KR100916194B1 - Magnesium alloy having high strength and high toughness - Google Patents

Abstract

The present invention relates to a high strength, high toughness magnesium alloy, and more particularly, to a magnesium alloy excellent in strength and toughness in which magnesium is the main component and manganese, zirconium, zinc, and copper are added thereto.

The magnesium alloy can simultaneously or separately form dispersed particles composed of Mn, Zr and the like and Mg-Zn precipitates through appropriate heat treatment, and also improves the homogeneity of microstructures by suppressing segregation through addition of Cu. It can show higher strength and toughness than magnesium.

The alloy can be used for magnesium alloy materials for automobiles or electronics that require high strength and high toughness simultaneously with the need for weight reduction.

Magnesium, high strength, high toughness

Description

High Strength High Toughness Magnesium Alloy {MAGNESIUM ALLOY HAVING HIGH STRENGTH AND HIGH TOUGHNESS}

1A is a state diagram of an Mg-Zn alloy containing no Mn or Zr.

Figure 1b is a state diagram of the Mg-Zn alloy containing 0.1% by weight Mn, 0.1% by weight Zr.

Figure 2 is a photograph of the casting mold of the Cu material used in the embodiment of the present invention.

3 is a schematic diagram of a sheet casting apparatus used in an embodiment of the present invention.

Figure 4 is a photograph of the magnesium alloy sheet produced by the thin plate casting method according to an embodiment of the present invention.

Figure 5a is a picture of the casting structure of the magnesium alloy (Mg-6Zn-0.1Mn-0.2Zr-0.3Cu) plate material prepared by the die casting method according to an embodiment of the present invention.

Figure 5b is a photograph after the T4 heat treatment of the magnesium alloy (Mg-6Zn-0.1Mn-0.2Zr-0.3Cu) plate material produced by the die casting method according to an embodiment of the present invention.

6 is a structural diagram of the cast state of the magnesium alloy (Mg-6Zn-0.3Mn-0.2Zr-0.3Cu) sheet material produced by the thin plate casting method according to an embodiment of the present invention.

FIG. 7 is a structure diagram showing fine dispersed particles after T4 heat treatment of a magnesium alloy (Mg-6Zn-0.3Mn-0.2Zr-0.3Cu) sheet prepared by a thin plate casting method according to an exemplary embodiment of the present invention.

8 is a graph showing the tensile properties after T4 heat treatment of the magnesium alloy sheet produced by the thin plate casting method according to an embodiment of the present invention.

The present invention relates to a magnesium alloy designed to be used industrially as a material for a wide range of parts, more specifically, magnesium as the main component and manganese (Mn), zirconium (Zr), zinc (Zn), copper (Cu) By adding, it is possible to form fine dispersed particles and precipitated particles in the microstructure simultaneously or separately through appropriate heat treatment, and to improve the homogeneity of the microstructure, and to provide superior strength and toughness compared to conventional magnesium. will be.

In general, magnesium alloy is the lightest alloy having a high specific strength, and can be used for general casting and high pressure casting, and is widely applied to automobile parts or aviation parts.

Looking at the composition of the representative magnesium alloy developed to date, first there is a high-strength magnesium alloy consisting of 8.3 to 9.7 wt% Al, 0.35 to 1.0 wt% Zn, 0.15 wt% or more Mn, 0.1 wt% or less Si, and residual magnesium, There is a highly stretched magnesium alloy consisting of 5.5 to 6.5 wt% Al, 0.22 wt% or less Zn, 0.13 to 0.6 wt% Mn, 0.5 wt% or less Si, and residual magnesium, and 2.5 to 3.5 wt% Al, 0.6 to 1.4 wt% Magnesium alloys for sheet materials which consist of Zn, 0.2% by weight or more, Mn, 0.1% by weight or less, Si, and residual magnesium. However, all of the alloy compositions must satisfy the conditions of 0.005% by weight or less of Fe, 0.03% by weight or less of Cu, and 0.002% by weight or less of Ni.

However, in the case of the conventional magnesium alloy, there is a problem that the toughness or strength is insufficient to be widely used as the material of the part.

The present inventors have diligently studied to solve the above-mentioned problems of the prior art, and as a result, through the metallurgy and thermodynamic considerations, dispersed particles composed of Mn and Zr, etc., may be generated in pure Mg and Mg-Zn-based magnesium alloys. Based on the thermodynamically calculated alloy design and the corresponding heat treatment process, the development of high strength and high toughness magnesium alloy can be widely used as a material for a wide range of components.

An object of the present invention is to add Mn and Zr to pure Mg or Mg-Zn-based alloys designed to enhance precipitation, thereby distributing fine dispersed particles and precipitated particles evenly or separately inside the microstructure, thereby providing a high strength high toughness magnesium alloy. To provide.

