JP7547263B2 - Heat-resistant aluminum alloys and heat-resistant aluminum alloy components - Google Patents

Description

The present invention relates to aluminum alloys and aluminum alloy components that are used in components that require high-temperature strength, such as pistons for internal combustion engines.

Al-Si alloys are widely used as aluminum alloys for casting. Among them, hypereutectic Al-Si alloys with a Si content of more than 12 wt% have high high-temperature strength and wear resistance, and are used in products that require heat resistance and wear resistance, such as pistons and compressor parts for internal combustion engines.

For example, Patent Document 1 (JP Patent Publication 8-134577) proposes an aluminum alloy for die casting with excellent high-temperature strength, wear resistance and vibration resistance, which contains Cu: 1-7 wt%, Si: 10-16 wt%, Mg: 0.3-2 wt%, Fe: 0.5-2 wt%, Mn: 0.1-4 wt%, Ti: 0.01-0.3 wt%, P: 0.001-0.02 wt%, and Ca: 0.0001-0.02 wt%, with the weight ratio of P/Ca adjusted to the range of 0.5-50.

In the aluminum alloy for die casting in the above-mentioned Patent Document 1, Mn is added to the Al-Si alloy and then rapidly cooled and cast, which causes fine crystallization of Al-Mn-Si compounds and Al-Mn-Fe-Si compounds, which have higher melting points than the aluminum parent phase, and is said to improve high-temperature strength in the temperature range around 200°C.

In addition, Patent Document 2 (JP Patent Publication 10-226840A) proposes an aluminum alloy for pistons that contains an Al-based composition of Si, Cu, Mg, Ni, P, Ti, Fe, and Mn, and that sets the blending ratios of the composition as follows: Si: 10-14 wt%, Cu: 3-5 wt%, Mg: 0.5-2 wt%, Ni: 1-3 wt%, P: 0.002-0.02 wt%, Ti: 0.1-0.3 wt%, Fe: 0.8 wt% or less, and Mn: 0.1-1.0 wt%, and sets the average grain size of the primary crystal Si grains to 20-60 μm.

In the aluminum alloy for pistons described in Patent Document 2, the addition of Cu, Ni, and Mn to an Al-Si alloy causes fine crystallization of Al-Ni-CuMn-Fe compounds, which have a higher melting point than aluminum, and is said to be able to maintain strength even at high temperatures of 350°C.

Japanese Unexamined Patent Publication No. 8-134577 Japanese Patent Application Publication No. 10-226840

Here, pistons for internal combustion engines have parts that reach high temperatures of 200°C or more during use, but also parts that reach temperatures below 200°C, and so in addition to mechanical strength at temperatures of 200°C or more, they are also required to have mechanical strength below 200°C.

However, although Al-Mn-Si, Al-Fe-Si and Al-Ni-Cu crystallized materials contribute to improving high-temperature strength at 200°C or higher, they do not contribute much to improving strength at temperatures around 150°C. Conversely, if there is a large amount of crystallized material, the amount of precipitates that contribute to improving strength at temperatures around 150°C decreases. In addition, a high Mn content reduces thermal conductivity, so parts such as pistons manufactured using aluminum alloys that contain a lot of Mn have the problem of being prone to temperature increases.

In view of the problems in the conventional technology described above, the object of the present invention is to provide a heat-resistant aluminum alloy for obtaining an aluminum alloy part having excellent mechanical properties in the temperature ranges of 150°C and 250°C, and a heat-resistant aluminum alloy part made of said heat-resistant aluminum alloy.

In order to achieve the above object, the inventors conducted extensive research into the composition of aluminum alloys and the structure of aluminum alloy members, and discovered that using precipitate-forming elements that have a small effect on the amount of precipitates is extremely effective in improving high-temperature strength, leading to the creation of the present invention.

That is, the present invention provides:
Si: 12.0-15.0wt%,
Cu: 4.0-5.0wt%,
Ni: 1.5-2.5wt%,
Mg: 1.5 to 2.5 wt%,
Fe: 0.2 to 0.8 wt%,
Ti: 0.1 to 0.2 wt%,
Zr: 0.05 to 0.15 wt%,
V: 0.05-0.15wt%,
P: 0.005 to 0.015 wt %,
The remainder is made of Al and unavoidable impurities.
The present invention provides a heat-resistant aluminum alloy.

The heat-resistant aluminum alloy of the present invention has a composition that can increase both the precipitates that contribute to improving the yield strength at around 150°C and the precipitates that contribute to improving the yield strength and strength at around 250°C.

