JP2000239776A - Cylinder block made by die casting and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder block by die casting capable of improving mechanical strength by heat treatment without generating blisters and having excellent high temp. strength. SOLUTION: This cylinder block made by die casting is made of an aluminum alloy contg. 5 to 6% Si, 4.5 to 5.5% Cu, 0.3 to 0.5% Mg and 0.3 to 0.8% Fe, in which the amt. of gas to be occluded in the product is <=1 cc/100 g-Al and having a structure in which Al2Cu and Al-Cu-Mg crystallized products of 10 to 20 μm average particle size are dispersed. It is produced in such a manner that the vacuum in the cavities of a die is reduced to <=100 millibar, next, oxygen is blown into the cavities under the pressure equal to or above the atmospheric pressure, and, after that, the molten metal of the aluminum alloy is press-fitted into the cavities. After die casting, heat treatment of solution heat treatment (480 to 510 deg.C×4 to 8 hr) → water quenching → aging treatment (160 to 180 deg.C×4 to 6 hr) may be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die-cast cylinder block which exhibits excellent mechanical properties and can be heat-treated, and a method for producing the same.

[0002]

2. Description of the Related Art An aluminum cylinder block is manufactured by a die casting method in which a molten aluminum alloy having a predetermined composition is pressed into a mold cavity. But,
According to the conventional die casting method, gas components remaining in the mold cavity are entrained in the die cast product, causing casting defects such as blow holes and causing a decrease in mechanical strength. As the gas component, in addition to the residual air, there are a release agent applied to the inner surface of the mold and water vapor derived from a lubricant applied to the plunger of the die casting machine. There is known a vacuum die casting method in which a cavity is evacuated and then an aluminum alloy melt is press-fitted in order to eliminate adverse effects of gas components remaining in the cavity. In the vacuum die casting method, in order to remove gas from the cavity, the cavity is evacuated before injecting the molten aluminum. The degree of vacuum in the cavity is reduced to 200 to 50 by evacuation.
Although the pressure can be reduced to about 0 mbar, the degree of vacuum cannot be further reduced due to the intrusion of air from the joint of the mold.
In addition, since air is mixed when the molten aluminum is injected into the sleeve, even if the product is obtained by the vacuum die casting method, the entrainment of gas is smaller than that of the normal die casting product, but it is still Casting defects such as porosity due to gas entrainment are detected.

[0003] An oxygen die casting method has been developed to solve the drawbacks of the vacuum die casting method (Japanese Patent Application Laid-Open No. Sho 50-2).
No. 1143). In the oxygen die casting method, oxygen is filled in the cavity at a pressure higher than the atmospheric pressure in order to replace the gas in the cavity with oxygen. Since the oxygen fed into the cavity is blown out from the joints and the inlet of the mold, outside air is prevented from entering the cavity from the joints and the inlet of the mold. The supplied oxygen reacts with the molten aluminum to form fine Al ₂ O ₃ and is dispersed in the product, and does not adversely affect the die-cast product.

[0004]

It is also difficult to completely remove gas from the cavity by sending oxygen into the cavity at atmospheric pressure or higher. The residual gas is
This tends to occur when the cavity has a complicated shape.
That is, in a cavity of a mold having a complicated shape, a bottleneck to which oxygen is not supplied occurs, and in the bottleneck, gases such as air and water vapor remain without being replaced by oxygen. This residual gas is taken into the die-cast product and causes casting defects. Also, if the mechanical properties are improved by performing a heat treatment such as T6 treatment on the die-cast product, the product after the heat treatment swells due to the gas taken into the product. Due to blistering, most die cast products are used as non-heat treated materials.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem, and the mold cavity is evacuated prior to press-in of the molten aluminum alloy, and then oxygen is blown therein. This provides a die-cast cylinder block that completely removes gas components remaining in the cavity, prevents gas-induced casting defects, and exhibits excellent high-temperature fatigue strength even in diesel engines used in high-temperature environments. The purpose is to do. In order to achieve the object, the die-cast cylinder block of the present invention has a content of Si: 5 to 6% by weight, Cu: 4.5 to 5.5% by weight, Mg: 0.3 to 0.5% by weight, and Fe: 0.3-0.
Al ₂ Cu and Al-Cu-M having a composition of 8 wt%, the balance being substantially Al, the amount of occluded gas in the product being 1 cc / 100 g-Al or less, and having an average particle size of 10 to 20 μm.
The g-type crystallized material has a dispersed structure.

