JP2000017352A - Magnesium base composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the mechanical properties of the material by incorporating spherical and/or ellipsoidal Mg2Si particles having specified average particle size dispersed into a matrix composed of Mg or an Mg alloy. SOLUTION: This composite material is produced preferably by producing a performed body having Si particles of 3 to 100 μm average particle size blended so as to be contained by 1 to 15 wt.% therein and a carrier and next press- impregnating the preformed body with the molten metal of Mg or an Mg alloy. Moreover, the preheating temp. of the preformed body is controlled to 400 to 800 deg.C. In this way, only by the addition of a small amt. of the Si particles and casting at a low temp., a composite material having a high volume ratio in which fine spherical Mg Si particles are relatively uniformly dispersed can easily be obtd. This composite material is the one in which the spherical or ellipsoidal Mg2Si particles are uniformly dispersed in a volume ratio of 3 to 50%, particularly excellent in high temp. strength, rigidity and wear resistance and exhibiting low thermal expansibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnesium-based composite material.

[0002]

_2. Description of the Related Art Heretofore, it has been known that a magnesium alloy or a magnesium-based composite material in which a high volume fraction of Mg ₂ Si particles are finely and uniformly dispersed exhibits excellent mechanical properties (M. MABUCHI, KUBOTA, K.HIGASHI: J.Mater.Sci.31 (19
96) 1529-1535, JP-A-06-81068, etc.).

In order to obtain a magnesium alloy having a high volume fraction of Mg ₂ Si particles dispersed therein by casting, a magnesium alloy having a large amount of Si must be cast. When the addition amount of Si in the magnesium alloy is increased, the melting point of the magnesium alloy is significantly increased, and thus handling of the molten metal becomes extremely dangerous (explosion, combustion). In addition, since the fluidity of the molten metal deteriorates, it is difficult to produce a sound casting. Therefore, Japanese Patent Application Laid-Open No. 50-115617 proposes to produce a casting by subjecting a magnesium alloy having a high Si content to pressure casting at a low temperature. Japanese Patent Application Laid-Open No. 06-81068 discloses that a magnesium alloy having a high Si content is injection-molded in a semi-molten state. Also, in order to disperse the Mg ₂ Si particles finely and uniformly, see EESCHMID: Z. Met.
allkde.81 (1990) 11, Japanese Patent Application Laid-Open No. 06-81068,
It has been shown that the addition of (P) is effective.

On the other hand, JP-A-55-50447 discloses that a magnesium alloy is impregnated in a silicon carbide whisker, a silica-based, alumina-based or silica-alumina-based fiber compact by a high-pressure casting method, and magnesium is contained in a matrix. It has been proposed to react and deposit silicon compounds and magnesium-aluminum compounds.

[0005]

In the above method, the characteristics of the magnesium-based composite material cannot be sufficiently improved by dispersing Mg ₂ Si for the following reasons. When magnesium alloy of high Si is cast, high-pressure casting at low temperature or injection molding in semi-molten state, Si is crystallized as eutectic Mg ₂ Si or primary Mg ₂ Si I do.
The eutectic Mg ₂ Si is layered, while the primary crystal Mg ₂ Si is a coarse mass, both of which are crystallized as a compound having an angular shape. In addition, crystallized Mg ₂ Si tends to be coarse. The angular and coarse Mg ₂ Si is easily broken, and the properties of the magnesium alloy and the magnesium-based composite material cannot be sufficiently improved.

The miniaturization of Mg ₂ Si by adding P
The limit is an average particle size of about 10 to 15 μm. When silicon carbide whisker, silica-based, alumina-based or silica-alumina-based fiber and magnesium alloy are reacted in-situ to precipitate magnesium-silicon compound and magnesium-aluminum compound in the matrix,
The reaction product is formed relatively coarsely around the fiber that has contributed to the reaction. The intermetallic compound generated around the fiber is easily broken by a notch effect at a contact portion between the fiber and the intermetallic compound, and does not contribute much to the reinforcing effect. In addition, since the properties of the fibers are degraded by the reaction, there is a problem that the reinforcing effect of the fibers is also reduced.

