JP3195392B2 - Method for producing high strength and high toughness aluminum alloy casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is, for example, automobile parts, in particular strength, members to optimum high strength and high toughness aluminum alloy castings toughness is required (hereinafter, simply referred to as an aluminum alloy casting.) The method of casting It is about.

[0002]

2. Description of the Related Art Aluminum alloy forgings (for example, JIS 6061) have few internal defects.
It has the advantage of high reliability in terms of quality, such as excellent strength and toughness, but has the problem of high cost.
On the other hand, aluminum alloy castings (for example, JIS AC
4C) has the advantage of lower cost compared to forged products, but because of its low strength and toughness and low reliability, the product must be made larger and the weight increased, and a lightweight aluminum alloy is used. The merit of conversion is reduced.

[0003] One of the reasons that the strength and toughness of an aluminum alloy casting is lower than that of a forged product is that Si added to improve castability, particularly, lowers toughness. Conceivable.

[0004]

SUMMARY OF THE INVENTION In the present invention, the strength and toughness are improved by reducing the amount of Si, which is a toughness inhibiting element, as much as possible and by increasing the strength and toughness improving elements. A first object is to improve the alloy, and a second object is to easily cast the alloy casting by applying a predetermined pressure.

[0005]

[0006]

Means for Solving the Problems] aluminum case of the present invention
In the method of manufacturing a gold casting , Si: 2.5 to 4.4 w
t%, Cu: 1.5 to 2.5 wt%, Mg: 0.2 to
0.5 wt%, and the balance is substantially Al, or Si: 2.5 to 4.4 wt%, Cu: 1.5 to
2.5 wt%, Mg: 0.2-0.5 wt%, Sr:
The raw material is dissolved so that it contains 0.005 to 0.2 wt% and the balance is substantially Al, and the molten metal of the raw material is dissolved in 24.5 to 1 wt.
By applying a pressure of 47 MPa, cast into a mold by pressure casting, by the obtained member for solution treated first division
It solved the problem and the second problem.

Hereinafter, the present invention will be described in more detail. First, in the method for producing an aluminum alloy casting of the present invention
The reasons for limiting the chemical components of the raw materials and the amounts added are as follows. (A) Si Si affects toughness and castability. That is, when the amount of Si added is 2.5 wt% or less, castability is poor and casting cracks occur. When the amount of Si added is 4.4 wt% or more, the toughness decreases. Therefore, the addition amount of Si is set to 2.5 to 4.4 wt%. It is more preferable that the amount of Si added is 3.0 to 4.0 wt%.

(B) Cu Cu is a material effective for improving the strength. However, when the added amount of Cu is 1.5 wt% or less, there is no effect on the strength improvement. Further, the addition amount of Cu is
If the content is 2.5 wt% or more, the corrosion resistance and the stress corrosion cracking property deteriorate. Therefore, the addition amount of Cu is 1.5 to 2.5 wt.
%. The addition amount of Cu is 1.8 to 2.3 wt.
% Is more preferable.

(C) Mg Mg is a material effective for improving strength. However, when the added amount of Mg is 0.2 wt% or less, the effect of improving the strength is small. Also, the amount of Mg added is
If it is 0.5 wt% or more, the toughness decreases. Therefore, M
The amount of g added is 0.2-0.5 wt%. Note that M
The addition amount of g is more preferably 0.3 to 0.5 wt%.

(D) Sr In the raw material of the method for producing an aluminum alloy casting of the present invention, Sr is further added at 0.00
More preferably, the content is 5 to 0.2% by weight. Sr
Is an element effective for refining and spheroidizing eutectic Si, and affects the strength and toughness of an aluminum alloy casting. In particular, it contributes to stabilization of such mechanical properties. Sr is also an element effective in suppressing segregation of the eutectic structure. However, the amount of Sr added is 0.005 wt%.
Below, spheroidization and refinement of the eutectic Si phase are insufficient. When the amount of Sr added is 0.2 wt% or more, Sr
The compound crystallizes out and the mechanical properties, especially the elongation, decrease.
Therefore, the amount of Sr added is 0.005 to 0.2 wt.
% Is more preferable.

