JP3387548B2 - Manufacturing method of magnesium alloy molded product - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lightweight and high-strength magnesium alloy molded product, and more particularly to a method for manufacturing a molded product at low cost by utilizing the superplastic property of a specific magnesium alloy.

[0002]

2. Description of the Related Art Magnesium alloys are drawing attention in the recent trend of weight reduction in automobiles, home appliances and OA industries. However, a drawback of general magnesium alloys is that plastic working is difficult. Among such alloys, Mg-Li eutectic alloy is known to have superplastic properties. Superplastic forming such as blow forming utilizing this superplastic property is expected as a new processing technology for magnesium alloys.

[0003]

However, Mg-
In order to sufficiently develop the superplastic properties of the Li alloy to be suitable for superplastic forming such as blow forming, it is necessary to perform thermomechanical treatment such as rolling to refine the metal structure,
This causes a cost increase.

The present invention has been made in view of the problems of the prior art as described above, and an object of the present invention is to develop superplastic characteristics of a specific Mg-Li alloy at low cost and to perform pretreatment. The object of the present invention is to provide a method for directly producing a magnesium alloy molded product by superplastic forming without the need for the heat treatment.

[0005]

[Means for Solving the Problems] The inventors of the present invention can easily develop a fine structure required for superplastic forming of an Mg-Li alloy having a specific composition by cooling solidification or rapid solidification using a die such as die casting. The present invention has been accomplished, and the inventors have found that superplastic forming can be directly carried out while omitting the structure control by the conventionally used thermomechanical treatment, and arrived at the present invention.

[0006]

According to the present invention , lithium is contained in an amount of 6 to 10.5% by weight, and yttrium and calcium are each added in an amount of 0.3.
It is characterized in that a magnesium alloy containing 3 to 3% by weight with the balance being magnesium and unavoidable impurities is cast, cooled and solidified at that time, and the casting is directly subjected to superplastic forming without thermomechanical treatment. .

[0008]

[0009]Further, the present invention, Lithium 6-10.5
Wt%, and yttrium and calciumEach
0.3 to 3% by weight, and further 4% by weight or less
Aluminum and zinc, silver and ma
Selected from the group consisting of cancer, silicon and lanthanoids.
Contains at least one element and the balance is magnesium
And cast magnesium alloy consisting of inevitable impurities,
At that time, it is cooled and solidified, and the casting is subjected to thermomechanical treatment.
It is characterized in that it is directly superplastically formed without the use.

In the present invention, "cooling solidification" means both cooling solidification by a die such as die casting and rapid solidification.

The Mg-Li alloy becomes a eutectic alloy when the lithium content is about 6 to 10.5% by weight, and the molten metal of such an alloy is cooled and solidified by casting,
The alloy structure becomes finer, and superplasticity characteristics that enable superplastic forming such as blow molding are exhibited. Outside this range, the HCP single phase and the BCC single phase are obtained. Therefore, the lithium content of the Mg-Li alloy used in the present invention is 6
˜10.5% by weight, preferably 7.5 to 9% by weight.

When at least one of yttrium and calcium is contained in the above Mg-Li alloy, yttrium and / or calcium are fine Mg-Y-based and / or Mg-Ca-based compounds in the solidification stage. Has the effect of refining the solidified structure. Needless to say, such refinement of the structure further improves the superplastic property. In addition, yttrium and / or calcium other than those spent for such crystallization mainly form a solid solution in the BCC phase, solid-solution harden the alloy, and suppress changes over time such as recovery of the working structure of the alloy, It contributes to the improvement of room temperature strength and the stabilization of strength. If the amount of yttrium and / or calcium added exceeds 3% by weight, Mg-Y-based and / or Mg-Ca
Since the system-based compound begins to crystallize in the grain boundaries in a network form, superplasticity is impaired. The addition amount of yttrium and / or calcium is 0.3% by weight.
If it is less than the range, the effect of addition is insufficient. Therefore, the Mg-Li alloy used in the present invention is yttrium and / or
Alternatively, when calcium is contained, the amount of yttrium and / or calcium added is 0.3 to 3% by weight, preferably 0.5 to 2% by weight. It should be noted that Mg-Li alloy burns when dissolved in an oxygen-containing atmosphere, but when calcium is added to this Mg-Li alloy, combustion of Mg during melting in an oxygen-containing atmosphere is suppressed. Therefore, when the Mg-Li alloy used in the present invention contains calcium, the dissolution of the Mg-Li alloy can be carried out in a completely inert atmosphere or in the air.

In Mg-Li alloys, aluminum, zinc, silver, manganese, silicon, strontium, yttrium, scandium and lanthanoids (eg,
La, Ce, misch metal, etc.) are all known to contribute to improving the strength of the alloy. The strength of the alloy increases with the addition of these alloying elements, but the alloy strength is 4% by weight for aluminum and zinc, and 2% by weight for silver, manganese, silicon, strontium, yttrium, scandium and lanthanoids. The effect of increasing the alloying strength is saturated, and no further increase in alloy strength is observed even if it is added more. On the other hand, if aluminum and zinc are added in excess of 4% by weight, and if silver, manganese, silicon, strontium, yttrium, scandium and lanthanoids are added in excess of 2% by weight, the alloy may become brittle and the specific gravity of the alloy may increase. Becomes large, and the workability also deteriorates. Therefore,
In the Mg-Li alloy used in the present invention, the addition amount of aluminum and zinc is 4% by weight or less, preferably 1.0 to 3.0% by weight, and silver, manganese, silicon,
The amount of strontium, yttrium, scandium and lanthanoid added is 2% by weight or less, preferably 0.5 to 1.5% by weight.