[0006] In this die-cast cylinder block, the cavity of the mold is depressurized to a degree of vacuum of 100 mbar or less, and then oxygen is blown into the cavity at a pressure higher than the atmospheric pressure. Manufactured by press fitting. Further, in order to impart necessary mechanical properties, a solution treatment (48
0 to 510 ° C x 4 to 8 hours) → water quenching → aging treatment (1
Heat treatment at 60 to 180 ° C. for 4 to 6 hours) may be performed after die casting.

[0007]

After the cavity of the mold is depressurized to a degree of vacuum of 100 mbar or less, oxygen is blown at a pressure higher than the atmospheric pressure, and the blown oxygen flows at a much higher flow rate than the conventional oxygen die casting method. Flows and spreads to every corner of the cavity. Therefore, water vapor and the like derived from the release agent and the lubricant attached to the inner surface of the mold are sufficiently washed out by the oxygen flow. Since the molten aluminum alloy is press-fitted into the cavity in which the interior of the mold has been cleaned, the amount of gas involved in the molten alloy filling the cavity is significantly reduced. The obtained die-cast product has no casting defects such as blow holes and porosity caused by gas entrainment. In addition, Al ₂ Cu, Al-Cu-
Since the intermetallic compound such as Mg is crystallized, high-temperature strength and wear resistance are also improved. Furthermore, since there is no blistering during the heat treatment, the required strength can be imparted by precipitating Mg ₂ Si, CuAl ₂ or the like by the T6 treatment. For example, in the ordinary die casting method, the amount of occluded gas is 2-3 cc /
It is 100 g-Al, and when trying to secure the strength by heat treatment, blisters are generated, which often results in failure. In addition, porosity becomes a core of high-temperature fatigue fracture and lowers fatigue strength. In contrast, according to the present invention, the stored gas amount 1c
Since a product of c / 100 g-Al or less is obtained, blistering does not occur during heat treatment, and the high-temperature fatigue strength is improved.

Hereinafter, the components, contents, production conditions, and the like of the aluminum alloy used in the present invention will be described. Si: 5 to 6% by weight In addition to securing molten metal flowability at the time of casting, Mg ₂
It precipitates as Si and has the effect of improving the material strength.
However, when an excessive amount of Si exceeding 6% by weight is contained,
The elongation of the material is reduced, and burrs are likely to occur during casting.
Conversely, if the Si content is less than 5% by weight, the flow of the molten metal is poor, and poor wall thickness is likely to occur.

[0009] Cu: a solid solution in a matrix of 4.5 to 5.5% by weight , and is an alloy component effective for improving the material strength and the high-temperature fatigue strength. In addition, Al-Cu based, Al
-It becomes a crystallized substance such as a Cu-Mg system and is dispersed in a mesh form at the cast crystal grain boundary to improve high-temperature strength. When Cu is precipitated as CuAl ₂ by the aging treatment, it also has an effect of improving mechanical strength. In the conventional die casting material, since a mold having a large gate area through which the molten metal flows relatively slowly is used, fine dispersion of the molten metal does not occur. When the amount of Cu is increased under these conditions, a coarse Cu-based compound is crystallized. Therefore, even when Cu is added, the content is at most 2 to 3% by weight, which is required for an engine or the like exposed to a high-temperature atmosphere. High temperature fatigue strength. On the other hand, in the present invention, by adding 4.5% by weight or more of Cu, the high-temperature fatigue strength is increased, and the characteristics required for the cylinder block are imparted. However, when the Cu content is 5.5
When the content exceeds% by weight, intermetallic compounds such as Al ₂ Cu and Al—Cu—Mg crystallize coarsely and in large quantities, and the elongation decreases.

[0010] Mg: 0.3 to 0.5% by weight At the time of aging treatment, it precipitates as Mg ₂ Si to improve the material strength. However, when an excessive amount of Mg exceeding 0.5% by weight is included, defects such as oxide entrapment and poor flow of molten metal are likely to occur. Conversely, if the Mg content is less than 0.3% by weight, the amount of Mg ₂ Si deposited is insufficient, and sufficient strength cannot be obtained even by the T6 treatment. Fe: 0.3 to 0.8 wt% is an effective alloy component for preventing the press-fitted aluminum alloy from sticking to the mold. The Fe content of 0.3 wt% or more has the effect of preventing seizure. Become noticeable. But,
If the Fe content exceeds 0.8% by weight, Al—Fe—S
The i-type coarse crystals are formed, and the high-temperature fatigue strength is reduced.

