JP5025953B2 - Method for manufacturing wear-resistant products - Google Patents

Description

  The present invention relates to a method for manufacturing a wear-resistant product using an aluminum alloy, and more particularly to a manufacturing method suitable for manufacturing a product that requires high wear resistance, such as a cylinder portion of an engine block in an internal combustion engine. .

When a product requiring wear resistance is produced by casting using an aluminum alloy, a hypereutectic Al-Si alloy that crystallizes hard primary Si particles during casting is often used. This is because it is known that primary Si particles contribute to the wear resistance of cast products. For example, automotive engine blocks use hypereutectic Al-Si alloys and low pressure casting methods. Is mass-produced by
However, products cast using a hypereutectic Al-Si alloy tend to have a large primary Si particle size during the casting process, especially when manufactured by the low pressure casting method with a slow solidification rate. There is a problem that Si particles become large and the machinability in post-processing deteriorates.

In addition, when an engine block is manufactured by casting a liner separately molded into a cylinder part that requires wear resistance with an aluminum alloy molten metal by a die casting method, if the liner is made of an aluminum alloy, it is manufactured by an atomizing method. May be produced by a powder metallurgy method in which sintered hypereutectic Al-Si alloy particles or alumina particles are baked or solidified, or a spray forming method in which billets on which the particles after atomization are deposited are drawn (for example, patent documents) 1).
However, aluminum cylinder liners produced by powder metallurgy have the problem that the particle size of primary Si particles and alumina particles is small, and good cutting workability and wear resistance can be obtained, but the cost becomes high. is there.

  Therefore, it is conceivable to manufacture the liner by a low-speed filling and high-pressure casting method represented by a squeeze casting method and the like that can manage air entrainment defects with a hypereutectic Al—Si alloy. However, castings manufactured by squeeze casting can be cast at low cost and rapidly solidified, so that the size of primary Si can be reduced and good machinability can be obtained. The temperature of the molten metal in the sleeve, runner, and cavity is lowered before the molten metal is filled into the cavity, resulting in variations in the molten metal temperature that fills the casting. There was a problem that bias was likely to occur and stable wear resistance characteristics could not be obtained.

JP 2000-42709 A

  Inventors of the present application have conducted intensive research to provide a cast product with excellent wear resistance in such a current situation. As a result, low-pressure filling is performed using a hypereutectic Al-Si alloy, followed by rapid solidification under pressure. By heat-treating the product cast by the low-speed filling high-pressure casting method, the particle size of the primary crystal Si particles is made small enough not to impair the wear resistance of the product, and the primary crystal Si generated by the low-speed filling high-pressure casting method. It has been found that the uneven distribution of particles can be compensated by agglomerating eutectic Si to grow granular Si crystals, and the present invention has been completed.

  The present invention is capable of mass-producing products having excellent wear resistance and cutting workability at low cost by heat-treating a product cast by a low-speed filling high-pressure casting method using a hypereutectic Al-Si alloy. It is an object of the present invention to provide a method for producing a possible wear-resistant product.

