KR20100021563A - Mg-based alloy - Google Patents

Abstract

Disclosed is an Mg-based alloy which is characterized by containing Ag, as an additional material other than Zn, in an amount of 1.98 at% or less. This Mg-based alloy has a practically sufficient strength, while having desirably good ductility at room temperature which cannot be achieved by conventional Mg-based alloys. In addition, this Mg-based alloy has small anisotropy in strength characteristics.

Description

Mg group alloy {Mg-BASED ALLOY}

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

About this Mg group alloy, the various things shown by the following patent documents 1-8 have been developed conventionally.

In Patent Documents 2, 3, 4, 6 and 8, in order to improve the strength, rare earth elements, scandium and lithium are added. However, since these rare earth elements are rare elements rarely obtained on the earth, the price of the alloy is high and the versatility is low.

It is a 5-membered alloy containing 0.3-3 mass% of Ca in patent document 1 and containing Al, Sr, and Mn at the same time. In such an alloy, precipitates (crystallization) are formed at grain boundaries of Mg. In patent document 2, when Zr is 0.3% or more and 1.0% or less, and Ca contains 0.2% or more and 2.0% or less. (% Is mass%).

The alloy of patent document 8 has shown the Mg alloy developed as a casting material containing 3 to 8 weight% of Zn and 0.8 to 5 weight% of Ca.

In the experimental procedure of the present invention, grain boundary precipitates are formed due to excessive Ca content, and it is found that the ductility at room temperature is lowered. Esau lacks ductility.

The alloy of patent document 7 is an alloy developed as a casting material, Specifically, Ca is zero or 0.5 weight%, Zn is 1 weight%-7 weight%, In combination of zero, Ca is zero or 0.5 weight%, Zn When it is zero, since it is said that it has 0.2% yield strength of less than 75 MPa-less than 100 MPa, when Zn is less than 75 MPa and 1 weight%-7 weight%, it shows that it is insufficient strength to be used as a structural material. In terms of ductility, it is inferred that the inventors of the present invention have low concentrations of Ca in view of the above findings obtained in the experiments of the present invention.

Patent Document 5 shows an Mg-based alloy mainly containing Mn and Zn as additives, and a solution treatment is shown to obtain high strength, but the problem of complicated steps such as requiring an additional heat treatment of two-stage aging is shown. Have

In Document 8, although an alloy in which Cu is added by 10% by weight or less is developed, the addition of Cu has a drawback of significantly lowering the corrosion resistance of the Mg alloy.

In summary, at present, most of the members in which Mg alloys are used are manufactured by casting and die casting methods. In the future, Mg alloys are expected to be applied to transportation equipment such as automobiles and aircrafts, but casting method coarsens the material structure, lowers the ductility, and has a limitation in size, so that it cannot be applied to plates, bars, pipes, etc. There is this. On the other hand, there are Mg-Al-Zn (AZ-based alloys) or Mg-Zn-Zr (ZK-based alloys) in the practical Mg alloy for the whole body, but the strength of the whole body Mg alloy is insufficient, and the texture formed during hot working Because the strength used in the strength design is significantly different between the tensile load and the compressive load due to the influence of (the compressive strength is about 50% of the tensile strength of the commercial AZ31 rolled material). It is difficult. In order to achieve high strength of the Mg alloy, a method of adding a rare earth element and adding a large amount of alloying elements has been taken so far.

However, since rare earth elements are expensive, their versatility is low, and the addition of a large amount of alloying elements is accompanied by the formation of coarse compound phases, whereby high strength is obtained, but ductility is impaired. Therefore, there is a demand for the development of a new whole body Mg alloy which is rare earth element free and excellent in strength and ductility by adding an inexpensive alloy element.

Patent Document 1: Japanese Patent Publication No. 2007-70688

Patent Document 2: Japanese Patent Publication No. 2006-28548

Patent Document 3: Japanese Patent Publication No. 2006-16658

Patent Document 4: Japanese Patent Publication No. 2005-113235

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

Patent Document 6: Japanese Patent Publication No. 2003-226929

Patent Document 7: Japanese Patent Publication No. 2002-212662

Patent Document 8: Japanese Patent Application Laid-Open No. 6-25791

In view of such a situation, an object of the present invention is to provide an Mg-based alloy having not only sufficient strength in practical use but also ductility at room temperature, which cannot be conventionally desired, and small anisotropy in strength characteristics.