[0007] The present invention has been made in view of the circumstances described above, under normal casting conditions handling of molten magnesium alloy is able to sufficiently secure and, casting alone, fine, spherical, yet a high volume fraction Mg ₂ An object of the present invention is to provide a magnesium-based composite material having excellent mechanical properties by controlling the distribution of Mg ₂ Si by uniformly dispersing Si particles in a matrix.

[0008]

According to the present invention, there is provided a magnesium-based composite material comprising: a matrix made of magnesium or a magnesium alloy; and a spherical and / or elliptical Mg dispersed in the matrix and having an average particle size of less than 10 μm. ₂ Si particles.

The magnesium-based composite material of the present invention has a spherical and / or elliptical Mg having an average particle size of less than 10 μm.
₂ Si particles are contained in the matrix. This Mg ₂ S
When forming the magnesium-based composite material, the i-particles are in-situ reacted with the Si particles in the preform and the molten magnesium and / or magnesium alloy, and the fine particles of Mg ₂ Si particles are present at the place where the Si particles were present. It is formed and dispersed in a matrix. Therefore, Mg ₂ Si
The particles are present in the matrix with a spherical and / or elliptical shape.

[0010] Mg distributed in the matrix_TwoSi particles
By making the average particle size of the fine particles less than 10 μm,
Conventional Mg_TwoToughness and added strength compared to composite materials containing Si particles
The workability and strength are improved. In addition, Mg_TwoSi
The particles are formed by an in-situ reaction with the matrix melt
Therefore, it becomes spherical and / or elliptical spherical,
Formed in dendritic form_TwoMechanically Si
Has sharp edges and sharp edges as if crushed
(The gray-like particles in FIG. _TwoSi,
Particles indicated by arrows are oval), stress due to notch effect, etc.
No concentration occurs. Generally, the particles of the reinforcement are shown in FIG.
As shown, the finer the average particle size, the more the toughness of the composite material
It is known to improve. Therefore, the present invention
In the mixture, Mg_TwoThe average particle size of the Si particles is less than 10 μm.
This improves the toughness and workability compared to conventional materials.
In addition, improvement in strength and strength can be expected. Also Matric
Rod-shaped eutectic Mg_TwoSi and massive primary Mg_TwoSi is the minute
The stress collection due to the notch effect etc.
The inside hardly occurs and the mechanical properties are improved.

Further, it is possible to reduce the size of Mg ₂ Si particles which cannot be achieved by the conventional treatment such as addition of P.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION It is desirable that the Mg ₂ Si particles dispersed in the matrix of the magnesium-based composite material of the present invention be present alone in the matrix and be dispersed relatively uniformly. The magnesium-based composite material of the present invention prepares a preform having Si particles having an average particle diameter of 3 to 100 μm and a carrier mixed so as to be contained in the magnesium-based composite material in an amount of 1 to 15% by weight. It is preferable to manufacture the preformed body by a step and a step of impregnating the preformed body with magnesium or a magnesium alloy melt under pressure.

The carrier has a matrix strengthening effect of magnesium, a magnesium alloy, or an alloying element of the magnesium alloy such as aluminum, zinc, zirconium or the like, or a composite reinforcing effect with Mg ₂ Si having excellent properties. It is preferable to use fibers or particles of metal or ceramics. The amount of the Si particles added to the preform is preferably added to the preform so as to be contained in the magnesium-based composite material by 1 to 15% by weight. A more desirable addition amount is 2 to 10%.

The average particle diameter of the Si particles to be added to the preformed body can be about 3 to 100 μm, preferably in the range of 10 to 75 μm. The distribution of the Si particles in the preform is determined by a specific Mg ₂
In order to obtain a distribution of Si particles, the distribution is preferably uniform or unevenly distributed. The temperature of the molten metal at the time of impregnating the molten magnesium or magnesium alloy into the preform by pressure is preferably 800 ° C. or less.

