JP2005200743A - Aluminum alloy for casting and aluminum alloy casting product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy for casting having both adequate mechanical strength and thermal fatigue strength, and to provide an aluminum alloy casting product. <P>SOLUTION: The aluminum alloy for casting is required to have both of the mechanical strength and the thermal fatigue strength; and comprises aluminum as a base metal, in proportions of 4.0-7.0 wt.% Si, 0.4-1.0 wt.% Mg, 0.10 wt.% or less Cu and 0.3 wt.% or less Fe, respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aluminum alloy for casting and an aluminum alloy casting in which both mechanical strength and thermal fatigue strength are required.

  Cast aluminum alloys with improved mechanical strength and heat resistance include Al-Si-Cu-Mg quaternary or Al-Si-Cu-Ni-Mg quaternary cast alloys (for example, AC4D, AC8A, AC8B, AC8C (JIS standard)).

  These alloys contain Cu and Mg at the same time. By subjecting the castings made of these alloys to T6 heat treatment, the precipitates in the metal structure become denser and finer, and the castings have high mechanical strength. Show. In addition, since these precipitates are stable at high temperatures, the mechanical strength of the cast body is hardly lowered even during use in a high temperature atmosphere. However, precipitates that are stable at high temperatures adversely deteriorate the thermal fatigue life (thermal fatigue strength).

  On the other hand, there are Al—Si—Mg ternary casting alloys that do not contain Cu as casting aluminum alloys with improved thermal fatigue strength (for example, AC4C, AC4CH (JIS standard)).

  These alloys are also subjected to T6 heat treatment in the same manner as the Al—Si—Cu—Mg quaternary or Al—Si—Cu—Ni—Mg quaternary cast alloys described above, so that the precipitates in the metal structure are dense. The cast body exhibits high mechanical strength. In addition, since these precipitates are unstable at high temperatures, they do not disappear or become harmless during use in a high temperature atmosphere, and thermal fatigue strength is not deteriorated. However, Al-Si-Mg ternary cast alloys have a smaller amount of precipitates, so the mechanical properties are similar to those of Al-Si-Cu-Mg quaternary or Al-Si-Cu-Ni-Mg ternary cast alloys. Strength cannot be obtained.

Here, even in the case of Al-Si-Mg ternary cast alloys, by increasing the Mg content as in the A357 alloy (AA standard), the intermediate phase (Mg ₂ Si) precipitates the machine at room temperature. It is also possible to increase the mechanical strength. However, the A357 alloy is greatly softened when hot. For this reason, when the A357 alloy is applied to a place exposed to a high temperature such as the lower surface portion of the cylinder head, it is difficult to maintain the high strength obtained at room temperature for a long time.

  The present inventors previously proposed an aluminum alloy for casting in which fatigue strength and thermal fatigue strength are hardly deteriorated in a high-temperature environment by applying stabilization treatment to an Al—Si—Cu—Mg quaternary cast alloy ( Patent Document 1). Specifically, the casting aluminum alloy has a tensile strength of 320 MPa or more and a breaking elongation of 5% or more.

  FIG. 1 shows the relationship between the tensile strength and the thermal fatigue life of AC4D, AC4C, and the aluminum alloy for casting described in Patent Document 1 (hereinafter referred to as the pre-invention alloy). As shown in FIG. 1, the tensile strength of AC4D shown in region A is about 300 to 320 MPa, the thermal fatigue life is about 180 to 500 cycles, the tensile strength of AC4C shown in region B is about 270 to 300 MPa, and the thermal fatigue life. Is about 1000-1500 cycles, the tensile strength of the pre-invented alloy shown in region C is about 320-350 MPa, and the thermal fatigue life is about 700-1200 cycles.

