JPH0971834A - High heat resistant aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat resistant aluminum alloy particularly excellent in high temp. strength for an internal combustion engine as for the improvement of the high temp. characteristics of an aluminum alloy. SOLUTION: This alloy has chemical components expressed by the general chemical constitutional formula: Al100-(a+b+c) Cua Sib Mgc , where (a), (b) and (c) satisfy the ranges of 6wt.%<=a<=10wt.%, 6wt.%<=b<=13wt.% and 0.5wt.%<=c<=1.5 wt.%. Alternatively, it contains Ti and is expressed by the general chemical constitutional formula: Al100-(a+b+c+d) Cua Sib Mgc id , where (a), (b), (c) and (d) satisfy the ranges of 0.6wt.%<=a<=10wt.% 6wt.%<=b<=13wt.%, 0.5wt.%<=c <=1.5wt.% and 0wt.%<d<=0.1wt.%, and moreover, 6wt.%<=b<=8wt.% is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of high temperature properties of aluminum alloys, and more particularly to heat resistant aluminum alloys excellent in high temperature strength for internal combustion engines.

[0002]

2. Description of the Related Art Generally, aluminum alloys are often used at about 150 ° C. or lower for high temperature structures. When used at higher temperatures, 2000 series alloys and 4000 series alloys are used. In these alloys, it is desired as a characteristic that the decrease in strength at high temperature is small. Further, when used at high temperature, the creep property determined by the relationship between strain and time under a constant load becomes important. It is known that this creep strength is generally superior to a material having higher high temperature strength.

Conventionally, high heat resistant alloys such as AC8A have been used for aluminum parts used in high temperature environments such as pistons. As a known technique in this field, Applied Mechanical Engineering Complete Book 5 “Metal Material Engineering” 1979.
As an Al-Si based Al alloy casting, JIS AC8C
Is disclosed. This AC8C is Al-Si-Cu.
-Mg-based alloy (for example, Si9% -Cu3% -Mg1%-
The balance is Al), which is known as a heat-resistant alloy, has a small coefficient of thermal expansion, has a large thermal conductivity, and has excellent high-temperature strength and wear resistance, so it is used as an alloy for pistons of automobile engines and the like. Has been done. However, in recent years, the usage conditions of engines for automobiles have become more and more severe,
There is a growing need for alloys with high strength at high temperatures. Therefore, it is desired to develop an aluminum alloy casting having a high temperature strength higher than that of conventional materials.

[0004]

An object of the present invention is to study heat-resistant alloys such as engine piston materials suitable for use at higher temperatures, and to develop a high heat-resistant aluminum alloy having high high-temperature strength superior to conventional materials. provide. Further, the object of the present invention is to improve the material properties of high-temperature strength, in the composition range of the current commercial material, heat-resistant dispersed particles, that is, a high heat-resistant aluminum alloy excellent in high-temperature strength with an improved dispersed state of the compound, provide.

[0005]

[Means for Solving the Problems] The above-mentioned object is that the chemical component is a general chemical structural formula: Al _{100- (a + b + c)} Cu _a Si
_b is represented by Mg _C , and a, b and c are 6 wt% ≤ a ≤ 10 wt
%, 6 wt% ≤ b ≤ 13 wt%, 0.5 wt% ≤ c ≤ 1.5 wt
%, Which is achieved by the high heat resistant aluminum alloy.

[0006] Further, the above-mentioned object is, in the alloy,
Furthermore, it contains Ti and has a general chemical structural formula: Al.
_{100- (a + b + c + d)} Cu _a Si _b Mg _C Ti _d
a, b, c and d are 6 wt% ≤ a ≤ 10 wt%, 6 wt%
≦ b ≦ 13wt%, 0.5wt% ≦ c ≦ 1.5wt%, 0wt%
It is also achieved by a high heat resistant aluminum alloy characterized in that <d ≦ 0.1 wt%. further,
The above object is also achieved by a high heat resistant aluminum alloy characterized in that b is 6 wt% ≤ b ≤ 8 wt%.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention focuses on the fact that piston materials for internal combustion engines for automobiles, etc. contain a relatively large amount of Si and have a higher Cu than heat resistance in order to improve strength. This was done to secure castability to some extent and further improve high temperature strength. That is, the morphology and distribution of CuAl ₂ as an intermetallic compound are important for securing heat resistance strength, and it has been found that the high temperature strength can be further improved by making the amount and distribution of this intermetallic compound more appropriate. It was achieved by. According to the present invention, by mixing a predetermined amount of Cu and Si, it is possible to significantly improve high-temperature strength while ensuring properties such as linear expansion coefficient and thermal conductivity that are comparable to those of conventional materials. Incidentally, in the Al alloy of the present invention, 300 MPa or more at 200 ° C. and 250 MPa at 250 ° C.
The strength is 1.2 to 1.3 times that of the conventional material.

