JP6843353B2 - Mg alloy and its manufacturing method - Google Patents

Description

The present invention relates to an Mg alloy and a method for producing the same.

Magnesium alloy is known as the lightest metal among practical metals, and is currently being considered for application to railways, aircraft, automobiles, etc. as a lightweight material to replace aluminum alloy. However, the magnesium alloy wrought material is inferior in strength and workability at room temperature as compared with the aluminum alloy.

Various studies have been conducted, including the development of new wrought materials, in order to overcome the strength and workability of magnesium alloys at room temperature and expand their applications. For example, a conventional wrought magnesium alloy can obtain a strength exceeding 300 MPa by making crystal grains finer by strong processing and adding a rare earth metal element and zinc as alloy elements.

On the other hand, in addition to the development of high-strength alloys as described above, many studies have been conducted on the improvement of workability at room temperature. In these reported examples, the workability at room temperature is determined by pressing a ball head punch against a thin plate with a fixed outer circumference at a constant speed to deform the thin plate, and the height of the dent until the material breaks. Is evaluated by the Eriksen test, which evaluates by the Eriksen value (IE value).

In some reports, examples have been reported in which an alloy having excellent processability at room temperature comparable to that of an aluminum alloy has been developed by adding alloying elements and improving the rolling process.

In the Mg—Zn-based alloy to which Zr is added (see Patent Document 1), it has been conventionally considered that the crystal grains of the cast material are refined by Zr. However, recent research has found that the addition of Zr also refines the crystal grains of the wrought material produced by extrusion or rolling.

Japanese Unexamined Patent Publication No. 2002-266044

The Mg alloy developed by the prior art has many problems in practical use. With the Mg alloy to which a rare earth metal is added as an alloying element, it is possible to produce an alloy having excellent strength. However, in the Mg alloy to which the rare earth metal is added, the raw material cost is high because the expensive rare earth metal is used. In addition, the manufacturing cost is high because plastic working cannot be easily performed. Therefore, it is extremely unlikely that a general-purpose material that can be applied to automobiles and railways can be developed.

Further, the wrought material whose strength has been improved by refining the crystal grains by strong processing has already been work-hardened. Therefore, secondary processing at room temperature is extremely difficult. Not only that, it is also extremely difficult to manufacture a large member.

The strength tends to decrease as the secondary workability at room temperature improves. When developing alloys with an eye on application to automobile body panels, alloys that exhibit both strength and excellent secondary workability at room temperature are required. However, since the above alloys and processing methods cannot produce alloys having both strength and secondary workability, they have a 0.2% proof stress of 130 MPa and about 6.5 mm, which are required as mechanical properties that can be applied as automobile materials. It is difficult to develop an alloy having the Eriksen value of.

In view of the above problems, the present invention is a method for producing an Mg alloy by combining a Mg alloy having excellent processability, high strength and high ductility as a wrought material and a simple heat treatment without using an expensive rare earth metal. The purpose is to provide.

In order to achieve the above object, the Mg alloy of the present invention contains Zn of more than 2.0% by mass and less than 5% by mass, Ca of 0.25% by mass or more and 0.3% by mass or less , and 0.20% by mass. It contains Zr of 0.3% by mass or more and the balance is composed of Mg and unavoidable impurities. In the structure of the Mg alloy, nanometer-order Zn ₂ Zr precipitates are dispersed in the magnesium matrix, and Ca. Is segregated at the interface between the magnesium matrix and the Zn ₂ Zr precipitate, and the degree of orientation of the (0001) pole of the crystal grains of the Mg alloy measured by X-ray diffraction is based on the texture strength measured by X-ray diffraction. It is 6.0 or less and has a 0.2% resistance of 130 MPa to 250 MPa .

In the above configuration, preferably, the texture strength from 3 to 5.2.
The Eriksen value of the Mg alloy at room temperature is preferably 6.5 mm or more.
The tensile strength of the Mg alloy is preferably 200 MPa to 300 MPa.
The 0.2% proof stress of the Mg alloy is preferably 132 to 183 MPa.
The elongation at break of the Mg alloy is preferably 20% to 35% .

In order to achieve the above object, the method for producing an Mg alloy of the present invention comprises the step 1 of melting Mg, Zn, Zr and Ca having the above composition to obtain a cast solid, and the homogenization treatment of the cast solid to homogenize the cast solid. A step 2 of obtaining a solid, a step 3 of hot-working a homogenized solid to obtain a tangible solid, and a step 4 of dissolving the tangible solid to obtain a cooled solid are included. The homogenization treatment is carried out for a predetermined time in two steps of 350 ° C. and 400 ° C. to 450 ° C. to obtain a homogenized solid.
The cast solid is preferably obtained by any of quenching solidification casting, gravity casting and vacuum casting.
Preferably, the Mg alloy is further aged after step 4.

INDUSTRIAL APPLICABILITY The present invention can provide a general-purpose Mg alloy which has excellent strength and workability and can be obtained at low cost and a method for producing the same.