More specifically, by actively adding V, V-Si crystals are formed, resulting in a composition that exhibits excellent high-temperature strength at around 250°C. Because V-Si crystals contain almost no other precipitate-forming elements, the addition of V has only a very small effect on reducing the amount of precipitates, and a sufficient amount of precipitates allows the alloy to maintain high yield strength even at around 150°C.

In addition, by actively adding Zr, the cast structure can be refined. In addition, Zr-Si precipitates are formed, improving the yield strength at around 150°C.

The heat-resistant aluminum alloy of the present invention preferably further contains 0.01 to 0.10 wt% Mn. The more preferred Mn content is 0.01 to 0.05 wt%. The addition of Mn forms Al-Mn-Si and Al-Mn-Fe-Si crystals, which can further improve the yield strength and strength at temperatures around 250°C. Here, by setting the upper limit of the amount of Mn added to 0.10 wt%, the decrease in thermal conductivity can be suppressed.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Made of the heat-resistant aluminum alloy of the present invention,
In any cross section, the area ratio of precipitates is 5% or more, and the area ratio of crystallized particles having a major axis of 100 μm or less is 20% or more.
The present invention also provides a heat-resistant aluminum alloy member, characterized in that

The heat-resistant aluminum alloy member of the present invention has excellent yield strength at around 150°C because the area ratio of precipitates is 5% or more. In addition, the area ratio of precipitates with a major axis of 100 μm or less is 20% or more, so the heat-resistant aluminum alloy member has excellent yield strength and strength at around 250°C.

The heat-resistant aluminum alloy member of the present invention preferably has a 0.2% yield strength of 260 MPa or more at 150°C and a 0.2% yield strength of 120 MPa or more at 250°C. Because the heat-resistant aluminum alloy has these 0.2% yield strengths, it can be suitably used in heat-resistant members that are given different temperature histories (room temperature to high temperature) depending on the part and require high yield strength.

The heat-resistant aluminum alloy member of the present invention preferably has a tensile strength of 280 MPa or more at 150°C and a tensile strength of 140 MPa or more at 250°C. By having these tensile strengths, it can be suitably used in heat-resistant members that are given different temperature histories (room temperature to high temperature) depending on the part and require high strength.

The heat-resistant aluminum alloy of the present invention preferably has a thermal conductivity of 120 W/mK or more. With a thermal conductivity of 120 W/mK or more, it is possible to suppress the temperature rise of the heat-resistant aluminum alloy member, thereby expanding the range of application of the heat-resistant aluminum alloy.

The present invention also provides a piston for an internal combustion engine, characterized in that it is made of the heat-resistant aluminum alloy member of the present invention.

The internal combustion engine piston of the present invention is made of the heat-resistant aluminum alloy of the present invention, and has excellent durability at around 150°C, and excellent durability and strength at around 250°C. As a result, the internal combustion engine piston has high strength, durability, and reliability in a usage situation where some parts reach high temperatures of 200°C or higher during use, but other parts reach temperatures below 200°C.

The internal combustion engine piston of the present invention is made of the heat-resistant aluminum alloy member of the present invention, and has a high thermal conductivity. As a result, the temperature rise of the internal combustion engine piston is suppressed, and it can be used in a wide range of environmental temperatures.

The present invention provides a heat-resistant aluminum alloy for obtaining an aluminum alloy part having excellent mechanical properties in the temperature ranges of 150°C and 250°C, and a heat-resistant aluminum alloy part made of the heat-resistant aluminum alloy.

1 is a photograph showing the appearance of a casting in an example. 1 is an optical microscope photograph of a cross section of the casting of Example 1. 1 is an optical microscope photograph of a cross section of the casting of Example 2. 1 is an optical microscope photograph of a cross section of a casting of Comparative Example 1. 1 is an optical microscope photograph of a cross section of a casting of Comparative Example 2.

Representative embodiments of the heat-resistant aluminum alloy, heat-resistant aluminum alloy member, and piston for an internal combustion engine of the present invention will be described in detail below, but the present invention is not limited to these.

1. Heat-resistant aluminum alloy The heat-resistant aluminum alloy of the present invention has a composition that can increase both the precipitates that contribute to improving the yield strength at around 150° C. and the precipitates that contribute to improving the yield strength and strength at around 250° C. Each component will be described in detail below.

(1) Essential additive elements: Si: 12.0 to 15.0 wt% (preferably 12.5 to 13.5 wt%)
Silicon not only improves castability, but also forms crystals such as primary silicon and eutectic silicon, improving wear resistance, low linear expansion, and high-temperature strength. Furthermore, when aging is performed, it forms Mg-Si precipitates, improving tensile strength. This effect is significant at 12.0 wt% or more. On the other hand, if it exceeds 15.0 wt%, coarse primary silicon crystals, which are the starting points of fracture, are easily formed, decreasing tensile strength and elongation.