The preheating temperature of the preform is 400 to 80.
A range of 0 ° C. is preferred. The dispersed state of the Mg ₂ Si particles of the present invention is shown by a photograph of the structure (gray-like particles in FIG. 6A).
As shown in the figure, the individual Mg ₂ Si exists relatively solely in the matrix and is relatively uniformly distributed. Thereby, improvement in strength and toughness can be expected. In the casting of a high Si content Mg alloy by the conventional method, Mg ₂ Si
In the case of the ordinary gravity casting of (B), it becomes a coarse lump, and in the case of high pressure casting to a preform, a lump of Mg ₂ Si is formed around and around the fiber as shown in FIG. 6 (C). It is presumed that this facilitates stress concentration and propagation of fracture at the contact portion.

[0016] and Mg ₂ Si particles dispersed magnesium-based composite material of the carrier present invention formed using the alumina short fibers or aluminum borate whiskers, according to the conventional method Mg ₂ Si
FIG. 5 compares the mechanical properties of the dispersed magnesium-based composite material. FIG. 5 shows that the present invention has improved tensile strength compared to the conventional method. The magnesium-based composite material of the present invention can be manufactured by the method described below.

That is, when a magnesium alloy-based composite material is used, the average particle size of 1 to 15% by weight is 3 to 100 μm.
It can be produced by a first step of preparing a preformed body composed of m Si particles and a carrier, and a second step of impregnating the preformed body with a magnesium alloy melt under pressure to form a composite material. The addition amount of the Si particles is 1 to 15% by weight.
%, Desirably 2 to 10%. When the addition amount of the Si particles is small, the amount of Mg ₂ Si generated in the matrix is small, and it is not possible to expect a sufficient improvement in the properties of the composite material. On the other hand, S
When the addition amount of i-particles is large, about 3
The generation times of the Mg ₂ Si particles, (relationship Si content and tensile strength) 1, (the relationship between Si content and modulus) 2, 3
As shown in (Relationship between Si content and coefficient of thermal expansion), the toughness and the like of the composite material are remarkably reduced, and sufficient strength cannot be obtained. In order to obtain appropriate strength and toughness, the amount of generated Mg ₂ Si is desirably in the range of 3 to 50% by volume.

The particle size of the Si particles to be added is 3 to 100.
It is about μm, preferably 10 to 75 μm. If the average particle size of the Si particles is small, the Si particles are not easily carried in the preformed body, and are undesirably collected at the lower part of the formed body when the preformed body is manufactured. Therefore, it is difficult to uniformly disperse the Si particles in the compact. Also,
When the average particle size of Si particles is small, in-situ
Without reacting, it dissolves in the molten Mg and is crystallized in the matrix as eutectic or primary Mg ₂ Si. The Mg ₂ Si crystallized as the eutectic or primary crystal is in a layered or lump form, and does not contribute to improving the strength of the composite material, which is not preferable. On the other hand, if the average particle size of the Si particles is large, the reaction of the Si particles is not completed during casting, and unreacted Si
_{It is} not preferable because it remains in a state surrounded by 2Si. The presence of unreacted Si is undesirable because the interface between Si and Mg ₂ Si surrounding the Si is apt to be broken, and the strength of the composite material is significantly reduced. FIG. 4 shows a region where unreacted Si remains in the relationship between the preheating temperature of the compact and the Si particle diameter. Accordingly, a preferable range of the particle diameter of Si is determined from the requirement of the molten metal temperature of the matrix.

The carrier may be made of a metal which does not cause a reduction in strength due to a reaction or the like due to a composite with a magnesium alloy, or a ceramic fiber or particle.
Magnesium, magnesium alloy, or alloy elements of magnesium alloys that form the matrix, Al, Z
It is desirable to use n, Zr or the like, or fibers or particles of metal or ceramics having excellent properties and exhibiting a composite reinforcing effect with Mg ₂ Si.

The preform is made of Si particles or Si particles.
It is desirable to use a carrier for adjusting the amount of particles and Si particles, a porous body made of a binder or the like, or a case or a mold filled with Si particles, a carrier, or the like. The distribution of Si particles dispersed in the preform is desirably uniform or unevenly distributed in order to obtain a specific Mg ₂ Si particle distribution in the composite material.

The preformed body may be formed by using only a binder or the like without using a carrier as long as the amount of Si particles can be controlled. The amount of the support is preferably small since the porosity of the molded body increases if handling in the subsequent step is possible. As a second step, the preformed body is impregnated with a molten magnesium alloy under pressure. At this time, fine and spherical Mg ₂ Si is generated by the in-situ reaction.