The Mg group alloy of the invention 1 is characterized by containing 1.98 at% or less of Ag as an additive other than Zn.

Inventive 2 is an Mg group alloy according to Inventive 1, characterized in that Ca is further contained 0.61 at% or less as an additive material other than Zn and Ag.

Inventive 3 is the Mg group alloy according to Inventive 2, wherein Zr is further contained 0.17 at% or less as an additive material other than Zn, Ag, and Ca.

Inventive 4 is the Mg group alloy according to any one of Inventions 1 to 3, wherein the grain size is 0.1 µm to 25 µm.

(Effects of the Invention)

According to the inventions 1 to 4, by adding only an inexpensive alloying element, it is possible to provide an Mg-based alloy that is both superior in strength and ductility unprecedented in the past and has low anisotropy in strength.

Moreover, since the alloy element which damages corrosion resistance, such as Cu, was not used, the outstanding durability can also be expected.

The alloy of the present invention has an average Schmitt factor of 0.2 or more in the bottom sliding direction with respect to the load direction, and compared with the conventional AZ91 alloy (Mg-9 mass% Al-1 mass% Zn alloy) extruded material, which is a practical Mg alloy. Has the same distribution as That is, the alloy of the present invention is characterized by a low degree of integration of the bottom surface parallel to the extrusion direction.

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

1 is a flow chart showing the experimental procedure of Example 1. FIG.

2 is a graph showing an aging hardening curve at 160 ° C. of each alloy of Example 1. FIG.

3 is a graph showing an aging hardening curve at 200 ° C. of each alloy of Example 1. FIG.

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

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

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

7 is a TEM structure 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, and is a high magnification TEM image of FIG. 6.

8 is a TEM structure photograph of a 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 structure 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, and is a high magnification TEM image of FIG. 8.

10 is a flow chart showing the experimental procedure of Example 2. FIG.

Fig. 11 is an aging curve at 160 ° C. of the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 2, showing that the material subjected to solution treatment after casting and the solution solution subjected to solution treatment after hot extrusion was 1h. A graph showing a comparison.

12 is an aging curve at 200 ° C. of the Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy of Example 2, wherein the solution subjected to solution treatment after casting and the solution treatment after hot extrusion were 0.5 and 1 h. It is a graph showing a comparison of materials.

FIG. 13 is an aging curve at 160 ° C. of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2, and the solution subjected to solution treatment after casting and the solution treatment after hot extrusion. It is a graph which shows the comparison of 1h material.

14 is an aging curve at 200 ° C. of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2, and the solution subjected to solution treatment after casting and the solution treatment after hot extrusion. It is a graph which shows the comparison of 1, 4h material.

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

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

17 is a TEM structure photograph of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2 extruded at 350 ° C.

18 is a high magnification photograph of FIG. 17.

19 is an extrusion process of 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 ℃ and 350 ℃ This is a distribution of Schmitt factor in the bottom sliding direction with respect to the tensile load direction of the sample, the distribution is the same as that of the existing AZ91 alloy 400 ℃ extruded material, 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 a 350 ° C. extrusion material of the Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy of Example 2. FIG.

From the following examples, it can be seen that in the present invention, the age hardenability is improved by adding trace amounts of Ag, Ca, and Zr which are rare earth element-free and relatively easy to obtain. Further, it can be seen that not only hot extrusion of the alloy but also microcrystalline grain structure in which fine precipitates are dispersed, is excellent in strength and ductility, and is an Mg group alloy having lower anisotropy in strength than a conventional alloy. In addition, it can be expected from the examples and the technical common sense to exhibit the above effects in the following ranges.

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

In the composition range of 0.75 at% or more, the aging hardening is performed. However, in order to disperse the β 'precipitate that acts as a reinforcing phase of the Mg-Zn alloy, the Zn content is required as much as possible, so as to increase the strength. % Or more is preferable.

In order to disperse | distribute this rod-shaped (beta) 'precipitate further in large quantity and finely, it is preferable to set it as 1.92 at% or more.

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

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

If it exceeds 0.2at%, the aging hardenability does not change so much even if the added amount is increased. Therefore, in order to prevent the formation of a compound phase with constituent elements Zn or Ca or Zr, the upper limit is 0.2at% in the sense of suppressing the content as much as possible. It is preferable to set it as.

Moreover, if it is 0.08 at% or more, since it functions to accelerate nucleation of a precipitate, it is preferable to make a lower limit 0.08 at% or more.

For Ca: The maximum high dose of Ca to Mg is 0.82 at%.

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

Therefore, the upper limit was made into 0.61 at% or less.

In addition, as shown in FIG. 2, FIG. 3 of Example 1, even if the addition amount of Ca doubles, the change in age hardening characteristic is not found. Therefore, in order to prevent the formation of a compound phase with Zn or Ag or Zr as constituent elements, the upper limit is preferably 0.2at% in the sense of suppressing the content as much as possible.

Moreover, if it is 0.08 at% or more, since it functions to accelerate nucleation of a precipitate, it is preferable to make a lower limit 0.08 at% or more.

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

However, if it exceeds 0.17at%, the crystallization reaction exists in the vicinity of 650 degreeC, and coarse precipitate forms, and it was made into 0.17at% or less.

If it is 0.08 at% or more, it is preferable to make a minimum into 0.08 at% or more because a fine precipitate or Zr atom itself is expected to suppress the grain coarsening effect in solution formation and hot extrusion.

As mentioned above, the specific addition amount of each element is distribute | distributed so that the average particle diameter of a microcrystal grain structure may be made as small as possible to weaken the orientation of a crystal grain based on the result of the following Example.

(Example 1)

Each element was mix | blended so that it might become the alloy composition shown in Table 1, and it manufactured in the high frequency melting furnace using the iron crucible in argon atmosphere.

After sealing together with argon gas in a Pyrex (trademark) tube, the homogenization heat processing was performed for 48 h at 340 degreeC. The sample was cut | disconnected, and it enclosed in the Pyrex (trademark) tube with argon gas, and then solidified at 400 degreeC for 1 h, and quenched in ice-water.

It aged at the temperature of 160 degreeC and 200 degreeC using the oil bath. The hardness by aging was measured on the conditions of 1 kg of load and 15 second of holding time with the Vickers hardness tester.

Tissue observation was performed using a transmission electron microscope (TEM). The detail of the experiment procedure is shown in FIG.

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

Aging hardenability becomes favorable by adding Ag, Ag + Ca, Ag + Ca + Zr to Mg-2.3Zn alloy.

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

In Ag + Ca addition alloy, the aging hardness of the alloy which increased each element addition amount to 0.2at% was investigated.

However, no significant difference in aging characteristics can be found by increasing the amount added.

About each alloy shown in FIG. 4, FIG. 5, FIG. 6, and FIG. 8, the crystal grain size was measured by the cutting method (ASTM standard E112). The average grain size is about 100 μm with the Mg-2.3Zn binary alloy shown in FIG. 4, about 50 μm with the Mg-2.3Zn-0.1Ag alloy shown in FIG. 5, and Mg-2.3Zn-0.1Ag-0.1 shown in FIG. 6. It was about 50 micrometers with Ca alloy and about 10 micrometers with Mg-2.3Zn-0.1Ag-0.1Ca-0.17Zr alloy shown in FIG. It is found that the grain size decreases due to the addition of Ag and the complex addition of Ag + Ca, and the grain size becomes further finer by the addition of Zr.

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

In all the aging structures, rod-shaped precipitates extending in the c-axis direction of Mg are observed.

By adding Ag, Ag + Ca, Ag + Ca + Zr to the Mg-2.3Zn alloy, the precipitates became fine.

It is thought that the refinement of this precipitate is attributable to an increase in peak aging hardness.

In conclusion, in the alloy in which Ag + Ca and Ag + Ca + Zr are added in combination, good age hardenability is obtained.

(Example 2)

The detail of an experiment procedure is shown in FIG. The alloy compositions shown in Table 1 were mixed so that the alloy elements and casting was dissolved under CO ₂ + SF ₆ gas mixture atmosphere. Then, 48 h homogenization heat processing was equipped at 350 degreeC, flowing Ar gas. Thereafter, hot extrusion was performed at 300 ° C and 350 ° C. The conditions of hot extrusion were extrusion ratio 20 and ram speed 0.1mm / s. The material after extrusion was subjected to a solution treatment of 0.5 to 4 h at 400 ° C., aged at a temperature of 160 ° C. and 200 ° C., and Vickers hardness measurement was performed.

Moreover, the structure observation by the optical microscope and TEM was performed about the sample after extrusion.

11 and 12 show the aging curves of the 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 were almost the same when the material subjected to the solution treatment after casting and the solution treatment after the hot extrusion were compared.

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

There was no clear difference in the maximum hardness and the age hardening properties when the material subjected to the solution treatment after casting was compared with the material subjected to the solution treatment after hot extrusion.

15 is an optical microscope structure of hot extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca alloy at 350 ° C. When the crystal grain size was measured by the sectioning method using this photograph, the average grain size was 20 µm.

16 is an optical microscope 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 micrograph of FIG. 16, the structure after extrusion is divided into three of coarse uncrystallized particles (A), finely recrystallized particles (B) and indistinct regions (C). It is thought that the opaque area | region C corresponds to the TEM photograph of FIG. 17, and it turns out that it is a submicron microparticle recrystallized grain structure.

Fig. 18 is a structure in which the inside of the microcrystal of the submicron is enlarged, and fine rod-shaped precipitates of about several tens of nm inserted along the c-axis of Mg are observed.

16 and 17, the grain size of the hot-extruded Mg-2.3% Zn-0.1% Ag-0.1% Ca-0.17% Zr alloy was measured. In addition, since the obtained structure was not uniform, the long axis and short axis were measured about the crystal | crystallization of each area | region rather than a slice method, and the average value was called the crystal grain size. In addition, about the recrystallized particle (B) which is equiaxed with the unrecrystallized particle (A), the TEM photograph of FIG. 17 was used for the optical microscope photograph of FIG. 16, and the microcrystal region C of submicron. As a result, the unrecrystallized particles of (A) had an average particle size of 11 μm with a size distribution of about 5 to 25 μm, and the equiaxed recrystallized particles of (B) had an average particle size of 2.8 μm with a size distribution of about 1 to 5 μm. The submicron microparticle region of is found to have an average grain boundary of 0.75 µm with a size distribution of about 0.1 to 1 µm.

Room temperature tensile test and room temperature compression test were carried out in the extrusion direction for 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 with excellent aging hardenability. Run in parallel. The tensile test piece was a JIS 14B test piece and a distance between the gauge marks 20 mm. Compression test pieces were 9.5 mm in diameter and 14.3 mm in height. Tensile tests and compression tests were conducted under conditions of an initial strain rate of 10 ⁻³ s ⁻¹ .

The distribution of the Schmitt factor of the tensile load load direction, ie, the bottom slip direction with respect to the extrusion direction, is shown in Fig. 19 (the measurement data based on the table 2 is shown). The Schmidt factor distribution of the alloy of the present invention is uniformly distributed compared with 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, and the average value thereof is uniform. Becomes more than 0.20.

20 shows the stress-strain curves 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 curves of the tensile test in FIG. 20, and Tables 8 to 11 show measurement data corresponding to the stress-strain curves of the compression test in FIG. 20.

(Initial strain rate: 10 ^-3 s ^-1 . Tensile test piece shape: JIS14B (20mm between marks), compression test piece shape: diameter 9.5mm, height 14.3mm)

Table 12 shows tensile and compression 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 alloys 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 combine high strength and ductility, and It turns out that the anisotropy of the strength is also a small material.

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

The material of the present invention has high strength and high ductility, and can be used in transportation equipment such as automobiles, bikes, airplanes, and the like, which is expected to be lightened by replacement with the A1 member. In addition, since the mechanical properties of the material of the present invention are obtained without the need for additional heat treatment after hot working, it is also expected to be used as a member to be changed to the Mg alloy for the whole body currently used. In addition, in the sample after hot extrusion at 350 ° C., since the average grain size shows an ultrafine grain structure of about 500 mm, it may be applied as a superplastic material.

Claims (4)

As an Mg-based alloy based on Mg and Zn as an additive: An Mg-based alloy comprising Ag as 1.98 at% or less as an additive material other than Zn. The method of claim 1, Mg-based alloy, characterized in that Ca is further contained 0.61 at% or less as an additive material other than Zn and Ag. The method of claim 2, Mg-based alloy, characterized in that Zr is further contained 0.17 at% or less as an additive material other than Zn, Ag, and Ca. The method according to any one of claims 1 to 3, The crystal grain size is 0.1 micrometer-25 micrometers, Mg base alloy characterized by the above-mentioned.

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