It is a flow chart which shows the manufacturing method of the Mg alloy of this invention. It is a figure which shows the rolling process. It is a figure which shows the optical microscope image of the solution treatment material of the Mg alloy of Example 1. FIG. FIG. 5 is a (0001) pole figure showing the degree of orientation of the (0001) poles of the crystal grains of the treated material obtained by solution-treating the Mg alloy of Example 1 measured by X-ray diffraction. It is a figure which shows the X-ray diffraction pattern of the solution treatment material of the Mg alloy of Example 1. FIG. It is a figure which shows the tensile stress-strain curve of the solution-treated material of Example 1. The solution-treated material of Example 1 was measured using a transmission electron microscope. (A) is a HAADF-STEM image, and (b) to (d) are Zn, Zr, and Ca surfaces measured by EDS. It is a figure which shows the distribution. It is a three-dimensional atom map diagram obtained by a three-dimensional atomic probe, (a) is a three-dimensional distribution, (b) is _{an enlarged three-dimensional distribution near a Zn 2} Zr precipitate, and (c) is a selection of (b). It is a one-dimensional density profile obtained from the region. It is a figure which shows the relationship between the aging time and the Vickers hardness. It is a figure which shows the tensile stress-strain curve of the aging treatment material which was aged at 160 degreeC for 64 hours. It is a figure which shows the optical microscope image of the solution treatment material of Example 4. FIG. 5 is a (0001) pole figure showing the degree of orientation of the (0001) pole of the treated material obtained by solution-treating the Mg alloy of Example 4 measured from the rolled surface by X-ray diffraction. It is a figure which shows the tensile stress-strain curve of the solution-treated material of Example 4. It is a figure which shows the optical microscope image of the solution treatment material of the comparative example 1. FIG. It is a figure which shows the X-ray diffraction pattern of the solution treatment material of the comparative example 1. It is a figure which shows the (0001) pole figure obtained by the X-ray diffraction of the solution treatment material of the comparative example 1. FIG. It is a figure which shows the tensile stress-strain curve of the solution-treated material of the comparative example 1. FIG.

Hereinafter, the present invention will be described in detail with reference to some examples.
The Mg alloy of the present invention contains Zn of more than 2.0% by mass and less than 5.0% by mass, Ca of at least 0.25% by mass, and Zr of 0.20% by mass or more, and the balance. Consists of Mg and unavoidable impurities.
Specifically, examples of the composition of the Mg alloy include Mg-3Zn-0.3Zr-0.3Ca alloy and Mg-4Zn-0.3Zr-0.3Ca alloy.
Here, the numerical value described before Zn, Zr, and Ca is the mass% of each element.
The reason for the above composition is that it is composed of fine Zn and Zr or Mg, Zn, Zr formed during melting / casting of the Mg-Zn-Zr alloy or homogenization treatment before processing, and has a size of several tens of nanometers. This is because the growth of crystal grains is suppressed by the precipitate of.

Of the above precipitates, Zn ₂ Zr is dispersed at a relatively high density, and thus it can be considered to be effective for strengthening the material. Further, since the nano-sized precipitate is less likely to be the starting point of fracture, it can be considered that the precipitate does not affect the decrease in moldability at room temperature.

From the above, the Mg-Zn-Zr-based alloy has secondary workability at room temperature only by removing the strain introduced by subjecting the plate material to a solution treatment after processing without undergoing the conventional aging treatment. Can be expected. In addition, it is a new type of alloy that has the potential to exhibit excellent strength due to the nanoprecipitates formed during the pre-processing homogenization process.

In order to obtain the formability, strength and ductility of the Mg alloy, the Zn content is set to be larger than 2.0% by mass. If the Zn content is 5.0% by mass or more, the moldability deteriorates, so the Zn content is preferably less than 5% by mass.

When the amount of Ca added is 0.2% by mass, the degree of orientation of the (0001) pole does not decrease, but when 0.3% by mass of Ca is added, the texture of the (0001) pole is significantly reduced. The content is preferably at least 0.25% by mass or more.

In order to increase the strength, it is preferable that Zr is 0.20% by mass or more and the Ca content is at least 0.25% by mass or more.
Dispersion of nano-sized precipitates that are stable even at high temperatures compensates for the decrease in strength due to the decrease in crystal orientation, and it is possible to obtain superior strength compared to conventional alloys without impairing room temperature workability. By using Zr, which has been conventionally added as an element for refining the crystal grain structure of a cast material, the above-mentioned dispersion effect of nano-sized precipitates can be exhibited.

The structure of the Mg alloy of the present invention after solution treatment, which will be described later, will be described.
The structure of the Mg alloy after the solution treatment of the present invention, that is, the structure of the solution treatment material, has a structure in which a precipitate composed _{of Zn 2 Zr on the order of nanometers (nm) is dispersed in the magnesium matrix.} .. The precipitate consisting of Zn ₂ Zr, referred to as _Zn 2 Zr precipitates.