In the method for producing a magnesium alloy molded article according to the present invention, the molten Mg--Li alloy as described above is cast by a die such as a die casting to form a thin plate or near net case, for example. Solidify by cooling
Superplastic forming such as blow molding is directly carried out without subjecting the cast to heat treatment.

[0015]

【Example】

Examples 1 and 2 , Comparative Examples 1 to 17 and Comparative Example 1 Raw materials were charged and melted in a vacuum melting furnace in an argon atmosphere so that the alloys had the compositions (% by weight) shown in Table 1.
SUS304 material was used as the crucible, and no flux or the like was used. A 180 mm × 30 mm × 2 mm test piece was cast from the molten metal by a cold chamber die casting machine and cooled and solidified. The casting conditions were as follows. Molten metal temperature: 750 ° C Mold temperature: 300 ° C Casting pressure: 95 kgf / cm Die-casting injection speed: 1.2 cm / s Clamping time: 3 sec Test pieces are cut from the casting thus obtained and rolled. Tensile tests (tensile strength), specific gravity measurements and superplastic property tests were carried out without thermomechanical treatment. Test article
The case was as follows. Tensile test: by Instron tensile tester, test piece: thickness 2 mm, length 20 mm, width 20 mm, gauge length 10 mm, gauge width 5 mm, measured at 25 ° C., strain rate = 4 × 10 ⁻⁴ / s, measurement unit = MPa; specific gravity: Archimedes method; superplastic property test: temperature 350 ° C., gauge length 10 mm, strain rate = 2 × 10 ⁻⁴ / s; measurement results are as shown in Table 1.

[0016]

[Table 1]

From the data of the above examples and comparative examples it is clear that: Mg-L, which is the subject of the present invention.
i alloy does not require thermo-mechanical treatment as a pretreatment,
It is possible to directly superplastically form a magnesium alloy molded product. Yttrium and calcium are effective in improving the strength and stability of the strength at room temperature, and when used in a small amount, the elongation rate of superplasticity is improved. If the amount of lithium added deviates from the eutectic composition, no superplastic property is exhibited. The addition of a predetermined amount of aluminum, zinc, silver, manganese and lanthanoid contributes to the improvement of the strength of the Mg-Li alloy, and does not substantially impair the superplastic properties.

[0018]

EFFECTS OF THE INVENTION According to the present invention, a specific Mg-Li alloy exhibits superplastic properties at a low cost, and a magnesium alloy molded product is directly superplastically molded without the need for thermomechanical treatment as a pretreatment. It can be manufactured at low cost.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kohei Kubota 1333-2 Hara City, Ageo City, Saitama Prefecture Mitsui Mining & Smelting Co., Ltd. (72) Ryuji Ninomiya 1333-2 Ageo City, Saitama Prefecture Mitsui Metal Mining Company Inside Research Institute, Inc. (72) Inventor Tsutomu Sato 1333-2, Hara City, Ageo City, Saitama Prefecture Inside Research Center, Mitsui Mining & Smelting Co., Ltd. (72) Inventor Gunter Naite D-6350 Bad Nauheim Mainus Strasse 9 (72) ) Inventor Eberhard Eschmidt Germany D-88755 Arzena Uei Unter Frankfurt Iglauer Strasse 2 E (56) References JP-A-4-176839 (JP, A) JP-A-6-65668 (JP, A) JP Flat 6-25789 (JP, A) 49576 (JP, A) JP-A-6-279905 (JP, A) JP-A-6-279906 (JP, A) JP-A-3-502346 (JP, A) US Patent 5059390 (US, A) US Patent 3189442 (US, A) Fujitani et al., Superplasticity of Mg-8% Li alloy, microstructural change during deformation, light metal, Japan, March 30, 1992, Vol. 42, No. 3, P. 125-131 Higashi. K, Kubota, K, Neite. G, high temperature properties of superplastic magnesium-lithium b based alloy, Magnesium um Alloys Their App pl. , [Pap DGM Conf.], 1992, p. 293-300 Shimizu, Takeuchi, Effect of Ca addition on microstructure and properties of Mg and Mg-Li alloy, casting, Japan, March 27, 1991, Vol. 63, No. 3, P.I. 245-249 (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22F 1/06 C22C 1/02 C22C 23/00-23/06

Claims (2)

(57) [Claims] 1. Lithium 6 to 10.5% by weight, and yttrium and calcium 0.3 to 3% by weight, respectively .
A magnesium alloy molded product containing a magnesium alloy containing the balance of magnesium and unavoidable impurities, cooled and solidified at that time, and directly superplastically molded without subjecting the cast product to heat treatment. Manufacturing method. 2. Lithium 6-10.5 wt% and yttrium and calcium 0.3-3 wt% respectively .
And at least one element selected from the group consisting of 4 wt% or less of aluminum and zinc, and 2 wt% or less of each of silver, manganese, silicon and lanthanoid, and the balance of magnesium and inevitable impurities. A method for producing a magnesium alloy molded article, which comprises casting a magnesium alloy of the present invention, cooling and solidifying the resulting magnesium alloy, and directly superplastically forming the cast article without performing thermomechanical treatment.