KR101561147B1 - Mg-BASED ALLOY - Google Patents

Abstract

The Mg-based alloy of the present invention is an additive material other than Zn and is characterized by containing Ag at 1.98 at% or less. There is provided an Mg based alloy which is not only sufficiently strong in practical use but also has ductility at room temperature that can not be conventionally desired and which has a small anisotropy in strength characteristics.

Mg based alloy

Description

Mg based alloy {Mg-BASED ALLOY}

The present invention relates to a Mg-based alloy based on Mg, which is expected to be realized as a lightweight material changed to Al.

With respect to this Mg-based alloy, various ones shown in the following Patent Documents 1 to 8 have been conventionally developed.

In Patent Documents 2, 3, 4, 6 and 8, a rare earth element, scandium and lithium are added in order to improve the strength. However, since these rare earth elements are rare elements that are difficult to obtain on the earth, the price of the alloy is increased and the versatility is lowered.

Patent Document 1 discloses a quaternary alloy containing 0.3 to 3 mass% of Ca and containing Al, Sr, and Mn at the same time. In this alloy, precipitation (crystallization) is formed on the crystal grain boundaries of Mg. Patent Document 2 discloses a Mg alloy containing 0.3% or more and 1.0% or less of Zr and 0.2% or more and 2.0% or less when Ca is contained (% is% by mass)

The alloy of Patent Document 8 shows a Mg alloy developed as a casting material containing 3 to 8 wt% of Zn and 0.8 to 5 wt% of Ca.

In the experimental procedure of the present invention, it was found that the precipitation of grain boundaries was caused by excessive Ca content, and the ductility at room temperature was lowered. From these results, it was found that even in the cases of Patent Documents 1, 2, So that the ductility at the lower end is insufficient.

The alloy of Patent Document 7 is an alloy developed as a casting material. Specifically, Ca is zero or 0.5% by weight, Zn is 1% by weight to 7% by weight, Ca is zero or 0.5% by weight and Zn Is less than 75 MPa at the zero point, and has a 0.2% proof stress of less than 75 MPa to less than 100 MPa when the Zn content is 1 wt% to 7 wt%, which is insufficient strength for use as a structural material. As for the ductility, the inventors of the present invention have inferred from the above-mentioned knowledge obtained in the experiment of the present invention that the inclusion of Ca at a high concentration is low.

Patent Document 5 discloses a Mg-based alloy mainly containing Mn and Zn as an additive, and shows a solution treatment for obtaining high strength. However, there is a problem that a process such as an additional heat treatment requiring two-stage aging is complicated I have.

In Document 8, an alloy containing 10 wt% or less of Cu has been developed, but the addition of Cu has a drawback that the corrosion resistance of the Mg alloy is remarkably lowered.

In summary, at present, most of the members using Mg alloys are manufactured by casting and die-casting. In the future, the application of Mg alloy to transportation equipment such as automobile and aircraft is expected, but the casting method has a drawback that the structure of the material becomes coarse and the ductility is low and the size is limited, so that it can not be applied to the plate, . On the other hand, Mg-Al-Zn (AZ-based alloy) or Mg-Zn-Zr (ZK-based alloy) is available for practical Mg alloys for wrestling. However, strength of the Mg alloys for wrestling is insufficient, , The strength to be used for the strength design differs greatly when the tensile load is applied and when the compression load is applied (since the compressive strength of the commercially available AZ31 alloy rolled material is about 50% of the tensile strength) It is difficult. Up to now, a method of adding a rare earth element and adding a large amount of an alloy element has been taken in order to increase the strength of the Mg alloy.

However, since the rare earth element is expensive, the versatility is low, and the addition of a larger amount of the alloying element leads to formation of a coarse compound phase, which results in high strength but deteriorates ductility. Therefore, development of a new whole-body Mg alloy excellent in strength and ductility by addition of a rare-earth element-free and low-cost alloying element is required.

Patent Document 1: JP-A 2007-70688

Patent Document 2: JP-A-2006-28548

Patent Document 3: JP-A 2006-16658

Patent Document 4: JP-A No. 2005-113235

Patent Document 5: Japanese Patent Publication No. 2004-510057

Patent Document 6: JP-A-2003-226929

Patent Document 7: JP-A-2002-212662

Patent Document 8: JP-A-6-25791

In view of the foregoing, it is an object of the present invention to provide a Mg-based alloy having satisfactory ductility at room temperature as well as satisfactory strength in practical use, and a low anisotropy of strength characteristics.

The Mg-based alloy of the invention 1 is an additive material other than Zn and is characterized by containing Ag in an amount of 1.98 at% or less.

The invention 2 is characterized in that, in the Mg-based alloy according to the first aspect of the invention, Ca is further contained in an amount of 0.61 at% or less as an additive material other than Zn and Ag.

A third aspect of the invention is an Mg based alloy according to the second aspect, wherein Zr is further contained in an amount of 0.17 at% or less as an additive other than Zn, Ag and Ca.

A fourth aspect of the invention is the Mg-based alloy according to any one of the first to third aspects, characterized in that the crystal grain size is 0.1 탆 to 25 탆.

(Effects of the Invention)

By adding only the inexpensive alloying element according to the inventions 1 to 4, it has become possible to provide a Mg-based alloy having both strength and ductility that can not be expected in the past and which has a small anisotropy in strength.

In addition, since an alloy element which compromises corrosion resistance such as Cu is not used, excellent durability can be expected.

The alloy of the present invention has an average schmitt factor of 0.2 or more in the direction of the bottom slip with respect to the load load direction and is superior to the conventional AZ91 alloy (Mg-9 mass% Al-1 mass% Zn alloy) extruded material which is a practical Mg alloy, . That is, the alloy of the present invention is characterized in that the degree of integration of the bottom surface parallel to the extrusion direction is weak.

The alloy of the present invention has a compressive strength of 75% or more of the tensile proof strength, a small anisotropy of strength, and excellent mechanical properties.

1 is a flow chart showing an experimental procedure of the first embodiment.

2 is a graph showing the age hardening curve of each alloy of Example 1 at 160 캜.

3 is a graph showing the age hardening curve of each alloy of Example 1 at 200 ° C.

4 is a TEM micrograph of the Mg-2.3% Zn alloy of Example 1 at a peak aging step aged at 160 ° C.

5 is a TEM micrograph of the peak aging step aged at 160 ° C of the Mg-2.3% Zn-0.1% Ag alloy of Example 1. FIG.

6 is a TEM micrograph of the peak aging step aged at 160 ° C of the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 1. FIG.

FIG. 7 is a TEM micrograph of a peak aging step aged at 160.degree. C. of Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 1 and is a high magnification TEM photograph of FIG.

8 is a TEM micrograph of the peak aging step aged at 160 ° C of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 1. FIG.

9 is a TEM micrograph of a peak aging step aged at 160 ° C of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 1 and is a high magnification TEM photograph of FIG.

10 is a flow chart showing an experimental procedure of the second embodiment.

11 is an aging curve of the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 2 at 160 DEG C, and shows the relationship between the material after solution casting and the solution after hot extrusion FIG.

Fig. 12 is an aging curve of the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 2 at 200 ° C, showing that the material solution after casting and the solution- A graph showing a comparison of materials.

Fig. 13 is an aging curve of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2 at 160 deg. C and shows the solution after casting and the solution treatment after hot extrusion 1h is a graph showing a comparison of the materials.

FIG. 14 is an aging curve of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2 at 200.degree. C. and shows the result of the solution treatment after casting and the solution treatment after hot extrusion 1, 4h. Fig.

15 is an optical microscope photograph of Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy extruded at 350 ° C. of Example 2. FIG.

16 is an optical microscope photograph of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy extruded at 350 ° C. in Example 2.

17 is a TEM micrograph of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy extruded at 350 deg.