Incidentally, Sr has been conventionally used as Al which has a low solidification rate.
-Occasionally added to improve the eutectic Si phase of Si-based alloys. However, in the method for producing a casting having a high solidification rate such as the aluminum alloy casting of the present invention, the eutectic S
Since the effect of adding Sr was considered to be small because the i-phase crystallized finely, Sr was not added. However, the inventors of the present invention dare to add Sr to an aluminum alloy casting having a high solidification rate, and to add eutectic S
By making the i-phase finer and spheroidal, the mechanical properties of the aluminum alloy casting were developed without variation. In addition, there is also an effect of suppressing segregation of a eutectic structure which is easily generated by pressurization, and the addition of Sr has an effect of stably imparting excellent mechanical properties to an aluminum alloy casting.

[0012] The method for producing an aluminum alloy casting of the present invention.
The size of dendrite in the aluminum alloy casting obtained by the above method is preferably as follows . That is, the smaller the size of the dendrite, the better the strength and the toughness are. However, if the thickness exceeds 30 μm, the toughness is reduced. Note that the size of the dendrite is more preferably 25 μm or less.

The method for producing an aluminum alloy casting of the present invention.
The reasons for limiting the pressure applied to the molten metal in the pressure casting according to the above are as follows. Since the aluminum alloy casting according to the present invention has poor castability, the molten metal is 24.5-147M.
It is desirable to apply pressure at Pa. At a pressure of 24.5 MPa or less, shrinkage cavities occur in the thick part of the casting, which causes casting cracks. Further, when the pressure is 147 MPa or more, the castability hardly changes. Therefore, the pressure applied to the molten metal is 24.5 to 147 MPa. Note that this pressure is more preferably set to 29.4 to 98 MPa.

Further, the production of the aluminum alloy casting of the present invention
Regarding the heat treatment in the fabrication method, the higher the solution temperature, the better the elements such as Cu, Mg, and Si diffuse in the alloy, and the shorter the solution treatment time, the better. However, if the solution temperature is too high, a burning phenomenon occurs and the strength is significantly reduced. Therefore, as a condition for the solution treatment of the alloy, the alloy is held at 520 to 550 ° C. for 3 to 10 hours, and then quenched with water. In addition, it is 3 ~
It is more preferable to hold for 6 hours. Then, return temperature 1
Hold at 50-190 ° C for 2-10 hours. In addition, it is more preferable to hold at a return temperature of 160 to 180 ° C for 2 to 6 hours. By performing the solution treatment under such conditions,
Elements such as Cu, Mg, and Si, which could not be sufficiently dissolved in the Al matrix by the ordinary solution treatment, can be dissolved in the Al matrix in a sufficient amount and uniformly, and the eutectic Si phase is improved. Can be spheroidized.
As a result, the method for producing an aluminum alloy casting of the present invention
By the heat treatment, the strength and toughness of the aluminum alloy casting are remarkably improved as compared with the conventional heat treatment.

The size of the spheroidized eutectic Si phase is preferably 20 μm or less. Setting the size of the spheroidized eutectic Si phase in such a range greatly contributes to improvement in the strength and toughness of the aluminum alloy casting. Further, as described above, the addition of 0.005 to 0.2% by weight of Sr to the raw material of the method for producing an aluminum alloy casting of the present invention promotes the spheroidization of the eutectic Si phase, The size can be further reduced to 10 μm or less. Thus, the addition of Sr has a favorable effect on the strength and toughness of an aluminum alloy casting.

Further, in order to prevent the occurrence of defects due to entrainment of air into the molten metal during casting, it is desirable to apply a vacuum of 30 Torr or less before casting.

[0017]

In the present invention, the amount of Si to be added is suppressed and the size of dendrite in the matrix is reduced, so that the toughness of the aluminum alloy casting is improved. Further, in the present invention, the strength of the aluminum alloy casting was improved by adding predetermined amounts of Cu and Mg.

Deterioration of castability due to suppression of the added amount of Si can be minimized by performing pressure casting at a predetermined pressure. Further, the strength of the aluminum alloy casting can be increased by appropriate heat treatment. Thus, the present invention makes it possible to provide a high-strength, high-toughness aluminum alloy casting and a method of manufacturing the same at low cost. The aluminum alloy casting according to the present invention is naturally superior in strength and toughness to the conventional aluminum alloy casting and further to the conventional aluminum forged product. Therefore, Al <br/> Miniumu alloy casting according to the present invention has high reliability.

