JP2005177850A - Member for aluminum molten metal, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member for aluminum molten metal which has no sticking of aluminum and is hard to be peeled, and to provide a production method for producing the member by a simple method. <P>SOLUTION: The member for aluminum molten metal is obtained by providing the surface of a substrate 1 composed of a silicon nitride sintered compact comprising a sintering auxiliary by 1 to 20 mass% and having a relative density of ≥98% with silicon nitride crystals 3 having the grain size substantially same as that of the silicon nitride sintered compact in the substrate 1, and a porous layer 5 comprising voids 4 three-dimensionally continuously formed on the grain boundaries of the silicon nitride crystals 3, and in which the silicon nitride crystals 3 are three-dimensionally connected with each other. Preferably, the thickness of the porous layer 5 is ≥10 μm, 1 to 20 mass% of at least one kind selected from the group 3a elements in the periodic table is comprised as the sintering auxiliary, and the cutting strength at the inside from room temperature to 1,200°C in the silicon nitride sintered compact is ≥500 MPa. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is used in contact with a molten metal such as an aluminum alloy, such as a heater tube, a stalk, a thermocouple protection tube, a degassing rotor, a casting jig such as a mold, or an aluminum such as a die casting sleeve or a plunger tip. It is related with the member for molten metal, and its manufacturing method.

  Aluminum is used in various fields as a lightweight metal instead of conventional metals such as cast iron. For example, there is a strong demand for reducing the weight of automobiles in relation to environmental issues, and the use of aluminum for car body parts is being promoted.

  Such aluminum parts are usually manufactured by casting aluminum. In the melting and casting of aluminum, for example, stalks for supplying molten aluminum into a mold and thermocouple protective tubes for measuring the temperature of molten aluminum are ceramic sintered bodies as materials having excellent corrosion resistance and thermal shock resistance in recent years. Among them, the silicon nitride sintered body is being used as a molten metal member because of its high temperature strength and thermal shock resistance.

  The silicon nitride sintered body also has a problem that it reacts with the aluminum alloy and the aluminum alloy adheres to the jig surface.

  In order to solve this problem, there has been proposed a silicon nitride-based component for melting and casting aluminum composed of a silicon nitride sintered body containing Mg (see, for example, Patent Document 1).

  Further, a silicon nitride sintered body containing Y and Al and having a high Al concentration on the surface has been proposed (see, for example, Patent Document 2).

On the other hand, a molten aluminum member is proposed in which a metal silicon powder is applied to the surface of a silicon nitride sintered body and then etched in a nitrogen atmosphere to nitride the metal silicon to form a porous layer on the surface. (For example, refer to Patent Document 3).
JP-A-6-322457 JP-A-8-73286 JP 7-10664 A

  However, the silicon nitride component for melting and casting aluminum described in Patent Document 1 and the silicon nitride sintered body described in Patent Document 2 have a problem that an aluminum-based alloy adheres to the jig surface.

  Moreover, when a high pressure is applied to the surface of the molten aluminum member in which a porous layer is formed on the surface described in Patent Document 3 such as an aluminum die casting method, the adhesion strength between the porous layer on the surface and the substrate is low. There was a problem that the porous layer was easily peeled off.

  Accordingly, an object of the present invention is to provide a member for molten aluminum that does not adhere to aluminum and is difficult to peel off, and to provide a manufacturing method capable of producing such a member by a simple method.

  The member for molten aluminum of the present invention comprises 1-20% by mass of a sintering aid, and the average grain size of the silicon nitride sintered body of the substrate is formed on the surface of the silicon nitride sintered body having a relative density of 98% or more. A silicon nitride crystal having an average particle diameter substantially the same as the diameter, and a porous layer including voids formed three-dimensionally continuously at the grain boundaries of the silicon nitride crystal; It is characterized by.

  The thickness of the porous layer is preferably 10 μm or more.

  It is preferable that 1-20 mass% of at least 1 sort (s) of a periodic table group 3a element is included as a sintering auxiliary agent.

  The internal cutting strength of the silicon nitride sintered body from room temperature to 1200 ° C. is preferably 500 MPa or more.

  As a method for producing such a member for molten aluminum, an etching treatment with a corrosive gas is performed on at least a surface of a silicon nitride sintered body containing 1 to 20% by mass of a sintering aid and having a relative density of 98% or more in direct contact with molten aluminum. And removing a grain boundary phase containing a sintering aid and impurities to form a porous layer including voids formed continuously three-dimensionally at the grain boundaries of the silicon nitride crystal. is there.

  The corrosive gas is preferably a halogen gas and / or hydrogen.

  The etching treatment is preferably performed at a temperature of 800 to 1900 ° C.

  The etching process is preferably performed in plasma.

  In the molten aluminum member of the present invention, the adhesion of the aluminum-based alloy is due to the reaction between the sintering aid component contained in the silicon nitride sintered body and the aluminum-based alloy, and the surface of the dense silicon nitride sintered body is sintered. By removing the grain boundary phase containing the auxiliary agent, a porous layer in which voids are three-dimensionally continuous with the grain boundary is formed, and the silicon nitride crystals of the substrate and the porous layer have substantially the same average particle diameter. This is based on a new finding that the reaction with the molten aluminum alloy can be reduced. As a result, it is possible to reduce the adhesion of the aluminum-based alloy and to produce a molten aluminum member that is difficult to peel off.

  Moreover, when the thickness of the porous layer of a surface layer is 10 micrometers or more, reaction with an aluminum type alloy can fully be suppressed.

  Furthermore, by containing 1 to 20% by mass of at least one group 3a element in the periodic table as a sintering aid, sinterability is promoted, and a dense silicon nitride sintered body substrate can be easily obtained. Yes.

  In addition, since the internal cutting strength is 500 MPa or more from room temperature to 1200 ° C., the thermal shock resistance and use at high temperature are possible.

  The method for producing a member for molten aluminum according to the present invention includes etching a surface of a dense silicon nitride sintered body containing a sintering aid to remove the grain boundary phase containing the sintering aid and impurities, and silicon nitride. Since a porous layer in which crystals and voids are three-dimensionally continuous is formed, it is possible to produce a molten aluminum member that does not adhere to an aluminum alloy and is difficult to peel off.

  A gas atmosphere containing a halogen gas and / or hydrogen can cope with a complicated shape by a heat etching process at 800 to 1900 ° C. and is suitable for mass production.

  When the corrosive gas is a halogen gas and / or hydrogen, the oxide layer present at the grain boundary of the silicon nitride crystal can be efficiently removed.

  When the etching process is performed at a temperature of 800 to 1900 ° C., more efficient grain boundary phase removal can be performed.

  When the etching process is performed in plasma, the grain boundary phase can be safely and efficiently removed at a lower temperature.

  The present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a structure in the vicinity of the surface of a member for molten aluminum according to the present invention.

  According to FIG. 1, the member for molten aluminum of the present invention is constituted by a base 1 and a porous layer 5 provided on the surface of the base 1.

  It is important from the viewpoint of thermal shock resistance and strength that the substrate 1 is a silicon nitride sintered body containing a sintering aid in a proportion of 1 to 20% by mass and having a relative density of 98% or more. In particular, the strength of the silicon nitride sintered body of the substrate 1 has an internal cut-out strength of 500 MPa at least from room temperature to 1200 ° C. in order to ensure reliability when used in applications where high stress is generated such as aluminum die casting. The above is desirable.

  Known components can be used as the sintering aid. For example, an oxide of a group 3a element such as Y, Er, Yb, or Lu, or an oxide such as Al or Mg can be used. From the viewpoint of promoting sinterability, the group 3a element can be used. The oxide is excellent. What is necessary is just to mix | blend these sintering adjuvant components so that the total amount of oxide conversion may become a ratio of 1-20 mass% with respect to silicon nitride.

  If the content of the sintering aid is less than 1% by mass, sufficient strength cannot be obtained, and if it exceeds 20% by mass, the absolute amount of the grain boundary increases, so the amount of voids due to the porous layer 5 increases. Impact resistance and surface strength are reduced. Therefore, in order to have sufficient strength and to further improve the peeling and deficiency of the porous layer 5, the content is particularly preferably 2 to 15% by mass, and more preferably 3 to 10% by mass.

It is important that the average particle diameter of the silicon nitride crystal 3 of the porous layer 5 is substantially the same as the average particle diameter of the silicon nitride crystal of the silicon nitride sintered body constituting the substrate 1. By making the average particle diameters of the silicon nitride crystals of the substrate 1 and the porous layer 5 substantially the same, the structure is difficult to peel off, and the strength is not drastically reduced. Note that the above-mentioned substantially the same in the present invention, the average particle diameter A _L of the silicon nitride crystal 3 of the porous layer 5, 0.95A _S ≦ A _L with respect to the average particle diameter A _S of the silicon nitride crystal substrate 1 ≦ 1.05A A value that satisfies the _S relational expression.

  The porous layer 5 is composed of the silicon nitride crystal 3 and the void 4 surrounding it three-dimensionally, in order to reduce the reactivity with the aluminum-based alloy and to reduce the adhesion to the surface. It is. In such a structure, the porous layer 5 has a grain boundary phase containing a sintering aid and impurities existing at the grain boundaries of the silicon nitride crystal 3 over a specific depth from the substrate surface 2 in direct contact with the molten aluminum. It can be produced by removing and forming the voids three-dimensionally.

  Thus, there is a sintered body with high strength and high impact resistance inside, and a silicon nitride crystal that is sintered integrally with the sintered body is three-dimensionally bonded, and the silicon nitride crystal The surface 2 without the sintering aid does not easily react with the aluminum alloy, and therefore, the adhesion with the molten aluminum is small and there are many voids. Since the silicon nitride crystal is integrated continuously by three-dimensionally sintering from the substrate 1, the porous layer 5 is difficult to peel off from the substrate 1, and a highly reliable member for molten aluminum can be realized.

  The meaning of “three-dimensionally continuous” in the present invention means three-dimensional continuity and spatial connection, though not necessarily continuous on a flat surface such as a polished surface. Yes. That is, all the voids formed at the grain boundaries of the silicon nitride crystal are connected, and there is no or almost no grain boundary phase. In addition, the silicon nitride crystal is integrated in a state in which at least a part of each crystal is partially sintered and integrated with another adjacent crystal, and the partially connected state is connected in a three-dimensional manner. is there.

  The thickness of the porous layer 5 is preferably 10 μm or more, particularly 20 μm, further 30 μm or more, and more preferably 50 μm or more. Silicon nitride itself is made of a chemically stable compound having a covalent bond, so it has excellent corrosion resistance. However, if there is a sintering aid or impurity at the grain boundary, it easily reacts with the aluminum alloy. Although it adheres to the surface, since the viscosity of the aluminum-based alloy is relatively high by setting the thickness of the porous layer to 10 μm or more, the molten metal is less likely to reach the substrate 1 through the voids 3. Can be more reliably reduced.

  Although the upper limit of the thickness of the porous layer 5 is not particularly limited, for example, even if it is 200 μm, the effect is not changed. In order not to extremely reduce the strength of the molten aluminum member, 1 mm, particularly 700 μm, further 500 μm, and more preferably 300 μm is desirable.

  Such a member for molten aluminum is less likely to react with the aluminum-based alloy, so that the adhesion of aluminum or its alloy is extremely small even when in contact with the molten aluminum, and the member for molten aluminum is excellent in corrosion resistance and heat resistance. Can be used as

  Next, the manufacturing method of the member for molten aluminum of this invention is demonstrated.

The silicon nitride sintered body serving as the substrate can be produced by a known method. Specifically, the silicon nitride powder is made of a Group 3a element oxide of a peripheral discipline such as Y ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , Al ₂ O ₃ , MgO, AlN. , SiO ₂ and other sintering aids added in a total amount of 1 to 20% by mass, particularly 2 to 15% by mass, and further 3 to 10% by mass, in a desired molding means such as cold static After forming into an arbitrary shape by hydraulic press, cast molding, extrusion molding, etc., firing is performed.

  Firing is performed at a temperature of 1500 to 1950 ° C. for about 0.5 to 10 hours with a nitrogen-containing atmosphere length to obtain a sintered body having a relative density of 98% or more, particularly 98.5% or more, and further 99% or more. Examples of the firing method include normal pressure firing, nitrogen gas pressure firing, and hot isostatic firing, and in some cases, these can be combined.

  Next, it is important to etch the silicon nitride sintered body obtained as described above to remove the grain boundary phase. Two types of etching processes can be employed: a heat etching process in a corrosive gas and a plasma etching process in a corrosive gas plasma. Halogen gas and / or hydrogen can be used as the corrosive gas.

  In particular, hydrogen is preferable for the heat etching process, and halogen gas is preferable for the plasma etching process. Since halogen gas is highly corrosive and easily damages the etching furnace, the apparatus is likely to become large and suitable for plasma etching. As the halogen gas, at least one of chlorine gas, fluorine gas, bromine gas and iodine gas can be adopted, and chlorine gas is preferable in consideration of cost and grain boundary phase removal efficiency.

  In the case of the heat etching process, the etching process is performed in a temperature range of 800 to 1900 ° C. in a gas atmosphere containing at least the above corrosive gas. By removing the grain boundary phase component on the surface of the sintered body by this etching treatment, a surface layer having low reactivity with the aluminum-based alloy composed of the porous layer can be formed.

  When the temperature during this etching process is less than 800 ° C., the removal rate of the grain boundary phase is small. For example, even if the etching process is continued for 30 hours or more, a porous layer having a thickness of 5 μm or more may not be obtained. Not suitable for. In order to complete the treatment in a short time, a temperature of 900 ° C. or higher, further 1000 ° C. or higher, more preferably 1100 ° C. or higher is desirable. However, at temperatures exceeding 1900 ° C., silicon nitride itself is actively decomposed and large surface erosion occurs. Therefore, the pressure is set to 1900 ° C. or lower at atmospheric pressure. Needless to say, when the etching process is performed at a high pressure exceeding 1 atm, the upper limit of the etching process temperature is raised.

  Furthermore, in order to suppress a decrease in the bending strength of the substrate 1, it is desirable to perform an etching process at a temperature of 1600 ° C. or lower. In addition, with respect to the etching process time, it is desirable to perform the etching process for 10 minutes or more in any temperature condition in order to sufficiently remove.

  In the case of the plasma etching process, the corrosive gas is discharged into a plasma state, and the silicon nitride sintered body is disposed so as to be in contact with the plasma. In this treatment, it is not particularly necessary to raise the temperature, but in order to suppress temperature variation due to plasma, it is preferable to set the temperature to a constant temperature of 50 ° C. or higher by heating. Since the plasma etching process can be performed at a low temperature, it is preferable in terms of safety.

  According to such an etching method, it is possible to easily apply even to a complicated member or a large member, and it is possible to efficiently manufacture a member for molten aluminum having a surface having low reactivity with an aluminum-based alloy.

  The contact angle used in the present invention will be described. As shown in FIG. 2, when the molten metal 102 is placed on the member 101, if the wettability of the two is good, FIG. 2A is obtained, and the tangent line 103 and the member 101 at the interface between the member 101 and the molten metal 102 are obtained. The angle θ formed by the surface is the contact angle. On the other hand, when the wettability is poor, as shown in FIG. 2B, the molten metal 112 placed on the member 112 becomes three-dimensional and the contact angle θ increases.

First, raw material powder is prepared. That is, Y ₂ O ₃ powder and AL ₂ O ₃ powder were added to silicon nitride powder (average particle size 0.6 μm, oxygen content 0.7 mass%, α conversion rate 92%) so as to have the composition shown in Table 1, respectively. Then, after sufficiently mixing with a ball mill, the granules were dried and granulated with a spray dryer to produce granules, and the granules were filled in a mold and molded by press molding at a pressure of 100 MPa to produce a compact.

  The obtained molded body was put in a silicon carbide mortar, heated using a carbon heater to a temperature of 1750 ° C. in a normal pressure nitrogen atmosphere, held at this temperature for 5 hours, and further up to 1900 ° C. The temperature was raised and held for 5 hours. Thereafter, the furnace was cooled to produce a silicon nitride sintered body.

  The obtained silicon nitride sintered body was etched. As the etching process, an overheating etching process (shown as T in the table) and a plasma etching process (shown as P in the table) were performed. The etching conditions are shown in Table 1. The plasma etching was performed using a RIE (reactive ion etching) apparatus.

  Next, the silicon nitride sintered body was processed into a 20 mm square 5 t shape to prepare a test piece. The thickness of the porous layer was measured with a scanning electron microscope (SEM) after cutting the test piece.

  Thereafter, the above silicon nitride sintered body was used as a sample, and a reaction test with an aluminum alloy was performed. The reaction test was performed by placing an aluminum alloy on the surface of the etched silicon nitride sintered body, holding it at 1000 ° C. under a reduced pressure of 27 kPa for 10 hours, and then measuring the contact angle from the shape of the sample after cooling. It was. Further, the sample after the test was cut, and the thickness of the reaction layer at the interface was measured with a scanning electron microscope (SEM). The reaction layer is shown in Table 1.

The cutting strength of the substrate was measured at room temperature and at a high temperature of 1200 ° C. after processing from the substrate to a size of 3 × 4 × 40. The intensity was measured based on JIS R 1601 and JIS R 1604.

  Sample No. of the present invention. Nos. 1 to 20 had a contact angle of 100 ° or more and a reaction layer thickness of 3 μm or less. In particular, sample No. 1 subjected to a heat etching process and a plasma etching process at 900 ° C. or higher. As for 1-8 and 10-20, the contact angle was 130 degrees or more and the thickness of the reaction layer was less than 1 micrometer.

  On the other hand, a sample No. outside the scope of the present invention that was not etched. Nos. 21 to 25 had a contact angle of 90 ° or less and a reaction layer thickness of 5 μm or more.

It is a schematic sectional drawing which shows the structure | tissue near the surface of the member for molten aluminum of this invention. It is for demonstrating a contact angle, (a) is explanatory drawing in case wettability is good, (b) is explanatory drawing in case wettability is bad.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base | substrate 2 ... Base | substrate surface 3 ... Silicon nitride-type crystal 4 ... Void 5 ... Porous layer

Claims (8)

An average substantially the same as the average particle size of the silicon nitride sintered body of the substrate on the surface of the substrate made of the silicon nitride sintered body containing 1 to 20% by mass of a sintering aid and having a relative density of 98% or more. A member for molten aluminum, comprising: a silicon nitride crystal having a particle size; and a porous layer including voids formed continuously three-dimensionally at grain boundaries of the silicon nitride crystal. A member for molten aluminum, wherein the porous layer has a thickness of 10 μm or more. The member for molten aluminum according to claim 1, comprising 1 to 20% by mass of at least one element of Group 3a elements of the periodic table as a sintering aid. The member for molten aluminum according to claim 1 or 2, wherein an internal cutting strength of the silicon nitride sintered body from room temperature to 1200 ° C is 500 MPa or more. Particles containing 1 to 20% by mass of a sintering aid and etching contact with a corrosive gas on at least the surface of a silicon nitride sintered body having a relative density of 98% or more that is in direct contact with molten aluminum and containing a sintering aid and impurities. A method for producing a member for molten aluminum, comprising removing a boundary phase and forming a porous layer including voids formed continuously three-dimensionally at grain boundaries of a silicon nitride crystal. 6. The method for producing a molten aluminum member according to claim 5, wherein the corrosive gas is a halogen gas and / or hydrogen. The method for producing a molten aluminum member according to claim 5 or 6, wherein the etching treatment is performed at a temperature of 800 to 1900 ° C. The method for producing a member for molten aluminum according to claim 5 or 6, wherein the etching treatment is performed in plasma.

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