18 is a high magnification photograph of Fig.

Fig. 19 is a graph showing the results obtained by extruding the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy and Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2 at 300 ° C and 350 ° C The distribution of the Schmitt factor in the direction of the bottom slip with respect to the tensile load load direction of the sample is the same as that of the AZ91 alloy of 400 ° C and the density of the bottom surface texture is low.

20 is a graph showing a stress-strain curve obtained by a room temperature tensile test and a compression test of an extruded material of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2 at 350 캜.

From the following examples, it can be seen that the aging hardenability is improved by adding a small amount of Ag, Ca, and Zr, which are rare-earth element-free and relatively easy-to-obtain elements, in the present invention. Further, it is found that not only the alloy is hot-extruded but also a micro-crystal grain structure in which fine precipitates are dispersed is formed, and it is an Mg-based alloy having strength as well as ductility and lower strength anisotropy than conventional alloys. In addition, it can be predicted that the above-mentioned effects will be exerted in the following ranges based on the embodiments and technical common sense.

For Zn: The maximum amount of Zn in Mg is 2.4 at%.

In the composition range of 0.75 at% or more, age hardening is performed, but in order to disperse the rod-like? 'Precipitate serving as the reinforcing phase of the Mg-Zn alloy and achieve high strength, the Zn content is required as much as possible, % Or more.

In order to further disperse the rod-like β 'precipitate in a larger amount and finely disperse it is preferable to be 1.92 at% or more.

Ag: The solubility of Ag in Mg is high, and its maximum capacity is 3.82 at%.

When the solution heat treatment after casting is performed at 400 ° C, when the Ag content exceeds 0.98 at%, coarse precipitates are formed, which may deteriorate the mechanical properties.

If the content exceeds 0.2 at%, the age hardening property does not significantly change even if the addition amount is increased. Therefore, in order to inhibit the formation of the compound phase with Zn, Ca or Zr which is a constituent element, .

On the other hand, if it is 0.08 at% or more, the function of promoting nucleation of the precipitate is promoted, so that the lower limit value is preferably 0.08 at% or more.

For Ca: The maximum capacity of Ca in Mg is 0.82 at%.

When the solution heat treatment after casting is carried out at 400 ° C, when the Ca content exceeds 0.61 at%, coarse grain boundary precipitates are formed and the mechanical properties are impaired.

Therefore, the upper limit was set to 0.61 at% or less.

Further, as shown in Fig. 2 and Fig. 3 of Example 1, no change in the age hardening characteristics can be found even when the addition amount of Ca is doubled. Therefore, in order to inhibit the formation of the compound phase with Zn, Ag or Zr as the constituent element, it is preferable to set the upper limit to 0.2 at% in order to suppress the content as much as possible.

On the other hand, if it is 0.08 at% or more, the function of promoting nucleation of the precipitate is promoted, so that the lower limit value is preferably 0.08 at% or more.

For Zr: The maximum capacity of Zr in Mg is 1.04 at%.

However, when the content exceeds 0.17 at%, a saturation reaction occurs at around 650 DEG C and coarse precipitates are formed, so that the content is 0.17 at% or less.

If it is 0.08 at% or more, it is preferable that the lower limit is set to 0.08 at% or more because the fine precipitate or the Zr atom itself is expected to have a crystal particle coarsening inhibiting effect upon solution formation and hot extrusion.

As described above, the specific addition amount of each element is distributed based on the results of the following examples so as to make the average grain size of the microcrystalline grain structure as small as possible and weaken the orientation of the crystal grains.

(Example 1)

Each element was blended so as to have the alloy composition shown in Table 1, and was produced in a high-frequency melting furnace using an iron crucible under an argon atmosphere.

A Pyrex tube was sealed together with argon gas, and then subjected to a homogenization heat treatment at 340 占 폚 for 48 hours. The sample was cut, sealed in a Pyrex (registered trademark) tube together with argon gas, and then solidified at 400 ° C for 1 hour and quenched in ice water.

