JP2588554B2 - Member for molten aluminum and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a member having good corrosion resistance to molten aluminum, high mechanical strength and high thermal shock resistance, and a method for producing the same.

[Prior art] Stokes, Ladle, which handles molten aluminum
Conventionally, cast iron members coated with corrosion-resistant ceramic powder have been widely used for immersion heater protection tubes, gas injection members, melt pump members, melt stirring members, melt stoppers and seats, toys, and the like. . However, the metal material of such a member tends to dissolve in the molten aluminum that comes into contact with it, and therefore the quality of the molten aluminum decreases. Further, there is a problem that the corrosion-resistant ceramic coating does not have a sufficient adhesive force to the metal material and thus easily peels off, so that it must be applied every day. Furthermore, since it is made of metal such as cast iron, there is also a problem that it is relatively heavy and handling is not easy.

Therefore, recently, members for molten aluminum of ceramics such as silicon nitride or silicon carbide have been used instead of metal members.

[Problems to be Solved by the Invention] However, since these ceramic members for molten aluminum are conventionally manufactured by a reaction sintering method of nitriding or carbonizing metallic silicon, they have a bending strength of only about 30 kg / mm ^2. In addition, they could not withstand mechanical stress and impact during use. Further, since these ceramic members have a relatively low density, the surface is rough and the molten aluminum is easily welded. Moreover, even those having relatively good bending strength do not have sufficient thermal shock resistance, and thus are easily broken by thermal shock.

Ceramics with sufficient strength and thermal shock resistance, such as Si ₃ N ₄ ceramics, sialon, and silicon carbide, have poor wettability with molten aluminum, but the aluminum adheres little by little due to use. As the amount of aluminum increases, the amount of adhered aluminum increases particularly near the surface of the molten metal.

Accordingly, an object of the present invention is to provide a member for molten aluminum in which an inner layer having high bending strength, good corrosion resistance to molten aluminum, high density and high thermal shock resistance is coated with an outer layer containing BN as a main component, in which aluminum does not easily adhere. To provide.

Another object of the present invention is to provide a method for manufacturing such a member for molten aluminum.

[Means for Solving the Problems] In view of the above object, as a result of intensive research, it has been found that by forming an outer layer mainly composed of BN on silicon nitride or sialon-based ceramics, adhesion of molten aluminum is suppressed, The present inventors have found that the life of the molten metal member can be significantly prolonged, and have reached the present invention.

That is, the member for molten aluminum according to the present invention is:
An inner layer made of silicon nitride or sialon-based ceramics composed of silicon nitride, Al ₂ O ₃ and a sintering aid, and an outer layer obtained by coating and sintering the inner layer with a ceramic powder containing BN and SiO _2. , the outer layer is mainly composed of BN, mainly _{BN-SiO 2 -Al 2 O 3} - , characterized in that it consists of a sintering aid.

Further, the method for producing a member for molten aluminum of the present invention,
Shaped body of silicon nitride or sialon ceramics were coated with a ceramic powder containing BN and SiO _2, 1,600-19
It is characterized by sintering at 00 ° C.

The silicon nitride or sialon-based ceramic is Si ₃ N ₄ 7
0% by weight or more and one of oxides of Group IIIa element of the periodic table
It contains at least 20% by weight of one or more kinds and at most 20% by weight of Al ₂ O ₃ .

As for Si ₃ N ₄ , the α phase should be contained in an amount of 65% by weight or more. If the α phase is less than 65% by weight, the sinterability is low, and the mechanical strength is low due to the low sintering density. The content of the α phase is preferably at least 85% by weight.

Group IIIa element oxides that can be used in the present invention are Y ₂ O ₃ , L
a ₂ O ₃ , CeO _{2 and the} like. These oxides mainly act as sintering aids. Y is most preferably ₂ O _3, if Y ₂ O ₃ to perform normal pressure sintering or gas pressure sintering is preferably 3 to 10 wt%. If the content of Y ₂ O ₃ is less than 3% by weight, the sintered density is not sufficient, and if the content of Y ₂ O ₃ exceeds 10% by weight, the high-temperature strength of the obtained sintered body is significantly reduced. In order to perform the normal pressure sintering or the gas pressure sintering, a relatively large amount of Y ₂ O ₃ is required. Y ₂ O ₃
Is more preferably 5 to 7% by weight.

With respect to Al ₂ O _3, preferably in the range of 3-7%. If it is less than 3% by weight, sinterability is low and sintering density is low. On the other hand, when it exceeds 7% by weight, the obtained sintered body has a remarkably low high-temperature strength. A more preferred Al ₂ O ₃ content is 3 to 5% by weight.

The silicon nitride or Iaron-based ceramic of the present invention may further contain AlN or a solid solution thereof of 15% by weight or less. Here AlN solid solution can also be referred to as AlN polytype, AlN, containing Si ₃ N ₄ and Al ₂ O _3, the content of AlN is about 68
% By weight. The preferred content of AlN or AlN solid solution is 1
９9% by weight. If it is less than 1% by weight, the obtained sintered body has a remarkably low high-temperature strength, and if it exceeds 9% by weight, sufficient sinterability cannot be obtained, and the strength of the sintered body decreases. AlN or A
A more preferable content of the 1N solid solution is 2 to 9% by weight.

The ceramic powder having the above composition is mixed in a ball mill using ethyl alcohol, methyl alcohol or the like as a solvent. An organic binder such as polyvinyl alcohol and polyvinyl butanol is added to the obtained powder mixture at a ratio of 0.5 to 1% by weight based on the ceramic component, and the mixture is spray-dried and granulated to a desired size.

After the ceramic granules are sieved to a particle size of 200 to 60 mesh, they are formed by a cold isostatic press (CIP) at a pressure of about 700 to 1500 kg / cm ² . The molded body obtained by the CIP method is degreased by heating, trimmed, polished with sandpaper, and cut to a desired length.

Before sintering, the green body is coated with a ceramic powder containing BN and SiO _2. In a preferred embodiment BN is 40 to 60 wt%, SiO ₂ is 40 to 60 wt%. The coating layer can be formed by spraying or brushing. For coating, organic solvents such as alcohols, ethers, ketones, alkanes, aromatic hydrocarbons and the like are used together with an organic binder. This ceramic powder coating layer needs to have a thickness of at least 0.5 mm in order to obtain a sufficient effect.

The silicon nitride or sialon-based ceramic molded body coated with the ceramic powder according to the present invention is sintered in a nitrogen atmosphere at a gas pressure of 300 kg / mm ² or less. Both normal pressure sintering and gas pressure sintering can be used.

As used herein, the term "normal pressure sintering" refers to sintering performed at atmospheric pressure without pressing, and the term "gas pressure sintering" refers to sintering performed under gas pressure without pressing. means.

Normal pressure sintering is more preferable because it does not require complicated sintering equipment. In this sintering method, the nitrogen gas is usually 2 kg / cm ² or less. The density of the sintered body increases as the pressure of the nitrogen gas increases.

In the present invention, the sintering temperature is 1600 to 1900 ° C. 1600
If the temperature is lower than 0 ° C, sufficient sintering density cannot be obtained, and if it is higher than 1900 ° C, Si ₃ N ₄ may be decomposed. Preferred sintering temperature is 1
700-1800 ° C.

Also, a sintered body of silicon nitride or sialon-based ceramics can be coated with a ceramic powder containing BN and SiO ₂ to form an outer layer containing BN as a main component. In this case, the coating liquid for forming the coating layer is the same as that described above, and the sintering conditions are also the same. However, since it is a sintered body, a preferable sintering temperature is 1600 ° C. to 1700 ° C.

The sintered body of silicon nitride or sialon ceramics is
When AlN or an AlN solid solution is contained in an amount of 15% by weight or less, it has a composition represented by the following general formula: Si _6-z Al _z O _z N _8-z (where 0 <z ≦ 4.2).

And also Si ₃ N ₄ 50 wt% or more, Li, Na, Ca, Mg , and 20 wt% or less of one or more oxides of Y and rare earth elements, Al ₂ O
_{3 When} containing 20% by weight or less and AlN or 15% by weight or less of an AlN solid solution, the following general formula: M _x (Si, Al) ₁₂ (O, N) ₁₆ (where M is Li, Na, One or more of Ca, Mg, Y and rare earth elements, and has a composition represented by 0 <x ≦ 2). The sialon of this composition is an α-phase sialon, and α
-Sialon consists of 10-70% by weight of the alpha phase, 20-90% by weight of the beta phase and 0.1-10% by weight of the vitreous phase.

The sintered body of silicon nitride or sialon ceramics is 50
Kg / mm ² or more bending strength, density of 90% or more of theoretical and 40
It has a thermal shock temperature ΔT of 0 ° C. or more. 80-90% by weight Si ₃
N _4, 5 to 10 wt% of Y ₂ O _3, 3 to 7 wt% of Al ₂ O ₃ and 2
In the case of a sintered body composed of ９9% by weight of AlN or AlN solid solution,
The flexural strength is 70 kg / mm ² or more, the density is 95-99%, and the thermal shock temperature ΔT is 450 ° C. or more.

When sintering a compact of BN and silicon nitride was coated with a ceramic powder containing SiO ₂ or sialon ceramics sintered body is obtained having a two-layer structure, the outer layer is mainly composed of BN, mainly BN-SiO consisting of _{2 -Al 2 O 3 -Y 2 O} 3.
The inner layer has substantially the same composition as the ceramic starting material powder. The thickness of the outer layer is 5 to 50 μm, and BN
, The member has remarkably good resistance to molten aluminum welding and has improved oxidation resistance. It is considered that the formation of this outer layer occurs by the following mechanism. In other words, the presence of SiO _{2 on the} surface raises the glass layer at the grain boundary to the surface, so that BN can be sintered on the surface. Al ₂ O ₃ and Y ₂ O ₃ sucked from the layer of silicon nitride or sialon-based ceramics act to enable sintering of BN.

Thus for molten aluminum material of the present invention has a two-layer structure, the inner layer consists of silicon nitride or sialon ceramics having a high mechanical strength and impact resistance, the outer layer is mainly BN-SiO ₂ -Al ₂ O welding resistance against molten aluminum to consist of ₃ -Y ₂ O ₃ is good. Therefore, this member has remarkably high resistance to impact load, thermal shock and welding. Furthermore, corrosion resistance to aluminum is sufficient. Therefore, the member for molten aluminum of the present invention has a remarkably long life.

[Examples] The present invention will be described in more detail with reference to the following examples.

Example 1 6.5 wt% of 85.6 wt% Si ₃ N ₄ powder (particle size 0.8 μm)
Y ₂ O ₃ powder (particle size 1.0 μm), 2.9% by weight AlN polytype (solid solution) powder (particle size 0.8 μm) and 4.8% by weight Al ₂ O
_Three powders (particle diameter: 0.1 μm) were added and mixed in isopropyl alcohol by a ball mill. After drying, 10% of a 5% concentration polyvinyl alcohol solution was added to the powder mixture, and the mixture was placed in a rubber press and cold isostatically pressed (CIP) with a hydrostatic pressure of 1 ton / cm ² to form a compact. The formed body was coated with a ceramic powder paste consisting of 40 parts by weight of BN powder, 40 parts by weight of SiO ₂ powder, and 50 parts by weight of collodion and 4-methyl-2-pentanone. The dried thickness of the coating layer was about 1 mm. Then 1750
Sintering was performed in a nitrogen atmosphere at 1 ° C. and 1 atm for 5 hours. After sintering
Ceramic powder remaining on the surface was removed. The member of the obtained sialon sintered body had the following characteristics.

The relative density of 99.0% Bending strength ^{* (Atsushi} Muro) 80 Kg / mm ² Flexural strength ^{* (1000 ℃) 80Kg / mm} 2 thermal shock temperature [Delta] T 600 ° C. Note *: four-point bending test (the lower span 30 mm, the upper spans 10m
m).

This member is cut, and its cross section is scanned by a scanning electron microscope (SE
M). FIG. 1 is an SEM photograph, which clearly shows a two-layer structure (the gray part is the inner layer of the sialon and the white part is the outer layer). Infrared analysis confirmed that the outer layer contained BN. The presence of Al and Si in the outer layer was confirmed by electron probe microanalysis (EPMA). Since Y ₂ O ₃ is an essential component for sintering, it is considered that Y ₂ O ₃ is certainly present in the sintered outer layer. This Y ₂ O ₃ is drawn from the underlying silicon nitride or sialon-based ceramics layer.

This member was immersed in molten aluminum. As a result, it was found that corrosion and welding were not substantially caused by the molten aluminum even after immersion for 6 months. In addition, it was able to withstand the mechanical shock during immersion and the thermal shock caused by taking in and out. Therefore, it can be seen that the device can be used for one year or more without repair.

Example 2 82.7 wt% of Si ₃ N _4, 5.8 wt% of Y ₂ O _3, 3.8 wt% of A
except for using l ₂ O ₃ and 7.7 wt% of AlN polytype as a ceramic material, Example 1 was repeated.

 The obtained member was immersed in molten aluminum.

As a result, the members were hardly dissolved in the molten aluminum even after immersion for 6 months as in Example 1.

Example 3 A molded body was formed using the same ceramic material as in Example 1 and by the same method. 80% Si by weight around the compact
Filled with powder consisting of ₃ N ₄ powder and 20 wt% BN powder, 1
Sintering was performed at 750 ° C. and 1 atm for 5 hours in a nitrogen atmosphere. Next, the surface of the obtained sintered body was coated with the same ceramic powder paste as in Example 1, and sintered at 1650 ° C. and 1 atm for 3 hours in a nitrogen atmosphere.

 The obtained member was immersed in molten aluminum.

As a result, the members were hardly understood in the aluminum melt even after immersion for 6 months as in Examples 1 and 2.

As described above [Effect of the invention], molten aluminum member of the present invention has a two-layer structure, the inner layer consists of sintered silicon nitride or sialon ceramic, outer layer primarily BN-SiO ₂ -Al ₂ O
Since consisting ₃ -Y ₂ O _3, can be destroyed, cracks, weld, to withstand long-term use without causing corrosion. In addition, since a cast iron pipe is not used, it is lightweight, and there is no need to understand in a molten aluminum. Therefore, it is possible to prevent quality deterioration of the molten aluminum.

The aluminum melt member of the present invention having such features is suitably used for Stokes, ladle, immersion heater protection tube, gas injection member, melt pump member, melt stirring member, melt stopper and seat, toy, and the like. can do.

[Brief description of the drawings]

FIG. 1 is a scanning micrograph showing the crystal structure of the cross section of the member of Example 1.

Claims (11)

(57) [Claims] 1. An inner layer made of silicon nitride or sialon ceramics comprising silicon nitride, Al ₂ O ₃ and a sintering aid, and said inner layer is coated with a ceramic powder containing BN and SiO ₂ and sintered. made consists of a outer layer, the outer layer is mainly composed of BN, mainly _{BN-SiO 2 -Al 2 O 3} - molten aluminum member, characterized in that it consists of a sintering aid. 2. The member for molten aluminum according to claim 1, wherein said silicon nitride or sialon-based ceramic has a bending strength of 50 kg / mm ² or more, and 90% of a theoretical value.
A member for molten aluminum, having the above density and the thermal shock temperature ΔT of 400 ° C. or more. 3. The member for molten aluminum according to claim 1, wherein the silicon nitride or the sialon-based ceramic is 70% by weight or more of Si ₃ N _{4, and the third} nitride of the periodic table. A member for molten aluminum, comprising one or more of oxides of group elements and not more than 20% by weight and Al ₂ O _{3 not} more than 20% by weight. 4. The member for molten aluminum according to claim 1, wherein said silicon nitride or sialon-based ceramic has a general formula: Si _6-z Al _z O _z N _8-z (where 0 <z ≦ 4.2) a β-sialon having at least 70% by weight of Si ₃ N ₄ , at least one oxide of an element of Group IIIa element of the periodic table and at most 20% by weight, and Al ₂ O ₃ A member for molten aluminum, comprising 20% by weight or less and AlN or 15% by weight or less of an AlN solid solution. 5. The member for molten aluminum according to claim 1, wherein said silicon nitride or sialon-based ceramic has a general formula: M _x (Si, Al) ₁₂ (O, N) ₁₆ (where 0 <X ≦ 2, M represents one or more of Li, Na, Ca, Mg, Y and rare earth elements), wherein 10 to 70% by weight of α-phase sialon and β Consisting of 20 to 90% by weight of a phase sialon and 0.1 to 10% by weight of a crow phase, 50% by weight or more of Si ₃ N ₄ and one or two of oxides of Li, Na, Ca, Mg, Y and rare earth elements Not less than 20% by weight
A member for molten aluminum, comprising 20% by weight or less of Al ₂ O ₃ and 15% by weight or less of AlN or an AlN solid solution. 6. A member for molten aluminum according to any one of claims 1 to 5, wherein said outer layer has a thickness of 5 to 50 μm. 7. A member for molten aluminum according to any one of claims 1 to 6, wherein said member is Stokes, a ladle, an immersion heater protective tube, a member for gas injection, a molten metal pump member, A member for molten aluminum, which is any one of a molten metal stirring member, a molten metal stopper and a seat, and a toy. 8. A method for manufacturing a member for molten aluminum comprising an inner layer made of silicon nitride or sialon-based ceramics and an outer layer containing boron nitride as a main component, wherein the molded body of silicon nitride or sialon-based ceramics is made of BN and SiO. ₂ is coated with a ceramic powder containing, 1600-19
A method characterized by sintering at 00 ° C. 9. The method according to claim 8, wherein said ceramic powder coating has a thickness of 0.5 mm or more. 10. The method according to claim 8, wherein the sintered body of silicon nitride or sialon-based ceramic is coated with a ceramic powder containing BN and SiO ₂ and sintered at 1600 to 1900 ° C. A method comprising: 11. The method according to claim 10, wherein the coating of the ceramic powder has a thickness of 0.5 mm or more.