The manufacturing method of the wear-resistant product according to the present invention that achieves the above-described object is that the time required for filling the mold cavity with the melt of the hypereutectic Al—Si alloy is filled at a low speed of 1 second or more and 20 MPa. The low-speed high-pressure casting process in which the product is cast by rapid solidification under pressure at the above-mentioned high pressure, and the cast product obtained in the low-speed high-pressure casting process is heat-treated in a temperature range of 520 ° C. to 550 ° C. And a heat treatment step for aggregating acicular eutectic Si to grow the size of the granular Si crystal in the range of 2 to 20 μm (Claim 1).
At this time, in order to prevent blister defects and product deformation during the heat treatment process, the amount of gas contained in the molten eutectic Al-Si alloy used for casting is 0.4 cc / 100 g or less, and further 0.2 cc / 100 g. It is preferable to adjust to the following. Furthermore, it is desirable to manage the type of lubricant, mold release agent, dilution rate, coating method, etc. so as to minimize the entrainment of gas during the filling of the molten metal (claim 2).
Further, when casting a product using a hypereutectic Al-Si alloy, any method may be used as long as the molten metal filled in the mold cavity is a high temperature and the molten metal has a high cooling rate. However, in the low-pressure and high-pressure casting process, in order to suppress the temperature drop of the molten metal in the middle of filling, for example, an injection sleeve is eliminated in the mold in which a powder mold release agent having heat insulation properties is applied to the mold cavity surface. It is more desirable to include a casting step of pressurizing the molten metal after the molten metal is directly filled from the molten metal furnace.
In addition, the Si content of the hypereutectic Al—Si alloy is preferably less than 17 wt%.
Further, when an engine block is manufactured as a wear-resistant product, a liner for a cylinder portion that is particularly required to have wear resistance is prepared by the method described in any one of claims 1 to 4, and the aluminum A cylinder bore surface is formed by setting a liner made in an engine block casting mold and casting it with an aluminum alloy molten metal by a die casting method.
At this time, the aluminum liner manufactured through the low-pressure and high-pressure casting process and the heat treatment process is used for casting an engine block without cutting the inner surface of the aluminum liner that has been cut at both end faces while maintaining the draft at the time of manufacture. It is preferable to set it in a mold and cast it with molten aluminum metal (Claim 6).

According to the method for manufacturing a wear-resistant product according to the present invention, the size of primary crystal Si of a product cast with a hypereutectic Al—Si alloy can be suppressed to a range of 2 to 20 μm , and a low-speed filling high pressure The uneven distribution of primary Si particles generated by the casting method can be compensated for by growing into granular Si crystals by agglomeration of eutectic Si, so it not only has excellent wear resistance but also has excellent machinability. Product.

  Moreover, according to the method for manufacturing an abrasion-resistant product according to claim 2, the type of lubricant, mold release agent, dilution rate, application method, etc. used to minimize gas entrainment during filling. A heat treatment process that grows granular Si crystals by agglomerating acicular eutectic Si by adjusting the amount of gas contained in the hypereutectic Al-Si alloy melt to 0.4cc / 100g or less after being controlled. In this case, no blisters are produced, and there is no risk of product deformation.

  According to the method for manufacturing a wear-resistant product according to claim 3, the hypereutectic Al-Si alloy melt is filled in the mold cavity coated with the powder release agent in the high-pressure casting process. Since the molten metal is pressurized, the temperature of the molten metal flowing into the mold cavity becomes more uniform without lowering during filling, so the primary Si deposited in the cast product must be made smaller in size. In addition to this, it is possible to reduce the unevenness of the precipitated primary Si particles. Therefore, the wear resistance can be further improved.

  And according to the manufacturing method of the wear-resistant product according to claim 4, it is possible to perform casting without being affected by a decrease in molten metal temperature when the Si content of the hypereutectic Al-Si alloy is smaller. Based on the above knowledge, the Si content of the hypereutectic Al-Si alloy was set to less than 17 wt%, so that the management range of casting conditions was expanded, and casting became easier, and the size and distribution of primary crystal Si particles The bias can be reduced. On the other hand, the number of Si particles decreased as the Si content decreased, so that the number of granular Si crystals formed by the agglomeration and growth of acicular eutectic Si produced in the heat treatment process does not change, and should be compensated sufficiently. As a result, the wear resistance is improved.

According to the engine block manufacturing method of claim 5 , the aluminum liner manufactured by the method of any one of claims 1 to 4 is set in an engine block casting mold. Since the cylinder bore surface is formed by casting with an aluminum alloy molten metal by the die casting method, it is lighter and lower in cost than when casting a normal cast iron liner, and the cylinder part is It can be excellent in wear resistance and machinability.

