WO2008133217A1

WO2008133217A1 - Magnesium alloy for casting and magnesium alloy cast

Info

Publication number: WO2008133217A1
Application number: PCT/JP2008/057644
Authority: WO
Inventors: Yuki Okamoto; Kyoichi Kinoshita; Motoharu Tanizawa; Kazuhiko Yoshida
Original assignee: Kabushiki Kaisha Toyota Jidoshokki
Priority date: 2007-04-20
Filing date: 2008-04-14
Publication date: 2008-11-06
Also published as: EP2138594A1; US20100119405A1; JP2008266734A

Abstract

A casting magnesium alloy characterized by containing 1-5 mass% copper (Cu), 0.1-5 mass% calcium (Ca), and 0.1-5 mass% silver (Ag) based on the whole alloy, with the remainder being magnesium (Mg) and incidental impurities. Due to the incorporation of Cu and Ca, crystals of not only an Mg-Cu compound but an Mg-Ca compound separate out so as to form a three-dimensional network structure at the boundary between Mg crystal grains. The three-dimensional network structure inhibits boundary sliding, which is apt to occur especially at high temperatures, to improve high-temperature strength and high-temperature creep resistance. Due to the addition of Ag, the Mg crystal grains are fine and a dense three-dimensional network structure having high continuity is formed. Furthermore, Ag exerts less adverse influences on the thermal conductivity of the magnesium alloy.

Description

Description Magnesium alloy for fabrication and Magnesium alloy ^ Technical Field

The present invention relates to a magnesium alloy for fabrication suitable for use at high temperatures. Technical scene

Magnesium alloy, which is lighter than aluminum alloy, is being widely used as an aeronautical vehicle material from the viewpoint of weight reduction. However, since magnesium alloys are not sufficient in strength and heat resistance depending on the application, further improvement in properties is required.

For example, a common magnesium alloy is AZ91D (ASTM symbol). Since the thermal conductivity of AZ91D is about 73 WZmK, if it is used for a member that is used in a high temperature environment or generates heat during use, heat dissipation may not be performed well, and the member may be thermally deformed. In particular, if a low alloy alloy is used as the magnesium alloy used for the inner cylinder block of the inner Luseki, the cylinder head is thermally deformed, the heat is trapped in the cylinder block, and the cylinder bore is deformed. Adverse effects such as increased friction and reduced airtightness occur. For this reason, there is a demand for a magnesium alloy that has a high heat conductivity and can perform heat dissipation well and is suitable for use at high temperatures.

For example, Mg- 3% Cu- case! ^ Of l% Ca (unit is "mass ⁰ I") Unshiruberitsu of Maguneshiumu alloy with is, that included high-Rere C u mosquito Unshiruberitsu, AZ 9

It is higher than the ID implied rate. However, depending on the conditions of use, creep resistance at high temperatures may not be sufficient.

JP-A-6- 25791, 0.8 to 5 mass ^_0/0 calcium and (Ca),

0 to: L 0 mass ^_0/0 of copper and (Cu), and 3-8 mass ^_0/0 »bゝ(Zn), it is a magnetic Shiumu alloy containing disclosed. Magnesium described in JP-A-6-25791 Although the alloy shows high strength at room temperature and high temperature, the ¾i conductivity is not described, and it is unclear whether the addition of zinc affects the thermal conductivity of the magnesium alloy. Disclosure of the invention

In view of the above problems, an object of the present invention is to provide a magnesium alloy for forging that is suitable for use at high temperatures. Another object of the present invention is to produce a ceramic made of the magnesium alloy.

As a result of diligent research, the inventors of the present invention have added copper as an alloying element of magnesium alloy together with copper and strength russia, thereby preventing creep resistance at high temperatures without adversely affecting the auscultation of the magnesium alloy. Based on this, the present invention has been achieved.

That is, use of magnesium alloys of the present invention, the can and the whole was 1 0 0 mass ^_0/0, and more than 1 wt% 5 wt% or less of copper (C u), 0. 1 wt% to 5 wt% The following calcium (C a) and 0.1 mass ⁰ /. Above 5 wt ^_0/0 following silver (A g), wherein the balance being made of magnesium and (M g) and unavoidable impurities. The magnesium alloy for forging of the present invention contains Cu and Ca, so that a crystallized product of Mg-Ca compound together with Mg-Cu compound is networked to the grain boundary of Mg crystal grains. Crystallized into a three-dimensional network. The three-dimensional network structure suppresses intergranular slip, which becomes particularly active at high temperatures, and improves high-temperature strength and creep resistance at high temperatures.

Furthermore, the magnesium alloy for forging of the present invention contains Ag together with Cu and Ca, so that the Mg crystal grains become fine and a highly continuous and dense three-dimensional network structure is formed. Ag, unlike other additive elements such as aluminum, has little adverse effect on the ¾f conductivity of the magnesium alloy.

In the present specification, “X—Y compounds” and the like are compounds having X and Y as X ₂ Y as shown in the formula, for example, as X ₂ Y.

The recorded magnesium alloy of the present invention is a ceramic made of the forging magnesium alloy of the present invention. The magnesium compound of the present invention is 1 mass% or more and 5 mass% or less of copper (C u), 0.1 mass% or more and 5 mass% or less of calcium (Ca), 0.1 mass% or more and 5 mass A pouring process of pouring an alloy intensifier containing silver (Ag) in an amount of not more than% and the balance of magnesium (Mg) and unavoidable impurities;

A solidification step of cooling and solidifying the alloy after the pouring step;

It is obtained through the process. Brief Description of Drawings

FIG. 1 is a graph showing the acceptance rate of magnesium alloys with different alloys. Fig. 2 is a graph showing the amount of stress reduction 40 hours after the start of the test in the stress relaxation test of magnesium alloys with different alloy yarn destruction.

Figure 3 is a graph plotting the JBI stress applied to the specimen every 10 minutes against the stress relaxation test time.

Figures 4A and 4B show Mg-3 mass ⁰ / oCu-1 mass ⁰ /. FIG. 5 is a drawing-substituting photograph showing a metal alloy of Ca alloy (# 01).

Figure 5 A and Figure 5 B is, M g- 3 mass ⁰ / oC u- 1 wt% C a- 0. 1 mass ^{_{0/0 A g (# 02}} ) is a drawing-substitute photograph showing a metal «alloy.

Fig. 6 A and Fig. 6 B are Mg 3 mass% Cu-1 mass. /. C a— 1% by mass A g

(# 03) A drawing-substituting photograph showing the metal structure of the alloy.

FIG. 7A and FIG. 7B are photographs in place of drawings showing the metal structure of Mg—3 mass% Cu—1 mass% (: a—2 mass% 8 g (# 04) alloy.

FIG. 8A and FIG. 8B are photographs, which substitute for a drawing, showing the metal structure of the Mg 3 mass% u-1 mass% 0 a-3 mass% 8 g (# 05) alloy. BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the forging magnesium alloy of the present invention will be described below.

The magnesium alloy for forging of the present invention includes copper (Cu), calcium (Ca) and silver

(Ag) with the balance being magnesium (Mg) and inevitable impurities It is characterized by.

In the magnesium alloy for use in the present invention, the Mg-Cu-based compound and the IVlg-Ca-based compound are crystallized in Mg crystals by adjusting the contents of Cu, Ca and Ag to appropriate amounts. Crystallizes in the form of a network (three-dimensional network) at the grain boundary. Since a three-dimensional network structure with little discontinuity is formed at the crystal grain boundary, the effect of suppressing grain boundary sliding is high.

The content of Cu is the entire use of magnesium alloys is 100 mass ^_0/0, 5% by mass or less 1 mass% or more. If the Cu content is 1% by mass or more, Mg-Cu compounds will crystallize sufficiently at the grain boundaries. If the Cu content is less than 1% by mass, the Mg—Cu compound is insufficiently crystallized at the crystal grain boundary, so the strength is low. The preferable Cu content is 2% by mass or more. On the other hand, as the amount of Cu increases, the amount of Mg-Cu compound that crystallizes at the grain boundary becomes excessive, resulting in a brittle yarn and lowering the strength. The preferred Cu content is 4 mass. /. It is as follows.

The magnesium alloy for t according to the present invention contains Ca and Ag together with Cu. C a and Ag are considered to contribute to the formation of a three-dimensional network structure along with Cu by ¾E. Specifically, it is speculated that the Mg—Ca compound will crystallize at the grain boundary together with the Mg—Cu compound, and a dense three-dimensional network structure will be formed due to the additive effect of Ag.

The content of Ca is 0.1 mass% or more and 5 mass% or less when the total magnesium alloy is 100 mass ⁰ / o. If the content of Ca is 0.1% by mass or more, the Mg—Ca compound is sufficiently crystallized at the grain boundary. In addition, the addition of Ca to the magnesium alloy increases the ignition temperature of the magnesium alloy, thus preventing combustion that may occur when the magnesium alloy is intensified. A preferable Ca content is 0.5% by mass or more. On the other hand, if the Ca content exceeds 5% by mass, the amount of grain boundary crystallized products increases too much, and mechanical properties such as tensile strength and elongation decrease, which may cause problems in post-processing. is there. A preferable Ca content is 3% by mass or less, and further 2% by mass or less.

The content of A g is ^ magnesium alloy for the entire 100 mass ⁰ /. And when

0.1 mass ^_0/0 over 5 mass ^_0/0 or less. There in food chromatic amount of A g is 0.1 mass ^_0/0 or more For example, the solid-liquid range becomes narrow and the Mg crystal grains become fine, so that an elegant three-dimensional network structure is formed. The greater the Ag content, the smaller the Mg grain size and the wider the grain boundary crystallization, improving the high-temperature strength and creep resistance at high temperatures. As the amount increases, the fluidity of the molten metal tends to decrease and the cost increases, which is not economical. Therefore, the content of Ag is 5% by mass or less. Preferably, the content of Ag is 4% by mass or less, and further 3% by mass or less.

The forging magnesium alloy of the present invention described above can be used in various fields such as automobiles and electric power as well as in the fields of space and aviation. In addition, as a member made of the magnesium alloy for ftit of the present invention, it is possible to make use of its high temperature characteristics, such as products used at high temperatures ^^, such as compressors, pumps, various cases, etc. Also used for engine parts used under high temperature and high load, especially for cylinder heads of internal combustion engines, cylinder blocks and oil vans, impellers for internal turbochargers, automobiles, etc. Examples include transmission cases.

The magnesium alloy ceramic of the present invention is a ceramic made of the magnesium alloy for forging according to the present invention described in detail above. That is, the magnesium alloy cake of the present invention is obtained through a pouring step and a solidification step, and the pouring step is performed in an amount of 1% by mass or more and 5% by mass when the whole is 100% by mass. and the following copper (C u), and 0.1 wt% to 5 wt ^_0/0 following calcium (C a), 0. 1 mass ⁰ / o more than 5 mass ⁰ following silver and (a g), the In addition, the step of pouring the molten alloy consisting of magnesium (Mg) and the inevitable impurities in the remainder, the solidification step is a step of cooling the solid alloy after the pouring step to solidify it.

The magnesium alloy of the present invention is not limited to normal gravity pressure but may be die-cast. It does not matter whether it is used for sand molds or molds. There is no particular limitation on the solidification rate (cooling rate) in the solidification step, and solidification for forming a three-dimensional network structure may be appropriately selected according to the size of the koji. If solidified by general solidification, network-like metal fibers can be obtained. Further, it is desirable that the magnesium alloy for magnesium and the magnesium compound of the present invention are release materials. In addition, after heat treatment, You can improve it.

As mentioned above, although the embodiment of the magnesium alloy for forging and the magnesium alloy product of the present invention has been described, the present invention is not limited to the above embodiment. The present invention can be carried out in various forms that are subject to change, improvement, improvement and the like within the scope not departing from the gist of the present invention.

Hereinafter, the present invention will be specifically described with reference to examples.

Several specimens with different alloy element contents in the magnesium alloy were produced, and their characteristics were evaluated and the yarns were observed.

[Specimen # ο 1 to # 0 5 ί «]

Chloride flux was applied to the inner surface of a $ Λ crucible preheated in an electric furnace, and weighed pure magnesium ingot, pure Cu, and pure Ag as needed, and dissolved. Furthermore, weighed Ca was added to this molten metal maintained at 75 ° C., and the boiling preparation process) o

The agitation was sufficiently stirred to completely dissolve the raw materials, and then kept calm for a while. The various molten alloys obtained in this way were poured into molds of a predetermined shape (the pouring process) and solidified in the air atmosphere (solidification process), and pieces of # 0 1 to # 0 5 (magnesium alloy steel) Forged). The obtained test piece was 30 mm × 30 mm × 20,000 mm. Table 1 shows the chemical composition of each specimen.

[Measurement of rate of appreciation]

In addition to the # 0 1 to # 0 5 pieces prepared in the above procedure, commercially available AZ 9 1 D (composition is shown in Table 1). The thermal conductivity was determined. The test results are shown in Table 1 and Fig. 1.

[Stress relaxation test]

The specimens # 0 1 to # 0 5 shown in Table 1 were subjected to stress relaxation, and the creep resistance of the magnesium alloy was examined. The stress relaxation test measures the process by which the stress decreases over time when a load is applied to a specified amount of deformation during a crack. Specifically, in an air atmosphere at 200 ° C, a compressive stress of 10 OMPa was applied to the test piece, and time was taken so that the displacement of the piece at that time was kept constant. The compressive stress was reduced with the passage of time. Table 1 and Fig. 2 show the amount of stress reduction 40 hours after the start of the test. Figure 3 shows a graph created by plotting the compressive stress applied to the specimen every 10 minutes.

[Observation of metal fibers]

The surfaces of test pieces # 01 to # 05 shown in Table 1 were observed. The surface was observed by observing the cross section cut out from each specimen with a metal microscope. The metal yarns on the surface of # 01 to # 05 !; the weaves are the forces shown in Fig. 4A to Fig. 8A and Fig. 4B to Fig. 8B, respectively. Magnification, Figures 4B-8B (b) The same section was observed at high magnification.

As shown in Fig. 4A, specimen # 01 had a three-dimensional network structure in which intermetallic compounds were crystallized at the grain boundaries. In Fig. 4B, CuMg ₂ appears brighter at the grain boundaries, and Mg ₂ Ca appears darker by EPM A (electron probe microanalyzer) and XRD (X-ray diffraction). Ri fi ^. In addition, as can be seen from FIGS. 5A to 8A, in the pieces # 02 to # 05, the three-dimensional network structure force is finer and more continuous than # 01. In FIGS. 5B to 8B, it was confirmed by EP MA and XRD that CuMg ₂ appeared bright at the grain boundaries and Mg ₂ Ca appeared dark.

Incidentally, according to the EPMA and XRD, Ag in纖片# 02 to # 05, was it possible to ¾ ^ be primarily as a grain boundary in A g ₃ M g.

[table 1]

The pieces from # 〇 1 to # 05 were superior in terms of conductivity as compared to AZ 91 D. The thermal conductivity of the # 01 specimen without Ag was 155 WZmK. In the # 05 piece, there was no decrease in ¾f conductivity due to the addition of Ag. In addition, the higher the Ag content, the smaller the amount of stress decrease 4 hours after the start of the stress relaxation test at 200 ° C. In particular, the # 03, # 04, and # 05 specimens showed excellent creep resistance even for # 01 and AZ 91 D specimens that did not contain Ag for 40 hours from the start of the test. (Figure 3).

Each piece of the above, Rei_11 3 mass%, and a constant Ca in 1 wt ^_0/0. In any of the test pieces, each of the above tests within the range of 2.7 mass% to 3.3 mass% for Cu and 0.7 mass% to 1.3 mass% for Ca. Si conductivity and creep resistance similar to those of the piece.

That is, a magnesium alloy containing Cu, Ca, and Ag with appropriate contents does not show a decrease in the conductivity due to the addition of Ag, and has excellent creep resistance at high temperatures.

Claims

The scope of the claims

1. When the whole is 100 mass%, 1 mass% or more and 5 mass% or less of copper (Cu), 0.1 mass% or more and 5 mass% or less of calcium (Ca), 0.1 mass ⁰ / _{0 to} 5% by mass of silver (Ag), and the balance consisting of magnesium (Mg) and inevitable impurities.

2. The magnesium alloy for fabrication according to claim 1, wherein the copper (Cu) is 2% by mass or more and 4% by mass or less.

3. The calcium (Ca) is 0.5 mass ^_0/0 to 3 mass ^_0/0 less is claims铸造for magnesium alloy as set forth in claim 1, wherein.

4. The magnesium compound for ^ t according to claim 1, wherein said silver (Ag) is 0.1 mass% or more and 3 mass% or less.

5. The magnesium compound for ^ t according to claim 1, wherein the Mg-Cu compound and the Mg-Ca compound have a thread! ^ Crystallized at the grain boundary of the Mg crystal grain.

6. When whole is 100 mass%, and 1 mass% or more to 5% by weight of copper (. U), 0. 1 mass ^_0/0 or more and 5 mass% or less of calcium and (Ca), 0. 1 A pouring process of pouring a molten alloy containing at least 5% by mass of silver (Ag) and the remainder with magnesium (Mg) and unavoidable impurities and metal;

Magnesium composite characterized by being obtained through

7. The magnesium alloy according to claim 6, wherein the Mg—Cu compound and the Mg—Ca compound have a network crystallized structure at the grain boundaries of the Mg crystal grains.