[0019]

【Example】

(First Embodiment) An embodiment according to the present invention will be described below.
In the first embodiment, Si: 4.0 wt%, Cu:
The raw material was melted and cast so as to form an aluminum alloy having a composition of 2.0 wt% and Mg: 0.3 wt%, and the balance substantially consisting of Al and unavoidable impurities, thereby producing a suspension arm.

First, a casting apparatus shown in FIG. 1 was used for casting. This casting apparatus is a pressure casting apparatus including a cavity 1 formed in a mold and a molten metal supply passage 3 connecting the cavity 1 and a melting furnace 2. At the time of casting, first, the temperature of the molten metal 4 is set to 720 ° C. in the melting furnace 2, and the composition thereof is 4.0 wt% of Si and 2.0 wt% of Cu.
%, Mg: 0.3 wt%, and the balance was adjusted to be an aluminum alloy consisting essentially of Al and unavoidable impurities. The casting was performed while maintaining the mold temperature at 200 ° C.

Hereinafter, the casting method will be described. First, the vacuum pump 5 is operated, the inside of the cavity 1 is evacuated through the vacuum path 6, and the pressure in the cavity 1 is reduced by 15%.
Torr. Immediately before the completion of the vacuum process, the pressure reducing pump 7 is operated to reduce the pressure in the reservoir 9 and the molten metal supply passage 3 through the reduced pressure path 8, thereby separating the molten metal 4 in the melting furnace 2 from the partition member 10. It was raised to just below.

Simultaneously with the completion of this step, the partition member 10 was quickly raised, and the communication path 11 between the cavity 1 and the molten metal supply path 3 was communicated. At this time, the molten metal 4 flows into the cavity 1 due to the pressure difference between the cavity 1 and the molten metal supply passage 3. At this time, the speed (gate speed) when the molten metal passed through the weir portion 12 was 3000 mm / s.

Next, at the same time as the cavity 1 is filled with the molten metal 4, the partition member 10 is lowered to seal the cavity 1, and the pressing member 13 is lowered so as to have a pressure of 98 MPa. The melt inside was solidified under pressure. The cast material thus obtained was subjected to a solution treatment at 535 ° C. for 3 hours. As a result, Cu, Mg, and Si could be rapidly and uniformly dissolved in the matrix in a sufficient amount. Subsequently, quenching was performed with water at 80 ° C., and thereafter, tempering was performed at 160 ° C. for 5 hours to obtain a suspension arm as an alloy casting. The minimum thickness of the suspension arm was 3 mm.

A tensile test was performed on the obtained suspension arm. As a result, the strength of this suspension arm was 382.2 MPa , and the elongation indicating toughness was 1
4%. The structure of the suspension arm was observed with an optical microscope. According to this observation, the size of the dendrite was about 20 μm in the matrix, and it was found that the eutectic Si phase was well spheroidized in the structure.

For comparison, a suspension arm was cast under the same conditions as in the first embodiment, except that the material was changed to a conventional aluminum alloy (JIS AC4CH). Note that the conventional aluminum alloy AC4CH is
i: 8.1 wt%, Mg: 0.3 wt%, the balance substantially consisting of Al and unavoidable impurities. The same tensile test as that of the first example was performed on the comparative product 1. As a result, the strength of this suspension arm is 29
It was 4 MPa and the elongation was 4%. The structure of the suspension arm was also observed with an optical microscope. According to this observation, the size of the dendrite was
It is up to about 35μm in click vinegar, eutectic Si in the tissue
It was found that the phases were not properly refined.

Further, using the casting apparatus used in the first embodiment, the relationship between the degree of vacuum in the cavity 1 in the vacuum process and the defective rate due to the entrainment of air into the molten metal 4 was examined. The result is shown in FIG. FIG. 2 shows that in the case of this casting apparatus, when the degree of vacuum is 30 Torr or less, the defect rate becomes almost zero. The relationship between the degree of vacuum in the cavity 1 and the defect rate is a relationship that holds for all cases using the above-described casting method, regardless of the shape of the cavity 1.