According to the engine block manufacturing method of claim 6 , the aluminum liner manufactured through the low- pressure and high-pressure casting process and the heat treatment process is processed by cutting both end faces without processing the inner surface. The engine block casting mold liner is set in a holder that has almost the same shape as the core at the time of manufacturing the liner, and is cast with molten aluminum metal, so the number of processing steps in liner manufacturing can be reduced, and engine block manufacturing is possible. Costs can be reduced and provided at low cost.
That is, since the manufacture of aluminum liner and the manufacture of engine block use the process of high-pressure solidification of molten metal in the same cooled mold, it is used to form the inner surface of the liner when producing (casting) the aluminum liner Incorporating a liner holder pin that has the same shape (diameter and gradient) as the core pin in the engine block casting mold increases the rigidity of the liner when it is cast into the cylinder part of the engine block. As a result, the deformation resistance due to the molten metal flow increases, and at the same time, the fitting accuracy between the liner inner surface and the holder pin is increased, so that it is possible to almost completely prevent the molten metal from being inserted therebetween. Therefore, it becomes possible to meet the high dimensional accuracy requirements for clearance management on the inner surface of the liner (for clearance management with respect to the cylinder piston), and as a result, it is possible to eliminate the machining process for the inner surface of the liner that was conventionally required. Therefore, the process can be reduced and the cost can be reduced.

Hereinafter, specific preferred embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the cast structure of wear-resistant products cast using a hypereutectic Al—Si alloy is usually low, and primary crystal Si particles with large horns, acicular eutectic Si and α- It consists of Al phase.

  Here, the primary Si particles contribute to the wear resistance, but if the size (particle size) is too small, the primary Si particles cannot contribute to the wear resistance, so the primary crystal Si particles may have a particle size of 2 μm or more. More preferably, it is more preferably 5 μm or more. However, if the particle size of the primary Si particles is larger than about 20 μm, the machinability in post-processing deteriorates, so the particle size of the primary Si particles is preferably in the range of 2 to 20 μm, more preferably 5 to 20 μm. It is preferable to set it as the range.

In addition, the uneven distribution of the primary Si particles affects the wear resistance of the cast product, and it is necessary to reduce the uneven distribution of the primary Si particles as much as possible.
Therefore, products cast by the low pressure casting method using Al-17% Si alloy (A: low pressure casting method) and products cast by the normal low speed high pressure casting method using Al-15% Si alloy (B: Squeeze method) and a product cast by a low-speed high-pressure casting method in which the molten metal is filled in a mold cavity coated with a powder release agent using an Al-15% Si alloy (C) : Powder low-speed, high-pressure casting method), and by observing the microstructure of the as-cast product (non-heat treated product) and the product (C) subjected to heat treatment after casting (product (D)), the primary crystal The size and distribution of Si particles were evaluated (see FIG. 2). The results are shown in Table 1.

Incidentally, the general casting conditions of the “low pressure casting method” referred to in the present specification is a method of casting using a low pressure casting machine at a casting pressure of 50 KPa or less. As the casting conditions of the “low speed high pressure casting method”, In this method, the time required for filling the mold cavity with the molten metal is set to 1 second or more, and the pressure applied when the molten metal filled in the mold cavity is solidified is cast at 20 MPa or more.
The low-pressure cast product (A) described above is cast at a mold temperature of 350 ° C., a molten metal temperature of 720 ° C., a molten metal pressure of 30 KPa, a mold filling time of 15 seconds, and a cycle time of 10 minutes. The low-speed high-pressure cast product (B) is cast at a mold temperature of 250 ° C., a molten metal temperature of 740 ° C., a casting pressure of 50 MPa, a mold filling time of 1.5 seconds, and a cycle time of 60 seconds. Further, the casting product (C) of the powder low-speed high-pressure casting method in which the mold cavity coated with the powder release agent is filled with the molten metal and then the molten metal is pressurized has a mold temperature of 200 ° C and a molten metal temperature of 715 ° C. , Casting pressure 70MPa, mold filling time 5 seconds, cycle time 90 seconds.

