JPH09272939A - Heat resistant and high strength aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an Al alloy having excellent high temp. strength without depending on the presence of heat treatment after casting by specifying the content of each componental element in an Al alloy and incorporating Cu largely in particular. SOLUTION: The compsn. of a heat resistant and high strength Al alloy is composed of by weight, 13 to 25% Si, 8 to 22% Cu, 0.2 to 1.5% Mg, 0.3 to 1.5% Fe, 0.1 to 2.5% Mn, 0.01 to 1.5% Ti, 1 to 5% Ni, 0.002 to 0.4% P, and the balance Al with inevitable impurities. Furthermore, the content of Cu is preferably regulated to 8 to 16% in the case its toughness shall be take into consideration. This Al allay is the one in which Cu is contained largely, comparted to that in the conventional one, and Al2 Cu compounds are formed as-cast to improve its high temp. strength. Thus, there is no need of executing heat treatment after casting in particular.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat resistant and high strength aluminum alloy suitable for high temperature and high load applications such as pistons of internal combustion engines.

[0002]

2. Description of the Related Art A piston of an internal combustion engine such as an automobile engine is required to be lightweight and excellent in high temperature strength since it moves at high speed under high temperature and high load. As a material suitable for such an application, an aluminum alloy for a piston, which is represented by a so-called low-ex alloy such as JIS-AC8A, which is lightweight, has excellent heat resistance, and has a low coefficient of thermal expansion, has been used so far.

In recent years, as the performance of internal combustion engines has improved, the operating environment of pistons has become higher in temperature. In order to deal with this, the present inventor has proposed a heat-resistant high-strength aluminum alloy for pistons having high strength at high temperature in Japanese Patent Laid-Open No. 64-73044. This alloy, by weight%, has Si: 12
~ 15%, Cu: 2-5%, Mg: 0.2-1.5%,
Co: 0.5-3%, Fe: 0.3-1%, Mn: 0.
1-1%, Ti: 0.01-0.2%, P: 0.002
˜0.025%, balance Al and unavoidable impurities.

Today, however, there is a strong trend toward higher performance of internal combustion engines, and it has been desired to develop aluminum alloys having higher high temperature strength.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-resistant high-strength aluminum alloy having further improved high-temperature strength as compared with the conventional heat-resistant high-strength aluminum alloy for pistons described above.

[0006]

According to the present invention, the above objects are achieved in terms of weight%: Si: 13 to 25%, Cu: 8 to 2
2%, Mg: 0.2 to 1.5%, Fe: 0.3 to 1.5
%, Mn: 0.1 to 2.5%, Ti: 0.01 to 1.5
%, Ni: 1 to 5%, P: 0.002 to 0.4%, and the balance: Al and unavoidable impurities.

Hereinafter, in this specification, "%" representing the content of each component element is used in the meaning of "% by weight" unless otherwise specified. The aluminum alloy of the present invention is improved in high temperature strength by containing a large amount of Cu as compared with the conventional one and by producing an Al ₂ Cu compound in an as-cast state. Since the Al ₂ Cu compound already exists in the as-cast state and contributes to high temperature strength, it is not necessary to perform heat treatment after casting. However, there is no inconvenience even if the heat treatment is performed after casting, and even if the heat treatment is carried out in a temperature range corresponding to solutionizing, aging, annealing, etc. which are usually used for aluminum alloys, the existence of Al ₂ Cu compound is substantially affected. Unless otherwise specified, high-temperature strength equivalent to that when heat treatment is not performed can be obtained.

The reason why the content of each component element is limited in the present invention will be described below. Si: 13 to 25% Si is an element effective in improving the wear resistance, but if it is less than 13%, the primary crystal Si cannot be stably crystallized and the effect cannot be secured. On the other hand, if it exceeds 25%, the liquidus temperature becomes high and the solidification temperature range at the time of casting widens, so that the castability deteriorates.

Cu: 8 to 22% Cu is an element that forms an Al ₂ Cu compound in the as-cast state to improve high-temperature strength, and if it is 8% or more, its effect is stably obtained. On the other hand, if it exceeds 22%, Al ₂ C
Not only is the toughness deteriorated by the excessive amount of the u compound produced, but also the specific gravity of the aluminum alloy increases, which is disadvantageous in terms of weight reduction. Especially when it is necessary to pay attention to the toughness, it is desirable to set it to 16% or less.

Mg: 0.2 to 1.5% Mg forms a Mg ₂ Si compound and strengthens the alloy, but if it is less than 0.2%, the effect cannot be obtained because the amount is small. On the other hand, even if the content exceeds 1.5%, the effect hardly increases. Fe: 0.3 to 1.5% Fe forms an Al ₃ Fe phase to improve high temperature strength. It also has the effect of preventing seizure from the casting mold during casting. These effects are weak at less than 0.3%, 1.5%
Even if the content exceeds 5, the effect is hardly increased.