The method of casting after the cavity 1 is evacuated as in the first embodiment is particularly effective in preventing the occurrence of defects due to air entrapment such as casting of thick members. (Second Embodiment) In the second embodiment, the same casting as that shown in FIG. 1 is carried out except that the cavity for the suspension arm according to the first embodiment is shaped like an automobile carrier. The aluminum alloy according to the present invention (Si: 3.
An alloy containing 0 wt%, Cu: 2.5 wt%, and Mg: 0.4 wt%, and the balance substantially consisting of Al and unavoidable impurities) was cast. The casting conditions were a melt temperature of 700 ° C., a mold temperature of 200 ° C., and a degree of vacuum of 15 T for the cavity 1 before the melt was poured.
orr, the gate speed was 1000 mm / s, and the pressure applied by the pressure member 13 was 78.4 MPa.

As a heat treatment of the cast material, 53
After solution treatment at 5 ° C. for 3 hours, quenching was performed in water at 80 ° C., and tempering was performed at 180 ° C. for 3 hours. Thus, the vehicle carrier of the second embodiment was obtained, and its minimum thickness was 5 mm. The size of the dendrite in the matrix was about 20 μm. For comparison, the material was a conventional aluminum alloy (JIS AC4).
A carrier for an automobile was cast under the same conditions as in the second embodiment except that CH) was changed to Comparative Example 2. Tensile tests of the vehicle carriers of the second example and the comparative example 2 were performed. As a result, the strength of the vehicle carrier of the second embodiment is 401.8.
MPa , and the elongation was 10%. On the other hand, Comparative Example 2
Has a strength of 303.8 MPa ,
The elongation was 6%. Thus, it is clear that the vehicle carrier of the second embodiment exhibited much higher strength and toughness than that of Comparative Example 2.

That is, in an Al-Si-Cu-Mg alloy, Cu: 2.0 wt%, Mg: 0.3 wt%, Si:
1.0, 2.0, 3.0, 4.0, 5.0, 6.0,
An alloy consisting of 7.0 wt% and the balance Al was melted, poured under the conditions of a melt temperature of 800 ° C. and a mold temperature of 150 ° C., and solidified while applying a pressure of 49 MPa to the melt to obtain a 30 mm diameter. 7 cylindrical test piece material
I got one.

For comparison, gravity casting was performed using the same mold and the same alloy under the conditions of a melt temperature of 760 ° C. and a mold temperature of 150 ° C. with a pressure of about 9.8 × 10 ⁻³ MPa. I got another 7 pieces of material. A JIS No. 4 test piece was cut out from this test piece material, the test piece was subjected to a solution treatment at 530 to 540 ° C. for 4 hours according to the composition, then quenched in water at 80 ° C., and then at 160 ° C. for 4 hours. Was tempered. A tensile test was performed using the heat-treated test piece thus obtained. This result is shown in FIG.
Shown in

As can be seen from FIG. 3, sufficient elongation cannot be expected when the amount of Si added is 4.4 wt% or more in both pressure casting and gravity casting. Further, in the case of pressure casting of 49 MPa, when the addition amount of Si is 4.4 wt% or less, there is more elongation than when the addition amount of Si is 1.0 wt% by gravity casting. Next, the result of examining the crack occurrence rate of the cast product when the amount of Si added is changed in the first evaluation test will be described. This evaluation test was performed as follows.

That is, a test piece was cast from an alloy having the same composition as in the above-described tensile test under the same conditions and using a mold in a cylindrical mold having a maximum diameter of 20 mm and a minimum diameter of 8 mm. Using this test piece, the occurrence of cracks was visually evaluated. The result is shown in FIG. As can be seen from FIG. 4, in the case of gravity casting, the amount of Si added is 5.0 w.
If it is less than t%, cracks will occur. On the other hand, 49MPa
In the case of pressure casting, the addition amount of Si was 2.5 wt.
%, Cracks did not occur.

According to the results of the above tensile test and crack generation defect rate test, in order to obtain a casting which does not generate casting cracks and shows sufficient elongation (toughness), it is necessary to perform high-pressure casting. In addition, at the time of high-pressure casting of 49 MPa, the amount of Si added must be in the range of 2.5 to 4.4 wt%. (Second Evaluation Test) The reason for limiting the amount of Cu to be added will be described by a second evaluation test.
In the second evaluation test, the result of measuring the change in the tensile strength of the cast product when the amount of Cu added is changed will be described. The second evaluation test was performed as follows.