In order to increase the strength of the Mg alloy of the present invention, it is preferable to make the crystal grains finer. Further, it is desirable to strengthen the magnesium matrix by solid solution strengthening in which Zn is dissolved as an alloying element at a high concentration in the magnesium matrix, and to strengthen the precipitation by dispersing the precipitate. That is, in order to increase the strength of the Mg alloy by precipitation strengthening, the finer the size of the precipitate and the higher the number density, the better. Specifically, _{the size of the Zn 2} Zr precipitate is 18.7 ± 5.3 nm in width and 35.0 ± 13.3 nm in length. The density of Zn ₂ Zr precipitates is at least 1.47 × 10 ²⁰ / m ³ , for example 3.08 × 10 ²⁰ / m ³ . Further, Ca is segregated at the interface between the magnesium matrix and the Zn _{2 Zr precipitate.}

When the Mg alloy of the present invention is measured by X-ray diffraction, the degree of orientation of the (0001) poles of the crystal grains of the Mg alloy is 6.0 in terms of the strength of the (0001) poles in the (0001) pole diagram measured from the rolled surface. It is as follows.

When the moldability of the Mg alloy is measured with an Eriksen tester, the Eriksen value at room temperature is 6.5 mm or more. Further, the Eriksen value is 7.9 to 8 mm at 6.5 mm or more.

The 0.2% proof stress of the Mg alloy of the present invention is 130 to 250 MPa or more, the tensile strength of the Mg alloy is 200 MPa to 300 MPa, and the breaking elongation of the Mg alloy is 20% to 35%.

The Vickers hardness of the Mg alloy of the present invention can be 50 HV or more.

The Mg alloy of the present invention can be produced by the following steps.
FIG. 1 is a flow chart showing a method for producing the Mg alloy of the present invention. As shown in FIG. 1, the Mg alloy of the present invention is
Step 1 of melting Mg, Zn, Zr and Ca to obtain a cast solid,
Step 2 of homogenizing the cast solid to obtain a homogenized solid and step 3 of hot-working the homogenized solid to obtain a tangible solid.
Step 4 of dissolving a tangible solid to obtain a cooled solid,
It can be manufactured by a process including.

The cooled solid obtained in step 4 may be aged to produce an Mg alloy.

Hereinafter, each step will be described.
(Step 1)
In the process of obtaining a cast solid, Mg and Zn, Zr, and Ca, which are the compositions of the above Mg alloy, are melted in an iron crucible to form a molten metal, which is poured into a mold or the like and cooled to cast the cast solid. obtain. Specifically, for example, an alloy having the above composition can be melted using a high-frequency induction melting furnace and cast using an iron mold.
The melting furnace used for melting is not limited to the high-frequency induction melting furnace, and other devices may be used as long as an alloy having a desired composition can be produced. The cast solid may be obtained by any of quenching solidification casting, gravity casting and vacuum casting. High productivity and low cost cast solids can be obtained by quenching solidification casting.

(Step 2)
This is a step of homogenizing a cast solid to obtain a homogenized solid. In the homogenization treatment, the distribution of the metal of each component present in the cast solid is homogenized, and the precipitate formed during the cooling of the molten metal is solid-solved in the matrix. The homogenization treatment is a heat treatment for solid-solving the precipitate formed during the cooling of the molten metal in the magnesium matrix in step 1. In particular, in the region where Zn is macrosegregated to a high concentration, the alloy melts when heat treatment is started at around 460 ° C., for example, 400 ° C. to 460 ° C., or 400 ° C. to 450 ° C. For example, it is formed at around 340 ° C. during casting to suppress the initial melting of the Mg—Zn phase, and the Zn distribution is homogenized by heat treatment at 450 ° C. The homogenization treatment is carried out, for example, at 350 ° C. for 24 hours and at 450 ° C. for 4 hours.

The conditions of the homogenization treatment are not limited to the above conditions (24 hours at 350 ° C. + 4 hours at 450 ° C.). The heat treatment may be performed under the condition that the alloying element is solid-solved in the magnesium matrix by the heat treatment under a predetermined temperature and time condition.

(Step 3)
This is a step of hot-working a homogenized solid by rolling or extrusion to obtain a tangible solid. As the hot working, rolling, extrusion, or forging can be used. For example, the rolling process can be performed using a rolling machine. The cast material can be processed into a plate material by a rolling process.
FIG. 2 is a diagram showing a rolling process. As shown in FIG. 2, the rolling step can be performed after the homogenization treatment. There are conditions for rolling such as sample temperature, roll temperature, rolling reduction, roll peripheral speed, and presence / absence of intermediate heat treatment. Examples of these are shown in Table 1.

As shown in Table 1, an example of the roll temperature and sample temperature when rolling from 10 mm to 5 mm in sample thickness is 200 ° C., the rolling reduction is, for example, 13.1%, and the peripheral roll speed is 1 m / min. Examples of the roll temperature and sample temperature when rolling from a sample thickness of 5 mm to 1 mm are 200 ° C. and 300 ° C., a rolling reduction is, for example, 20.5%, and a roll peripheral speed is 1 m / min. Intermediate heat treatment may be applied during rolling. The conditions for the intermediate heat treatment are, for example, 450 ° C. for 5 minutes.
The plate material may be manufactured by any method such as rolling, forging or extrusion as long as it is a wrought processing method capable of producing the above-mentioned fine structure.

(Step 4)
This is a step of solution-treating a tangible solid to obtain a solution-treated material, that is, a cooled solid. Among the precipitates formed during hot working, a precipitate composed of Mg and Zn (MgZn ₂ phase) is contained in the matrix. This is a heat treatment step carried out in order to form a recrystallized structure that is solid-solved in. The solution treatment can be performed by heating in an electric furnace, for example. The solution treatment may be carried out by heat treatment at a predetermined temperature and for a predetermined time so that the precipitate formed during the hot working in step 3 is solid-solved in the matrix and a recrystallized structure is formed. The solution treatment may be performed at, for example, 350 to 450 ° C. for about 0.5 to 8 hours, but the longer heat treatment time leads to an increase in manufacturing cost, so the solution treatment time may be the minimum necessary time. A cooled solid is obtained by cooling the solution after the solution treatment.

(Step 5)
This is a step of further aging the cooled solid after the solution treatment to obtain an aging treatment material of Mg alloy. This step can be performed as needed. The aging treatment is a heat treatment step for dispersing the precipitates in the solution-treated material and imparting strength.

The aging treatment in step 5 is a heat treatment process in which the precipitate is dispersed in the solution-treated material to impart strength. That is, it is a step of heat-treating a cooled solid in which the alloying element obtained in the solution treatment is supersaturated to obtain a Mg alloy of the present invention having high strength and improved ductility and good workability. The aging treatment can be performed using an oil bath (oil bath). The temperature of the oil bath may be controlled in a constant temperature bath.

The aging treatment can be performed at, for example, 140 to 200 ° C. The aging treatment is carried out, for example, in the time range from reaching the maximum altitude, that is, 5 to 6 hours to 10 hours or more, more preferably 100 hours.

(Microstructure after aging treatment)
In the method for producing an Mg alloy of the present invention, in the Mg alloy after the aging treatment, a precipitate composed of Mg and Zn (MgZn ₂ phase) is formed in _{addition to the Zn 2 Zr precipitate.}

According to the Mg alloy of the present invention, conventionally, when excellent room temperature moldability is imparted, only a material having low strength can be obtained, whereas it is relatively inexpensive without using expensive and resource-poor heavy rare earth metal elements. It is possible to provide an Mg alloy having excellent room temperature strength and moldability that satisfies the characteristics required for automobile applications, depending on the combination of various alloying elements and its fine structure.

According to the Mg alloy of the present invention, Zr, which has been conventionally added as an element for refining the crystal grain structure of the cast material, is used to exhibit the above-mentioned dispersion effect of nano-sized precipitates, thereby being stable even at high temperatures. The nano-sized precipitates compensate for the decrease in strength due to the decrease in crystal orientation, and can obtain superior strength to conventional Mg alloys without impairing the workability at room temperature.

According to the method for producing an Mg alloy of the present invention, a relatively inexpensive alloy element and a production method combining simple rolling and heat treatment are required for automobile application without using an expensive and resource-poor heavy rare earth metal element. It is possible to produce an Mg alloy having excellent room temperature strength and moldability at low cost.

According to the method for producing an Mg alloy of the present invention, by subjecting a solution treatment after rolling, the orientation of crystal grains can be randomly oriented, thereby imparting excellent moldability. If the orientation of the crystal grains is randomly oriented, the strength drops sharply, but by forming nano-sized precipitates that are stable even at high temperatures, it is possible to obtain an Mg alloy that has both formability, strength, and ductility.
Next, examples of the present invention will be described in detail.

As the Mg alloy of Example 1, an Mg alloy having the following composition was produced. The numbers before Zn, Zr, and Ca of the Mg alloy additive indicate mass%.
Alloy composition: Mg-4Zn-0.3Zr-0.3Ca alloy The homogenization treatment was carried out at 350 ° C. for 24 hours and at 450 ° C. for 4 hours.
The conditions of the homogenization treatment are the same as those of Example 1 in Examples 2, 3, 5 to 8 and Comparative Examples 1 to 9 described later.

The stretching process was performed using a rolling mill manufactured by Uenotex Co., Ltd. (custom-made product, serial number: H9132). In rolling, the plate material was rolled at a temperature of 200 ° C., a roll temperature of 200 ° C., and no intermediate heat treatment. The rolling conditions are shown in Table 2. The temperature of the plate material, the roll temperature, and the presence or absence of intermediate heat treatment are indicated as follows.
Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / None

The solution treatment was carried out at 450 ° C. for 2 hours. The solution treatment is expressed as follows.
Solution treatment: 2 hours at 450 ° C

FIG. 3 is a diagram showing an optical microscope image of the solution-treated material of the Mg alloy of Example 1. The optical microscope image was measured using an optical microscope (Elipse, LV-100) manufactured by Nikon Corporation.
In the Mg alloy observed in FIG. 3, the crystal grain size calculated by the intercept method is 7.7 μm. The crystal grain size was calculated according to the linear intercept method (E112-13) of the American Society for Testing and Materials (ASTM).

FIG. 4 is a (0001) pole figure showing the degree of orientation of the (0001) poles of the crystal grains of the solution-treated material obtained by solution-treating the Mg alloy of Example 1 measured by X-ray diffraction. The analysis software (Textools, v3.3) manufactured by ResMat was used for the analysis of the pole figure.
The texture intensity (also called maximum random distribution, mrd or degree of integration) of the (0001) poles measured by X-ray diffraction shown in FIG. 4 is 4.8, and the (0001) poles are in the rolling surface normal direction (ND). It was found that it was inclined from the direction) to the rolling direction (RD direction).
Here, the intensity of the (0001) pole is a measure indicating the relative intensity of the degree of orientation of the (0001) pole (1 is defined as when randomly oriented).

FIG. 5 is a diagram showing an X-ray diffraction pattern of the solution-treated material of the Mg alloy of Example 1. The vertical axis represents the X-ray diffraction intensity (arbitrary scale), and the horizontal axis represents the angle (°), that is, 2θ, which is an angle corresponding to twice the angle of incidence of X-rays on the atomic plane θ. X-ray diffraction was measured using a Rigaku SmartLab device.
As shown in FIG. 5, in the solution-treated material of the Mg alloy of Example 1, it was found that the _{Zn 2 Zr phase was present in the magnesium matrix.}

FIG. 6 is a diagram showing a tensile stress-strain curve of the solution-treated material of Example 1. The vertical axis of FIG. 6 is stress (MPa), and the horizontal axis is strain (%).
Table 3 shows 0.2% proof stress (also called yield strength) obtained from the stress-strain curve shown in FIG. 6, tensile strength, elongation, and formability (index Erichsen value) evaluated by the Erichsen test. The stress-strain curve was measured using an Instron (Model 5567), and the Eriksen test was measured using an Eriksen (111 type) tester.

As shown in Table 3, in the solution-treated material of Example 1, the 0.2% proof stress was 176 MPa, the tensile strength was 265 MPa, the elongation was 29%, and the Eriksen value was 7.5 mm. It turned out to have.

The result of examining the structure of the solution-treated material of the Mg alloy of Example 1 in more detail with a scanning transmission electron microscope will be described.
FIG. 7 shows (a) HAADF-STEM images observed using a transmission electron microscope of the solution-treated material of Example 1, and (b) Zn, (c) Zr, and (d) Ca measured by EDS. It is a figure which shows the plane distribution of. HAADF-STEM images (High-angle Annular Dark Field Scanning Transmission Electron Microscopy) were observed with a FEI scanning transmission electron microscope (Titan, G280-200). For elemental analysis by energy dispersion (also called Energy Dispersion Spectroscopy, EDS), an EDS elemental analyzer (Super X) manufactured by FEI was used.
As shown in FIG. 7, it can be seen that the precipitate composed of Zn and Zr, that is, the Zn ₂ Zr phase is densely dispersed in the magnesium matrix. Due to the presence of these precipitates, the bottom surface has a low degree of orientation, but exhibits a high yield strength.

FIG. 8 is a three-dimensional atom map diagram obtained by a three-dimensional atom probe. FIG. 8A is a three-dimensional distribution of alloying elements, and FIG. 8B is an enlarged three-dimensional distribution of alloying elements near a _{Zn 2 Zr precipitate.} (C) is a diagram showing the atomic distribution in the depth direction of (b). A three-dimensional atom probe (also called 3DAP) applies a high voltage to a sample, detects ions that evaporate from the surface of the sample in an electric field with a mass spectrometer, and deepens the individually detected ions. This is a method of measuring a three-dimensional atomic distribution by continuously detecting in the vertical direction and arranging the ions in the order of detection. The three-dimensional atomic probe was made by the inventor (Kazuhiro Takarano) of the National Institute for Materials Science, and a mass spectrometer (ADLD detector) manufactured by Kameka Co., Ltd. was used for ion analysis.

From the results of X-ray diffraction and 3DAP analysis, _{it was confirmed that these precipitated phases were Zn 2} Zr phases (see FIG. 5), and from FIG. 8, Ca _{segregated at the interface between the Zn 2} Zr phase and the magnesium matrix. It turned out to be.

(Aging treatment of Mg alloy of Example 1)
The aging treatment of the solution-treated material of the Mg alloy of Example 1 was carried out at 160 ° C. for 500 hours.
FIG. 9 is a diagram showing the relationship between the aging time and the Vickers hardness. The vertical axis is the Vickers hardness (HV), and the horizontal axis is the aging treatment time (hours). As shown in FIG. 9, it can be seen that the hardness of the solution-treated material increases when the aging time is about 10 hours.

FIG. 10 is a diagram showing a tensile stress-strain curve of an aged material that has been aged at 160 ° C. for 64 hours. Table 4 shows the 0.2% proof stress, tensile strength, and elongation obtained from the stress-strain curve.

As shown in Table 4, in the aging treatment material of Example 1, the 0.2% proof stress is 194 MPa, the tensile strength is 269 MPa, and the elongation is 17%.

The solution-treated material for the Mg alloy of Example 2 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 450 ° C

As shown in Table 3, the crystal grain size of the solution-treated material of Example 2 was 8.6 μm, and the texture strength was 4.2. It was found that the _{Zn 2} Zr phase was present in the magnesium matrix as in the solution-treated material of the Mg alloy of Example 1. Further, as shown in Table 3, in the solution-treated material of Example 2, the 0.2% proof stress is 173 MPa, the tensile strength is 268 MPa, the elongation is 27%, and the Eriksen value is 6.7 mm, which is a high formability. Was found to have.

The solution-treated material for the Mg alloy of Example 3 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr-0.3Ca alloy Rolling: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Soluble-free treatment: 2 hours at 450 ° C Table As shown in 3, the crystal grain size calculated by the section method was 6.9 μm, the texture strength was 5.2, and it was found that the particles were dispersed in the rolling direction.
As shown in Table 3, the solution-treated material of Example 3 has a 0.2% proof stress of 183 MPa, a tensile strength of 271 MPa, and an elongation of 27%, and has a high moldability of 6.8 mm in terms of Eriksen value. It turned out.

In Example 4, the solution-treated material was produced as follows, except that first, melting and casting were performed by quenching solidification casting to produce a cast plate having a thickness of 4 mm.
Alloy composition: Mg-4Zn-0.3Zr-0.3Ca alloy Homogenization treatment: Homogenization treatment was carried out at 350 ° C. for 5 hours and at 420 ° C. for 4 hours.
Rolling: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 200 ° C / Soluble-free treatment: 420 ° C for 2 hours

FIG. 11 is an optical microscope image of the solution-treated material of the Mg alloy of Example 1. An optical microscope image was obtained using an optical microscope (Elipse, LV-100) manufactured by Nikon Corporation.
In the Mg alloy observed in FIG. 11, the crystal grain size calculated by the intercept method is 7.5 μm.

FIG. 12 is a (0001) pole figure showing the degree of orientation of the (0001) pole of the solution-treated material of the Mg alloy of Example 4 measured from the rolled surface by X-ray diffraction.
The degree of integration of (0002) poles (also called maximum random distribution, mrd or degree of integration) measured by X-ray diffraction shown in FIG. 12 was 3.5.

FIG. 13 is a diagram showing a tensile stress-strain curve of the solution-treated material of Example 4. The vertical axis of FIG. 6 is stress (MPa), and the horizontal axis is strain (%).
As shown in FIGS. 13 and 3, in the solution-treated material of Example 4, the 0.2% proof stress was 179 MPa, the tensile strength was 269 MPa, and the elongation was 25%, and the Eriksen value was 7.8 mm. It was found to have sex.

The solution-treated material for the Mg alloy of Example 5 was prepared as follows.
Alloy composition: Mg-3Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Soluble-free treatment: 2 hours at 450 ° C Table As shown in 3, the crystal grain size of the solution heat-treated material of Example 5 was 10.1 μm, and the texture strength was 3.0. It was found that the _{Zn 2} Zr phase was present in the magnesium matrix as in the solution-treated material of the Mg alloy of Example 1. Further, as shown in Table 3, in the solution-treated material of Example 5, the 0.2% proof stress is 132 MPa, the tensile strength is 243 MPa, the elongation is 31%, and the Eriksen value is 7.9 mm, which is a high formability. Was found to have.

The solution-treated material for the Mg alloy of Example 6 was prepared as follows.
Alloy composition: Mg-3Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 450 ° C. As shown in Table 3, the crystal grain size of the solution treatment material of Example 6 was 9.7 μm, and the texture strength of the bottom texture was 3.4. It was found that the _{Zn 2} Zr phase was present in the magnesium matrix as in the solution-treated material of the Mg alloy of Example 1. Further, as shown in Table 3, in the solution-treated material of Example 6, the 0.2% proof stress is 145 MPa, the tensile strength is 247 MPa, the elongation is 33%, and the Eriksen value is 7.1 mm, which is a high formability. Was found to have.

The solution-treated material for the Mg alloy of Example 7 was prepared as follows.
Alloy composition: Mg-3Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Soluble-free treatment: 2 hours at 450 ° C Table As shown in 3, the crystal grain size of the solution heat-treated material of Example 7 was 11.3 μm, and the texture strength of the bottom surface texture was 4.0. It was found that the _{Zn 2} Zr phase was present in the magnesium matrix as in the solution-treated material of the Mg alloy of Example 1. Further, as shown in Table 3, in the solution-treated material of Example 7, the 0.2% proof stress is 180 MPa, the tensile strength is 260 MPa, the elongation is 28%, and the Eriksen value is 6.5 mm, which is a high formability. Was found to have.

The solution-treated material for the Mg alloy of Example 8 was prepared as follows.
Alloy composition: Mg-3Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 450 ° C. As shown in Table 3, the crystal grain size of the solution treatment material of Example 8 was 14.7 μm, and the texture strength of the bottom texture was 4.5. It was found that the _{Zn 2} Zr phase was present in the magnesium matrix as in the solution-treated material of the Mg alloy of Example 1. Further, as shown in Table 3, in the solution-treated material of Example 8, the 0.2% proof stress is 144 MPa, the tensile strength is 251 MPa, the elongation is 32%, and the Eriksen value is 6.5 mm, which is a high formability. Was found to have.

(Comparative Example 1)
The solution-treated material for the Mg alloy of Comparative Example 1 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Soluble-free treatment: 2 hours at 375 ° C Figure 14 is a comparison. It is a figure which shows the optical microscope image of the solution heat-treated material of Example 1. FIG. The crystal grain size of the solution-treated material of Comparative Example 1 calculated by the section method was 7.9 μm.

FIG. 15 is a diagram showing an X-ray diffraction pattern of the solution-treated material of Comparative Example 1. Similar to FIG. 4, the vertical axis is the X-ray diffraction intensity (arbitrary scale), and the horizontal axis is the angle 2θ (°).
As shown in FIG. 15, it was confirmed that the solution-treated material of Comparative Example 1 _{did not form the Zn 2 Zr phase, unlike the case of Example 1.}

FIG. 16 is a diagram showing a (0001) pole figure obtained by X-ray diffraction of the solution-treated material of Comparative Example 1.
As shown in FIG. 16, the solution-treated material of Comparative Example 1 had a strong bottom texture, and the texture strength of the (0001) pole was 10.6.

FIG. 17 is a diagram showing a tensile stress-strain curve of the solution-treated material of Comparative Example 1. The vertical axis of FIG. 17 is stress (MPa), and the horizontal axis is strain (%).
As shown in FIG. 17, in the solution-treated material of Comparative Example 1, the 0.2% proof stress was 160 MPa, the tensile strength was 262 MPa, the elongation was 34%, and the Eriksen value was only 3.5 mm (Table). 3).

(Comparative Example 2)
The solution-treated material for the Mg alloy of Comparative Example 2 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 375 ° C. As shown in Table 3, the crystal grain size of the solution treatment material of Comparative Example 1 was 9.0 μm, and the texture strength of the bottom texture was 14.7. Similar to Comparative Example 1, _{it was confirmed that the Zn 2} Zr phase was not formed. Further, as shown in Table 3, in the solution-treated material of Comparative Example 1, the 0.2% proof stress is 164 MPa, the tensile strength is 259 MPa, the elongation is 34%, and the Eriksen value is as low as 2.8 mm. I found out.

(Comparative Example 3)
The solution-treated material for the Mg alloy of Comparative Example 3 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Soluble-free treatment: 2 hours at 375 ° C As shown in Table 3. In addition, the crystal grain size of the solution heat-treated material of Comparative Example 3 was 10.8 μm, and the texture strength of the bottom surface texture was 13.9. Similar to Comparative Example 1, _{it was confirmed that the Zn 2} Zr phase was not formed. Further, as shown in Table 3, in the solution-treated material of Comparative Example 3, the 0.2% proof stress is 149 MPa, the tensile strength is 258 MPa, the elongation is 30%, and the Eriksen value is as low as 2.7 mm. I found out.

(Comparative Example 4)
The solution-treated material for the Mg alloy of Comparative Example 4 was prepared as follows.
Alloy composition: Mg-4Zn-0.3Zr alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 375 ° C. As shown in Table 3, the crystal grain size of the solution treatment material of Comparative Example 4 was 13.7 μm, and the texture strength of the bottom texture was 13.4. Similar to Comparative Example 1, _{it was confirmed that the Zn 2} Zr phase was not formed. Further, as shown in Table 3, in the solution-treated material of Comparative Example 1, the 0.2% proof stress is 144 MPa, the tensile strength is 256 MPa, the elongation is 28%, and the Eriksen value is as low as 2.6 mm. I found out.

(Comparative Example 5)
The solution-treated material for the Mg alloy of Comparative Example 5 was prepared as follows.
Alloy composition: Mg-5Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Soluble-free treatment: 2 hours at 450 ° C Table As shown in 3, it was confirmed that the crystal grain size of the solution heat-treated material of Comparative Example 5 was 13.4 μm, and the Zn ₂ Zr phase was not formed. Further, the solution-treated material of Comparative Example 5 had a strong bottom surface texture, and the texture strength of the (0001) pole was 7.3.
As shown in Table 3, it was found that the solution-treated material of Comparative Example 5 had a 0.2% proof stress of 146 MPa, a tensile strength of 262 MPa, and an elongation of 23%, and had a low Eriksen value of only 4.4 mm. It was.

(Comparative Example 6)
The solution-treated material for the Mg alloy of Comparative Example 6 was prepared as follows.
Alloy composition: Mg-5Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 200 ° C / 200 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.
Solution treatment: 2 hours at 450 ° C. As shown in Table 3, the crystal grain size of the solution treatment material of Comparative Example 6 was 11.9 μm, and the texture strength of the bottom texture was 3.6. Similar to Comparative Example 1, _{it was confirmed that the Zn 2} Zr phase was not formed. Further, as shown in Table 3, in the solution-treated material of Comparative Example 6, the 0.2% proof stress is 124 MPa, the tensile strength is 257 MPa, the elongation is 30%, and the Eriksen value is only 6.4 mm. Do you get it.

(Comparative Example 7)
The solution-treated material for the Mg alloy of Comparative Example 7 was prepared as follows.
Alloy composition: Mg-5Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Soluble-free treatment: 2 hours at 450 ° C Table As shown in 3, the crystal grain size of the solution heat-treated material of Comparative Example 7 was 11.2 μm, it had a strong bottom texture, and the texture strength of the (0001) pole was 8.3. Similar to Comparative Example 1, _{it was confirmed that the Zn 2} Zr phase was not formed. Further, as shown in Table 3, in the solution-treated material of Comparative Example 7, the 0.2% proof stress is 157 MPa, the tensile strength is 269 MPa, the elongation is 31%, and the Eriksen value is as low as 3.1 mm. I found out.

(Comparative Example 8)
The solution-treated material for the Mg alloy of Comparative Example 8 was prepared as follows, but the solution-treated material could not be obtained because the rolling process could not be performed.
Alloy composition: Mg-4Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.

(Comparative Example 9)
The solution-treated material for the Mg alloy of Comparative Example 9 was produced as follows, but the solution-treated material could not be obtained because the rolling process could not be performed.
Alloy composition: Mg-5Zn-0.3Zr-0.3Ca alloy Stretching: Plate temperature / Roll temperature / Presence / absence of intermediate heat treatment: 300 ° C / 300 ° C / Yes
The intermediate heat treatment was performed at 450 ° C. for 5 minutes.

From Examples 1 to 8 and Comparative Examples 1 to 9, it was found that the following points should be satisfied in order to obtain excellent room temperature workability, that is, a large Eriksen value.
Degree of orientation of the (0001) plane of crystal grains: The texture strength measured by X-ray diffraction is 6 or less.
From Example 1 and Comparative Example 1, at least 0.25% by mass or more of Ca is contained. The addition of Ca has a role of reducing the degree of orientation of the (0001) plane.
The amount of Zn added is preferably 2.0% by mass to less than 5.0% by mass, more preferably 3.0% by mass to less than 5.0% by mass. From Comparative Example 3, when Zn is added up to 5.0% by mass, the Eriksen value tends to decrease sharply.

From Examples 1 to 8 and Comparative Examples 1 to 9, it was found that the following points should be satisfied in order to obtain excellent strength, that is, 130 to 250 MPa with a 0.2% proof stress.
The formation of fine precipitates. From Example 1 and Comparative Examples 1 to 4, high volume fraction precipitates are formed in the samples exhibiting 0.2% proof stress exceeding 160 MPa.
It should contain at least Ca having the above composition. From the comparison between Example 1 and Comparative Example 1, the volume fraction of the precipitate is dramatically increased by the addition of Ca (see FIGS. 5 and 15). From this, the addition of at least Ca is indispensable for the formation of the precipitate.
The concentration range of Zn is preferably larger than 2.0% by mass and less than 5.0% by mass. Further, it is desirable that it is in the range of 3.0% by mass to 4.5% by mass.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Nor.

Claims (9)

Mg alloy
Zn that is greater than 2.0% by mass and less than 5% by mass,
Ca of 0.25% by mass or more and 0.3% by mass or less,
Zr of 0.20% by mass or more and 0.3% by mass or less,
The balance consists of Mg and unavoidable impurities.
In the structure of the Mg alloy, nanometer-order Zn ₂ Zr precipitates are dispersed in the magnesium matrix, and Ca segregates at the interface between the _{magnesium matrix and the Zn 2} Zr precipitates.
The degree of orientation of the (0001) poles of the crystal grains of the Mg alloy measured by X-ray diffraction is such that the texture strength measured by X-ray diffraction is 6.0 or less and the 0.2% resistance is 130 MPa to 250 MPa. , Mg alloy. The Mg alloy according to claim 1 , wherein the texture strength is 3 to 5.2. The Mg alloy according to claim 1 or 2 , wherein the Eriksen value of the Mg alloy at room temperature is 6.5 mm or more. The Mg alloy according to any one of claims 1 to 3 , wherein the tensile strength of the Mg alloy is 200 MPa to 300 MPa. The Mg alloy according to any one of claims 1 to 4 , wherein the 0.2% proof stress of the Mg alloy is 132 to 183 MPa. The Mg alloy according to any one of claims 1 to 5 , wherein the elongation at break of the Mg alloy is 20% to 35%. The method for producing an Mg alloy according to any one of claims 1 to 6.
Step 1 of melting Mg, Zn, Zr and Ca having the above composition to obtain a cast solid.
Step 2 of homogenizing the cast solid to obtain a homogenized solid, and step 3 of hot-working the homogenized solid to obtain a tangible solid.
Step 4 of dissolving the tangible solid to obtain a cooled solid,
Including
In the step 2, the homogenization treatment is performed for a predetermined time in two steps of 300 ° C. to 350 ° C. and 400 ° C. to 450 ° C. to obtain the homogenized solid.
Manufacturing method of Mg alloy. The method for producing an Mg alloy according to claim 7 , wherein the cast solid is obtained by any of quenching solidification casting, gravity casting and vacuum casting. The method for producing a Mg alloy according to claim 7 or 8 , wherein the Mg alloy is aged after the step 4.