Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/04—Alloys based on magnesium with zinc or cadmium as the next major constituent

Definitions

• the present invention relates to a magnesium alloy excellent in high temperature strength. Specifically, it relates to a fine particle-dispersed magnesium alloy with excellent high temperature strength.
• Magnesium has a specific gravity of 1.74, which is the lightest industrial metal material, and its mechanical properties are not inferior to those of aluminum alloys. It has been attracting attention as a material that responds to the transformation.
• magnesium alloy is already used as a head cover material for automobile wheels and engines. Recently, there is a strong demand for weight reduction of all components, and the scope of application of magnesium alloys is expanding further. For example, it is considered that a magnesium alloy is applied to structural parts such as engine blocks that become high temperature and functional parts such as pistons. For example, when the Biston is made from aluminum alloy to magnesium alloy, not only the weight of the part itself but also the weight of other parts can be further reduced by reducing the inertia weight.
• Magnesium alloy products usually consist of forged products, including die-cast products
• Mg_A1 series alloys (ASTM standard 1 AM 60 B, AM 50 A, AM 20 A, etc.) contain 2 to: 12% A 1 and a small amount M n is added, the Mg side is ⁇ _ Mg solid solution and ⁇ — Mg! 7 A 1! It is a eutectic system of two compounds. 7 A 1 age hardening by the second interphase precipitation occurs. Also, the solution improves strength and toughness. Also, A l 5 ⁇ : 10%, Z n :!
• Mg-A 1 -Zn system AS TM standard 1 AZ 9 1 D etc.
• Mg-A 1- Crystallize Mg-A 1- Crystallize
• Mg- ⁇ n-based alloys when 2% Zn is added to Mg, the highest strength and elongation can be obtained with forging, but the forging property is improved and a healthy deposit is obtained. To obtain it, a larger amount of Zn is added.
• Mg _ 6% Z n alloy has a tensile strength of 2 units of 17 kg Zmm when fabricated, and is improved by T 6 treatment, but is considerably inferior to Mg-A 1 system. .
• An example of the M g ⁇ Z n system is ZCM 6 3 0 A (M g-6% Z n-3% C u-0.2 M n).
• a quasi-crystal with ⁇ — Mg is formed by hot forming after forging an Mg — Z n — Y alloy.
• the crystal phase is finely and uniformly dispersed in the structure.
• Quasicrystals are quasicrystalline phase-reinforced magnesium alloys that are much harder than crystalline compounds of approximate composition and have excellent strength and stretchability.
• the composition is limited to Mg—1 to 10 at% Z n ⁇ 0.1 to 3 at ° / 0 Y.
• the forged structure of the Mg- g ⁇ -— alloy has a quasicrystalline eutectic structure at the ⁇ -Mg crystal grain boundary.
• Mg alloys for sand-type forging such as AZ 9 1 C and ZE 4 1 have a predetermined strength by heat treatment such as T 6 and ⁇ 5 after alloy fabrication. These alloys are precipitation hardened alloys. Therefore, heat treatments such as ⁇ 6 and ⁇ 5 are required to adjust the strength to a predetermined level and to stabilize the characteristics over a long period of time. In addition, when exposed to room temperature or higher (generally 50 ° C or higher) for a long time, aging precipitation of dissolved elements occurs, and the alloy structure gradually changes, so the characteristics may change.
• Mg-Zn-Y alloy disclosed in Japanese Patent Laid-Open No. 2 0 0 2-3 0 9 3 3 2
• the forged material is a common eutectic alloy, and the strength is a commercially available alloy with a similar composition such as ZE 4 1 It was equivalent.
• aging alloys such as A Z 9 1 C and Z E 4 1 are always aging above room temperature because of the low thermal stability of precipitates.
• the high-strength magnesium alloy of the present invention has been made in view of such circumstances.
• the objective is to improve the strength of Mg-Zn-RE alloys, particularly the high temperature strength.
• the present inventors can obtain nanoparticles having a complicated structure derived from a quasicrystal in a crystalline magnesium matrix. A high-strength magnesium alloy with a dispersed structure is obtained. The present invention has been reached.
• the present invention is an invention of a high-strength magnesium alloy.
• zinc is 2.0 to 10%
• zirconium is 0.05 to 0.2%
• rare earth elements are 0.2 to 1.5. %, With the balance being magnesium and inevitable impurities.
• yttrium As the rare earth element (R E), yttrium (Y) is preferably exemplified.
• the magnesium alloy of the present invention has the following general formula:
• R E is a rare earth element
• a, b, and c are atomic% of zinc (Z n), zirconium (Z r), and rare earth element (R E), respectively, and ⁇ a
• the magnesium alloy of the present invention having the above composition has the following characteristics.
• (1) ⁇ -Mg crystal grains occupy 50% or more of the volume, and ⁇ -Mg crystal grain boundaries have nanoparticles with a complex structure such as quasicrystals or approximate crystals.
• a quasicrystal is a new ordered structure that does not have translational properties and is not allowed in crystallography, and has 5 or 10 times symmetry and a quasiperiodic arrangement.
• a 1 — P d 1 Mn, A 1 Cu-Fe, Cd-Yb, Mg-Zn-Y, etc. are known as alloys that produce quasicrystals. Due to its unique structure, it has unique properties such as high hardness, high melting point, and low ⁇ compared to ordinary crystals.
• Fine precipitates (1 ⁇ m or less) are uniformly dispersed in ⁇ - ⁇ g crystal grains. This fine precipitate improves the strength of the magnesium alloy of the present invention.
• the main fine precipitates are approximate crystals and Mg-Y intermetallic compounds.
• the approximate crystal is a quasicrystal (an intermetallic compound having a structure and composition similar to that of MggZneYj, and is a relative of the quasicrystal.
• the c_Mg phase occupies 50% or more of the volume, and has quasicrystals and similar crystal grains at the a-Mg grain boundary. Since these grains pin the movement of grain boundaries, the grain growth is suppressed. For this reason, strength reduction due to crystal coarsening does not occur even at high temperatures. In addition, fine crystals are precipitated in the grains. The main fine precipitates are approximate crystals and Mg_Y intermetallic compounds.
• FIG. 1A shows an S-organ structure photograph of Example 1
• FIG. 1B shows an SEM structure photograph of a comparative example
• FIG. 2 shows an enlarged photograph of the grains of Example 1 of Mg 6 ⁇ — 0.1 Zr — O. 9 Y (atomic%) forged material.
• Fig. 3 is an enlarged photograph of the grain boundary (strictly speaking, the eutectic-like part) of Example 1 M g— 6 ⁇ ⁇ — 0. l Z r — 0.9 9 Y (atomic%) Indicates.
• all the predetermined additive elements are added to molten Mg and mixed uniformly, and then formed into a mold.
• the method is not limited, and methods such as gravity fabrication, die casting, and rheocasting are adopted.
• the magnesium alloy of the present invention is preferably not only forged, but also heat-treated after forging and accompanied by hot working and heat treatment steps after forging.
• the rare earth elements constituting the magnesium alloy of the present invention include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr ), Neodymium (N d), promethium (P m), samarium (S m), plutonium (E u), gadolinium (G d), terbium (T b), dysprosium (D y), Examples include holmium (H o), erbium (E r), thulium (T m), ytterbium (Y b), and lutetium (L u). Of these, yttrium (Y) is preferred.
• Example 1 Except for the following raw materials, the same conventional material Mg-3Zn-0. 5Y was fabricated as in Example 1.
• Fig. 1A shows the SEM structure photograph of Example 1
• Fig. 1B shows the SEM structure photograph of the comparative example.
• Example 1 has a woven KyoAkiragumi in overview similar to Comparative Example, alpha-M g grain boundaries approximate crystal (Example 1) or M g 3 Z n 6 quasicrystal (Comparative Example).
• the shape of the eutectic structure differs between Example 1 and the comparative example, and in Example 1, the eutectic structure 'is finely and uniformly dispersed throughout.
• the M g Example 1 - 6 Z n - 0. l Z r - 0. 9 Y shows an enlarged photograph of the grains of ⁇ material.
• Example 1 From JIS No. 4 boat type ingot of Example 1 (Mg_6Zn—0.1Zr-0.9Y) and comparative example (Mg—3 ⁇ —0.5 ⁇ ) described above, Round bar tensile test specimens with a parallel part ⁇ 5 X 25 mm were collected and subjected to a tensile test at room temperature and 150 ° C. Similarly, tensile tests were performed on Examples 2 to 4 with different composition ratios and AZ 9 1 C—T 6 and ZE 4 1 A—T 5 which are conventional materials. The test conditions were AG-2550 kND made by Shimadzu Corporation as the tensile tester, and the tensile speed was 0.8 mm / mi ⁇ . The results are shown in Table 1 below. Table 1
• the forged materials of Examples 1 to 4 are superior in tensile strength at 150 ° C. as compared with conventional forged materials such as comparative examples.
• the decrease in strength accompanying the temperature increase from room temperature to 1550 ° C is very small.
• the cause may be an increase in fine precipitates in the -Mg crystal grains. Fine precipitates such as approximate crystals and Mg Y-based intermetallic compounds have high thermal stability, so they are considered to function effectively as dislocation barriers even at 150 ° C.
• the magnesium alloy of the present invention has nanoparticles derived from quasicrystals at the Mg crystal grain boundaries, and fine crystals are precipitated in the grains, so that strength reduction due to crystal coarsening does not occur even at high temperatures. As a result, high strength can be maintained even at high temperatures. Normally, increasing the rare earth element content increases the cost but increases the high-temperature strength. For example, WE 54 has high strength, though it is extremely expensive, due to the rare earth content of nearly 10% and T 6 heat treatment. The present invention can produce high-temperature strength as high as that of the conventional heat-treated material without any heat treatment.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Forging (AREA)
• Powder Metallurgy (AREA)

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• 2004
  • 2004-09-21 JP JP2004273364A patent/JP2006089772A/ja active Pending
• 2005
  • 2005-09-21 WO PCT/JP2005/017912 patent/WO2006033458A1/ja not_active Ceased
  • 2005-09-21 EP EP05788143A patent/EP1813689A4/de not_active Withdrawn
  • 2005-09-21 US US11/663,298 patent/US20070204936A1/en not_active Abandoned

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