Cu: 4.0 to 5.0 wt% (preferably, 4.2 to 4.6 wt%)
Cu not only improves mechanical properties at room temperature through solid solution strengthening, but also has the effect of crystallizing as an Al-Cu compound and contributing to improving mechanical properties even at high temperatures. This effect is significant at 4.0 wt% or more. On the other hand, at more than 5.0 wt%, it is consumed as a crystallized product, and the amount of Al-Cu compounds that precipitates during aging treatment decreases, resulting in a decrease in mechanical properties at temperatures below 200°C.

Ni: 1.5 to 2.5 wt% (preferably, 1.5 to 2.2 wt%)
Ni forms Al-Ni crystals, which contribute to improving high-temperature strength, and is particularly effective in improving high-temperature strength at 250°C or higher. This effect is significant at 1.5 wt% or more. Conversely, at more than 2.5 wt%, coarse Al-Ni-Cu crystals that become the starting point of fracture are likely to form. In addition, it reduces the Al-Cu aging precipitate phase, which contributes to improving mechanical properties in the temperature range below 200°C.

Mg: 1.5 to 2.5 wt% (preferably, 1.5 to 2.1 wt%)
Mg contributes to improving strength through solid solution strengthening, and also forms Mg-Si precipitates when aging is performed, further improving strength. This effect is significant at 1.5 wt% or more. Conversely, if it exceeds 2.5 wt%, the parent phase becomes too hard, reducing ductility.

Fe: 0.2 to 0.8 wt% (preferably, 0.2 to 0.6 wt%)
Fe forms Al-Fe-Si crystals, which contributes to improving high-temperature strength. It also contributes to preventing seizure of the mold during die casting. This effect is significant at 0.2 wt% or more. Conversely, if it exceeds 0.8 wt%, the Al-Fe-Si crystals tend to become coarse.

Ti: 0.1-0.2wt%
Ti contributes to making the cast structure finer, and at the same time, forms Ti-based crystals and contributes to improving high-temperature strength. This effect is remarkable at 0.1 wt% or more. %, the crystallized particles tend to become coarse, the elongation tends to decrease, and the strength tends to decrease.

Zr: 0.05-0.15wt%
Zr contributes to making the cast structure finer, and at the same time forms Zr--Si precipitates, contributing to improving the mechanical properties at temperatures below 200° C. This effect becomes significant at a content of 0.05 wt % or more. On the other hand, if it exceeds 0.15 wt %, the crystallized particles tend to become coarse, and the elongation and strength tend to decrease.

V: 0.05-0.15wt%
V contributes to refining the cast structure, and at the same time, forms V-Si crystals, which contribute to improving high-temperature strength. This effect is remarkable at 0.05 wt% or more. If it exceeds 15 wt%, the crystallized products tend to become coarse, the elongation decreases, and the mechanical strength tends to decrease. Furthermore, the V-Si crystallized products contain almost no Ni, Cu, or Mg. Therefore, the addition of V does not lead to a reduction in the amount of precipitates that contributes to improving mechanical properties below 200°C.

P: 0.005-0.015wt%
P has the effect of refining primary crystal Si. This effect is significant at 0.005 wt% or more. Conversely, if it exceeds 0.015 wt%, the fluidity during casting deteriorates and casting defects occur. It becomes easier.

(2) Optionally Added Elements Mn: 0.01 to 0.10 wt% (preferably, 0.01 to 0.05 wt%)
Mn forms Al-Mn-Si and Al-Fe-Mn-Si crystals, and contributes to improving high-temperature strength. This effect is significant at 0.01 wt% or more. If the content exceeds 0.10 wt%, the thermal conductivity decreases, and the heat-resistant aluminum alloy member becomes easily heated to high temperatures.

The method for producing the heat-resistant aluminum alloy of the present invention having the above composition is not particularly limited as long as it does not impair the effects of the present invention, and an aluminum alloy having the desired composition may be produced by any of the various methods known in the art.

2. Heat-resistant aluminum alloy member The heat-resistant aluminum alloy member of the present invention is made of the heat-resistant aluminum alloy of the present invention, and in any cross section, the area ratio of precipitates is 5% or more, and the area ratio of crystallized particles with a major axis of 100 μm or less is 20% or more. Since the area ratio of precipitates is 5% or more, the aluminum alloy member has excellent yield strength at around 150°C. Furthermore, since the area ratio of crystallized particles with a major axis of 100 μm or less is 20% or more, the aluminum alloy member has excellent yield strength and strength at around 250°C. Here, coarse crystallized particles with a major axis of more than 100 μm are not preferred because they become the starting point of fracture.

The method for determining the area ratio of precipitates and crystallized particles with a major axis of 100 μm or less is not particularly limited, and various conventionally known methods may be used. For example, the heat-resistant aluminum alloy member may be cut at an arbitrary cross section, and the resulting cross-sectional sample may be observed with an optical microscope or a scanning electron microscope to determine the overall proportion of precipitates and crystallized particles. Depending on the observation method, the cross-sectional sample may be subjected to mechanical polishing, buff polishing, electrolytic polishing, etching, or the like.

It is also possible to calculate the amount of precipitates and crystallized matter using thermodynamic calculation software, etc., and use the obtained values. In this case, it is preferable to confirm that the calculated values are appropriate by comparing them with direct observations.

The heat-resistant aluminum alloy member preferably has a 0.2% yield strength of 260 MPa or more at 150°C and a 0.2% yield strength of 120 MPa or more at 250°C. Because the heat-resistant aluminum alloy has these 0.2% yield strengths, it can be suitably used in heat-resistant members that are given different temperature histories (room temperature to high temperature) depending on the part and require high yield strength. A more preferable 0.2% yield strength at 150°C is 270 MPa or more, and a more preferable 0.2% yield strength at 250°C is 130 MPa or more.

In addition, it is preferable that the heat-resistant aluminum alloy member has a tensile strength of 280 MPa or more at 150°C and a tensile strength of 140 MPa or more at 250°C. By having these tensile strengths, it can be suitably used in heat-resistant members that are given different temperature histories (room temperature to high temperature) depending on the part and require high strength. A more preferable tensile strength at 150°C is 285 MPa or more, and a more preferable tensile strength at 250°C is 150 MPa or more.

The heat-resistant aluminum alloy preferably has a thermal conductivity of 120 W/mK or more. With a thermal conductivity of 120 W/mK or more, the temperature rise of the heat-resistant aluminum alloy component can be suppressed, and the range of application of the heat-resistant aluminum alloy can be expanded. A more preferable thermal conductivity of the heat-resistant aluminum alloy is 130 W/mK or more.

The shape and size of the heat-resistant aluminum alloy member are not particularly limited, and may be any of the various conventionally known members, so long as the effects of the present invention are not impaired. Furthermore, the manufacturing method of the heat-resistant aluminum alloy member is not particularly limited, and may be manufactured using the heat-resistant aluminum alloy of the present invention, using any of the various conventionally known methods, so long as the effects of the present invention are not impaired.

The piston for an internal combustion engine of the present invention is made of the heat-resistant aluminum alloy member of the present invention and has a high thermal conductivity. As a result, the temperature rise of the piston for an internal combustion engine is suppressed, and the piston can be used in a wide range of environmental temperatures.

The shape and size of the piston for an internal combustion engine are not particularly limited, and can be any of various conventionally known materials, so long as the effects of the present invention are not impaired. Furthermore, the manufacturing method of the piston for an internal combustion engine is not particularly limited, and it can be manufactured using the heat-resistant aluminum alloy member of the present invention, using any of various conventionally known methods, so long as the effects of the present invention are not impaired.

The above describes representative embodiments of the present invention, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention.

Example
Molten aluminum alloys having compositions (wt %) shown in Table 1 as examples were subjected to molten metal treatments such as slag removal treatment with flux, static treatment, and degassing treatment, and then cast into the shapes shown in Fig. 1 using gravity die casting at a pouring temperature of 740±10°C and a cooling rate of 30°C/min.

Each of the resulting castings was subjected to aging treatment at 220°C for 6 hours, and then cut into round bar-shaped test pieces (parallel portion length 25 mm, parallel portion diameter 6 mm). Tensile tests were performed on the resulting test pieces at temperatures of 150°C and 250°C. The tensile test conditions included preheating at the test temperature for 100 hours. The obtained tensile properties are shown in Table 2.

From the results in Table 2, it can be seen that the heat-resistant aluminum alloy member of the present invention has a 0.2% yield strength of 260 MPa or more at 150°C and a 0.2% yield strength of 120 MPa or more at 250°C. In addition, the tensile strength at 150°C is 80 MPa or more, and the tensile strength at 250°C is 140 MPa or more.

The cross sections of the castings having the compositions of Examples 1 and 2 were mirror-polished, and the area ratios of crystallized particles with major axes of 100 μm or less were measured by optical microscope observation (field number: 6). The area ratios of crystallized particles in Examples 1 and 2 were 21.4% and 21.9%, respectively. Representative optical microscope photographs of Examples 1 and 2 are shown in Figures 2 and 3, respectively.