As shown in Table 1 above, in the product (A) cast by the low pressure casting method, the number of primary crystal Si particles in 1 mm ² is as small as about 270, and the size of primary crystal Si particles is 20 to There are 27% of 45 μm particles and 25% of 46-60 μm particles, indicating that the machinability is poor.
On the other hand, in the product (B) cast by the normal low speed filling high pressure casting method (squeeze method), the number of primary Si particles in 1 mm ² is increased to about 350, and the size of the primary Si particles is Machinability is improved because 48% of particles of 20-45 μm are eliminated and particles of 46 μm or more are eliminated and the size is reduced as a whole, but wear resistance is poor due to uneven distribution of primary Si particles It is expected to be.
On the other hand, in the product (C) cast by the powder low-speed high-pressure casting method in which the mold cavity coated with the powder release agent is filled with the molten metal and then the molten metal is pressurized, the first in 1 mm ² The number of primary Si particles is as large as about 600, and the size of primary Si particles is further reduced to 11% of 20-45 μm particles, and the size of primary Si particles is also small. However, there is a bias in the distribution of primary Si particles, which is expected to have poor wear resistance.

On the other hand, a product (C) cast by a powder low-speed high-pressure casting method in which a mold cavity coated with a powder release agent is filled with a molten metal and then the molten metal is pressurized is subjected to heat treatment at 540 ° C. for 1 hour. In the product (D), since the structure of the eutectic part before heat treatment becomes finer, the number of granular Si crystals formed by aggregation and growth of eutectic Si by heat treatment increases, and the primary crystal Si particles in 1 mm ² The total number of particles and the number of granular Si crystals that have grown by the aggregation of eutectic Si particles is very large, about 1120, which compensates for the uneven distribution of primary Si particles, as shown in FIG. Since the Si particles are present uniformly throughout, it is expected that the wear resistance is good.

Next, with respect to the products (A) to (D), the wear resistance and seizure resistance were evaluated by the following methods, respectively. The result is shown in the graph of FIG.
<Abrasion test>
Rotate a disk made of the same material as the liner, and perform a pin-on-disk type wear test in which a pin of the same material as the piston ring is pressed at a constant load for a certain period of time while spraying lubricant on the surface to determine the wear depth. .
<Baking test (ring-on-disk type)>
Rotate a disk made of the same material as the liner, press the ring made of the same material as the piston ring while dripping lubricating oil on the surface, gradually increase the load on the ring, and increase the surface pressure at which the friction coefficient suddenly increases. Ask.

  As can be seen from FIG. 3, the wear depth of the product (A) cast by the low pressure casting method is 4.5 μm, the baking surface pressure is 8 MPa, and the product cast by the low speed filling high pressure casting method (squeeze method) ( The wear depth of B) is 3.6μm, the baking surface pressure is 5MPa, and it is cast by the powder low-speed filling high-pressure casting method in which the melt is filled after filling the mold cavity coated with the powder release agent. The wear depth of the finished product (C) is 2.2 μm and the baked surface pressure is 8 MPa, while the product (D) obtained by heat-treating the product (C) has a wear depth of 0.9 μm and the baked surface pressure. Became 13MPa. From this, it was confirmed that wear resistance and seizure resistance were improved as the size of the primary crystal Si particles was small, the number of Si particles was large, and the distribution of Si particles was not biased. Incidentally, the smaller the wear depth and the higher the seizure surface pressure, the better the wear resistance.

  On the other hand, if gas is entrained in the casting product or if the gas content in the molten metal is high, blisters (so-called “blister”) and deformation are generated in the product during the heat treatment process, adversely affecting the function and quality of the product. May give. Therefore, it is necessary to prevent air or gas generated by reacting with the molten metal during filling from being caught during product casting. Therefore, it is necessary to perform casting under a laminar flow condition by limiting the type of release agent applied to the mold cavity surface, the type of lubricant applied to the plunger, and application conditions. It is necessary to select a release agent and a lubricant that have as few gas generating components as possible, and to make the application conditions by controlling the application amount to the minimum necessary amount. However, even if the casting conditions are controlled in this way, blistering and deformation may occur depending on the heat treatment process conditions when the amount of gas contained in the molten metal is 0.4 cc / 100 g or more. It is necessary to control the amount of gas in the molten metal, and it is desirable that the amount of gas in the molten metal be 0.2 cc / 100 g or less under conditions where the heat treatment temperature is high.

Table 2 below shows the results of examining the blisters produced in the product when the cast product was heat treated at 530 ° C. and 540 ° C. for 2 hours. Blistering is eliminated by limiting the amount of release agent applied from 200cc to 100cc, but when the amount of gas in the molten metal exceeds 0.4cc / 100g, blistering is generated, and at a heat treatment temperature of 540 ° C, 0.2 cc When it exceeds / 100g, some blisters are generated.
The release agent used here is a commercially available silicone-based water-soluble release agent diluted by a factor of 100, and the release agent is applied by a spray method. This is the total amount applied to both the movable mold and fixed mold of the cavity.

  In addition, the size of the primary crystal Si particles in the cast product is greatly affected by the melt temperature and cooling rate, and when cast under casting conditions where the melt temperature is high when the mold cavity is filled and the cooling rate is fast, the primary crystal Si particles are said to be smaller.

  Therefore, in the present invention, a high-pressure casting process is used in which a molten product of hypereutectic Al-Si alloy is slowly filled into the mold cavity and then the product is cast by rapid solidification under pressure. Since this is likely to occur, it is desirable to reduce the decrease in molten metal temperature as much as possible. That is, it is better not to fill the molten metal into the mold cavity through the injection sleeve, but to use a mold cavity in which a powder release agent having a heat insulating property is applied in advance. It is desirable to fill the mold cavity directly from the melt furnace into the mold cavity without using the injection sleeve when filling, and then pressurize the molten metal filled into the mold cavity with a pressurizer or the like. In some cases, the powder release agent may be applied by diluting the powder into the release agent, but a method of directly attaching the heat insulating powder to the mold surface by electrostatic application or the like is more effective.

According to such a low-speed high-pressure casting method, it is possible to eliminate the temperature drop of the molten metal when it is supplied to the injection sleeve, and the molten metal is directly fed into the mold cavity coated with the powder release agent. It is possible to suppress the temperature drop of the molten metal in the middle of filling the mold cavity, and in addition, after filling the mold cavity, pressurizing the molten metal from the outside (with a pressurizer), the mold The powder release agent that has separated the cavity surface from the molten metal is momentarily crushed so that the molten metal enters the powder and comes into direct contact with the mold cavity surface. Then, the molten metal in the mold cavity is rapidly cooled and cast at a high solidification rate. As a result, as shown in FIG. 2, the primary Si particles have a smaller particle size and the distribution of the primary Si particles is relatively small compared to products cast by a normal low pressure casting method or squeeze method. Abrasion resistance and machinability are improved.
In addition, for details of the powder low-speed high-pressure casting method in which the molten metal is filled in the mold cavity coated with the powder release agent referred to in the present invention and then the molten metal is pressurized, JP-B-6-88119 Since it is described in the publication, the patent 3204568 publication, the patent 3480875 publication, etc., detailed description here is abbreviate | omitted.

  On the other hand, the required quality required for engine blocks and cylinder liners, particularly the required quality for wear resistance and machinability, is very high, so it is difficult to overfill the mold cavity coated with the powder release agent as described above. Even if casting is performed by a low-speed high-pressure casting method in which a crystalline Al—Si alloy is directly filled and pressed, the distribution of primary Si particles may not reach the required level.

  When a specific heat treatment is applied to a product cast from a hypereutectic Al—Si alloy, as shown in FIG. 4, acicular eutectic Si aggregates in the region where primary Si particles do not exist due to the bias. The number of granular Si particles that grow in the same size order (particle size) as the crystalline Si particles and exhibit wear resistance has increased, and the uneven distribution of primary Si particles has been compensated for Understood.