  From the highest tensile strength, the alloys of the present invention are AC4D and AC4C. The thermal fatigue life is AC4C, pre-invention alloy, and AC4D in order from the longest life. From this, it can be seen that the pre-invention alloy is an aluminum alloy for casting aiming at a higher tensile strength than AC4D and a thermal fatigue life substantially equivalent to AC4C. In addition to the pre-invention alloy, an aluminum alloy for casting having improved thermal fatigue strength or fatigue strength (toughness) has been proposed (see Patent Documents 2 and 3).

JP 2001-262262 A Japanese Patent Laid-Open No. 10-251790 Japanese Patent Laid-Open No. 11-293430

  In recent years, in casting aluminum alloys, further improvement in mechanical strength and thermal fatigue strength has been desired. In particular, a casting aluminum alloy having a tensile strength comparable to that of AC4D and the previous invention alloy and having a thermal fatigue strength equal to or higher than that of AC4C, that is, an aluminum alloy for casting having the characteristics of region D in FIG. 1 is desired. .

  An object of the present invention, which was created in view of the above circumstances, is to provide an aluminum alloy for casting and an aluminum alloy casting in which both mechanical strength and thermal fatigue strength are good.

To achieve the above object, the casting aluminum alloy according to the present invention is a casting aluminum alloy that requires both mechanical strength and thermal fatigue strength.
4.0 to 7.0 wt% Si,
0.4 to 1.0 wt% Mg,
Cu is 0.10 wt% or less,
Fe is 0.3 wt% or less,
It is included in the ratio. Here, in addition to Si, Mg, Cu, and Fe, Sr may be further included at a ratio of 0.005 to 0.030 wt%.

  On the other hand, the aluminum alloy casting according to the present invention is formed of the cast aluminum alloy casting described above. Here, the casting may be subjected to T6 heat treatment.

  According to the present invention, an excellent effect is obtained that an aluminum alloy casting having both high tensile strength and thermal fatigue strength can be obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

The aluminum alloy for casting according to a preferred embodiment of the present invention is an aluminum base material,
4.0 to 7.0 wt% Si,
0.4 to 1.0 wt% Mg,
Cu is 0.10 wt% or less, preferably 0.05 wt% or less,
Fe is 0.3 wt% or less, preferably 0.2 wt% or less,
It is made to contain in the ratio. The aluminum alloy for casting according to the present embodiment may further contain Sr in a proportion of 0.005 to 0.030 wt% in addition to Si, Mg, Cu, and Fe.

  The “aluminum base material” here is a substantially pure aluminum material composed of Al and inevitable impurities.

  On the other hand, the aluminum alloy casting according to a preferred embodiment of the present invention is prepared by melting the molten aluminum alloy by adjusting the addition amount of each element so as to have the same chemical composition as the above-described casting aluminum alloy. It is composed of a cast body obtained by casting using a molten alloy. Here, the aluminum alloy casting according to the present embodiment has a tensile strength of 300 MPa or more, preferably 320 MPa or more, and a thermal fatigue life of 1200 cycles or more, preferably 1500 cycles or more. Moreover, it is good also as an aluminum alloy casting which concerns on this Embodiment by giving T6 heat processing to the obtained casting.

  The intended final product can be obtained by appropriately performing various treatments such as finishing on the obtained aluminum alloy casting.

  In addition, the "thermal fatigue life" said here performs the thermal fatigue test which gives the thermal cycle which makes low temperature-> high temperature-> low temperature (for example, 100 degreeC-> 250 degreeC-> 100 degreeC) with respect to aluminum alloy casting, It represents the number of repetitions (cycles) until the material reaches fracture in a test in which the total strain amplitude value is a predetermined value (for example, about ± 0.5%).

  Next, the operation of the present embodiment will be described.

  FIG. 2 shows the relationship between the Mg content and the tensile strength in an aluminum alloy casting using a casting aluminum alloy having a Si content of 4 wt% and 7 wt%. A straight line 21 in FIG. 2 is an aluminum alloy casting with a Si content of 4 wt%, and a straight line 22 is an aluminum alloy casting with a Si content of 7 wt%.