Since the handling of molten Mg at high temperatures involves a high risk of explosion and combustion, it is desirable that the temperature of the molten metal be 800 ° C. or lower, which allows relatively safe handling.
For this reason, it is necessary to preheat the molded body and use it for casting.
It is desirable that the preform be preheated to 400 to 800 ° C. If the preheat of the preformed body is lower than this, impregnation of the molten metal into the preformed body becomes difficult, deformation and cracking of the formed body occur, and the reaction between Si and Mg does not sufficiently proceed. It is not preferable because Si in the reaction remains in the composite material. If the preheating temperature of the preform is too high, M
The pouring of the molten metal is dangerous, and the Mg ₂ S
This is not preferable because partial coarsening of i occurs. By setting the preheating temperature of the preform in the range of 400 to 800 ° C., the impregnation of the magnesium alloy melt becomes smooth,
Reaction also occurs easily.

By adjusting the size of the Si particles and the preheating temperature of the preform, even if the temperature of pouring the magnesium alloy is set to 800 ° C. or lower, a sound M without unreacted Si can be obtained.
It is possible to produce a magnesium-based composite material in which g ₂ Si particles are dispersed. That is, a high volume ratio Mg ₂ Si particle-dispersed Mg-based composite material in which fine spherical Mg ₂ Si particles are dispersed relatively uniformly can be easily obtained only by adding a small amount of Si particles and casting at a low temperature.

Since Mg ₂ Si produced by the reaction is distributed mainly at the site where the original Si particles existed, if the distribution of the Si particles is controlled at the time of forming the compact, the distribution state of the Mg ₂ Si particles is controlled. be able to. Therefore, Mg ₂ Si
When it is desired to perform partial strengthening by using the method described above, a preformed body in which a large amount of Si particles are distributed in necessary portions may be prepared. By the above manufacturing method, spherical or oval spherical fine Mg ₂ Si particles having a diameter of about 10 μm or less existed in the matrix relatively independently, and were relatively uniformly distributed.
Mg ₂ Si volume ratio 3 to 50% of the magnesium-based composite material of the particles.

According to the present invention, a Mg ₂ Si particle-dispersed magnesium-based composite material having excellent mechanical properties and toughness can be obtained. In particular, it is a low thermal expansion magnesium alloy composite material having excellent high-temperature strength, rigidity, and wear resistance. This is because the obtained magnesium alloy composite material has a fine and spherical Mg ₂ S
This is because i-particles are relatively uniformly dispersed in the matrix and have a high volume ratio. In addition, Si
By unevenly distributing the particles, the Mg ₂ Si particles can also be unevenly distributed in the matrix.

[0026]

The present invention will be specifically described below with reference to examples. (Example 1) The magnesium-based composite material of the present invention was manufactured by the following manufacturing method. First, as a first step, S
A porous preform having i particles dispersed therein was prepared. In this example, alumina short fibers were used as a carrier for Si particles. When a composite material is used, the volume fraction of the alumina short fiber is 15% and the weight percentage of Si is 5% (other 0%).
%, 1%, 2%, 3%, and 10% of each sample) The alumina short fibers and the Si particles were weighed and then stirred and mixed in water. At this time, a small amount of a surfactant was added so that the dispersion state of the alumina short fibers and the Si particles was improved. Further, after adding a small amount of alumina binder, they were suction-filtered and pressed to be shaped so that the volume fraction of the alumina short fiber became 15%. After drying the molded body at room temperature, it was baked at 1000 ° C. for 2 hours to obtain a preliminary molded body (each of the above samples).

In the second step of impregnating the molten magnesium with pressure, the preformed body is preheated to 700 ° C. in the atmosphere, and then heated at 250 ° C.
The molten magnesium alloy was poured into a mold preheated to 750 ° C. and poured at 750 ° C. where the molten magnesium alloy could be safely handled. Then 90
Pressure was applied at 0 kg / cm ² for 60 seconds to form a composite. After compounding, it was removed from the mold and air-cooled. As a result, a sound magnesium-based composite material having no unreacted Si was produced. That is, only the addition of a small amount of Si particles and the casting conditions at a low temperature disperse the fine spherical Mg ₂ Si particles relatively uniformly and at a high volume ratio as shown in the photograph of the structure in FIG. The obtained magnesium-based composite material was obtained.