And aging was carried out at 160 DEG C and 200 DEG C using an oil bath. The hardness due to aging was measured by a Vickers hardness meter under the conditions of a load of 1 kg and a holding time of 15 seconds.

Tissue observation was performed using a transmission electron microscope (TEM). Details of the experimental procedure are shown in Fig.

2 and 3 show changes in hardness at aging at 160 ° C and 200 ° C. From these roads, the maximum hardness reached about 100 h in the aging at 160 ° C. and about 10 h in the 200 ° C. aging.

Aging hardenability is improved by adding Ag, Ag + Ca and Ag + Ca + Zr to the Mg-2.3Zn alloy.

The highest hardness of the alloy with Ag + Ca + Zr added to Mg-2.3Zn alloy reached 100Hv.

The aging hardness of the alloy in which the addition amount of each element was increased to 0.2 at% in the Ag + Ca addition alloy was examined.

However, even if the addition amount is increased, a clear difference in the aging characteristics can not be found.

For each of the alloys shown in Figs. 4, 5, 6 and 8, the crystal grain size was measured by the slicing method (ASTM standard E112). The average crystal grain size was about 100 탆 for the Mg-2.3Zn binary alloy shown in Fig. 4, about 50 탆 for the Mg-2.3Zn-0.1Ag alloy shown in Fig. 5, Mg-2.3Zn-0.1Ag-0.1 Ca alloy of about 50 占 퐉, and Mg-2.3Zn-0.1Ag-0.1Ca-0.17Zr alloy shown in Fig. 8 was about 10 占 퐉. It is found that the addition of Ag and the combined addition of Ag + Ca reduce the crystal grain size, and further the addition of Zr makes the crystal grain size finer.

4 to 9 show the TEM microstructure of the peak aging step in the aging at 160 ° C of the alloy, respectively.

In all the aging tissues, a rod-like precipitate extending in the c-axis direction of Mg is observed.

Ag, Ag + Ca and Ag + Ca + Zr were added to the Mg-2.3Zn alloy, and the precipitate became finer.

It is believed that the fine size of this precipitate is caused by an increase in the peak aging hardness.

As a conclusion, good aging hardenability can be obtained in an alloy containing a combination of Ag + Ca and Ag + Ca + Zr.

(Example 2)

The details of the experiment procedure are shown in Fig. The alloying elements were mixed so as to have the alloy composition shown in Table 1, and the mixture was melted in a CO ₂ + SF ₆ mixed gas atmosphere and cast. Thereafter, a homogenization heat treatment was performed at 350 DEG C for 48 hours while flowing Ar gas. Thereafter, hot extrusion was performed at 300 캜 and 350 캜. The conditions of the hot extrusion were an extrusion ratio of 20 and a ram speed of 0.1 mm / s. The extruded material was subjected to solution treatment at 400 ° C for 0.5 to 4 hours and aging treatment was performed at 160 ° C and 200 ° C to measure Vickers hardness.

The extruded sample was observed under an optical microscope and TEM.

11 and 12 show the aging curves of Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy at 160 ° C and 200 ° C.

The maximum hardness and the age hardening characteristics are almost the same when the material subjected to solution treatment after casting is compared with the material subjected to solution treatment after hot extrusion.

13 and 14 show the aging curves of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy at 160 ° C and 200 ° C.

When the material subjected to solution treatment after casting and the material subjected to solution treatment after hot extrusion were compared, there was no clear difference between the maximum hardness and the aging hardening characteristics.

FIG. 15 is an optical microscopic structure of hot extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy at 350.degree. Using this photograph, the crystal grain size was measured by the slicing method, and the average crystal grain size was 20 μm.

16 is an optical microscopic structure of hot extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy at 350 ° C. 17 and 18 show the TEM structure of the copper alloy.

In the optical microscope photograph of FIG. 16, the structure after extrusion is divided into three regions: coarse unrecrystallized particles (A), fine recrystallized particles (B) and unclear regions (C). It is considered that the unclear region (C) corresponds to the TEM photograph of FIG. 17, and it is found that it is a sub-micron fine grain recrystallized grain structure.

FIG. 18 shows a structure in which the microcrystals of the sub-micron are enlarged, and a fine rod-like precipitate of about several ten nanometers is observed along the c-axis of Mg.

From FIG. 16 and FIG. 17, the crystal grain sizes of the hot extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy were measured. In addition, since the obtained structure was not uniform, the long axis and the short axis were measured for each region, not the slice method, and the average value thereof was referred to as a grain size. For the recrystallized grains (A) and the recrystallized grains (B), the optical microscope photographs of FIG. 16 and the submicron fine crystalline regions (C) were used. As a result, the unrecrystallized particles of (A) had a size distribution of about 5 to 25 占 퐉, an average particle size of 11 占 퐉, an equiaxed recrystallized particle (B) of size distribution of about 1 to 5 占 퐉, Of the submicron fine particle region has a size distribution of about 0.1 to 1 占 퐉 and an average grain boundary of 0.75 占 퐉.

A room temperature tensile test and a room temperature compression test were performed on the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy and Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Run parallel. The tensile test specimen had a distance of 20 mm between the JIS 14B test piece and the gauge points. The compression test piece had a diameter of 9.5 mm and a height of 14.3 mm. The tensile test and the compression test were carried out under the conditions of an initial strain rate of 10 ^-3 s ^-1 .

The distribution of the Schmitt factor in the tension load direction, that is, the bottom slip direction with respect to the extrusion direction, is shown in Fig. 19 (the measurement data based on which is shown in Table 2). The Schmitt factor distribution of the present invention alloy is uniformly distributed compared to the existing AZ91 alloy (Mg-9 mass% Al-1 mass% Zn alloy) extruded material because the degree of integration of the bottom surface parallel to the extrusion direction is weak, Is 0.20 or more.

20 shows the stress-strain curve obtained by room temperature tensile test and compression test of Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy extruded at 350 ° C. Tables 3 to 7 show measurement data corresponding to the stress-strain curve of the tensile test in FIG. 20, and Tables 8 to 11 show measurement data corresponding to the stress-strain curve of the compression test in FIG.

(Initial strain rate: 10 ^-3 s ^-1 . Tensile test specimen shape: JIS 14B (distance between gauge points: 20 mm), compression specimen shape: diameter 9.5 mm, height 14.3 mm)

Table 12 shows tensile and compressive tests of Mg-2.3% Zn-0.1% Ag-0.1% Ca and Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy extruded at 300 ° C. and 350 ° C. The results are summarized.

From these results, the hot-extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca and Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloys both have high strength and high ductility It is found that the anisotropy of the proof stress is also a small material.

It is considered that the expression of excellent mechanical properties with high strength and high ductility and small anisotropy of strength is related to a decrease in the degree of integration of microcrystalline grains and bottom texture and fine precipitates in the grains.

The material of the present invention can be used in transportation equipment, for example, an automobile, a bike, an airplane, etc., which has high strength and high ductility and is expected to be lightened by substitution with the A1 member. In addition, since the mechanical properties of the material of the present invention can be obtained without requiring additional heat treatment after hot working, it is expected to be a member which is changed to a currently used wrought Mg alloy. In addition, since the sample after hot extrusion at 350 占 폚 shows an ultrafine grain structure having an average crystal grain size of about 500 mm, it is likely to be used as a super plastic component.

Claims (5)

As the Mg based alloy: At least 0.74 at% Zn, not more than 0.99 at% Zn, not more than 0.08 at% and not more than 1.98 at% Ag, not less than 0.08 at% and not more than 0.61 at% Ca, and not less than 0.08 at% and not more than 0.17 at% Zr, And an inevitable impurity. delete delete The method according to claim 1, And the crystal grain size thereof is 0.1 to 25 占 퐉. The method according to claim 1, And an average Schmitt factor of 0.2 or more.

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