  As shown in FIG. 2, in an aluminum alloy casting having a Si content in the range of 4 to 7 wt%, it can be confirmed that a tensile strength of 320 MPa or more is obtained when the Mg content is 0.4 wt% or more.

  FIG. 3 shows the relationship between the Mg content and the thermal fatigue life in an aluminum alloy casting using a casting aluminum alloy having a Si content of 4 wt% and 7 wt%. A straight line 31 in FIG. 3 is an aluminum alloy casting with a Si content of 4 wt%, and a straight line 32 is an aluminum alloy casting with a Si content of 7 wt%.

  As shown in FIG. 3, in an aluminum alloy casting having a Si content in the range of 4 to 7 wt%, it can be confirmed that a thermal fatigue life of 1500 cycles or more is obtained when the Mg content is 1.0 wt% or less.

  2 and 3 shown above, an aluminum alloy casting having a Si content of 4 to 7 wt% and an Mg content of 0.4 to 1.0 wt% has a tensile strength of 320 MPa or more and a thermal fatigue life of 1500 cycles or more. Can be confirmed.

  Here, in the aluminum alloy casting in which the Mg content is in the range of 0.4 to 1.0 wt%, as shown in FIG. 2, the tensile strength is improved as the Si content is increased, but the displacement is compared. Small. However, in an aluminum alloy casting in which the Mg content is in the range of 0.4 to 1.0 wt%, as shown in FIG. 3, the thermal fatigue life is greatly improved as the Si content decreases. Therefore, the Si content is preferably 4.0 to 6.0 wt%. In this range, when importance is attached to the tensile strength of the aluminum alloy casting, the Si content is increased, and when importance is attached to the thermal fatigue strength of the aluminum alloy casting. Reduce the Si content.

  Moreover, in the aluminum alloy casting in which the Mg content is in the range of 0.4 to 1.0 wt%, as shown in FIG. 2, the tensile strength is improved as the Mg content is increased, as shown in FIG. As the Mg content decreases, the thermal fatigue life is improved. Therefore, the Mg content is preferably 0.5 to 1.0 wt%. In this range, when the tensile strength of the aluminum alloy casting is emphasized, the Mg content is increased, and when the thermal fatigue strength of the aluminum alloy casting is emphasized. Reduce the Mg content.

  In addition, the relationship between Cu content and thermal fatigue life in aluminum alloy castings using aluminum alloy for casting with Si content of 4.0 wt%, Mg content of 1.0 wt%, and Fe content of 0.2 wt% Is shown in FIG.

  As shown by a straight line 41 in FIG. 4, the thermal fatigue life is improved as the Cu content decreases, and in an aluminum alloy casting having a Cu content in the range of 0.10 wt% or less, 1500 cycles or more. It can be confirmed that a thermal fatigue life can be obtained. In particular, the Cu content is preferably 0.05 wt% or less, at which a thermal fatigue life of 1700 cycles or more can be obtained.

  The reason why the content of Fe in the aluminum alloy for casting is 0.3 wt% or less is that when the content of Fe, which is an impurity, exceeds 0.3 wt%, the toughness of the aluminum alloy casting is remarkably lowered, and consequently the thermal fatigue strength This is because of a decrease. The smaller the Fe content, the better the thermal fatigue life. Therefore, the Fe content is preferably 0.2 wt% or less.

  By producing an aluminum alloy casting using the casting aluminum alloy according to the present embodiment, the tensile strength and the thermal fatigue strength are combined at a high level, specifically, a tensile strength of 300 MPa or more, preferably 320 MPa or more. And a thermal fatigue life of 1200 cycles or more, preferably 1500 cycles or more. For this reason, by using the aluminum alloy casting according to the present embodiment to produce a cylinder head for an internal combustion engine, a cylinder having a tensile strength comparable to AC4D and an alloy of the previous invention and a thermal fatigue strength equal to or higher than AC4C A head is obtained. Therefore, although it is a cylinder head excellent in tensile strength, even if the thermal cycle condition of engine operation / stop is repeatedly applied, the mechanical characteristics are not deteriorated and are stable.

  In addition, in the aluminum alloy for casting according to the present embodiment, eutectic Si is refined and spheroidized by further containing Sr in a proportion of 0.005 to 0.030 wt% in addition to Si, Mg, Cu, and Fe. Therefore, the thermal fatigue strength can be further improved.

  Furthermore, since the aluminum alloy casting according to the present embodiment is hardly deteriorated in thermal fatigue strength even when subjected to T6 heat treatment, the tensile strength can be further increased without substantially damaging the high thermal fatigue strength.

  In addition, the use of the aluminum alloy casting according to the present embodiment is not limited to the cylinder head, and for example, it is also applied to a cylinder block (or piston) for an internal combustion engine, a turbine, a hydraulic cylinder body, and the like. be able to.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

(Example 1)
Aluminum base material
4.0 wt% Si,
0.4 wt% Mg,
0.2 wt% Fe,
0.03wt% Cu,
The molten aluminum alloy for casting contained in the ratio is melted. Casting is performed using the molten alloy to produce an aluminum alloy casting.

(Example 2)
An aluminum alloy casting is produced in the same manner as in Example 1 except that the Mg content is 1.0 wt%.

(Example 3)
An aluminum alloy casting is produced in the same manner as in Example 1 except that the Si content is 7.0 wt%.

Example 4
An aluminum alloy casting is produced in the same manner as in Example 2 except that the Si content is 7.0 wt%.

(Example 5)
An aluminum alloy casting is produced in the same manner as in Example 2 except that the Cu content is 0.10 wt%.

(Example 6)
An aluminum alloy casting is produced in the same manner as in Example 1 except that the Fe content is 0.3 wt%.

(Comparative Example 1)
An aluminum alloy casting is produced in the same manner as in Example 2 except that the Si content is 3.0 wt%.

(Comparative Example 2)
An aluminum alloy casting is produced in the same manner as in Example 2 except that the Si content is 9.0 wt%.

(Comparative Example 3)
An aluminum alloy casting is produced in the same manner as in Example 1 except that the Fe content is 0.4 wt%.

(Comparative Example 4)
An aluminum alloy casting is produced in the same manner as in Example 2 except that the Cu content is 0.20 wt%.

  Table 1 shows the tensile strength (MPa) and thermal fatigue life (cycle) of the aluminum alloy castings of Examples 1 to 6 and Comparative Examples 1 to 4. Here, the thermal fatigue life is the number of repetitions (cycles) when the strain value reaches a predetermined value by performing a thermal fatigue test that gives a thermal cycle of one cycle of low temperature → high temperature → low temperature for each alloy casting. did. Moreover, based on the data of Table 1, the relationship between a thermal fatigue life and tensile strength is shown in FIG.

  As shown in Table 1 and FIG. 5, each of the aluminum alloy castings of Examples 1 to 6 has a tensile strength of 305 to 355 MPa (median is 313 to 352 MPa) and a thermal fatigue life of 1230 to 1934 cycles. The target values (tensile strength of 300 MPa or more, thermal fatigue life of 1200 cycles or more) were satisfied. Each of the aluminum alloy castings of Examples 1 to 5 had a thermal fatigue life of 1505-1934 cycles, and all satisfied a preferable thermal fatigue life (1500 cycles or more). Among these aluminum alloy castings, in particular, the aluminum alloy casting of Example 2 has a tensile strength of 345 to 350 MPa (median is 348 MPa), a thermal fatigue life of 1750 cycles, and both are satisfied at a high level. It was.

  On the other hand, the aluminum alloy casting of Comparative Example 1 has a Si content of 3.0 wt%, which is less than the specified range (4.0 to 7.0 wt%), so the castability is poor, and porosity (porosity) or shrinkage is found inside the casting. Many casting defects such as nests occurred. As a result, the variation in the tensile strength became large (294 to 342 MPa (median value was 318 MPa)), and the target tensile strength was sometimes not obtained. Further, the thermal fatigue life varies greatly, and data cannot be obtained.