FIG. 1 is a graph showing the relationship between the Si content and the tensile strength of the magnesium-based composite material and the pure magnesium material obtained by the above method. As shown by the black marks in FIG. 1, pure magnesium and magnesium alloy (AM50
Alloy) Samples with 3%, 5% and 10% co-Si addition
This shows that the tensile strength is improved at both room temperature and 250 ° C. as compared with those not added.

FIG. 2 is a graph showing the relationship between the amount of Si, the elastic modulus, and the hardness of the magnesium-based composite material obtained by the above method. As shown in FIG. 2, the elastic modulus and the hardness increase as the amount of Si added increases. FIG. 3 is a graph showing the relationship between the Si amount and the coefficient of thermal expansion of the magnesium-based composite material obtained by the above method. The coefficient of thermal expansion decreases as the amount of Si added increases.

FIG. 4 shows the relationship between the Si particle diameter and the preheating temperature of the compact, which affects the reactivity of Si. The mark ○ indicates that there was no unreacted Si in the manufactured composite, and the mark × indicates unreacted Si.
Is present. In the present embodiment, a fiber molded body according to the above-described method was prepared as a preformed body. However, as long as the porous body in which the molten metal can be impregnated and Si particles are dispersed, its manufacturing method, structure, and the like are arbitrary. Good.

In the present embodiment, the volume fraction of the alumina short fiber was set to 15% in view of the hybrid composite reinforcement of the Mg ₂ Si particles in consideration of the reinforcing effect of the alumina short fiber on the magnesium-based composite material. FIG. 6A shows a photograph of the composite material structure of this example. This is obtained by performing in-situ reaction between Si particles and molten magnesium alloy under relatively low-temperature casting conditions and high-pressure casting for a short time. In addition, since this method is a liquid phase reaction by high-pressure casting, defects due to volume expansion and shrinkage due to the reaction hardly occur. In addition, since cooling is relatively fast, coarsening of the generated Mg ₂ Si particles hardly occurs.

As the reinforcing particles are finer as shown in FIG. 7, the toughness of the composite material is improved. Therefore, the fine Mg ₂ Si particles as in the present invention can be expected to have improved strength. Therefore, the improvement of the mechanical properties of the present composite material cannot be achieved by the conventional method such as addition of P. By setting the average particle size of the Mg ₂ Si particles to 10 μm or less, improvement in toughness, workability, and strength can be expected as compared with conventional materials. In addition, the Mg ₂ Si particles are spherical or elliptical, are not sharp and do not have sharp edges, and thus are compared to rod-like eutectic Mg ₂ Si and massive primary Mg ₂ Si (FIG. 6).
(B) and (C)), stress concentration due to a notch effect or the like is unlikely to occur. This is also a major factor in improving the toughness and strength of the composite. Furthermore, the eutectic or primary Mg ₂ Si according to the conventional method is crystallized around the fiber and surrounding the fiber, which facilitates stress concentration and propagation of fracture at the contact portion.

In the present composite material, M having an average particle size of 2 to 3 μm
g ₂ Si existed relatively solely in the matrix and was relatively uniformly distributed (FIG. 6 (A)). Thereby, improvement in the strength and toughness of the composite material can be expected. And Mg ₂ Si dispersed magnesium-based composite material obtained by the present method, the comparison of the mechanical properties of Mg ₂ Si dispersed magnesium-based composite material according to the conventional method as a comparative example shown (Figure 5).

The magnesium alloy composite of the comparative example was prepared by adding Mg-3% Si to an alumina short fiber preform (Vf15%).
The alloy was cast under high pressure under the same casting conditions as in the present method. The structure is shown in FIG. In the comparative example, massive M
g ₂ Si is crystallized so as to surround the fibers. The composite material obtained in this example is an Mg ₂ Si dispersed magnesium-based composite material having better mechanical properties and toughness than the conventional composite material of the comparative example shown in FIG. In particular, it was a low thermal expansion magnesium alloy composite material having excellent high-temperature strength, rigidity, and wear resistance. This is because the obtained magnesium alloy composite material has fine and spherical Mg ₂ Si particles dispersed relatively uniformly and has a high volume ratio.

Example 2 An aluminum borate whisker was used as a carrier. Since the diameter of aluminum borate whisker is about 1 μm and the length is about 10 μm, it is fine.
It was possible to carry finer Si particles. Thus, a molded article was produced in the same manner as in Example 1 using Si particles having an average particle diameter of 10 μm, and a photograph of the structure of the composite material obtained by pressure casting is shown in FIG.

In the obtained composite material, Mg ₂ Si was dispersed more uniformly than in the case of Example 1 in FIG. 6A, and excellent mechanical properties (FIG. 5) were exhibited. (Example 3) A mixed powder obtained by mixing Mg powder and Al alloy powder at a ratio of 4: 1 was used as a carrier. To this, 3 wt% of Si particles were added, mixed, and then compacted to form a porosity of 40%.
% Of a green compact was produced. In order to prevent surface oxidation and nitridation of the Mg and Al alloy powder, the powder was preheated at 500 ° C. in an argon atmosphere. Mold temperature 300 ° C, pouring temperature 8
The composite was obtained by pressure casting at 00 ° C.

In the obtained composite material, Mg ₂ Si having an average particle size of 3 to 5 μm was dispersed in the magnesium alloy around the magnesium powder, as shown in the structure photograph of FIG. Also,
An Al-Mg compound was generated around the Al alloy powder. Since this composite material does not contain ceramics, it is a high-performance magnesium alloy-based composite material that can be easily processed later.

[0038]

According to the magnesium-based composite material of the present invention, fine, spherical and / or elliptical Mg ₂ Si particles having an average particle diameter of less than 10 μm are dispersed in a matrix.
The Mg ₂ Si particles further improved the toughness and strength of the material. In particular, it is a low thermal expansion magnesium alloy composite material having excellent high-temperature strength, rigidity, and wear resistance. This is because, in the obtained magnesium alloy composite material, fine spherical and / or elliptical Mg ₂ Si particles are relatively uniformly dispersed and have a high volume ratio.

The Si particles are supported on a carrier and
Since it is obtained by impregnating a magnesium and / or magnesium alloy melt at a temperature of not more than ° C. under pressure, production is easy.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the amount of Si on the tensile strength of a composite material of an example.

FIG. 2 is a graph showing the influence of the amount of Si on the elastic modulus and hardness of the composite material of the example.

FIG. 3 is a graph showing the influence of the amount of Si on the thermal expansion coefficient of the composite material of the example.

FIG. 4 is a graph showing the relationship between the preheating temperature of the compact and the Si particle diameter which affect the reactivity of Si of the composite material of the example.

FIG. 5 is a bar graph comparing the tensile strengths of the composite materials of Examples and Comparative Examples.

FIG. 6 (A) is a photograph showing Mg ₂ Si particle dispersion in the structure of the composite material of this example. (B) is a photograph of a structure showing a dispersion of Mg ₂ Si when a conventional high Si-containing Mg alloy is gravity cast. (C) Mg obtained by casting a high Si content Mg alloy on a conventional alumina fiber preform at a high pressure
FIG. 4 is a micrograph showing the structure of ₂ Si particles dispersed therein.

FIG. 7 is a graph showing a relationship between a reinforcing material particle diameter and a tensile strength in a composite material.

FIG. 8 is a photograph showing the structure of a composite material when aluminum borate whiskers are used as a carrier.

FIG. 9 is a photograph of a structure of a composite material when a magnesium powder is used as a carrier.

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[Procedure amendment]

[Submission date] August 18, 1998 (1998.8.1)
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 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshihiro Shimizu 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi F-1 term in Toyota Central Research Laboratory, Inc. 4K020 AA21 AA25 AC02

Claims (1)

[Claims] 1. A matrix made of magnesium or a magnesium alloy, and an average particle size dispersed in the matrix is 10 μm.
Less than spherical and / or elliptical Mg ₂ Si particles;
A magnesium-based composite material comprising: