WO2008133218A1 - Magnesium alloy for casting and magnesium alloy cast - Google Patents

Abstract

A casting magnesium alloy characterized by containing 1-5 mass% copper (Cu) and 0.1-5 mass% calcium (Ca) based on the whole alloy and containing tin (Sn) in such an amount that the ratio of the mass of Sn to that of the Ca, Sn/Ca, is 0.1-3, with the remainder being magnesium (Mg) and incidental impurities. Due to the incorporation of Cu, Ca, and Sn, crystals of not only an Mg-Cu compound but an Mg-Ca-Sn compound separate out so as to form a network structure (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. Since the Sn forms a compound preferentially with the Ca, it exerts less adverse influences on thermal conductivity than the other additive elements.

Description

 Description ^ Magnesium alloy and magnesium alloy ^^ Technical field

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

 Magnesium alloys, which are lighter than aluminum alloys, are being widely used as aviation vehicle materials and the like from the viewpoint of weight reduction. However, the magnesium alloy is not sufficient in bowing and heat resistance depending on the application, and therefore further improvement in properties is required.

 For example, a common magnesium alloy is AZ 91D (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 magnesium alloy with a low conductivity is used as the magnesium alloy used for the cylinder head of the inner thigh and the cylinder block, the cylinder head is thermally deformed, the heat is accumulated 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 need for a magnesium alloy that has high heat conductivity and that can perform heat dissipation well and is suitable for use at high temperatures.

For example, Mg- 3% Cu- l% "mass _^0/0" if thief (units of Ca :). Xie Unshiruberitsu magnesium alloys with, by including the high Unshiruberitsu Cu, AZ9 Higher than 1D flf conductivity. However, there are some cases where the creep resistance at high temperature is not sufficient depending on the usage conditions.

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

And 0-10 mass _^0/0 copper (C u), and 3-8 mass _^0/0 of zinc (Z n), the magnetic Shiumu alloy containing disclosed. Magnesium described in JP-A-6-25791 There is no description of the power-conductivity, which shows high strength at room temperature and high temperature, and it is unclear whether the addition of zinc affects the thermal conductivity of magnesium alloys. 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. It is also intended to produce a ceramic material made of a magnesium alloy.

 As a result of diligent research, the present inventors have improved the cleaving resistance at high temperatures without adversely affecting the ¾i conductivity of the magnesium alloy by adding tin as an alloying element of the magnesium alloy together with copper and strength russium. Based on this, the present inventors have reached the present invention.

 That is, when the total magnesium alloy of the present invention is 100% by mass, 1% by mass to 5% by mass of copper (Cu) and 0.1% by mass or more and 5% by mass or less of canorecium ( (Ca), and a mass ratio (Sn / Ca) from 0.1 to 3 with respect to Ca, and the balance is composed of magnesium (Mg) and inevitable impurities. And

 The magnesium alloy for forging of the present invention contains Cu, Ca, and Sn, so that a crystallized product of Mg—Ca—Sn compound together with Mg—Cu compound is network-like (at the grain boundary of Mg crystal grains). Crystallizes in 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. In addition, Mg—Ca—S compounds are relatively brittle, but Mg—Ca—Sn compounds in which part of C— of Mg—Ca compounds is replaced with Sn have high strength. As a result, 3 daughters of magnesium alloy improve. As will be explained in detail later, Sn forms a compound preferentially with Ca, so it has less influence on conductivity than other additive elements such as aluminum.

In the present specification, the description of “X—Y compound” or the like is, for example, a compound having X and 分 as shown by 示₂で in the composition formula.

In addition, the magnesium alloy product of the present invention is a magnesium alloy for use in the present invention. This is a fake. The magnesium alloy porcelain of the present invention is

When whole was 1 00 wt%, and 1 mass% or more to 5% by weight of copper (Cu), 0. 1 wt% to 5 wt _^0/0 following calcium and (C a), to the C a ¾ to mass ratio

(Sn / C a) 0.1 to 3 tin (Sn), and a pouring process for pouring an alloy that consists of magnesium (Mg) and unavoidable impurities. A solidification step of cooling and solidifying the molten alloy after the pouring step;

 It is obtained through the process. Brief Description of Drawings

 Fig. 1 is a graph showing the thermal conductivity of magnesium alloys with different alloy yarns. 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 compositions.