  However, the phenomenon that the wear resistance is improved by heat treatment of the cast product is considered to be a property unique to hypereutectic Al-Si alloys. In the case of hypereutectic Al-Si alloys using hypoeutectic Al-Si alloys, As shown in FIG. 5, the inventors confirmed that a thin plate-like eutectic Si grows into a slightly larger rod shape by heat treatment and does not become particles as shown in FIG. Yes.

Next, heat treatment conditions according to the present invention applied to a product cast from a hypereutectic Al—Si alloy will be described.
Incidentally, in each Example described in this specification, heat treatment was performed by accommodating the cast product directly inside the electric furnace.

Using a hypereutectic Al-Si alloy (Al-15% Si alloy), the cylinder liner cast into the engine block is cast by the low-speed high-pressure casting method described above, and the cylinder liner is heated from 500 ° C to 570 ° C. The microstructure of the product that was heat-treated for 1 hour at different temperatures in increments of 10 ° C. and then water-cooled after the heat treatment was observed. The results are shown in FIGS. 6a and 6b.
The cylinder liner produced here has a solidus temperature of 577 ° C.

When the microstructure shown in FIG. 6 is observed, acicular eutectic Si grows when the heat treatment temperature reaches 500 ° C., and the size (particle size) of the eutectic Si particles is the same level as that of the primary Si particles. When the heat treatment temperature is 540 ° C. or higher, the primary Si particles and the grown granular Si crystals become almost uniformly dispersed. However, it is understood that when the temperature exceeds 560 ° C., the primary Si particles begin to bond with each other, and the particle size of the primary crystal Si particles becomes a size (20 μm) or more that degrades the machinability.
From this, it is judged that the heat treatment temperature is preferably in the range of 500 ° C to 550 ° C, and most preferably in the range of 540 ° C to 550 ° C.

When the cast product is heat-treated in the range of 520 ° C. to 550 ° C., blisters are generated or deformed due to the influence of gas contained in the casting. In general, if the molten metal is filled into the mold cavity at a low speed, gas entrainment that affects the product is suppressed, so that blistering can be prevented, but if the heat treatment is performed at a temperature of 530 ° C or higher, the molten metal Blisters are generated under the influence of gas dissolved in the inside. Accordingly, it is desirable to adjust the amount of gas contained in the hypereutectic Al—Si alloy melt to be used to 0.4 cc / 100 g or less, and to 0.2 cc / 100 g or less when the heat treatment temperature is 540 ° C. or more.
However, even if the amount of gas in the molten metal is adjusted, if there is a gas generating component that reacts with the molten metal while the mold is full, the gas is absorbed into the molten metal and blisters and deformation are generated during heat treatment. It is necessary to control the release agent to be applied and the components and types of the lubricant to be applied to the plunger, as well as the application conditions of the release agent and the lubricant.

Next, using the cylinder liner as a cast product, the heat treatment temperature was kept constant at 520 ° C., heat treatment was performed for 1 hour, 4 hours, and 7 hours, and the microstructure of the product cooled with water after the heat treatment was observed. The result is shown in FIG.
When the microstructure in FIG. 7 is observed, acicular eutectic Si grows when heat-treated at 520 ° C. for 1 hour and begins to grow to the same size order as the primary Si particles. The granular Si crystals grown from the eutectic became almost uniformly dispersed. From this, it is understood that if the heat treatment temperature is 520 ° C., which is considerably lower than the solidus temperature of the cast product, a considerable time is required for the heat treatment.

Then, using the cylinder liner as a cast product, the heat treatment temperature was raised to 540 ° C and 550 ° C, heat treatment was performed for 1 hour, 2 hours, and 4 hours, respectively, and the microstructure of the product cooled with water after the heat treatment was observed. did.
FIG. 8 shows the microstructure when the heat treatment temperature is 540 ° C., and FIG. 9 shows the microstructure when the heat treatment temperature is 550 ° C.

As shown in FIG. 8, when the heat treatment temperature is 540 ° C., the granular Si crystal grown from the needle-like eutectic already has a structure in which the heat treatment time is 1 hour, and the heat treatment time is 4 hours. Even so, there was not much change.
When the heat treatment temperature is 550 ° C., as shown in FIG. 9, the heat treatment time is 1 hour, and the granular Si crystal grown from the needle-like eutectic becomes a substantially uniformly dispersed microstructure. After 2 hours, the primary Si particles started to bond with each other, and the primary Si particle size became larger than the size (25 μm) to deteriorate the machinability.
From this, it is presumed that the heat treatment time is short if the heat treatment is performed at a temperature close to the solidus temperature of the cast product.

Next, the influence of the Si component ratio (wt%) in the hypereutectic Al-Si alloy on wear resistance and castability (productivity) was examined.
As the hypereutectic Al-Si alloy, Al-15% Si alloy and Al-17% Si alloy were used to cast the cylinder liner in the same manner as above, and the distribution of Si particles before and after heat treatment, respectively. The biased state of was observed. The microstructure is shown in FIG.
Incidentally, as the heat treatment conditions, heat treatment was performed at a heat treatment temperature of 540 ° C. for 1 hour.

As shown in the microstructure shown in FIG. 10, as the Si content increases, the molten metal temperature needs to be cast at a higher temperature, and is easily affected by a decrease in the molten metal temperature during the filling process. Since the uneven distribution of the sheath becomes large, it can be seen that when cast under the same conditions, the size of the primary Si particles is smaller in the 15% Si alloy than in the 17% Si alloy, and the uneven distribution is small.
From this, it is possible to perform casting with a lower Si content without being affected by the lowering of the molten metal temperature, so that the management range of casting conditions is widened and casting becomes easier, and the size of primary Si particles and It is understood that the distribution bias is also reduced.

  On the other hand, if the Si content is low, the amount of primary Si particles crystallized is naturally reduced, and the wear resistance is also deteriorated accordingly. However, as shown in the microstructure shown in FIG. 10, even in an alloy having a low Si content (15% Si-based alloy), acicular eutectic Si grows by heat treatment, and the size of the primary Si particles increases. It grows into granular Si crystals of the same size, and it can be seen that the overall metal structure has a large number of Si particles and excellent wear resistance.

  If the Si content exceeds 20%, the primary Si particle size before heat treatment is often relatively large, and it is possible to reduce the uneven distribution of Si particles by the heat treatment process. Crystalline Si particles may be enlarged by heat treatment, but they will not be reduced, so that the machinability is deteriorated. For this reason, the ratio of the Si component in the hypereutectic Al—Si alloy is more preferably less than 17 wt%.

  Further, when an engine block is manufactured as a wear-resistant product, a cylinder part liner that is particularly required to have wear resistance is manufactured by the above-described method using a hypereutectic Al-Si alloy. Then, the cylinder bore surface is formed by setting the aluminum liner in an engine block casting mold without machining the inner surface and casting it with an aluminum alloy molten metal by a die casting method.

  At that time, a liner set holder (bore pin) having the same shape as the core used to form the inner surface of the liner when producing (casting) the aluminum liner can be installed in the engine block casting mold. desirable.

That is, in die casting, it is necessary to cast a product with a draft angle in order to release the product from the mold smoothly. Therefore, even when an aluminum liner is cast, it is necessary to provide a draft to the core forming the inner surface of the liner, and as a result, a gradient is formed on the inner surface of the liner.
On the other hand, when casting a liner into an engine block, if the gap between the inner surface of the liner and the bore pin that holds the liner is set too large, the molten metal enters the gap, and the molten metal enters the bore pin. A problem occurs that the next liner cannot be installed due to adhesion. However, if the setting of the gap with the bore pin is small, there is a problem that the liner cannot be mounted when the temperature of the bore pin rises with casting and the outer diameter (bore diameter) increases. Therefore, it is necessary to process the inner surface of the liner with very high dimensional accuracy, which increases the cost of the liner.
Therefore, a bore pin having the same size as the core used to cast the aluminum liner, that is, the core used to form the inner surface of the aluminum liner, and the same draft angle is used as the engine block molding die. By installing and casting the above aluminum liner on the bore pin, the gap between the inner surface of the liner and the outer peripheral surface of the bore pin can be almost eliminated. As a result, molten metal enters between the liner and the bore pin. And can solve the problem that the liner cannot be installed on the bore pin. In addition, the thickness of the aluminum liner is increased as much as the gradient is applied, and the strength and rigidity are increased accordingly, so that the effect of being less susceptible to deformation due to the molten metal during filling can be expected.
In addition, since the liner made of aluminum can be used as it is after being cast, both ends are cut to remove the sprue part and overflow part, heat treated, and then brought into the engine block casting process. Processes can be reduced and inventory can be eliminated.

Macro structure photograph explaining the uneven distribution of Si particles before and after heat treatment. Microstructure photographs explaining the relationship between various casting methods and the size and distribution of primary Si particles. The graph explaining the relationship between the unevenness of the size and distribution of primary Si particles and the wear resistance and seizure resistance. Microstructure photograph explaining the heat treatment temperature and the growth state of eutectic Si particles. Microstructure photograph explaining heat treatment of hypoeutectic Al-Si alloy and growth state of eutectic Si. Microstructure photograph explaining the heat treatment temperature and the growth state of eutectic Si particles. Microstructure photograph explaining the heat treatment temperature and the growth state of eutectic Si particles. Microstructure photograph explaining the heat treatment time and the growth state of eutectic Si particles when the heat treatment temperature (520 ° C) is kept constant. Microstructure photograph explaining the heat treatment time and the growth state of eutectic Si particles when the heat treatment temperature (540 ° C) is kept constant. Microstructure photograph explaining the heat treatment time and the growth state of eutectic Si particles when the heat treatment temperature (550 ° C) is constant. Microstructure photograph explaining the uneven distribution of Si particles before and after heat treatment due to the difference in Si content in hypereutectic Al-Si alloy.

Claims (6)

Low-speed and high-pressure casting process in which the time required to fill the mold cavity with the melt of hypereutectic Al-Si alloy is filled at a low speed of 1 second or more, and is rapidly quenched and solidified at a high pressure of 20 MPa or more. Then, the cast product obtained in the low-speed and high-pressure casting process is heat-treated in a temperature range of 520 ° C. to 550 ° C. to agglomerate acicular eutectic Si in the cast product, thereby reducing the size of the granular Si crystal to 2 A method for producing a wear-resistant product comprising: a heat treatment step for growing in a range of ˜20 μm.   The method for producing a wear-resistant product according to claim 1, wherein the amount of gas contained in the hypereutectic Al-Si alloy molten metal is adjusted to 0.4 cc / 100 g or less.   The low-pressure high-pressure casting step includes a casting step of pressurizing the molten metal after the molten metal is filled in a mold cavity coated with a powder release agent. A manufacturing method for wearable products.   The method for producing a wear-resistant product according to any one of claims 1 to 3, wherein the Si content of the hypereutectic Al-Si alloy is less than 17 wt%.   The wear-resistant product is an aluminum liner produced by the method described in any one of claims 1 to 4, and the liner is set in an engine block casting die and an aluminum alloy is formed by a die casting method. A method for manufacturing an engine block, wherein a cylinder bore surface is formed by casting with molten metal.   6. The method of manufacturing an engine block according to claim 5, wherein an aluminum molten metal is set in the mold for casting the engine block without processing an inner surface of the aluminum liner manufactured through the low speed and high pressure casting process and the heat treatment process. An engine block manufacturing method characterized by casting.