That is, in an Al—Si—Cu—Mg alloy, Si: 3.0 wt%, Mg: 0.3 wt%, Cu:
0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0
wt%, the alloy consisting of the balance Al
The molten metal was poured into a mold under the conditions of a molten metal temperature of 800 ° C. and a mold temperature of 150 ° C., and the molten metal was cast under a pressure of 49 MPa to obtain seven cylindrical test piece materials having a diameter of 30 mm.

A JIS No. 4 test piece was cut out from this test piece material, and the test piece was subjected to 530 to 54 in accordance with the composition.
After solution treatment at 0 ° C. for 4 hours, quenching was performed in water at 80 ° C., and tempering was performed at 160 ° C. for 4 hours. A tensile test was performed using the heat-treated test piece thus obtained. The result is shown in FIG. As can be seen from FIG. 5, when the added amount of Cu is 1.5 wt% or less, the tensile strength decreases. Also, it is known that when a large amount of Cu is added, the corrosion resistance and the stress corrosion cracking property are deteriorated. From FIG.
It can be seen that even if Cu is added at 2.5 wt% or more, the tensile strength hardly improves. Therefore, at the time of 49 MPa pressure casting, a cast product having tensile strength and excellent corrosion resistance and stress corrosion resistance can be obtained when the amount of Cu added is in the range of 1.5 to 2.5 wt%. (Third Evaluation Test) The dendrite size in the matrix and the reason for limitation will be described by a third evaluation test. In the third evaluation test, a result of measuring a change in elongation (toughness) of a cast product when the size of dendrite in the matrix is changed will be described. The third evaluation test was performed as follows.

That is, Si: 3.0 wt%, Mg:
0.3 wt%, Cu: 2.0 wt%, the balance being substantially A
An aluminum alloy having a composition consisting of 1 and unavoidable impurities was melted, and the molten metal was poured into a mold under the conditions of a molten metal temperature of 750 ° C and a mold temperature of 150 ° C. Casting was performed by changing the pressure applied to the molten metal to obtain a cylindrical test piece material having a diameter of 30 mm.

A JIS No. 4 test piece was cut out from the test piece material, the test piece was subjected to a solution treatment at 535 ° C. for 4 hours, and then quenched in water at 80 ° C.
Tempering was performed at 4 ° C. for 4 hours. A tensile test was performed using the heat-treated test piece thus obtained. At this time, the test piece used for the tensile test was cut, and the size of the dendrite at the center of the cut cross section was measured. FIG. 6 shows the relationship between dendrite size and elongation of each test piece.

As can be seen from FIG. 6, when the size of the dendrite exceeds 30 μm, the elongation sharply decreases. Therefore, the size of the dendrite in the matrix is set to 30 μm or less. (Fourth Evaluation Test) The reason for limiting the casting pressure will be described by a fourth evaluation test. First
It is known that elongation, crack occurrence rate, and tensile strength in the evaluation test and the second evaluation test are closely related to the fineness of the structure of the material. In the above-described first and second evaluation tests, casting was performed by applying a casting pressure of 49 MPa. In the fourth evaluation test, this pressure was changed to obtain an optimum casting pressure.

In the fourth evaluation test, the result of measuring the size of dendrite in the matrix in the casting when the casting pressure is changed will be described. The fourth evaluation test was performed as follows. That is, S
i: 3.0 wt%, Mg: 0.3 wt%, Cu: 2.0
The raw material was melted so as to be an aluminum alloy having a composition of Al substantially in wt%, and a test piece material was cast using a cylindrical mold having a diameter of 30 mm at a molten metal temperature of 750 ° C. At this time, the mold temperature was set to 250 ° C. and 100 ° C.
C., and the size of the dendrite when the casting pressure was changed was measured. FIG. 7 shows the results of the fourth evaluation test.