The aluminum alloy used in the present invention is:
In addition, 0.005 to 0.0, which is effective for refining eutectic Si,
5% by weight of Sr, 0.05 effective for refining cast crystal grains
０．３0.3% by weight of Ti and 0.0001-0.02% by weight of B, etc. Pb, Bi, and the like usually contained as impurities are as low as possible (specifically, 0.
(0.05% by weight or less) is preferable from the viewpoint of preventing deterioration of mechanical properties. The molten aluminum alloy adjusted to a predetermined composition is subjected to degassing, deslagging, and the like according to a conventional method. At the time of smelting, it is preferable to go through a step of holding at 740 to 760 ° C. for 30 minutes or more in order to float and separate inclusions such as oxides in the molten metal. As a result, the number of inclusions, which is one of the causes of a decrease in fatigue strength, is reduced, and the number of inclusions that can be discriminated by observation with the naked eye or a 10-fold loupe, that is, K ₁₀
The value becomes 0.01 / cm ² or less.

Atmosphere adjustment of mold cavity : Before press-fitting the molten aluminum alloy into the mold, the cavity is evacuated and then oxygen is blown in at a pressure higher than the atmospheric pressure. When the pressure in the cavity is reduced to a degree of vacuum of 100 mbar or less, gas components such as N ₂ in the cavity are reduced. In order to reduce the pressure to a degree of vacuum of 100 mbar, it is preferable to fill the joints of the mold with a sealing material to prevent the invasion of outside air. Next, when oxygen is blown in at a pressure higher than the atmospheric pressure, the blown oxygen flows at high speed to reach every corner of the cavity, a release agent applied to the inner surface of the mold, a lubricant applied to the plunger, and the like. The water vapor derived from the water is completely washed out by the oxygen flow, and even in a cavity having a complicated shape, the atmosphere becomes free from air, water vapor and the like. At this time, since the cavity is maintained at a pressure higher than the atmospheric pressure, intrusion of outside air is suppressed.

Since the molten aluminum alloy is press-fitted into the cavity whose atmosphere has been adjusted, no harmful gas components such as air and water vapor are caught in the aluminum alloy when the molten aluminum alloy cools and solidifies in the cavity. Further, oxygen in the cavity reacts with the molten aluminum alloy, and the reaction product Al ₂ O ₃ is dispersed as fine particles in the matrix, so that the resulting die-cast product does not have an adverse effect. With such an atmosphere adjustment,
The amount of occluded gas contained in die-cast products is 1cc / 100
It can be reduced to g-Al or less. The obtained die-cast product has a greatly reduced occluded gas volume,
When the conventional die-cast product is heat-treated, blisters generated on the product surface are not detected, and the mechanical strength can be improved by heat treatment such as T6 treatment. Also, a small amount of occluded gas means that there is no blowhole, porosity, etc., which is a starting point of high temperature fatigue failure, and in this respect, it can be said that the product is a die cast product excellent in high temperature strength. Further, Al ₂ Cu and Al—C having a high melting point and an average particle size of 10 to 20 μm.
High-temperature strength and fatigue strength are also improved by having a structure in which u-Mg-based crystallized materials are dispersed. In order to maintain high-temperature strength, it is necessary to disperse crystallized substances such as Al ₂ Cu and Al—Cu—Mg finely to prevent a decrease in matrix strength at high temperatures. However, a crystallized substance such as an Al ₂ Cu, Al—Cu—Mg system having an average particle diameter exceeding 20 μm is a starting point of fatigue fracture.

[0014]Heat treatment: solution treatment (480-510 ° C x
4-8 hours) → Water quenching → Aging treatment (160 ~ 180 ℃
× 4-6 hours) The obtained die-cast product has an extremely low occluded gas amount.
The gas expands due to the heating during heat treatment, causing blisters.
I will not let you. Therefore, using a casting method other than die casting
Similar to the manufactured aluminum material, heat treatment such as T6 treatment
Mg by reason _Two Si, CuAl_Two And other intermetallic compounds
It can be precipitated to increase the mechanical strength. Heat treatment
By heating at 480-510 ° C for 4-8 hours.
After the alloy component is dissolved in the matrix,
Quench in water at 0 ° C, and then at 160-180 ° C for 4-6 hours
Heating T6 treatment is employed.

The obtained cylinder block is combined with a piston to assemble a vehicle engine. Although this cylinder block is a material having good wear resistance, the high-temperature wear resistance may be insufficient at the contact surface with the piston ring exposed to a severe atmosphere. Therefore, FIG.
As shown in (1), the cylinder liner 2 is fitted into the contact surface with the piston ring 1 to protect the cylinder block 3.
The cylinder liner 2 is made of, for example, high Si having good wear resistance.
It is separately manufactured from an aluminum alloy, and is inserted and set in the cylinder block 3 by a method such as cold fitting, shrink fitting, or casting. The cylinder liner 2 may be made of cast iron, or may be an aluminum liner whose inner surface is subjected to composite plating with SiC powder.