Another object of the present invention is to provide a magnesium alloy with markedly improved toughness, particularly elongation, of the alloy by suppressing the macro segregation generated in the casting process due to the addition of Mn and Zr through the addition of Cu.

Magnesium alloy according to the present invention for achieving the above object, contains 5.0 to 10.0% by weight of Zn, 0.05 to 0.5% by weight of Mn, 0.02 to 0.5% by weight of Zr, the balance of Mg and other unavoidable impurities There is a compositional feature.

1A and 1B show a state diagram calculated with a commercial thermodynamic calculation program FactSage ^™ , which is a state diagram of Mg-Zn alloys containing no Mn and Zr, and an Mg-Zn alloy containing 0.1 wt. Mn and 0.1 wt. It is showing a state diagram.

According to this, in the case of Mg-Zn alloy containing no Mn and Zr, only a stable region exists in Mg single phase, whereas in the case of Mg-Zn alloy containing Mn and Zr, single phase region does not exist and Mg and Mn ₂ It can be seen that there is a region where two phases of Zr coexist.

It is difficult to expect a thermodynamic equilibrium solidification process in practical casting processes, and since it often involves non-equilibrium solidification, it is assumed that alloy elements such as Mn or Zr are employed above equilibrium employment in non-equilibrium solidification. In the heat treatment process, particles composed of Mn and Zr may be uniformly generated in a matrix by the same mechanism as that of precipitation.

In addition, a phase composed of Mn, Zr, etc. may be formed at the boundary or inside of a dendrite phase even in a solidification process in which it is difficult to expect supersaturation of the solute due to a very low cooling rate.

That is, the core of the present invention is to add Mn and Zr to the precipitation-enhanced Mg-Zn-based alloy to produce dispersed particles composed of Mn and Zr as a main component in the microstructure, and separately composed of Mg and Zn By generating the precipitated particles in the microstructure at the same time with the dispersed particles to be able to exhibit an excellent strength compared to the existing alloy.

In addition, the alloy may further contain 0.05 to 0.5% by weight of Cu in order to prevent macro segregation of the alloy which may occur due to the addition of Mn and Zr.

The reason for limitation of each said component is as follows, respectively.

Zinc (Zn) must be added in at least 5% by weight to form precipitated particles, and if it exceeds 10% by weight, a significant amount of the eutectic phase present in the casting structure remains in the tissue even after T4 heat treatment. It is maintained at 10% by weight or less because it causes the mechanical properties, in particular the elongation is weak.

Manganese (Mn) is added together with zirconium (Zr) to form an intermediate phase such as Mn ₂ Zr, present in the form of dispersed or precipitated particles in the microstructure, thereby improving the strength and toughness of magnesium, less than 0.05% by weight When added to the alloy, the effect is not sufficient, and when added to the alloy containing Zr in excess of 0.5% by weight, coarse Mn ₂ Zr phase is crystallized in the molten metal state before the solidification process, which causes a decrease in elongation of the cast material. Therefore, it is maintained at 0.5% by weight or less.

Zirconium (Zr) is added together with manganese (Mn) to form an intermediate phase such as Mn ₂ Zr, and present in the form of dispersed particles or precipitated particles in the microstructure, thereby improving the strength and toughness of magnesium, less than 0.02% by weight When added to the alloy, the effect is not sufficient, and when added in excess of 0.5% by weight to the alloy to which Mn is added, coarse Mn ₂ Zr phase is crystallized in the molten metal state before the solidification process, which causes a decrease in elongation of the cast material. Therefore, it is maintained at 0.5% by weight or less.

Copper (Cu) acts to prevent macro segregation of manganese (Mn) and zirconium (Zr) during casting of the alloy, and when added in less than 0.05% by weight, the effect of preventing segregation is not sufficient, and more than 0.5% by weight If added, the castability and corrosion resistance of the alloy are lowered, so it is maintained at 0.5% by weight or less.

Hereinafter, the present invention will be described in more detail based on examples of the present invention.

EXAMPLE

Using pure Mg (99.9%) and Mg-0.4 wt% Zr master alloy, Mg-2.5 wt% Mn master alloy, pure Zn (99.995%), pure Cu (99.99%), shown in Tables 1 and 2 below. Mg-Zn-Mn-Cu-Zr based alloys as prepared were prepared through induction melting.

The prepared alloy was cast by the die casting method and the sheet casting method, respectively. In the embodiment of the present invention, the mold casting method and sheet casting method are used, but for example, sand casting, gravity casting, pressure casting, continuous casting, die casting, precision casting, spray casting, reaction casting, etc. It is not limited to a specific casting method.