  The aluminum alloy casting of Comparative Example 2 had a tensile strength of 345 to 359 MPa (median value was 352 MPa), which exceeded the target value. However, since the Si content was 9.0 wt%, which was larger than the specified range, the thermal fatigue life was 780 cycles, which was significantly below the target value.

  The aluminum alloy casting of Comparative Example 3 had a tensile strength of 320 MPa, which exceeded the target value. However, since the Fe content was 0.4 wt%, which was higher than the specified range (0.3 wt% or less), the thermal fatigue life was 674 cycles, which was lower than the target value. Comparison between Example 6 and Comparative Example 3 confirmed that the thermal fatigue life was significantly reduced with an increase in Fe content.

  The aluminum alloy casting of Comparative Example 4 had a tensile strength of 342 to 350 MPa (median value was 346 MPa), which exceeded the target value. However, since the Cu content is 0.20 wt%, which is larger than the specified range (0.10 wt% or less), the thermal fatigue life is 1055 cycles, which is lower than the target value.

  Each of the aluminum alloy castings of Examples 1 to 6 has a tensile strength improved by about 12 to 26% compared to the AC4C casting, and the thermal fatigue life is about 2.4 to 3.6 times that of the AC4D casting. It was. In particular, each aluminum alloy casting of Examples 1 to 5 had a thermal fatigue life of about 3.0 to 3.6 times that of the AC4D casting.

  Therefore, when mechanical parts are required, the parts that could only be manufactured by AC4D (cast products) are manufactured from the aluminum alloy castings of Examples 1 to 6, and the life of the parts is increased by about 2.4 to 3.6 times. can do. In particular, when manufactured with each aluminum alloy casting of Examples 1 to 5, the life of the parts can be increased by about 3.0 to 3.6 times. Moreover, when thermal fatigue strength is required, parts that could only be produced by AC4C were produced from the aluminum alloy castings of Examples 1 to 6, and if the same strength was obtained, the cross-sectional area of the parts was about 12 to 26. % Can be reduced. For this reason, the part can be thinned by the amount corresponding to the reduction in the cross-sectional area, and the weight of the part can be reduced.

  As a result, when the weight of the component is approximately the same as that of the conventional component, the thermal load that can be applied to the engine by manufacturing the engine for the internal combustion engine with each aluminum alloy casting of Examples 1 to 6 and The mechanical load can be increased. Therefore, engine output can be improved. In addition, when the thermal load and mechanical load on the parts are the same as those of the conventional parts, the weight of the engine can be reduced by manufacturing the engine for the internal combustion engine with each aluminum alloy casting of Examples 1 to 6. Can do. Therefore, the fuel efficiency of the engine can be improved.

It is a figure which shows the characteristic of the aluminum alloy for casting which concerns on suitable one embodiment of this invention. It is a figure which shows the relationship between Mg content and tensile strength. It is a figure which shows the relationship between Mg content and a thermal fatigue life. It is a figure which shows the relationship between Cu content and a thermal fatigue life. It is a figure which shows the relationship between the thermal fatigue life and tensile strength of each aluminum alloy casting in an Example.

Claims (4)

In aluminum alloys for casting where both mechanical strength and thermal fatigue strength are required,
4.0 to 7.0 wt% Si,
0.4 to 1.0 wt% Mg,
Cu is 0.10 wt% or less,
Fe is 0.3 wt% or less,
An aluminum alloy for casting, characterized in that it is contained in a proportion of   2. The aluminum alloy for casting according to claim 1, further comprising Sr in a proportion of 0.005 to 0.030 wt% in addition to Si, Mg, Cu, and Fe.   An aluminum alloy casting characterized by being formed from a cast aluminum alloy casting according to claim 1 or 2. The aluminum alloy casting according to claim 3, wherein the casting is subjected to T6 heat treatment.

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