[0016]

EXAMPLE Si: 5.2% by weight, Cu: 5.0% by weight,
The molten aluminum alloy containing 0.4% by weight of Mg and 0.4% by weight of Fe was degassed, and inclusions were separated from the molten metal by maintaining the temperature at 750 ° C. for 45 minutes, followed by deslagging. For the die used for die casting,
A vacuum was drawn at 0 mbar / sec and the cavity was evacuated to 75 mbar. Then, oxygen was blown into the cavity at a pressure of 1500 mbar, and blowing was continued until oxygen gas was blown out from the joint of the mold. In this way, the cavity was adjusted to an atmosphere free of gas components such as air and water vapor.

When the temperature of the molten metal drops to 680 ° C., the molten aluminum alloy is pressed into the cavity of the mold whose atmosphere has been adjusted, and the engine block for a light vehicle having a width of 10 cm, a length of 30 cm, and a height of 20 cm is moved at a plunger speed of 1 mm. .8
m / sec, gate speed 80m / sec, melt filling time 0.5
Die casting was performed under the conditions of seconds and a solidification time of 15 seconds. A test piece was cut out from the obtained product, the microstructure was observed, and the particle size of the crystallized product and the amount of occluded gas were measured. 490 ° C x 5
Mechanical properties at 250 ° C. were investigated for the products that had been subjected to a heat treatment of time solution heat → water quenching → 170 ° C. × 5 hours tempering. Table 1 shows the survey results. For comparison, a product obtained from an aluminum alloy having the same composition by a normal die casting method (Comparative Example 1) and a product obtained from an aluminum alloy having a Cu content of 3.1% by weight under the same conditions as in the present invention. (Comparative Example 2) was similarly subjected to occluded gas measurement and mechanical test.

[0018]

As can be seen from the test results in Table 1, in Comparative Example 1 manufactured by the ordinary die-casting method, blisters generated after the heat treatment did not become a product, and the mechanical properties varied greatly. It is presumed that the occurrence of blisters and the variation in mechanical properties are due to a large amount of occluded gas. Also,
In Comparative Example 2 having a small Cu content, although no blistering was observed after the heat treatment, the tensile strength and the fatigue strength at high temperatures were low. On the other hand, in the example of the present invention in which the Cu content was increased to 5.0% by weight, the heat treatment did not cause blistering, and exhibited excellent tensile strength and fatigue strength in a 250 ° C. high temperature atmosphere. This is because the increased amount of Cu is reduced by the aging treatment in the same manner as Mg ₂ Si.
l ₂ , Al-Cu, Al-Cu-M
The result is that g-based crystallization enhances heat resistance, improves material strength, and eliminates blowholes, porosity, etc., which are the starting points of fatigue fracture.

[0020]

As described above, the cylinder block made of die-casting of the present invention has an occluded gas amount of 1 cc / 10.
Since it is made of an aluminum alloy having a very low Cu content of 0 g-Al or less and having a high Cu content, the mechanical strength can be improved by heat treatment without blistering, and there is no blowhole or porosity which is a starting point of fatigue fracture. It shows excellent high-temperature strength as compared with conventional die-cast products.
Therefore, it is suitably used as a cylinder block exposed to a severe high-temperature atmosphere such as a diesel engine.

[Brief description of the drawings]

FIG. 1 is a cylinder block to which the present invention is applied.

[Explanation of symbols]

1: piston ring 2: cylinder liner 3: cylinder block

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/057 C22F 1/057 F02F 1/00 F02F 1/00 D // C22F 1/00 601 C22F 1 / 00 601 602 602 611 611 651 651B 691 691B 691C

Claims (3)

[Claims] 1. Si: 5 to 6% by weight, Cu: 4.5 to 5% by weight
5.5% by weight, Mg: 0.3-0.5% by weight, Fe:
Containing 0.3 to 0.8% by weight, with the balance having a substantially Al composition, and the amount of occluded gas in the product being 1 cc / 100 g-A
1 or less, and Al ₂ Cu and A having an average particle size of 10 to 20 μm.
A die-cast cylinder block having a structure in which l-Cu-Mg crystallized substances are dispersed. 2. The cavity of the mold is depressurized to a degree of vacuum of 100 mbar or less, and oxygen is blown into the cavity at a pressure higher than the atmospheric pressure.
4.5 to 5.5% by weight, Mg: 0.3 to 0.5% by weight,
Fe: 0.3 to 0.8% by weight, the balance being substantially A
1. A method of manufacturing a cylinder block made of die-casting, wherein a molten aluminum alloy having a composition of l is press-fitted into a cavity. 3. After die casting, 480-510 ° C. × 4-
Solution treatment in 8 hours, water quenching, then 160-1
The method for producing a die-cast cylinder block according to claim 2, wherein the aging treatment is performed at 80C for 4 to 6 hours.