In the case of a casting having a general wall thickness, hot water flows sufficiently in the mold at a mold temperature of 100 ° C. However, when the minimum thickness is reduced to about 3 mm, the mold temperature is reduced to 250 mm.
If the temperature is not raised to ° C., the hot water will not flow sufficiently in the mold. That is, when the mold temperature is 250 ° C., as is clear from FIG. 7, when the casting pressure is 24.5 MPa or less, the size of the dendrite rapidly increases from 30 μm, and the elongation is large as described in the third evaluation test. descend. On the other hand, even if the casting pressure is increased to 147 MPa or more, the size of the dendrite hardly changes and the elongation does not change. In addition, raising the casting pressure is difficult in terms of equipment and costs. Therefore, the casting pressure is set to 24.5 to 147 MPa.

In the first and second evaluation tests, a casting pressure of 49 MPa was applied to the molten metal.
Although the addition amounts of Si and Cu have been limited, as can be seen from FIG. 7, when the casting pressure is in the range of 24.5 to 147 MPa, the size of the dendrite hardly changes. Since the characteristics are related to the size of the dendrite, the limitation of the addition amount of Si and Cu in the first evaluation test and the second evaluation test is that the casting pressure is 24.5.
147 MPa. The tensile strength and elongation of the aluminum alloy casting according to (5 Evaluation Test) The present invention, in order to compare with that of the conventional aluminum alloy casting and a conventional aluminum alloy forged product was subjected to a fifth evaluation test. An aluminum alloy casting according to the present invention was prepared using the same raw materials as in the first embodiment under the same conditions as those for preparing the aluminum alloy casting of the first embodiment. A conventional aluminum alloy casting was prepared using the conventional aluminum alloy (JIS AC4CH) under the same conditions as those for preparing the aluminum alloy casting of the first embodiment. Furthermore, conventional aluminum alloys (JIS 60
61), a conventional aluminum alloy forged product was prepared. However, in the fifth evaluation test, castings and forgings were formed on the cylindrical test piece material of 30 mm prepared in the first evaluation test, and this test piece material was subjected to JIS.
A test piece having the shape of a No. 4 test piece was cut. The conventional aluminum alloy AC4CH contains 8.1% by weight of Si,
It consists of 0.3% by weight of Mg, the balance being substantially Al and unavoidable impurities. Conventional aluminum alloy 60
61 is 0.6% by weight of Si and 1.0% by weight of Mg
And the balance substantially consists of Al and unavoidable impurities.

The specimen thus prepared was subjected to a tensile test, and its tensile strength and elongation were evaluated. Fifth
FIG. 8 shows the results of the evaluation test. As is clear from FIG. 8, the tensile strength and the elongation of the aluminum alloy casting according to the present invention are much better than those of the conventional aluminum alloy casting. It surpassed that of the product. Therefore, the aluminum alloy casting according to the present invention can be used for producing automobile parts which need to be reduced in weight and exhibit improved strength. (Sixth Evaluation Test) In order to compare the fatigue strength of the aluminum alloy casting according to the present invention with that of a conventional aluminum alloy forging,
A sixth evaluation test was performed. An aluminum alloy casting according to the present invention was prepared using the same raw materials as in the first embodiment under the same conditions as those for preparing the aluminum alloy casting of the first embodiment. In addition, conventional aluminum alloys (JIS 60
61), a conventional aluminum alloy forged product was prepared. However, in the sixth evaluation test, castings and forgings were formed on the cylindrical test piece material of 30 mm prepared in the first evaluation test, and this test piece material was subjected to JIS.
A test piece having the shape of a No. 4 test piece was cut.

The specimen thus prepared was subjected to a fatigue strength test, and the fatigue strength when the specimen was repeatedly exposed to a load and a non-load cycle was evaluated. In addition, the test piece was attached to a rotary bending stress tester operated at a speed of 300 rpm. FIG. 9 shows the results of the sixth evaluation test.
Fatigue strength of the aluminum alloy casting according to the present invention, the conventional aluminum alloy forged product that was to surpass it, Figure 9 clearly show. Therefore, the aluminum alloy casting according to the present invention has higher toughness than the conventional aluminum alloy forging, and such excellent toughness lasts longer than that of the conventional aluminum alloy forging. (Third Embodiment) In the third embodiment, under the same casting conditions as those for producing the suspension arm of the first embodiment, Si: 4.0 watts was used.
An aluminum alloy according to the present invention, which contains a predetermined amount of Sr in addition to t%, Cu: 2.0 wt%, and Mg: 0.4 wt%, and is substantially composed of Al and unavoidable impurities, and has a diameter of 30 mm. A cylindrical test piece material was obtained. The amount of Sr added is 0, 0.002, 0.00
5, 0.01, 0.05, 0.1, 0.2, 0.3 wt
%. A JIS No. 4 test piece was cut out from this test piece material, and the test piece was subjected to a solution treatment under the same solution treatment conditions as those applied to the suspension arm of the first embodiment. The heat-treated test piece thus obtained was cut, and the maximum grain size of the eutectic Si phase at the center of the cut cross section was measured. The result is shown in FIG.