In the case of die casting, a copper (Cu) mold as shown in FIG. 2 is used to melt a molten metal maintained at a temperature of 700 ° C. after re-dissolving the alloy of the composition under a mixed gas atmosphere of CO ₂ and SF ₆ . It injected into the metal mold | die maintained at the temperature of 90 degreeC, and cast the board | plate material of length 150mm, width 30mm, and thickness 3mm.

In addition, in the case of sheet casting, a sheet casting machine as shown in the schematic diagram of FIG. 3 was used, and the alloy was dissolved under a mixed gas atmosphere of CO ₂ and SF ₆ as in the mold casting, and maintained at a temperature of 700 ° C. The molten alloy was transferred to a tundish controlled at the same temperature and then injected between two cooling rolls which were cooled with water, and a thin plate having a length of 5 m, a width of 70 mm, and a thickness of 2 mm was cast. At this time, the interval between the cooling roll was 2 mm, the speed of the roll was maintained at 4 ~ 4.5 m / min.

The plate cast as described above was heat treated (T4) at 330 ° C. for 2 hours, and then aged at 150 ° C. for 24 hours (T6).

For the heat-treated specimens, microstructures were observed through an optical microscope, a scanning electron microscope, and a transmission electron microscope.

5A and 5B show the casting structure of the Mg-6Zn-0.1Mn-0.3Zr-0.3Cu alloy sheet material produced by the die casting method and the structure after T4 heat treatment, respectively, and the casting structure has a coagulation cell spacing of 20 to 30 µm. Phosphorous isotropic crystal structure is shown and the secondary phase with Mg coexists after heat processing.

Figure 6 shows the microstructure of the casting state of the Mg-6Zn-0.3Mn-0.2Zr-0.3Cu alloy sheet material produced by the thin plate casting method, the thin plate casting structure shows an equiaxed crystal solidification structure as in the case of the die casting method It can be seen that the cell spacing is 5 ~ 10㎛ finer than the mold casting method.

As a result of observing the Mg-6Zn-0.3Mn-0.2Zr-0.3Cu alloy sheet produced by the thin sheet casting method with TEM after T4 heat treatment, as shown in FIG. 7, a large amount of fine particles were dispersed in the microstructure. This dispersed particle increases with Zr content and contributes to the strength improvement of the alloy, as can be seen from the tensile test results of FIG. 8.

In addition, the heat-treated specimen was prepared into a tensile test piece having a gauge length of 12.6 mm, a width of 5 mm, and a thickness of 1 mm, and then subjected to a tensile test at a strain rate of 6.4 × 10 ⁻⁴ S ⁻¹ .

The composition and the tensile test results of the alloy produced by die casting and sheet casting are shown in Table 1 and Table 2, respectively.

TABLE 1

Alloying Properties of Magnesium Alloy Plate Prepared by Mold Casting Method According to Embodiment of the Invention and Mechanical Properties after T4 Heat Treatment

TABLE 2

Alloying Properties of Magnesium Alloy Plate Prepared by Sheet Casting Method According to Embodiments of the Invention and Mechanical Properties after T4 and T6 Heat Treatment

As can be seen from Table 1, when the T4 heat treatment is performed, the tensile strength increases by 10% or more in comparison with the case where only Zr is added to the Mg-Zn alloy and when Zr and Mn are added at the same time, the elongation is increased. It can be seen that increases about three times or more.

In addition, as can be seen from Tables 1 and 2, regardless of the casting method such as mold casting or sheet casting, in the case where additional copper (Cu) is added to the alloy, the elongation is remarkably improved compared with the case where it is not. I can see

That is, the magnesium alloy according to the embodiment of the present invention can be seen that the toughness is particularly markedly increased compared to the conventional magnesium alloy.

The magnesium alloy according to the present invention not only generates a large amount of fine dispersed particles and precipitated particles in the microstructure, but also exhibits superior strength and toughness compared to the existing magnesium alloy by suppressing macro segregation in the casting process.

The magnesium alloy according to the present invention may be used as a processing material or a casting material, and may be manufactured as a high strength, high toughness magnesium alloy sheet material, an extruded material, a casting, and the like, which are practically applicable to automobiles and the electronics industry.

Claims (2)

A high strength, high toughness magnesium alloy sheet produced by casting and heat-treating an alloy containing, in weight percent, Zn: 5.0 to 10.0, Mn: less than 0.05 to 0.5, Zr: less than 0.02 to 0.4 and the remainder being magnesium and other unavoidable impurities. The high strength high toughness magnesium alloy sheet material according to claim 1, which further contains 0.05 to 0.5% by weight of Cu.

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