JP5046178B2 - Magnesium alloy material and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnesium alloy material made of a magnesium alloy and obtained by drawing, and a method for producing the alloy material. In particular, the present invention relates to a magnesium alloy material having excellent warm characteristics.

  Magnesium is lighter than aluminum and has higher specific strength and specific rigidity than steel and aluminum, and is expected to be used in the body of various electrical products in addition to aircraft parts and automobile parts. In recent years, wires, pipes, plates and the like made of magnesium alloys containing magnesium as a main component have been developed. A wire or pipe made of a magnesium alloy can be obtained by drawing a base material such as an extruded material. Patent Documents 1 and 2 disclose that a magnesium alloy material having high strength and high toughness can be obtained by subjecting the obtained drawn material to heat treatment at 150 to 300 ° C. Further, Patent Document 3 discloses that a magnesium alloy pipe excellent in the balance between high strength and high toughness can be obtained by adding Ca.

JP2003-293069 JP 2004-232075 A JP 2006-16655 A

  The conventional magnesium alloy materials disclosed in Patent Documents 1 to 3 have excellent strength and toughness when the use environment temperature is about room temperature. However, conventional magnesium alloy materials do not have sufficient mechanical properties when used in a warm environment where the operating environment temperature is about 100 ° C to 200 ° C. Development of magnesium alloy materials with excellent mechanical properties is desired.

  Accordingly, a main object of the present invention is to provide a magnesium alloy material having excellent warm characteristics. Another object of the present invention is to provide a method for producing a magnesium alloy material capable of producing a magnesium alloy material having excellent warm characteristics.

  The inventors of the present invention investigated the influence of the additive element of the alloy and the temperature during the measurement test of the mechanical properties on the heat-treated material obtained by heat-treating the drawn materials having various alloy compositions at various temperatures. As a result, the present inventors have obtained knowledge that a magnesium alloy material having excellent warm characteristics can be obtained by subjecting a drawn magnesium alloy material having a specific composition to a heat treatment at a specific temperature. Based on this knowledge, the alloy material of the present invention is defined.

Specifically, the first invention magnesium alloy material contains, in mass%, Al: 2.0 to 8.0%, Zn: 0.1 to 2.0%, Mn: 0.01 to 2.0%, Ca: 0.1 to 3.0%, The balance is made of Mg and impurities, and is subjected to drawing processing, and satisfies the tensile strength TS (MPa) shown in the following formula (I).
Formula (I) TS ≧ (26-0.1 × T) × A + (239-0.77 × T)
However, A: Al content (% by mass), T: Tensile strength test temperature (° C.), and 100 ≦ T ≦ 200.

The second magnesium alloy material of the present invention contains, in mass%, Al: 2.0 to 4.0%, Zn: 0.1 to 2.0%, Mn: 0.01 to 2.0%, Ca: 0.1 to 3.0%, with the balance being Mg and impurities. It has a drawing process and a creep strain of 0.25% or less. Creep strain is determined by a creep test performed under the following test conditions.
Test conditions Test temperature: 125 ° C, load: 50 MPa, test time: 100 hours

  The third present invention magnesium alloy material contains Al: more than 4.0% and 8.0% or less, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0%, with the balance being Mg. And is drawn, and has a creep strain of 0.20% or less. The creep strain is determined in the same manner as the test conditions for the creep test of the second magnesium alloy material of the present invention.

The said magnesium alloy material of this invention can be manufactured with the following this invention manufacturing method. The production method of the magnesium alloy material of the present invention is a base material made of a magnesium alloy containing Al: 2.0-8.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0% by mass%. And a step of performing the following heat treatment I or heat treatment II on the obtained drawn material.
Heat treatment I The obtained drawn material is heat treated at a temperature of more than 400 ° C.
Heat treatment II The obtained heat-treated material is subjected to a first heat treatment at a temperature of 350 ° C. or higher, and the heat-treated material subjected to the first heat treatment is subjected to a second heat treatment at a temperature in the range of 150 to 250 ° C.

  The magnesium alloy material of the present invention has excellent warm properties such as high strength and low creep strain even in warm environments of 100 ° C to 200 ° C. Therefore, the magnesium alloy material of the present invention can be expected to be used in such a warm environment. The magnesium alloy material of the present invention excellent in such warm characteristics can be produced by the production method of the present invention comprising the step of subjecting the drawn material to the heat treatment at the specific temperature. The present invention will be described in detail below.

The magnesium alloy constituting the magnesium alloy material of the present invention contains the following additive elements, with the balance being Mg and impurities.
[Additive elements] Unit is mass%
Al: 2.0-8.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0%
A magnesium alloy containing elements such as Al, Zn, and Mn in the above range can improve mechanical properties such as strength, elongation, and corrosion resistance as compared with magnesium alone. In addition to these elements, a magnesium alloy to which Ca is added in the above range has an effect of suppressing crystal grain growth during recrystallization by heat treatment after plastic working such as drawing. Therefore, this Ca-containing magnesium alloy does not produce coarse crystals that greatly reduce plastic workability unlike an alloy that does not contain Ca, so that it can have a good balance between strength and toughness. . Therefore, the magnesium alloy material of the present invention can be suitably used for materials that are subjected to secondary processing. Further, Ca can enhance the flame retardancy of the magnesium alloy, and effectively prevents the alloy from being burned by heat treatment.

  As a magnesium alloy having the above composition, an AZ-based or AM-based magnesium alloy in the ASTM symbol, to which Ca in the above range is added, can be used. Examples of AZ-based magnesium alloys include AZ21, AZ31, AZ61, and AZ80, and examples of AM-based magnesium alloys include AM60 and AM100. Impurities are mainly inevitable impurities. Inevitable impurities include Fe, Cu, Ni, Si and the like.

  In the magnesium alloy material of the present invention, a base material made of a magnesium alloy having the above composition is drawn. As the base material, a magnesium alloy having the above composition is melted and cast, and the obtained cast material is subjected to rolling or extrusion, or a commercially available rolled material or extruded material can be used. Before the drawing, the base material may be subjected to a heat treatment such as a solution treatment. Drawing is performed using a wire drawing die or a roller die. Drawing conditions are: processing temperature: 250 ° C. or less (preferably 100 ° C. or more, more preferably 150 ° C. or more), rate of temperature rise to processing temperature: 1 ° C./sec to 100 ° C./sec, processing degree (cross section reduction) Rate): 3 to 25% / 1 pass, linear speed: 1 m / min or more, cooling rate after processing: 0.1 ° C./sec or more. The higher the processing temperature, the higher the drawing workability of the workpiece, and for example, processing with a large degree of processing becomes possible. Alternatively, the drawing process may be performed at room temperature without heating. When performing drawing at room temperature, for example, the degree of processing per pass is reduced (although depending on the alloy composition, it is generally 15% or less, preferably 10% or less), or once with the above-mentioned heating. It is preferable to perform pre-heat treatment after carrying out the process to make the crystal finer and to improve the drawing workability of the work material before drawing. Preliminary heat treatment conditions include heating temperature: 200 ° C. or more and 400 ° C. or less (preferably 250 ° C. or more and 350 ° C. or less), and holding time: about 15 to 60 minutes. Such a drawing process is applied to the base material for one or more passes to obtain a drawn material. When drawing over multiple passes, perform intermediate heat treatment for each pass or multiple passes (for example, 2 to 3 passes) to recover strain introduced into the work piece by drawing or recrystallize. The refinement of the formed crystal grains can be promoted. Intermediate heat treatment conditions include heating temperature: 100 ° C. or more and 400 ° C. or less (preferably 150 ° C. or more), and holding time: about 5 to 20 minutes. The drawing process is preferably performed using a lubricant.

  By applying the heat treatment I or the heat treatment II to the drawn material that has been subjected to the drawing process, the magnesium alloy material of the present invention having excellent warm characteristics can be obtained.

  The heating temperature of the heat treatment I is over 400 ° C. Below 400 ° C., a magnesium alloy material having a predetermined warm characteristic cannot be obtained. As the heating temperature is higher, a magnesium alloy material having superior warm characteristics can be obtained. The melting temperature varies depending on the alloy composition, particularly the Al content. The holding time is preferably 10 to 120 minutes, more preferably 15 to 60 minutes.

  In the heat treatment I, a one-step heat treatment is performed, whereas in the heat treatment II, the heat treatment is performed in two steps of a first heat treatment and a second heat treatment. The heating temperature of the first heat treatment is 350 ° C. or higher. As the heating temperature is higher, a magnesium alloy material having superior warm characteristics can be obtained. The holding time is preferably 10 to 120 minutes, more preferably 15 to 60 minutes. The first heat treatment may be performed under the same conditions (heating temperature) as the heat treatment I.

  The second heat treatment corresponds to aging and is performed at a lower temperature for a longer time than the first heat treatment. Specifically, the heating temperature of the second heat treatment is 150 to 250 ° C. The holding time is preferably 2 to 24 hours, more preferably 8 to 16 hours. When the first heat treatment is performed under the same conditions (heating temperature) as the above heat treatment I, by performing the second heat treatment for a long time at such a relatively low temperature, the creep characteristics are further improved as compared with the case of only the heat treatment I. Can be improved. When the heating temperature of the first heat treatment is 350 to 400 ° C., a magnesium alloy material having the same warm characteristics as the magnesium alloy material subjected to the heat treatment I can be obtained by further performing the second heat treatment. If the heating temperature of the second heat treatment is less than 150 ° C, if the heating temperature of the first heat treatment exceeds 400 ° C, the effect of further improving the creep characteristics cannot be obtained, and the heating temperature of the first heat treatment is 350 ° C to 400 ° C. In this case, a magnesium alloy material having excellent warm characteristics cannot be obtained. The heating temperature of the second heat treatment is more preferably 150 to 200 ° C., and when it exceeds 250 ° C., the warm characteristic is conversely lowered.

  Examples of the magnesium alloy material of the present invention obtained by subjecting the drawn material to the specific heat treatment include various forms obtained by drawing such as wires, bars, and pipes. The magnesium alloy material of the present invention has excellent strength and creep characteristics in a warm environment of 100 to 200 ° C. Specifically, in the magnesium alloy material of the present invention, the tensile strength TS satisfies the above formula (I). As shown in the examples described later, the present inventors performed heat treatment at various temperatures on a drawn material made of a magnesium alloy having a different content of additive elements. Tensile strength at ˜200 ° C. was measured. Then, the present inventors have found the above formula (I) by estimating the influence of the additive element content on the tensile strength and the use temperature from the measurement results. In a magnesium alloy material having the same composition, the tensile strength TS in the range of 100 to 200 ° C. tends to increase as the heating temperature of the heat treatment I or the heating temperature of the first heat treatment II is increased. A magnesium alloy material whose tensile strength TS does not satisfy the formula (I) in a temperature range of 100 ° C. to 200 ° C. cannot be said to have sufficient strength in a warm environment. The magnesium alloy material of the present invention has a creep strain of 0.25% or less (when the Al content is 2.0 to 4.0% by mass) or 0.20% or less (when the Al content is more than 4.0% by mass and 8.0% by mass or less). ) Is satisfied. In a magnesium alloy material having the same composition, the creep strain tends to decrease when the heating temperature of the heat treatment I or the heating temperature of the first heat treatment II is increased.

  The tensile strength is measured according to the tensile test method specified in JIS Z 2241 (1998). In particular, the test piece is heated to a temperature selected from the range of 100 ° C to 200 ° C. The gauge distance is 15mm and the strain rate is 0.001 / s. The creep strain is measured according to the creep test method defined in JIS Z 2271 (1999). The test conditions are as follows: test temperature: 125 ° C., load: 50 MPa, test time: 100 hours.

  The magnesium alloy material of the present invention is excellent in warm characteristics and can be expected to be used in an environment of a temperature range of 100 to 200 ° C. Moreover, the manufacturing method of the magnesium alloy material of this invention can manufacture the magnesium alloy material which is excellent in the said warm characteristic.

An embodiment of the present invention will be described.
An extruded material (φ16 mm bar) made of a magnesium alloy having the composition shown below was prepared, and the extruded material was drawn out under the following conditions to obtain a drawn material with φ8.0 mm. This drawn material was heat-treated under the conditions shown in Tables 1 and 2. The samples subjected to the heat treatment were subjected to a tensile test and a creep test under the following conditions, and the tensile strength and creep strain were measured. The results are shown in Tables 1 and 2. In Tables 1 and 2, “expression value” is a value calculated from the following expression.
TS ≧ (26-0.1 × T) × A + (239-0.77 × T)
A: Al content (% by mass), T: Tensile test temperature (100, 125, 150, 200 ° C), TS: Tensile strength (MPa)

[Composition] Unit is mass%
Composition I (Ca-added AZ31 equivalent alloy material); Al: 3.2, Zn: 0.77, Mn: 0.35, Ca: 1.01, balance Mg
Composition II (Ca-added AZ61 equivalent alloy material); Al: 6.2, Zn: 0.65, Mn: 0.32, Ca: 1.22, balance Mg
[Drawing conditions]
Degree of processing per pass: 15-17% (total degree of processing: 75%)
Processing temperature: Select from 140 to 180 ℃
[Tensile test conditions]
Test temperature conforming to the tensile test method specified in JIS Z 2241 (1998): 100, 125, 150, 200 ° C
Strain rate: 0.001 / s
Gage distance of sample: 15mm
[Creep test conditions]
Test temperature in accordance with creep test method specified in JIS Z 2271 (1999): 125 ° C
Load (stress): 50MPa
Test time: 100 hours

  As shown in Tables 1 and 2, samples that were heat-treated at a temperature exceeding 400 ° C on the drawn material and samples that were aged after being heat-treated at a temperature of 350 ° C or higher were temperatures of 100 to 200 ° C. Over the entire temperature range, the tensile strength is high, and the creep strain is 0.25% or less for the sample of composition I and 0.20% or less for the sample of composition II. Therefore, these samples are presumed to have excellent strength and good creep characteristics in a warm environment. In addition, a sample that has been heat-treated (aged) at a temperature between 150 and 250 ° C. after heat treatment at a temperature of 350 ° C. or higher has even better creep characteristics.

  Although not shown in Table 2, when heat treatment was performed by changing the heating temperature of the second heat treatment to a temperature exceeding 250 ° C. for sample No. 6-10, the temperature was higher than that of sample No. 6-10. The inter-characteristics deteriorated.

  From the above, after drawing, heat treatment is performed at a temperature higher than 400 ° C, or heat treatment is performed at a temperature of 350 ° C or higher, and then aging is performed, so that strength and creep characteristics are obtained in a warm temperature range of 100 to 200 ° C. It was confirmed that a magnesium alloy material having excellent resistance can be produced.

  Hereinafter, a process of obtaining TS ≧ (26−0.1 × T) × A + (239-0.77 × T) from the test result will be described. From the above test results, it is considered that the tensile strength is easily influenced by the Al content and the influence degree of Ca is small. Therefore, when the Ca content is 3.0 mass% or less, the influence is O, and the relationship between the tensile strength at each test temperature (100 ° C, 150 ° C, 200 ° C) and the Al content is as follows. It is considered that the Al content changes linearly in the range of 2.0 to 8.0 mass%. In addition, when composition I (Al content: 3.2 mass%) at a test temperature of 100 ° C., sample No. 3-2 (tensile strength: 212 MPa) and sample No. 3-3 (tensile strength: 215 MPa) ) Between the sample No.6-2 (tensile strength: 261 MPa) and sample No.6- when the composition is II (Al content: 6.2 mass%). Between 3 (tensile strength: 265 MPa) or between sample No. 6-5 (tensile strength: 261 MPa) and sample No. 6-6 (tensile strength: 264 MPa). A boundary is considered to exist. Therefore, when the intermediate value between the samples is used as a boundary and a region having excellent tensile strength at 100 ° C. is expressed, the following equation (i) is obtained. Test temperature: 150 ° C and 200 ° C, as in the case of 100 ° C, with the intermediate value between the above samples as the boundary, a region with excellent tensile strength at 150 ° C and a region with excellent tensile strength at 200 ° C Is expressed by the following equations (ii) and (iii). Note that the numerical value is obtained by rounding down the decimal part and includes some errors.

Test temperature: 100 ℃ TS ≧ 16 × A + 162 ... Formula (i)
Test temperature: 150 ° C TS ≧ 11 × A + 124 ... Formula (ii)
Test temperature: 200 ° C TS ≧ 6 × A + 85 ... Formula (iii)

In the formulas (i) to (iii), the coefficient A changes with the test temperature T (° C.), and the coefficient A and the test temperature are considered to have a linear relationship (proportional relationship). Therefore, when the relationship between the coefficient of A and the test temperature T in the above formulas (i) to (iii) is obtained, it is expressed by the following formula.
(Coefficient of A) =-0.1 × T + 26

In the formulas (i) to (iii), the TS axis intercept changes with the test temperature T (° C.), and this intercept and the test temperature are considered to have a linear relationship. Therefore, when the relationship between the intercept in the above formulas (i) to (iii) and the test temperature T is obtained, it is expressed by the following formula.
(TS axis intercept) = -0.77 x T + 239

  The magnesium alloy material of the present invention can be suitably used for structural materials such as wires, pipes, and bars constituting automobile parts, etc., which are used in a warm environment where the operating environment temperature is 100 to 200 ° C. it can. Moreover, the manufacturing method of this invention magnesium alloy material can be utilized for manufacture of the magnesium alloy material which is excellent in a warm characteristic.

Claims (5)

In mass%, Al: 2.0-8.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0%, the balance consists of Mg and inevitable impurities,
Drawing process has been applied,
A magnesium alloy material satisfying the following tensile strength.
When Al content (mass%) is A, tensile strength test temperature (° C) is T, and tensile strength (MPa) is TS, 100 ≦ T ≦ 200
TS ≧ (26-0.1 × T) × A + (239-0.77 × T) In mass%, Al: 2.0-4.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0%, the balance consists of Mg and inevitable impurities,
Drawing process has been applied,
Magnesium alloy material characterized by a creep strain of 0.25% or less.
However, the creep test conditions are as follows: test temperature: 125 ° C., load: 50 MPa, test time: 100 hours. In mass%, Al: more than 4.0% and 8.0% or less, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0%, the balance consists of Mg and inevitable impurities,
Drawing process has been applied,
Magnesium alloy material characterized by a creep strain of 0.20% or less.
However, the creep test conditions are as follows: test temperature: 125 ° C., load: 50 MPa, test time: 100 hours. In mass%, Al: 2.0-8.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0% , the balance is made of magnesium alloy composed of Mg and inevitable impurities A process of pulling out the base material;
And a step of heat-treating the obtained drawn material at a temperature of more than 400 ° C. In mass%, Al: 2.0-8.0%, Zn: 0.1-2.0%, Mn: 0.01-2.0%, Ca: 0.1-3.0% , the balance is made of magnesium alloy composed of Mg and inevitable impurities A process of pulling out the base material;
A step of subjecting the obtained drawn material to a first heat treatment at a temperature of 350 ° C. or higher;
A process for producing a magnesium alloy material, comprising the step of subjecting the heat treatment material subjected to the first heat treatment to a second heat treatment at a temperature in the range of 150 to 250 ° C.