Furthermore, the proportions (area fractions) of crystallized particles in the castings having the compositions of Examples 1 and 2 were calculated using Thermo-Calc, a commercially available integrated thermodynamic calculation software capable of performing thermodynamic equilibrium calculations and phase diagram calculations based on the CALPHAD method, and were found to be 21.4% and 21.9%, respectively. These values show good agreement with the above-mentioned measured values, and it was confirmed that the values calculated using Thermo-Calc were valid. Based on these results, the values calculated using Thermo-Calc were used as the area fractions of crystallized particles for the castings having the compositions of Examples 3 to 6. The area fractions of crystallized particles for each casting are shown in Table 2.

In addition, because it is difficult to determine the exact amount (area ratio) of crystallized material in the parent phase (Al) by image analysis due to the effects of shrinkage and expansion, it was calculated using Thermo-Calc. Furthermore, the area ratio of precipitates was calculated from the area ratio of precipitates and the area ratio of the parent phase (Al). The area ratio of precipitates (%) is calculated as "100 - (area ratio of precipitates + area ratio of parent phase (Al))". The obtained values are shown in Table 2. It can be seen that for all the castings obtained as examples, the area ratio of precipitates was 5% or more, and the area ratio of precipitates was 20% or more.

Furthermore, the thermal conductivity of each casting was measured using the laser flash method. The values obtained are shown in Table 2. It can be seen that all the castings obtained as examples have a high thermal conductivity of 120 W/mK or more.

Comparative Example
Castings were obtained in the same manner as in the Examples, except that the compositions shown as Comparative Examples in Table 1 were used. Tensile properties and thermal conductivity were evaluated in the same manner as in the Examples. The obtained tensile properties are shown in Table 2.

Comparative Examples 3 and 4 have 0.2% yield strengths of 142 MPa and 125 MPa at 250°C, respectively, but only 249 MPa and 246 MPa at 150°C. Comparative Example 5 has high 0.2% yield strengths at 150°C and 250°C, but has a low thermal conductivity (117 W/mK).

The area ratios of precipitates and crystallized matter were determined in the same manner as in the examples. The values obtained are shown in Table 2. Here, in the comparative examples, the area ratios of crystallized matter were directly observed for the castings having the compositions of Comparative Example 1 and Comparative Example 2, and were found to be 15.7% and 19.5%, respectively. The area ratios of crystallized matter calculated by Thermo-Calc were 21.4% and 21.9% for Comparative Example 1 and Comparative Example 2, respectively, and it was confirmed that these values were in good agreement with the values obtained by direct observation. Representative optical microscope photographs of Comparative Example 1 and Comparative Example 2 are shown in Figures 4 and 5, respectively.

From Table 2, it can be seen that the amounts of both crystallized matter and precipitates are smaller in Comparative Examples 1 and 2 than in the Examples. In Comparative Examples 3 and 4, which showed high strength at 250°C, the amount of crystallized matter is sufficient, but the amount of precipitates is small. In Comparative Example 5, the high-temperature strength is improved by increasing the amount of Mn added, resulting in a low thermal conductivity.

Claims (7)

Si: 12.0-15.0wt%,
Cu: 4.0-5.0wt%,
Ni: 1.5-2.5wt%,
Mg: 1.5 to 2.5 wt%,
Fe: 0.2-0.8wt%,
Ti: 0.1 to 0.2 wt%,
Zr: 0.05 to 0.15 wt%,
V: 0.05-0.15wt%,
P: 0.005 to 0.015 wt %,
The remainder is made of Al and unavoidable impurities.
A heat-resistant aluminum alloy characterized by: Further, Mn: 0.01 to 0.10 wt % is contained;
The heat-resistant aluminum alloy according to claim 1 . The heat-resistant aluminum alloy according to claim 1 or 2 is used.
In any cross section, the area ratio of precipitates is 5% or more, and the area ratio of crystallized particles having a major axis of 100 μm or less is 20% or more.
A heat-resistant aluminum alloy member characterized by the above. The 0.2% proof stress at 150 ° C. is 260 MPa or more,
0.2% proof stress at 250°C is 120 MPa or more;
The heat-resistant aluminum alloy member according to claim 3, The tensile strength at 150°C is 280 MPa or more,
The tensile strength at 250°C is 140 MPa or more;
5. The heat-resistant aluminum alloy member according to claim 3 or 4, Thermal conductivity is 120 W/mK or more;
The heat-resistant aluminum alloy member according to any one of claims 3 to 5, The heat-resistant aluminum alloy member according to any one of claims 3 to 6,
A piston for an internal combustion engine, comprising: