Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
• • 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
• • 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
  • C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent

Definitions

• the present invention relates to a magnesium alloy having both high strength and high ductility; and a production process thereof.
• magnesium is lighter in weight than iron or aluminum, its use as a light-weight substitute for members made of an iron steel material or aluminum alloy material is under investigation.
• Ordinary magnesium alloys have, however, lower strength than the other metal structure materials such as iron steel, aluminum alloy and titanium alloy.
• An AZ91 material for die casting which is said to have relatively high strength, has strength as low as 160 MPa.
• industrial parts are required to have, at a moving part thereof, a percent elongation of at least 4 to 5%, but ordinary magnesium alloys do not have sufficient ductility. Even the above-described AZ91 material has a percent elongation of only about 3%.
• a magnesium alloy having a composition represented by the formula: Mg 100 - a-b-c Ca a Zn b X c (wherein, X represents one or more than one elements selected from the group consisting of Y, Ce, La, Nd, Pr, Sm and Mm (misch metal); and 0.5 ⁇ a ⁇ 5 atomic %, 0 ⁇ b ⁇ 5 atomic %, and 0 ⁇ c ⁇ 3 atomic % with the proviso that 1 ⁇ a+b+c ⁇ 11 atomic %), and having a structure in which one or more of Mg-Ca, Mg-Zn and Mg-X intermetallic compounds have been finely dispersed in a Mg mother phase composed of a fine crystalline material.
• the above-described magnesium alloy having intermetallic compound(s) can be obtained as a high strength magnesium alloy in the powder form by rapid solidification of a molten alloy having the above-described composition by atomization or the like method. It can be molded or formed into even complex shaped products by hot plastic processing (refer to Japanese Patent Laid-Open No. 41065/1997).
• M is one or more elements selected from Al and Zn;
• Ln is one or more elements selected from Y, Ce, La, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Mm (misch metal), or a mixture of rare earth elements; and 0.5 ⁇ a ⁇ 5 atomic %, and 0.2 ⁇ b ⁇ 4 atomic %, with the proviso that 1.5 ⁇ a+b ⁇ 7 atomic %); having a crystal grain size less than 2,000 nm; and having a long period hexagonal structure in a part or whole region of the crystals.
• the above-described magnesium alloy having a long period hexagonal structure can be prepared as a high strength and high ductility magnesium alloy in the powder form by rapid solidification of a molten alloy having the above-described composition by atomization or the like method.
• plastic processing at an extrusion ratio of from 3 to 20, extrusion goods made of the magnesium alloy can be obtained (refer to Japanese Patent Laid-Open No. 2002-256370).
• the above-described magnesium alloys each has a percent elongation not greater than 5%, which is almost a limit value when they are used for moving portions of industrial parts. Thus, they do not have sufficient ductility.
• the industrial parts using the above-described magnesium alloys therefore have a drawback: design freedom is greatly limited and they are not suited for practical use.
• the magnesium alloy having a long period hexagonal structure is said so that it could be formed into a molded product by casting using a copper mold with a large cooling rate.
• molded products thus obtained must be relatively small in order to raise its cooling rate.
• this magnesium alloy has a drawback that any size of a molded product cannot be produced freely.
• An object of the present invention is to overcome the above-described drawbacks and provide a magnesium alloy which is inexpensive, has a good yield, can be molded or formed into any size, and has both high strength and high ductility; and a production method of the magnesium alloy.
• the magnesium alloy of the present invention comprises from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y, each based on the total amount, at a Zn/Y composition ratio falling within a range of from 0.6 to 1.3, and further comprises Mg 3 Y 2 Zn 3 which is an intermetallic compound and Mg 12 YZn having a long period structure.
• the magnesium alloy according to the present invention has, as well as the above-described composition, both the intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure, it is able to have both high strength and high ductility. Either one of or both of strength and ductility become insufficient when the content of Zn is less than 1 atomic % or exceeds 4 atomic % and that of Y is less than 1 atomic % or exceeds 4.5 atomic %, based on the total amount of the magnesium alloy.
• the magnesium alloy of the present invention is required to satisfy the Zn/Y composition ratio which falls within a range of from 0.6 to 1.3 in order to incorporate both the intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure in the alloy without failure.
• the Zn/Y composition ratio is less than 0.6 or exceeds 1.3, the magnesium alloy does not always contain either one or both of the intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure.
• the magnesium alloy of the present invention preferably contains from 2 to 3.5 atomic % of Zn and from 2 to 4.5 atomic % of Y, each based on the total amount, at a Zn/Y composition ratio falling within a range of from 0.8 to 1.2, in order to have both higher strength and higher ductility.
• the magnesium alloy of the present invention may contain from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y, based on the total amount, and contain, as a remaining portion, Mg and inevitable impurities. Alternatively, it may contain from 0.1 to 0.5 atomic % of Zr, based on the total amount, and contain as a remaining portion Mg and inevitable impurities.
• Incorporation of Zr in the magnesium alloy of the present invention within the above-descried range enables to impart a miniaturized alloy structure to the magnesium alloy. Miniaturization effect of the alloy structure cannot be attained when the content of Zr is less than 0.1 atomic % based on the total alloy amount. On the other hand, when the content of Zr exceeds 0.5 atomic % based on the total alloy amount, formation of the intermetallic compound Mg 3 Y 2 Zn 3 is sometimes disturbed.
• the magnesium alloy of the present invention is able to have higher strength by the addition, to the above-described composition, of a small amount of at least one element selected from the group consisting of La, Ce, Nd, Sm and Yb. Moreover, the magnesium alloy of the present invention can be obtained as a composite by adding a reinforcing material such as fibers and particles.
• the magnesium alloy of the present invention can be produced by a process comprising casting an Mg alloy containing from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y, each based on the total amount, at a Zn/Y composition ratio falling within a range of from 0.6 to 1.3; and plastic processing of the cast product obtained in the above-described step into an alloy structure containing an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure.
• the material is melted in a high-frequency melting furnace, for example, at 700°C to yield a molten alloy.
• the molten alloy is poured into a mold, followed by casting.
• a cooling rate during the casting is preferably 10 K/sec or less. This cooling rate is much lower than that of atomization method or twin-roll method employed for rapid solidification, that is, 10 4 K/sec or greater. It is also much lower than that of roll casting method or quenched copper mold method, that is, 10 3 to 10 2 K/sec.
• ordinarily employed molds such as metal mold, graphite mold and sand mold can be used for casting and a copper mold or water-cooled copper mold is not necessary, which leads to a reduction in the production cost.
• the cast product thus obtained is subjected to plastic processing, whereby a molded or formed product can be obtained.
• the molded or formed product is a magnesium alloy containing from 1 to 4 atomic % of Zn and from 1 to 4.5% of Y, based on the total alloy amount, at a Zn/Y composition ratio falling within a range of from 0.6 to 1.3.
• it further contains from 0.1 to 0.5 atomic % of Zr and as a remaining portion Mg and inevitable impurities. It contains both an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure.
• the molded or formed product is able to have both high strength and high ductility.
• the molten alloys thus obtained were poured into metal molds, followed by casting at a cooling rate not greater than 10K/sec, whereby rod materials were obtained.
• the rod materials were heated to a temperature range of from 350 to 450°C in an electric furnace, and then extruded at an extrusion ratio of 10, whereby extrusion goods were obtained.
• each of the resulting extrusion goods was identified by X-ray diffraction and transmission electron microscope, whereby the presence or absence of an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure was confirmed.
• Test pieces were cut from the extrusion goods. Their 0.2% proof stress, tensile strength and elongation were measured by conducting a tensile test on them at normal temperature. The results are shown in Table 1.
• each of the resulting extrusion goods was identified by X-ray diffraction and transmission electron microscope, whereby the presence or absence of an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure was confirmed.
• Test pieces were cut from the extrusion goods. Their 0.2% proof stress, tensile strength and elongation were measured by conducting a tensile test on them at normal temperature. The results are shown in Table 1.
• magnesium alloys obtained in Examples 1 to 14 containing, based on the total alloy amount, from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y at a Zn/Y composition ratio falling within a range of from 0.6 to 1.3, and containing both an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure have both high strength and high ductility, because they are markedly superior to known WE54-T6 material and AZ91 material in each of strength (0.2% proof stress, tensile strength) and ductility (elongation).
• the magnesium alloy obtained in Comparative Example 7 containing Zn in an amount less than the invention range of from 1 to 4 atomic % and Y in an amount less than the invention range of from 1 to 4.5 atomic % does not have the intermetallic compound Mg 3 Y 2 Zn 3 so that it does not have sufficient strength. It is also apparent that the magnesium alloy obtained in Comparative Example 8 containing Zn in an amount exceeding the invention range of from 1 to 4 atomic % and Y in an amount exceeding the invention range of from 1 to 4.5 atomic % contains both the intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure but it does not have sufficient ductility.
• the magnesium alloy which is inexpensive, can be produced at a high yield, and has both high strength and high ductility; and a production process of the magnesium alloy.
• the magnesium alloy contains from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y at a Zn/Y composition ratio ranging from 0.6 to 1.3, and contains both an intermetallic compound Mg 3 Y 2 Zn 3 , and Mg 12 YZn having a long period structure. It may contain from 2 to 3.5 atomic % of Zn and from 2 to 4.5 atomic % of Y at a Zn/Y composition ratio falling within a range of from 0.8 to 1.2.
• It may contain from 1 to 4 atomic % of Zn, from 1 to 4.5 atomic % of Y and from 0.1 to 0.5 atomic % of Zr and contains, as a remaining portion, Mg and inevitable impurities.
• An alloy structure having both an intermetallic compound Mg 3 Y 2 Zn 3 and Mg 12 YZn having a long period structure is available by casting an Mg alloy containing from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y at a Zn/Y composition ratio ranging from 0.6 to 1.3, followed by plastic processing.

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• 2004
  • 2004-09-28 JP JP2004280878A patent/JP4500916B2/ja not_active Expired - Lifetime
• 2005
  • 2005-09-26 EP EP05020951A patent/EP1640466B1/fr active Active
  • 2005-09-26 DE DE602005015799T patent/DE602005015799D1/de active Active
  • 2005-09-27 US US11/235,229 patent/US20060065332A1/en not_active Abandoned

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