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

FIG. 4A and FIG. 4B are photographs in place of drawings showing the metal «of Mg-3 mass% Cu-1 mass ⁰ / oCa alloy (# 01).

FIG. 5A and FIG. 5B are photographs in place of drawings showing the metal structure of the Mg-3 mass ⁰ / oCu-1 mass ⁰ / _o Ca-0. 1 mass ⁰ / oS n (# 02) alloy.

 Fig. 6 A and Fig. 6 B are Mg-3 mass% Cu 1 mass% Ca-1 mass% Sn

(# 0 3) is a drawing-substituting photograph showing a metal yarn cage of an alloy.

 FIG. 7A and FIG. 7B are drawings-substituting photographs showing the metal structure of the Mg—3 mass% Cu—1 mass% Ca—2 mass% Sn (# 04) alloy.

Fig. 8 A and Fig. 8 B are Mg-3 mass% <u-1 mass. FIG. 5 is a drawing-substituting photograph showing the metallographic structure of the / ₀ Ca—4 mass% Sn (# 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 comprises copper (Cu), calcium (C a) and tin (Sn), with the balance being magnesium (Mg) and inevitable impurities.

 In the magnesium alloy for forging of the present invention, by adjusting the contents of Cu, Ca and Sn to appropriate amounts, the crystallized product of Mg—Ca—Sn compound as well as Mg—Cu—S compound can be obtained. It crystallizes in a network (three-dimensional network) at the grain boundaries of Mg grains. Because it is a network with few discontinuous parts, it has a high effect of suppressing grain boundary sliding.

The Cu content is 1% by mass or more and 5% by mass when the total magnesium alloy is 100% by mass. /. It is as follows. If the Cu content is 1% by mass or more, Mg-Cu compounds will crystallize sufficiently at the grain boundaries. The Cu content is 1 mass. If it is less than ₀ , the strength of the Mg-Cu compound is low due to insufficient crystallization at the grain boundaries. The preferred 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 crystal grain boundary becomes excessive, resulting in a brittle paper weave. The preferred Cu content is 4 mass. /. It is as follows.

 The magnesium alloy for forging of the present invention contains Ca and Sn together with Cu. Ca and Sn, together with Cu, contribute to the formation of a three-dimensional network structure as a grain boundary. Specifically, the Mg-Ca-Sn compound and the Mg-Cu-Sn compound crystallize at the grain boundary, and a good three-dimensional network structure is formed with few discontinuities.

The content of C a, upon the entire ¾ for magnesium alloy is 100 mass _^0/0, not more than 1 mass% to 5 mass% 0.5. If the content of C a is 0.1% by mass or more, the Mg—C a—Sn compound is sufficiently crystallized at the grain boundary. In addition, adding Ca to the magnesium alloy increases the ignition of the magnesium alloy, preventing combustion that may occur when the magnesium alloy is made intense. Preferred content of Ca is 0.5 mass. /. That's it. On the other hand, when the Ca content exceeds 5% by mass, the amount of grain boundary crystallized products increases, and mechanical properties such as tensile strength and elongation decrease, resulting in problems in post-processing. is there. A preferable Ca content is 3% by mass or less, and further 2% by mass or less.

 The Sn content is 0.1 to 3 in terms of mass ratio (Sn / Ca) to calcium (Ca). If the Sn content is 0.1 mass% or more, Mg

The -Ca-Sn compound is sufficiently crystallized. On the other hand, when the content ratio of Sn increases, The Mg-Ca-Sn compound is divided from the three-dimensional network structure and crystallizes in the crystal grains, making it difficult to form a good three-dimensional network structure. As a result, the creep resistance tends to decrease. In addition, when Sn is added excessively, ^ produces not only Mg—Ca—Sn compounds but also Mg—Sn compounds. Mg-Sn compounds are low melting point compounds, and therefore creep resistance is improved. Therefore, the Sn content is 3 or less with SnZCa. If SnZCa is 3 or less, formation of a low melting point compound is suppressed. Further, if SnZCa is 2 or less, a good three-dimensional network structure with little discontinuity is formed, and the high-temperature bow daughter and the creep resistance at high temperature are improved. That is, the preferred Sn content is 311 O &, 2 or less, and 1.5 or less.

 Sn forms a compound with Ca preferentially over Mg and Cu. Therefore, Cu and Mg-Cu compounds with high thermal conductivity are not adversely affected, and as a result, the conductivity of the magnesium alloy is unlikely to decrease. From this, considering the stoichiometric ratio of SnZCa of MgCa-Sn compounds, the mass ratio of Sn to Ca (Sn / Ca) is 3 or less, or 0.1 or more 2 The following is preferable, and there is almost no Sn that forms a compound with an Mg—Cu compound, and crystallization of the low melting point compound described above is also suppressed.

 The magnesium alloy for t according to the present invention described above can be used in various fields such as automobiles and electric power as well as space and aviation. In addition, as a member made of a magnesium alloy for forging according to the present invention, a product used under a high temperature environment, for example, a compressor, a pump, various cases, etc. Components used and engine parts used under high temperature and high load, especially cylinder heads, cylinder blocks and oil vans for internal combustion engines, turbocharger impellers for internal combustion engines, and transmitters used for automobiles, etc. Case.

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 case of the present invention is obtained through a pouring step and a solidification step, and the pouring step is 1% by mass or more and 5% by mass when the whole is 100% by mass. / ₀ and less copper (Cu), 0. 1 mass _^0/0 or more The upper 5 mass _^0/0 following calcium (Ca), weight ratio of the C a and (Sn / Ca) in 0.1 to 3 of tin (Sn), wherein the balance magnesium (Mg) not The process of pouring molten alloy composed of unavoidable impurities into the molten metal and the solidification process are processes of cooling and solidifying the alloy after the pouring process.

 The magnesium alloy of the present invention is not limited to normal gravity pressure fabrication, but may be die cast fabrication. In addition, the sand mold, mold, etc. used for dredging can be used. There is no particular limitation on the solidification rate (cooling rate) in the solidification process, and the solidification rate to the extent that a three-dimensional network structure is formed can be selected as appropriate according to the size of the clot. If solidified by general solidification, a network-like metal string is obtained. In addition, the magnesium alloy and the magnesium compound for use in the present invention are preferably free materials. Furthermore, the characteristics of, may be improved by heat treatment later.

 As described above, the embodiment of the forging magnesium alloy and the magnesium compound of the present invention has been described, but the present invention is not limited to the above embodiment. The present invention can be implemented in various forms that have been changed or improved by those skilled in the art without departing from the scope 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 manufactured, and their characteristics were evaluated and their properties were observed.

 [Specimens # 01 ~ # 05

 Chloride flux was applied to the inner surface of a crucible preheated in an electric furnace, and a large amount of pure magnesium ingot, pure Cu, and pure Sn as required were dissolved. Furthermore, weighed Ca was added to this molten metal kept at 750 ° C.

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 atmosphere (solidification process). Forged. The obtained test piece was 30 mm × 30 mm × 200 mm. Table 1 shows the chemical composition of each specimen. Measurement of conductivity]

 In addition to the # 01 to # 05 test pieces prepared in the above procedure, the commercially available AZ 91 D (composition is shown in Table 1). Asked. The test results are shown in Table 1 and Fig. 1.

 [Stress relaxation test]

 For the specimens # 01 to # 05 and AZ91D shown in Table 1, stress relaxation was performed and the creep resistance of the magnesium alloy was examined. The stress relaxation test measures the process by which the stress when a load is applied to a specified amount of deformation during the test time decreases with time. Specifically, in an air atmosphere at 200 ° C, a compressive stress of 10 OMPa was applied to the piece, and the displacement of the piece at that time was kept constant so as to keep constant. The compressive stress was reduced. 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 piece 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 forces shown in Fig. 4A to Fig. 8A and Fig. 4B to Fig. 8B, respectively, on the surface of # 01 to # 05 are shown in Fig. 4A to Fig. 8B. Magnification, Figures 4B-8B (b) The same section was observed at high magnification.

In test piece # 01, as can be seen from FIG. 4A, a three-dimensional network structure strength formed by crystallization of an intermetallic compound at the grain boundary was obtained. In Fig. 4 (b), it is CuMg ₂ that appears bright at the grain boundary, and Mg ₂ C a that appears bright.

This was confirmed by A (electron probe microanalyzer) and XRD (X-ray diffraction). In addition, as shown in Figs. 5A and 6A, the pieces # 02 and # 03 have a three-dimensional network structure with finer and more connected mesh than # 01. In Fig. 5B and Fig. 6B, CuMg appears bright at the grain boundaries.

_2, look喑Ku was confirmed by EPMA and XRD to be a Mg ₂ Ca Oyohi TVIgCa Sn. On the other hand, in specimens # 04 and # 05, as can be seen from each of FIGS. 7A, 7B, 8A, and 8B, the crystallized material is inside the crystal grains. As a result of crystallization, a three-dimensional network structure was not completely formed. Here, in FIG. 7B and FIG. 8B, the crystallized material crystallized in the grain boundary and in the vertical axis is indicated by arrows at least one place. In FIG. 7B and FIG. 8B, Ga is an intragranular crystallized product and Gb is a grain boundary crystallized product. EPMA and XRD confirmed that MgC a Sn crystallized in the grains. In addition, in specimen # 05, Mg ₂ Sn, a low melting point compound, was detected by XRD.

 [table 1]

 # 01〜: The test piece of ίί05 was superior in terms of convection and deviation than A Ζ 91 D. The thermal conductivity of the # 01 test piece not containing Sn was 155 WZmK, but no decrease in! Rf conductivity due to the addition of Sn was observed in the # 02 to # 04 test pieces. On the other hand, in # 05 where the Sn content is excessive, although the excellence is superior to A Z 91 D, the difference in the inductivity from # 01 is large.

In addition, the # 02 to # 04 specimens made of magnesium alloy containing Sn had less stress reduction than the specimen # 01 after 40B clearance from the start of wrinkle in the stress relaxation test at 200 ° C. . In other words, the addition of Sn to the Mg-Cu-Ca alloy (# 01) improved the creep resistance at high temperatures. This is presumed to be because # 02 to # 04 have a higher 3D network structure than # 01, which has many discontinuous parts in the 3D network structure. Meanwhile, 2 masses of Sn. # 04 with / o has better creep resistance after 40 hours than # 01 without Sn, but inferior to # 02 and # 03. The metal structure of # 04 is thought to be because the three-dimensional network structure was incompleter than # 02 and # 03. Contains 4% by mass of Sn # 05, three-dimensional network structure is incomplete, it is contemplated that M g ₂ S n which is a low melting compound containing Mutame, creep resistance was Koma匕.

 In addition, the # 02 and # 03 pieces had a greater stress drop than # 01 about 3 hours after starting, but the change in stress from 3 to 40 hours was small and stable. In addition, the # 04 specimen has a greater stress drop than # 01 and A Z9 ID about 3 hours after the start of the test, but the amount of stress change from 3 to 40 hours is small and stable. It was. (Figure 3)

 In addition, each of the above-mentioned pieces has a constant (: 11 is 3% by mass and Ca is 1% by mass. In any of the test pieces, Cu is 2.7%. /. If it is 3 mass% or less, and Ca is 0.7 mass% or more and 1.3 mass% or less, it exhibits the same conductivity and surface creep properties as the above-mentioned pieces.

 That is, a magnesium alloy containing Cu, Ca and Sn with appropriate contents shows no deterioration in conductivity due to the addition of Sn, and is excellent in creep resistance at high temperatures.

Claims

The scope of the claims 1. When the total is 100 mass%, 1 mass% to 5 mass% of copper (Cu), 0.1 mass ⁰ / o to 5 mass% of calcium (Ca), and the Ca A magnesium alloy for ^ t, which contains tin (Sn) with a mass ratio (Sn / Ca) of 0.1 or more and 3 or less, with the balance being magnesium (Mg) and inevitable impurities.  2. The magnesium alloy for t 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 alloy for forging according to claim 1, wherein the tin (Sn) has a mass ratio (SnZC a) to the calcium (Ca) of 0.1 or more and 2 or less. 5. The magnesium alloy for fabrication according to claim 1, wherein the Mg—Cu compound and the O ^ Mg—Ca—Sn compound have a structure crystallized in a network form at the grain boundary of the Mg crystal grains. 6. When the entirety is taken as 100 mass%, 1 mass% to 5 mass% of copper (C u), 0. 1 mass ⁰ / o or 5 mass _^0/0 following calcium and (Ca), the Pouring a hot metal alloy containing tin (Sn) with a mass ratio (Sn / Ca) of 0.1 to 3 in Ca, and the balance of magnesium (Mg) and inevitable impurities. The pouring hot water  A solidification step of cooling and solidifying the molten alloy after the pouring step; Magnesium combination characterized by being obtained through ^ ¾  7. The magnesium compound according to claim 6, wherein the Mg—Cu compound and the Mg—Ca—Sn compound have a network crystallized structure at the grain boundaries of the Mg crystal grains.