As can be seen from FIG. 10, Sr is 0.00
When added in an amount of 5 wt% or more, the effect of making the eutectic Si phase finer appears, and the mechanical properties, particularly, the elongation are improved. Also, Sr
When 0.2% by weight or more is added, the eutectic Si phase is refined, but the Sr compound is crystallized and the elongation is reduced. Thus, if the raw material of the method for producing an aluminum alloy casting of the present invention contains 0.005 to 0.2% by weight of Sr, the strength and toughness of the aluminum alloy casting are further improved and stabilized. Here, that the strength and toughness are stabilized means that, for example, the lower limit value of the elongation increases and approaches the upper limit value thereof, and the performance of the aluminum alloy casting, that is, the elongation hardly varies.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a pressure casting apparatus according to a first embodiment.

FIG. 2 is a graph showing a relationship between a degree of vacuum of a cavity and a defective entrainment rate in the pressure casting apparatus of the first embodiment.

FIG. 3 is a graph showing a change in elongation when the amount of Si added to an aluminum alloy casting is changed.

FIG. 4 is a graph showing a change in the crack occurrence rate when the amount of Si added to an aluminum alloy casting is changed.

FIG. 5 is a graph showing a change in tensile strength when the amount of Cu added to an aluminum alloy casting is changed.

FIG. 6 is a graph showing a change in elongation when the size of dendrite in a matrix of an aluminum alloy casting is changed.

FIG. 7 is a graph showing a change in dendrite size when the casting pressure of an aluminum alloy casting is changed.

FIG. 8 is a scatter diagram showing the relationship between elongation and tensile strength of the aluminum alloy casting according to the present invention, a conventional aluminum alloy casting, and a conventional aluminum alloy forging.

FIG. 9 shows the number of repeated load and non-load cycles and the present invention .
It is a graph which shows the relationship of the fatigue strength of such an aluminum alloy casting and the conventional aluminum alloy forging.

FIG. 10 is a graph showing a change in the maximum grain size of a eutectic Si phase when the amount of Sr added to an aluminum alloy casting is changed.

[Explanation of symbols]

 1: Cavity 2: Melting furnace 3: Melt supply path 4: Molten metal 5: Vacuum pump 6: Vacuum path 7: Decompression pump 8: Decompression path 9: Reservoir 10: Partition member 11: Communication path 12: Weir section 13: Addition Pressure member

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirokazu Onishi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Automobile Co., Ltd. (72) Inventor Yoji Awano 41 shares of Nagakute-cho, Yakumichi, Nagakute-cho, Aichi-gun, Aichi 1 share Inside Toyota Central Research Laboratory (72) Inventor Yoshihiro Shimizu 41, Chuchu-Yokomichi, Oji-cho, Nagakute-cho, Aichi-gun Aichi Prefecture Inside Toyota Central Research Laboratories Co., Ltd. No. 1 Inside Toyota Central Research Laboratory, Inc. (56) References JP-A-58-117850 (JP, A) JP-A-62-235436 (JP, A) JP-A-63-60251 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 21 / 04,27 / 09 C22C 21/00-21/18 C22F 1/04-1/057

Claims (1)

(57) [Claims] 1. Si: 2.5 to 4.4 wt%, Cu: 1.
5 to 2.5 wt%, Mg: 0.2 to 0.5 wt%
The balance is substantially Al or Si: 2.5.
To 4.4 wt%, Cu: 1.5 to 2.5 wt%, Mg:
0.2-0.5 wt%, Sr: 0.005-0.2 wt
% And the remainder is substantially dissolved to Al.
A pressure of 24.5 to 147 MPa is applied to the melt of the raw material.
And cast it into a mold by pressure casting.
Strength, high toughness aluminum characterized by being treated
Manufacturing method of alloy castings.