Mn: 0.1 to 2.5% Mn makes the acicular Al ₃ Fe phase agglomerate to improve the toughness, and forms a solid solution in Al to strengthen the matrix. Also, A
It contributes to the improvement of high-temperature strength to produce a l ₆ Mn. 0.
If it is less than 1%, these effects are weak, and if it exceeds 2.5%, the amount of Al ₆ Mn produced becomes excessive, and it becomes difficult to obtain good toughness.

Ti: 0.01 to 1.5% Ti has the effect of refining the structure and is necessary for stably ensuring good mechanical properties, and also contributes to the improvement of strength. If less than 0.01%, these effects cannot be obtained,
If it exceeds 1.5%, Al ₃ Ti is generated and the toughness deteriorates. Ni: 1 to 5% Ni forms compounds such as Al-Fe-Ni and Al-Cu-Ni to improve high temperature strength. If it is less than 1%, this effect is small, and if it exceeds 5%, Al ₃ Ni is crystallized to deteriorate the toughness.

P: 0.002-0.4% P has the effect of dispersing primary crystal Si and improving toughness. If less than 0.002%, this effect is small, 0.4%
Even if it exceeds or is contained, its effect hardly increases.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples. [Example] Alloy 1 according to the present invention having the chemical composition shown in Table 1
~ 4 were cast by the following procedure. An alloy having a composition other than P in Table 1 was melted at 800 ° C., degassed and P was added to adjust the composition to that shown in Table 1, and then the melt temperature was set to 7
It was poured into a boat mold at room temperature at 50 ° C.

A JIS No. 4 tensile test piece was produced from the obtained casting by machining, and a tensile test was carried out with a 20 ton autograph tester at a pulling speed of 1 mm / min. The test temperatures were four levels of room temperature, 150 ° C, 250 ° C and 300 ° C. At that time, for tests at high temperatures other than room temperature, heat treatment was performed at the same temperature as each test temperature for 100 hours and then subjected to the tests. This is because when the piston is actually used, the strength of the material decreases as the cumulative holding time at the operating temperature increases, and the strength is evaluated by approximating such actual machine conditions.

The tensile test results for alloys 1 to 4 according to the present invention are summarized in Table 3. [Comparative Example] For comparison, Alloy 5 having the chemical composition shown in Table 2
10 to 10 were cast by the same procedure as in the example. Among the obtained castings, alloys 5 to 9 which are conventional precipitation-strengthened alloys were subjected to solution treatment at 510 ° C. for 5 hours and then 2
Aging treatment was performed at 10 ° C. for 5 hours. Then, the tensile test piece was machined as in the example. At that time, alloy 10 had an extremely low toughness due to an excessive amount of Cu with respect to the composition range of the present invention, and a test piece could not be produced by machining.

Tensile tests were conducted under the same conditions as in the examples, using the test pieces prepared for alloys 5 to 9. Table 4 summarizes the obtained results.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

Comparing Tables 3 and 4, alloys 1-4 of the present invention are at room temperature and 150 ° C compared to conventional alloys 5-9.
Equivalent tensile strength at ℃, but at 250 ℃ and 300
It can be seen that the tensile strength is remarkably improved at ° C. In the above examples, the alloy of the present invention was tested in an as-cast state, but even when it was subjected to solution treatment and aging similarly to the comparative example after casting, the same tensile strength as in the as-cast state was obtained. That is, since the alloy of the present invention can obtain the same excellent high-temperature strength regardless of the presence or absence of heat treatment after casting, it is possible to reduce the cost by omitting the heat treatment as compared with the conventional alloy that requires solution treatment and aging. .

[0023]

As described above, according to the present invention,
Provided is a heat-resistant and high-strength aluminum alloy having higher high-temperature strength than ever before. Further, the alloy of the present invention exhibits the same excellent high temperature strength regardless of the presence or absence of heat treatment after casting, so that the cost can be reduced by omitting the heat treatment.

Claims (2)

[Claims] 1. By weight%, Si: 13 to 25%, Cu: 8 to 22%, Mg: 0.2 to 1.5%, Fe: 0.3 to 1.5%, Mn: 0.1 -2.5%, Ti: 0.01-1.5%, Ni: 1-5%, P: 0.002-0.4%, and the balance: Al and unavoidable impurities High strength aluminum alloy. 2. The heat-resistant and high-strength aluminum alloy according to claim 1, wherein Cu: 8 to 16% by weight.