JPH05245615A - Method for casting metal member covered with different kinds of metal - Google Patents

Abstract

PURPOSE:To enable casting of a metal member covered with different kinds of metal. CONSTITUTION:A sand core 10 having a surface 10a corresponding to the shape of the water jacket part of a cylinder block 22 is prepared. The surface 10a of the sand core is covered with a composite material 16 in which alumina fiber 12 is dispersed in the coating metal (pure Al) 14 whose melting point is lower than the temperature of molten metal of a base metal material (Mg alloy); the sand core is set in a casting mold; the molten metal of the base metal material is poured into the casting mold at a temperature lower than the melting point of the alumina fiber; and the cylinder block is cast. When the sand core is removed upon completion of the casting, the cylinder block 22 of which the wall of the water jacket is covered with the film 20 of the composite material is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting a metal member, and more particularly to a method for casting a metal member coated with a dissimilar metal.

[0002]

2. Description of the Related Art As one of the casting methods using a sand core, for example, as described in JP-A-63-260662, at least a part of the surface of the sand core is coated with a coating metal by thermal spraying or the like. A casting method known as a so-called transfer method has been conventionally known in which casting is performed by using a sand core coated with the above-described coating, and the coating metal is left on the surface of the product casting in a substantially intact state. There is.

According to such a casting method, the sand core is cast while being protected by being covered with the coating metal, and the coating metal is the mother metal when the molten base metal poured into the mold is solidified. Since it is integrated with the material metal, it is possible to prevent damage to the sand core, avoid defects such as pouring of molten metal and cracks, and easily collapse the sand core after casting is completed. Can be made

[0004]

However, in the above conventional casting method, in order to achieve good results, it is necessary that the coating metal on the surface of the sand core does not substantially melt even during casting. Therefore, the coating metal must have a melting point higher than that of the melt of the base metal, and therefore, by this method, a casting coated with a metal having a melting point lower than the temperature of the melt of the base metal. For example, it is not possible to cast a cylinder block made of magnesium alloy for an engine, in which the wall surface of the water jacket is coated with an aluminum alloy coating for the purpose of improving its corrosion resistance.

In view of the above-mentioned problems in the above conventional casting method, the present invention is different from the base metal regardless of whether the melting point of the coating metal is higher or lower than the temperature of the molten base metal. It is an object of the invention to provide an improved casting method that enables casting of metal parts coated with coated metal.

[0006]

According to the present invention, there is provided a casting method for a metal member coated with a dissimilar metal, and a molding surface corresponding to the outer shape of the metal member to be cast is provided. Prepare a mold having, cover at least a part of the molding surface of the mold with a composite material in which inorganic fibers are dispersed in a coating metal, the molten metal of the base metal in the mold melting point of the inorganic fibers It is achieved by a casting method characterized by pouring at a lower temperature.

[0007]

According to the above-mentioned constitution, at least a part of the molding surface of the mold is coated with the composite material in which the inorganic fibers are dispersed in the coating metal, and the molten metal of the base metal is filled with the inorganic fibers. It is poured into the mold at a temperature lower than the melting point. The composite material is heated to a temperature substantially the same as the temperature of the molten metal and the coating metal melts completely depending on its melting point, but the shape of the composite material is maintained by the inorganic fibers dispersed in the coating metal, and the inorganic fiber As a result, the liquid phase diffusion between the base metal element and the coating metal element is appropriately suppressed, so that when casting is completed, most of the composite material remains in substantially the same state, so that the predetermined surface of the metal member The state of the composite material is covered, and at the interface between the composite material and the base metal, an appropriate diffusion phenomenon of the metal element occurs, so that good adhesion between the composite material coating and the base metal is secured. It

[0008]

[Supplementary Explanation of Means for Solving the Problem] According to the result of the experimental research conducted by the inventor of the present application, when the volume ratio of the inorganic fibers in the composite material is less than 5%, particularly less than 4%, casting is performed. Occasionally, the molten coating metal flows out more easily than the composite material, so that the coating may have a non-uniform thickness or a portion where the coating is not substantially formed. On the contrary, when the volume ratio of the inorganic fibers exceeds 40%, especially 42%, the adhesion strength of the coating is caused by insufficient diffusion of the metal element at the interface between the coating and the base metal. Is greatly reduced. Therefore, in the casting method of the present invention, the volume ratio of the inorganic fibers in the composite material is 4 to 42%, particularly 5 to 40%.
It is preferably set to%.

When the average fiber length of the inorganic fibers dispersed in the coating metal is less than 10 μm, particularly less than 5 μm, the coating metal melted during casting is more likely to flow out than the composite material as in the case where the volume ratio of the inorganic fibers is low. Due to this, the thickness of the coating may become non-uniform, or a portion where the coating is not substantially formed may occur. On the contrary, when the average fiber length of the inorganic fibers exceeds 200 μm, it becomes difficult to uniformly coat the molding surface of the mold with the composite material by thermal spraying or the like. Therefore, in the casting method of the present invention, when the inorganic fibers are short fibers, the average fiber length of the inorganic fibers is 5 to 5.
It is preferably set to 200 μm, particularly 10 to 200 μm.

If the inorganic fiber is a fiber which has been conventionally used as a reinforcing fiber of a composite material, the average fiber diameter of the inorganic fiber may be any value. When the mold whose coated surface is to be coated with a composite material is a core, etc., wrap the long fibers around the core, etc., and immerse them in the molten metal of the coating metal to create a space between the individual long fibers. Since the coating film of the composite material can be formed around the core or the like by filling the coating metal, the inorganic fiber may be a long fiber. Further, the inorganic fiber has a melting point of the coating metal and a melting point higher than the temperature of the molten metal of the base metal, so long as the properties of the fiber can be maintained even in the melt of the coating metal, for example, ceramic fiber, carbon fiber, Although it may be made of any material such as metal fiber, ceramic fiber is preferable as the short fiber and carbon fiber is preferable as the long fiber from the viewpoint of stability of the coating metal in the melt.

The coating metal may be any metal whose melting point is lower than the temperature of the molten metal of the base metal. For example, a coating metal for improving the corrosion resistance of a magnesium alloy casting is the temperature of the molten magnesium alloy. Since it needs to have a lower melting point and a lower ionization tendency than
l, Zn, Sn and alloys thereof are preferable, and Al, Zn and alloys thereof are preferable in consideration of recyclability.

[0012]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Example 1 Alumina fiber (95 wt% Al ₂ O ₃ , 5 wt% SiO ₂ )
Sand for casting an engine cylinder block as shown in FIG. 1 by plasma spraying using a composite material powder made of pure Al (purity 98 wt%) having an average particle size of 120 μm. Surface 10 of core 10
A was coated with a composite material 16 made of pure Al 14 in which alumina fibers 12 were dispersed at a volume ratio of 10% to a thickness of 0.2 mm. The fiber diameter and fiber length of the alumina fiber are 5 each.
μm, 100 to 200 μm.

Next, although not shown in the figure, the sand core thus coated with the composite material is set in a mold for cylinder block casting, and a Mg alloy (JIS standard AZ91) at 750 ° C. is set in the mold. The molten metal is poured and removed after the molten metal is completely solidified and the mold is decomposed to collapse the sand core, whereby the wall surface of the water jacket 18 becomes the composite film 20 as shown in FIG. To form two cylinder blocks 22 which were coated with each other.

Next, one of the cylinder blocks was cut and the cross section of the water jacket portion was observed with an optical microscope. No cracks or peeling of the coating film were observed. Also, the thickness of the coating is a uniform thickness of about 0.2 mm,
No defective adhesion part of the composite material was observed. Further, as shown in FIG. 3, the coating 20 has an alumina fiber 1
2 was uniformly dispersed at a volume ratio of about 10%.

Further, when a part of the water jacket was cut out and the coating was analyzed by EPMA line in the thickness direction, most of the matrix of the coating remained the original pure Al, and defects such as voids in the matrix. At the interface 26 between the coating 20 and the base material 24.
It was confirmed that 1 was diffused into the Mg alloy of the base material over a range of about 50 μm in the thickness direction. Further, when a shear adhesion test piece was cut out from the water jacket and the adhesion strength of the coating was measured, it was found that the coating had a good adhesion strength of 50 to 80 MPa. Example 2 The volume ratio of the alumina fibers (average fiber diameter 5 μm, average fiber length 150 μm) in the composite material coating the sand core was set to various values, and the alumina fibers (average fiber diameter 5 μm, volume ratio 10%) were used. The Mg alloy cylinder block was cast under the same procedure and conditions as in Example 1 except that the average fiber length in 4) was set to various values, and the adhesion strength of the coating was measured. The results of these tests are shown in Figures 4 and 5.

As shown in FIG. 4, when the volume ratio of the alumina fiber is less than 5% or more than 40%, the adhesion strength of the coating becomes low, and particularly the volume ratio of the alumina fiber is less than 4%. It is understood that the adhesion strength of the coating is further lowered in the case of over 42%. The reason why the adhesion strength of the coating becomes significantly low when the volume ratio of the alumina fiber is low is presumed to be that pure Al melted during casting tends to flow out more easily than the composite material. It is speculated that the reason why the adhesive strength is remarkably lowered is that the diffusion of the metal element at the interface between the coating and the base metal is insufficient. Further, when the volume ratio of the alumina fiber was less than 5%, the coating thickness was non-uniform and there was a portion where the coating was not formed. Therefore, the volume ratio of the alumina fibers in the composite material is 4 to 42%, especially 5 to
It can be seen that it is preferably set to 40%.

Further, as shown in FIG. 5, it can be seen that when the average fiber length of the alumina fibers is less than 10 μm, particularly less than 5 μm, the adhesion strength of the coating becomes remarkably low. When the average fiber length of the alumina fibers is short, the coating thickness is non-uniform and there is a portion where the coating is not formed. Conversely, when the average fiber length of the alumina fibers exceeds 200 μm, thermal spraying is performed. The nozzle of the device was clogged with fibers and it was difficult to perform good thermal spraying. Therefore, the average fiber length of the alumina fibers (short fibers) in the composite material is 5 μm or more, especially 10 μm.
It is understood that it is preferable that the thickness is set to μm or more.

As inorganic fibers, alumina-silica fibers (47 wt% Al ₂ O ₃ , 53 wt% SiO ₂ ) having an average fiber diameter and an average fiber length of 5 μm and 100 μm, respectively, an average fiber diameter and an average fiber length of 5 μm and 100 μm, respectively. Similar results were obtained when the above silicon carbide fibers were used. Example 3 A cylinder block made of an Mg alloy was cast under the same procedure and conditions as in Example 1 except that pure Zn and pure Sn were used as the matrix metal of the composite material.
For comparison purposes, the surface of the sand core is made of pure Al, pure Zn, and pure S.
A cylinder block made of Mg alloy was cast under the same procedure and conditions as in Example 1 except that 0.2 mm was coated with only n.

Next, these cylinder blocks were cut to observe the water jacket portion, and the area ratio of the portion of the base material where the Mg alloy was exposed was measured. The results are shown in FIG. 6 together with the results of Example 1. From FIG. 6, when the surface of the sand core is coated only with the coating metal having a melting point lower than that of the base metal, the base metal cannot be coated well, and the lower the melting point of the coating metal is, the lower the melting point of the coating metal is. It is understood that the exposed area ratio of the base metal is high, whereas the surface of the base metal can be substantially completely covered when the surface of the sand core is covered with the composite material.

When the matrix metal of the composite material is pure Zn and pure Sn, an exposed portion of the base metal is generated, but since the exposed area ratio is about several percent, it is relative to the surface of the sand core. It is presumed that the exposed area ratio can be made 0% by slightly increasing the coating thickness of the composite material such as 0.3 mm.

Further, the surface of the sand core is coated with a Zn-based composite material, Sn
The interface between the base metal and the coating of the cylinder block formed by coating with the base composite material was subjected to EPMA line analysis in the thickness direction to measure the width of the diffusion layer. The results are shown in FIG. 7 together with the results of Example 1. It can be seen from FIG. 7 that the lower the melting point of the coating metal, the larger the width of the diffusion layer. Pure A, which has the highest melting point among the three types of coated metals used in the test
Also in the case of 1, the width of the diffusion layer is 50 μm or more, which is a value sufficient to secure good adhesion strength of the coating metal to the base metal. In order to evaluate the performance of the other cylinder block formed in the actual machine test example 1, that is, the cylinder block made of the Mg alloy in which the wall surface of the water jacket is coated with the Al-based composite material, a cylinder block of 8 cylinders 3000cc is used. Built into the gasoline engine of "Absorption pressure 650mmHg, rotation speed 400
Full load operation at 0 rpm 6 minutes "→" idling 1 minute "→
An actual machine test was performed by repeating this cycle with "stop 6 minutes" → "idling 1 minute" as one cycle.
The cooling water used was tap water, and as a comparative example, an actual machine test was conducted under the same conditions for a cylinder block made of an Mg alloy in which the wall surface of the water jacket was not covered.

As a result, as shown in Table 1 below,
In the cylinder block of the comparative example, it was confirmed that corrosion had occurred in the water jacket portion 50 hours after the start of the test, and the water jacket portion was damaged after 200 hours. However, in the cylinder block according to the first embodiment, the water jacket portion of the water jacket portion was removed even after 700 hours had elapsed. No defects such as corrosion were observed.

From the results of this actual machine test, it can be seen that the cylinder block formed according to the method of the present invention is far more durable than the cylinder block in which the wall surface of the water jacket is not covered.

[0024]

[Table 1] Test operation time [hr] 50 100 150 150 200 250 300 700 700 Example ○ ○ ○ ○ ○ ○ ○ Comparative example △ △ △ × − − − Note: ○: No abnormality △: Corrosion ×: Defect, cooling Water Leakage Also, in order to prevent corrosion of the wall surface of the water jacket in the cylinder block made of Mg alloy, it is conceivable to form a copper coating on the wall surface of the water jacket by the conventional transfer method. In the case of a cylinder block for use, the wall area of the war jacket is 4
There is also 000 cm ^2, and when the wall surface is coated with a film having a thickness of 0.2 mm, the volume becomes 80 cm ³ . The densities of copper and aluminum are 9.0 g / cm ³ and 2.7 g / cm ³ , respectively, so that by changing the metal of the coating from copper to aluminum, per cylinder block (9.0-2.7) A weight reduction of × 80 = 500 g can be achieved.

When the method of the present invention is applied to other engine parts such as a cylinder head, the weight of the entire engine can be reduced by about 1 kg.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to these embodiments, and various other embodiments within the scope of the present invention. It will be apparent to those skilled in the art that

For example, in each of the above-mentioned embodiments, the wall surface of the internal space of the metal part is coated with a different metal according to the method of the present invention. It may be any surface of the metal member formed by casting.

[0028]

As is apparent from the above description, according to the present invention, the composite material coated on the molding surface of the mold is heated to a temperature substantially the same as the temperature of the molten metal of the base metal. Melts completely depending on its melting point, but the shape of the composite material is maintained by the inorganic fibers dispersed in the coating metal, and the inorganic fibers moderately suppress the liquid phase diffusion between the base metal element and the coating metal element. Therefore, when the casting is completed, most of the composite material remains in a substantially intact state, so that the predetermined surface of the metal member is covered, and at the interface between the composite material and the base metal, In this case, a proper diffusion phenomenon of the metal element occurs, whereby good adhesion between the composite material coating and the base metal is secured. Therefore, it is possible to cast a metal member coated with a metal having a melting point lower than the temperature of the molten base metal, in which the coated metal is in good contact with the base metal.

[Brief description of drawings]

FIG. 1 is an enlarged partial sectional view showing a sand core for casting a cylinder block, which is coated with a composite material made of pure Al in which alumina fibers are dispersed.

2 is a Mg cast using the sand core shown in FIG.
It is a fragmentary sectional view showing a cylinder block made of an alloy.

FIG. 3 is an enlarged partial sectional view showing a water jacket portion of the cylinder block shown in FIG.

FIG. 4 is a graph showing the relationship between the volume fraction of alumina fibers in the composite material and the adhesion strength of the coating.

FIG. 5 is a graph showing the relationship between the average fiber length of alumina fibers in the composite material and the adhesion strength of the coating.

FIG. 6 is a graph showing the relationship between the melting point of the matrix metal of the composite material and the exposed area ratio of the Mg alloy.

FIG. 7 is a graph showing the relationship between the melting point of the matrix metal of the composite material and the width of the diffusion layer.

[Explanation of symbols]

 10 ... Sand core 12 ... Alumina fiber 14 ... Pure Al 16 ... Composite material 18 ... Water jacket part 20 ... Composite material coating 22 ... Cylinder block 24 ... Base material 26 ... Interface

Claims (1)

[Claims] 1. A method of casting a metal member coated with a dissimilar metal, wherein a mold having a molding surface corresponding to the outer shape of the metal member to be cast is prepared, and inorganic fibers are dispersed in the coated metal. A casting method characterized by coating at least a part of the molding surface of the mold with a composite material, and pouring the molten metal of the base metal into the mold at a temperature lower than the melting point of the inorganic fibers. ..