3.0 or more are present, and three or more peaks having an extreme density of 3.5 or more are present. For example, it is preferable that three or more peaks having an extreme density of 4.0 or more are present, and in particular, two or more peaks having an extreme density of 4.5 or more are preferably present. For example, it is preferable that two or more peaks having an extreme density of 5.0 or more are present.

The structure of the magnesium-based alloy contains at least one peak in which the angle of inclination of the (0002) plane with respect to the plate surface is less than 10 ° (including 0 °) and the extreme density is 2.5 or more. You may. In this case, not all of the crystal orientations of the (0002) plane are inclined by 10 ° or more and 70 ° or less with respect to the plate surface. In this structure, the inclination angle of the crystal orientation of the (0002) plane with respect to the plate surface is 0 °, the crystal whose (0002) plane is along the plate surface, and the inclination angle is more than 0 ° and less than 10 °, and (0002). ) There are also crystals whose surface is approximately along the surface of the plate. As described above, since the (0002) plane has crystals along the plate surface and crystals substantially along the plate surface, it is easy to secure the strength in the plate surface of the magnesium alloy plate material.

[Characteristic]
The magnesium alloy plate material is excellent in plastic workability at room temperature and also in strength. Specifically, it is preferable that at least one of the Eriksen value and the 0.2% proof stress is high. It is preferable that the magnesium alloy plate material has at least one of high breaking elongation and tensile strength.

(Eriksen value)
The Eriksen value of the magnesium alloy plate material can be 8.0 mm or more. When the Eriksen value is 8.0 mm or more, the plastic workability at room temperature is excellent. The Eriksen value is a value obtained in accordance with "Eriksen tester JIS B 7729 (2005)" and "Eriksen test method JIS Z 2247 (2006)".

In the case of Mg—Zn—Ca based alloys, the Eriksen value can be further set to 8.5 mm or more, and particularly 8.7 mm or more.
In the case of the Mg-Zn-RE alloy and the Mg-Zn-Ca-RE alloy, the Eriksen value can be further set to 8.3 mm or more, and particularly 8.5 mm or more.
In the case of the Mg-Zn-RE-Mn alloy, the Eriksen value can be further set to 8.2 mm or more, and particularly 8.4 mm or more.
The upper limit of the Eriksen value is practically about 10 mm.

(0.2% proof stress)
The 0.2% proof stress of the magnesium alloy plate material in the plate width direction can be 95 MPa or more. When the 0.2% proof stress in the plate width direction is 95 MPa or more, the strength in the plate width direction is excellent.

In the case of the Mg-Zn-Ca based alloy, the 0.2% proof stress in the plate width direction can be further set to 100 MPa or more, and particularly 115 MPa or more.
In the case of the Mg-Zn-RE alloy and the Mg-Zn-Ca-RE alloy, the 0.2% proof stress in the plate width direction can be further set to 110 MPa or more, and particularly 120 MPa or more.
In the case of the Mg-Zn-RE-Mn-based alloy, the 0.2% proof stress in the plate width direction can be further set to 120 MPa or more, and particularly 130 MPa or more.
The upper limit of the 0.2% proof stress in the plate width direction is practically about 160 MPa.

On the other hand, the 0.2% proof stress of the magnesium alloy plate material in the rolling direction can be 120 MPa or more. When the 0.2% proof stress in the rolling direction is 120 MPa or more, the strength in the rolling direction is excellent.

In the case of the Mg-Zn-Ca-based alloy and the Mg-Zn-Ca-RE-based alloy, the 0.2% proof stress in the rolling direction can be further set to 140 MPa or more, and particularly 145 MPa or more.
In the case of Mg-Zn-RE alloy, the 0.2% proof stress in the rolling direction can be further set to 125 MPa or more, and particularly 130 MPa or more.
In the case of the Mg-Zn-RE-Mn alloy, the 0.2% proof stress in the rolling direction can be further set to 130 MPa or more, and particularly 135 MPa or more.
The upper limit of the 0.2% proof stress in the rolling direction is practically about 180 MPa.

(Breaking elongation)
The breaking elongation of the magnesium alloy plate material in the plate width direction can be 28% or more. When the breaking elongation in the plate width direction is 28% or more, the breaking elongation in the plate width direction is large and the ductility in the plate width direction is excellent.

In the case of Mg-Zn-Ca based alloys, the elongation at break in the plate width direction can be further set to 30% or more, and particularly 35% or more.
In the case of Mg-Zn-RE alloys, Mg-Zn-Ca-RE alloys, and Mg-Zn-RE-Mn alloys, the elongation at break in the plate width direction can be further increased to 30% or more, particularly. It can be 32% or more.
Practically, the upper limit of the breaking elongation in the plate width direction is about 40%.

On the other hand, the breaking elongation of the magnesium alloy plate material in the rolling direction can be 26% or more. When the breaking elongation in the rolling direction is 26% or more, the breaking elongation in the rolling direction is large and the ductility in the rolling direction is excellent.

In the case of Mg—Zn—Ca based alloys, the elongation at break in the rolling direction can be further 28% or more, and particularly 30% or more.
In the case of Mg-Zn-RE alloys, Mg-Zn-Ca-RE alloys, and Mg-Zn-RE-Mn alloys, the elongation at break in the rolling direction can be further increased to 27% or more, particularly 29. It can be% or more.
Practically, the upper limit of the elongation at break in the rolling direction is about 32%.

(Tensile strength)
The tensile strength of the magnesium alloy plate material in the plate width direction can be 200 MPa or more. When the tensile strength in the plate width direction is 200 MPa or more, the tensile strength in the plate width direction is large and the strength in the plate width direction is excellent.

In the case of the Mg-Zn-Ca based alloy, the tensile strength in the plate width direction can be further set to 220 MPa or more, and particularly 230 MPa or more.
In the case of the Mg-Zn-RE alloy, the tensile strength in the plate width direction can be further set to 225 MPa or more, and particularly 235 MPa or more.
In the case of the Mg-Zn-Ca-RE alloy, the tensile strength in the plate width direction can be further set to 230 MPa or more, and particularly 240 MPa or more.
In the case of the Mg-Zn-RE-Mn-based alloy, the tensile strength in the plate width direction can be further set to 240 MPa or more, and particularly 250 MPa or more.
The upper limit of the tensile strength in the plate width direction is practically about 280 MPa.

On the other hand, the tensile strength of the magnesium alloy plate material in the rolling direction can be 220 MPa or more. When the tensile strength in the rolling direction is 220 MPa or more, the tensile strength in the rolling direction is large and the strength in the rolling direction is excellent.

In the case of the Mg-Zn-Ca based alloy, the tensile strength in the rolling direction can be further set to 225 MPa or more, and particularly 235 MPa or more.
In the case of the Mg-Zn-RE alloy, the tensile strength in the rolling direction can be further set to 230 MPa or more, and particularly 240 MPa or more.
In the case of Mg-Zn-Ca-RE alloy, the tensile strength in the rolling direction can be further set to 235 MPa or more, and particularly 245 MPa or more.
In the case of Mg-Zn-RE-Mn-based alloys, the tensile strength in the rolling direction can be further set to 245 MPa or more, and particularly 255 MPa or more.
Practically, the upper limit of the tensile strength in the rolling direction is about 300 MPa.

These 0.2% proof stress, elongation at break, and tensile strength are obtained as follows. A JIS 13B plate-shaped test piece whose longitudinal direction is along the plate width direction and a JIS 13B plate-shaped test piece whose longitudinal direction is along the rolling direction are produced from a magnesium alloy plate material. This test piece is subjected to a tensile test at room temperature in accordance with "Metallic Material Tensile Test Method JIS Z 2241 (2011)".

[Use]
The magnesium alloy plate material according to the embodiment can be suitably used for components of automobiles (body panels, parts around chassis), components of transport aircraft such as aircraft and railways, and components of electrical and electronic equipment.

[Manufacturing method of magnesium alloy plate]
The magnesium alloy plate material according to the embodiment includes a casting step of producing a cast plate material by a quenching solidification method, a rolling step of rolling the cast plate material to produce a rolled plate material, and a heat treatment step of applying a heat treatment to the rolled plate material. It can be manufactured by a method for manufacturing a magnesium alloy plate material.

[Casting process]
In the casting step, the molten metal having the above composition is cooled and solidified to produce a cast plate material having the composition of the magnesium-based alloy. This casting process is performed by a quenching solidification method in which the cooling rate (solidification rate) of the molten metal is high. Examples of the quenching solidification method include a double roll casting method (double roll continuous casting method). By this casting step, a diploid whose crystal orientation is inclined with respect to the plate surface is formed, and the crystal orientation of the (0002) plane is in various directions (plate width direction, casting direction, plate width direction) with respect to the plate surface. A cast plate material having a structure inclined in the direction between the casting direction and the casting direction is obtained.

The cooling rate is, for example, 100 ° C./s or higher. When the cooling rate is 100 ° C./s or higher, the cooling rate is high, so that it is easy to suppress the formation of coarse crystal grains and make the crystal grains finer. In addition, when the solute atoms are sufficiently solid-solved, the recrystallization mechanism changes as described later, the crystals become finer, and crystals inclined in various directions with respect to the plate surface are likely to be formed. The cooling rate is further preferably 500 ° C./s or higher, and particularly preferably 1000 ° C./s or higher. Practically, the upper limit of the cooling rate is 2000 ° C./s or less.

[Rolling process]
In the rolling process, the cast plate material is rolled to produce a rolled plate material. The rolling process is performed by using a rolling apparatus provided with rolling rolls arranged so as to face each other and inserting a cast plate material between the rolling rolls. At this time, the cast plate material is preheated to a specific temperature, and the rolling roll is set to a specific temperature. By this rolling process, a rolled plate material having fine crystal grains can be obtained. It is considered that this is because the twins formed in the casting process are recrystallized as nuclei depending on the temperature during rolling.

The preheating temperature of the cast plate material is the temperature of the cast plate material immediately before coming into contact with the rolling roll. Heating (preheating) of the cast plate material may be performed by separately providing a heating furnace. The transfer distance and transfer time are set so that the temperature of the plate material does not decrease between the time when the cast plate material comes into contact with the rolling roller and the temperature of the plate material immediately before contact with the rolling roller satisfies the temperature range described later. It is preferable to adjust the temperature of the cast plate material, provide a heat insulating cover for keeping the temperature of the cast plate material in the transport path, or control the temperature of the atmosphere.

The preheating temperature of the cast plate material is, for example, 250 ° C. or higher and 450 ° C. or lower, and the temperature of the rolling roll is, for example, 100 ° C. or higher and 300 ° C. or lower. By setting the preheating temperature of the cast plate material to 250 ° C. or higher and the temperature of the rolling roll to 100 ° C. or higher, it is easy to produce a rolled plate material having fine crystal grains. By setting the preheating temperature of the cast plate material to 450 ° C. or lower and the temperature of the rolling roll to 300 ° C. or lower, the crystal grains are less likely to become coarse. The preheating temperature of the cast plate material can be further set to 300 ° C. or higher and 425 ° C. or lower, and particularly 350 ° C. or higher and 400 ° C. or lower. The temperature of the rolling roll can be further set to 125 ° C. or higher and 250 ° C. or lower, and particularly 150 ° C. or higher and 200 ° C. or lower. The reduction rate per pass is preferably 10% or more and 30% or less, and the total reduction rate is preferably 25% or more and 90% or less.

[Heat treatment process]
The heat treatment step heats the rolled plate material. As a result, the strain introduced in the rolling process is removed. By this heat treatment step, the average crystal grain size is 15 μm or less, the crystal orientation of the (0002) plane is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and there are three or more peaks having an extreme density of 2.5 or more. A magnesium alloy plate having an existing structure can be produced. The mechanism by which a magnesium alloy plate having this structure is obtained is not known in detail, but is presumed as follows.

The recrystallization of a general magnesium alloy plate is considered to have a mechanism in which the recrystallized grains generated at the grain boundaries grow while rotating. In this case, the crystal orientation of the original crystal grains is the base, so that the recrystallization occurs. There is little change in orientation after that. On the other hand, in the present embodiment, the solute atoms are sufficiently solid-solved by quenching in the casting step, and a part of the solute atoms is segregated at the grain boundaries at the atomic level. Instead of the segregated solute atoms suppressing recrystallization from the grain boundaries, recrystallization with twins introduced during rolling occurs. The crystal orientation of the (0002) plane of these twins is inclined in various directions with respect to the plate surface. Therefore, in addition to recrystallizing these twins as nuclei, crystals in which the crystal orientation of the (0002) plane is inclined in various directions with respect to the plate surface are formed in the casting step, and (0002) It is considered that crystals in which the crystal orientation of the surface was inclined in various directions with respect to the plate surface were obtained. In addition, the magnesium alloy plate with a small average crystal grain size was obtained because the solute atoms that were sufficiently solid-solved by quenching in the casting process became a barrier to dislocations introduced during rolling, making it difficult for dislocations to act. It is probable that a large amount of twins were introduced into the material and recrystallization occurred with these twins as nuclei. By using the cast plate material, not all of the (0002) planes follow the plate surface even after the rolling step and the heat treatment step, and the crystal orientation is added not only in the plate width direction but also in the plate width direction. It is possible to form an inclined structure in the rolling direction and the direction between the plate width direction and the rolling direction.

The heating temperature of the rolled plate material is, for example, 300 ° C. or higher and 450 ° C. or lower, and the heat treatment time is, for example, 0.5 hour or longer and 3.0 hours or lower. By setting the heating temperature of the rolled plate material to 300 ° C. or higher and the heat treatment time to 0.5 hours or more, it is easy to remove the strain of the rolled plate material. By setting the heating temperature of the rolled plate material to 450 ° C. or lower and the heat treatment time to 3.0 hours or less, it is easy to suppress the coarsening of crystal grains. The heating temperature of the rolled plate material is more preferably 320 ° C. or higher and 420 ° C. or lower, and particularly preferably 350 ° C. or higher and 400 ° C. or lower. The heat treatment time is further preferably 0.75 hours or more and 2.5 hours or less, and particularly preferably 1.0 hours or more and 2.0 hours or less.

[Use]
The method for producing a magnesium alloy plate material can be suitably used for producing the magnesium alloy plate material.

[Action effect]
According to the magnesium alloy plate material according to the embodiment, the crystal grain size is small and the crystal orientation of the (0002) plane is inclined in various directions with respect to the plate surface, so that the crystal orientation, strength, and elongation can be determined. Since the anisotropy is small, it is excellent in plastic workability at room temperature and also in strength.

<< Test Example 1 >>
A magnesium alloy plate made of a magnesium-based alloy was prepared, and its plastic workability and mechanical properties at room temperature were evaluated.

[Sample No. 1-1, No. 1-2]
Sample No. of magnesium alloy plate material. 1-1, No. 1-2 was produced by the procedure of casting step → rolling step → heat treatment step in the same manner as the above-mentioned manufacturing method of magnesium alloy plate material. The conditions for each step are shown in Table 1.

[Casting process]
In the casting process, a cast plate material having a thickness of 4 mm was produced by a double roll casting method at a cooling rate of 1000 ° C./s. Sample No. The composition of 1-1 is an Mg—Zn—Ca alloy containing 1.5% by mass of Zn and 0.1% by mass of Ca as additive elements, and the balance is Mg and unavoidable impurities (in Tables 1 and 2). (Indicated by ZX10). Sample No. The composition of 1-2 is an Mg-Zn-Mm alloy containing 2.0% by mass of Zn as an additive element and 0.3% by mass of Mm (mischmetal), and the balance is Mg and unavoidable impurities (Table). In 1 and 2, it is indicated by ZE20). The elements contained in Mm and their contents were 52% by mass for Ce (cerium), 28% by mass for La (lanthanum), 15% by mass for Nd (neodymium), and 5% by mass for Pr (praseodymium).

[Rolling process]
In the rolling process, the temperature of the cast plate (rolling temperature), the temperature of the rolling roll, the reduction rate per pass, and the total reduction rate are the following conditions, and the cast plate material with a thickness of 4 mm is rolled to a thickness of 1 mm. A rolled plate material was produced.
Rolling temperature: 395 ° C
Rolling roll temperature: 200 ° C
Reduction rate: 20% / 1 pass Total reduction rate: 75%

[Heat treatment process]
In the heat treatment step, the rolled plate material was heat-treated under the following conditions of temperature and time.
Temperature: 350 ° C
Time: 1 hour

[Sample No. 1-101, No. 1-102]
Sample No. of magnesium alloy plate material. 1-101, No. As shown in Table 1, each of 1-102 has sample No. 1-1, No. Except for the difference between 1-2 and the casting process, Sample No. 1-1, No. It was produced through the same rolling step and heat treatment step with the same composition as 1-2. In the casting step, a molten metal was poured into a mold instead of the twin roll casting method, and a plate-shaped ingot (cast plate material) having a thickness of 4 mm was produced at a cooling rate of 10 ° C./s.

[Average crystal grain size]
The average crystal grain size of each sample was measured. This measurement was performed as follows. After inserting the sample into the SEM and creating a vacuum state, one observation field (surface) of 150 μm × 500 μm was taken under the conditions of room temperature and an acceleration voltage of 15 kV, and the crystal orientation of each crystal grain was taken for the entire observation field by the EBSD method. Color coding was performed separately. Image analysis was performed on the obtained mapping image using OIM 6.2.0 manufactured by TSL Solutions Co., Ltd. At this time, image analysis is performed using data points having a reliability coefficient CI value of 0.1 or more in the above analysis software to obtain the area of each particle, and the average value of the diameters of circles equal to each area is the average crystal grain size. And said. The results are shown in Table 2.

[Evaluation of plastic workability]
The plastic workability of each sample was evaluated by measuring the Eriksen value. The Eriksen value was determined in accordance with "Eriksen tester JIS B 7729 (2005)" and "Eriksen test method JIS Z 2247 (2006)". The results are shown in Table 2.

[Mechanical specific evaluation]
The mechanical properties of each sample were evaluated by measuring the tensile strength in the rolling direction (RD) and the plate width direction (TD), 0.2% proof stress, and breaking elongation by a tensile test. In this tensile test, a JIS 13B plate-shaped test piece whose longitudinal direction is along the plate width direction and a JIS 13B plate-shaped test piece whose longitudinal direction is along the rolling direction are prepared for each sample, and this test is performed. One piece was subjected to at room temperature in accordance with "Metallic Material Tensile Test Method JIS Z 2241 (2011)". The results are also shown in Table 2.

As shown in Table 2, the sample No. 1-1, No. No. 1-2 has an average crystal grain size of 15 μm or less, a high Eriksen value, and high mechanical properties in both the rolling direction and the plate width direction. That is, this sample No. 1-1, No. It can be seen that 1-2 is excellent in plastic workability at room temperature and also in mechanical properties. On the other hand, sample No. 1-101, No. In 1-102, the average crystal grain size is more than 15 μm, the Eriksen value is low, and the mechanical properties in both the rolling direction and the plate width direction are low.

Sample No. by the EBSD method. The pole figure of the (0002) plane of 1-1 was taken. The pole figure is shown in FIG. In this pole figure, the distribution state (magnitude of extreme density) of the crystal orientation of the (0002) plane is represented by color (red, orange, yellow, green, blue in descending order of extreme density). The center of this pole figure shows 0 ° with respect to the plate surface, and 90 ° with respect to the plate surface on the circumference. For convenience of explanation, a point inclined by 10 ° and a point inclined by 70 ° with respect to the plate surface are shown. It is indicated by a two-dot chain line circle. Although FIG. 1 is shown in gray scale, there are actually the above-mentioned colors.

As shown by the broken line circle in FIG. 1, the sample No. It can be seen that 1-1 has a structure in which the crystal orientation of the (0002) plane is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and three or more peaks having an extreme density of 2.5 or more are present. Specifically, in the pole view of FIG. 1, it can be seen that in addition to the plate width direction, there are a total of four peaks in the rolling direction and in the direction between the plate width direction and the rolling direction. The value of two of these four peaks is 3.0 or more and less than 4.0, and the value of the remaining two peaks is 4.0 or more and further 5.0 or more. In this way, the peaks are dispersed, that is, the crystal orientations are inclined in various directions, so that the sample No. It is considered that the Eriksen value of 1-1 and the mechanical characteristics were high. Further, in the pole figure of FIG. 1, it can be seen that the pole density at the center (0 °) is 2.5 or more, and further 3.0 or more.

Sample No. Although the pole figure of the (0002) plane in 1-2 is not shown, the sample No. The Eriksen value of 1-2 and the mechanical properties are the sample No. Since the results were as high as 1-1, the sample No. 1-2 is the sample No. 1 shown in FIG. It is considered that it has the same tissue as 1-1.

On the other hand, sample No. 1-101, No. Sample Nos. 1-102 had low Eriksen values and mechanical properties. It is considered that it has a different organization from 1-1. That is, the sample No. 1-101, No. The structure of 1-102 is the sample No. It does not have a structure in which the crystal orientation of the (0002) plane such as 1-1 is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and three or more peaks having an extreme density of 2.5 or more are present. ..

It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

Claims (9)

A magnesium alloy plate made of a magnesium-based alloy
The magnesium-based alloy is
Ca is 0.05% by mass or more and 0.3% by mass or less, rare earth element is 0.05% by mass or more and 0.5% by mass or less, and Zn is 0.5% by mass or more and 6.2% by mass or less. And the composition that the balance is Mg and unavoidable impurities, including
When the average crystal grain size is 15 μm or less and the pole view of the (0002) plane is taken by the EBSD method, the crystal orientation of the (0002) plane is inclined by 10 ° or more and 70 ° or less with respect to the plate surface, and its extreme density. A magnesium alloy plate having a structure having three or more peaks having a value of 2.5 or more. The magnesium alloy plate material according to claim 1, wherein Ca is replaced with one of 0.1% by mass or more and 0.65% by mass or less of Sr, or 0.15% by mass or more and 1.0% by mass or less of Ba. The magnesium alloy plate material according to claim 1, further comprising at least one of Sr of 0.1% by mass or more and 0.65% by mass or less and Ba of 0.15% by mass or more and 1.0% by mass or less. Claims 1 to 3 further include the structure in which the inclination angle of the crystal orientation of the (0002) plane with respect to the plate surface is less than 10 ° and the polar density thereof is 2.5 or more. The magnesium alloy plate material according to any one of the above. The magnesium alloy plate material according to any one of claims 1 to 4, further comprising Mn of 0.1% by mass or more and 0.8% by mass or less. The magnesium alloy plate material according to any one of claims 1 to 5, wherein the 0.2% proof stress in the plate width direction is 95 MPa or more. The magnesium alloy plate material according to any one of claims 1 to 6, wherein the Eriksen value is 8.0 mm or more. The magnesium alloy plate material according to any one of claims 1 to 7, wherein the elongation at break in the plate width direction is 28% or more. The magnesium alloy plate material according to any one of claims 1 to 8, wherein the tensile strength in the plate width direction is 200 MPa or more.