The reasons for limiting the chemical alloying components in the present invention will be described below. Si is an important element in the fluidity at the time of melting and casting of the aluminum alloy of the present invention, that is, castability and solidification shrinkage. Originally, Al-Cu alloys have a problem in castability, and therefore it is considered that Si is increased to some extent to improve the above-mentioned properties. However, when Si is increased to 13 wt% or more, the primary crystal Si also increases in a substantially proportional manner, and the plate-like crystal deteriorates mechanical properties, particularly toughness, and therefore is quantitatively regulated. Also, the liquidus temperature rises. That is, when Si exceeds 13 wt%, the effect of improving the above-mentioned properties such as castability is saturated, or rather the castability is impaired. On the other hand, if Si is less than 6 wt%, the effect of improving the above properties such as castability cannot be obtained. Therefore, in the present invention, Si is specified to 8 to 13 wt%. Further, the more preferable range of Si is 6 to 8 wt%.

Cu is an essential element for improving the strength of the matrix, and the strength increases as the content increases up to 4.5 wt%. When the capacity ratio of CuAl ₂ which is an intermetallic compound is further increased, the heat resistance strength is improved accordingly. However, if the amount is too large, the toughness decreases. Therefore, Cu is limited to 6 to 10 wt% in the present invention. If the Cu content exceeds 10 wt%, the toughness falls below the practical range, while if the Cu content is less than 6 wt%, the toughness falls within the conventional range.
It is not expected that the characteristics will be improved. Regarding Mg, it has the effect of improving the strength by the addition of a very small amount, and this is considered to be the precipitation of Mg ₂ Si compounds. In the present invention, Mg is 1.
If it exceeds 5 wt%, hardness tends to be high and brittleness is observed, while
If the Mg content is less than 0.5 wt%, the strength improving effect is not recognized. Therefore, in the present invention, Mg is limited to the range of 0.5 to 1.5 wt%.

Even when Ti is not added, the basic characteristics are secured by the above-mentioned other components. As an effect unique to Ti, there is an effect of preventing casting cracks, for example, shrinkage cavities by dispersing and cracking due to stress concentration. The Ti range of the present invention is more preferably 0 wt% <Ti ≤ 0.1 wt% or less, and most preferably 0.05 wt% <Ti ≤ 0.1. It is needless to say that the material of the present invention contains other components as an unavoidable impurity component of a normal level as an aluminum alloy casting.

[0011]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings of Examples. Examples Al alloys having chemical components shown in Table 1 are melted in an electric furnace,
After degassing with ethane hexachloride, JI at room temperature in the atmosphere
Cast into S boat mold (Fig. 6), length 195mm, height 39
mm, an upper side 33 mm, and a lower side 23 mm were produced.

[0012]

[Table 1]

The casting ingot obtained as described above was homogenized at a holding temperature of 480 ° C. for 3 hours.
After water quenching, T6 heat treatment was performed at 180 ° C. for 6 hours as a precipitation treatment. Next, a cylindrical tensile test piece was produced from the cast ingot, and a tensile test was performed using an Instron type tester. The obtained results are shown in FIG. As shown in FIG. 1, the aluminum alloy of this example, which is within the composition range of the present invention, has a temperature of 3 ° C. at 200 ° C.
It shows high high-temperature strength of 00 MPa or more and 250 MPa or more at 250 ° C., which is higher than that of conventional materials AC8A and AC8C, indicating that the material of the present invention is superior to the conventional material in tensile strength.

Comparative Example An Al alloy having the chemical composition shown in Table 2 was melted by the same method as described above and cast under the same conditions.

[0015]

[Table 2]

As shown in FIG. 1, the strength of the comparative material (No. 5) in which Cu was 5 wt% below the lower limit was insufficient. Also,
As a result of measuring the elongation of each comparative material, the elongation was increased in the comparative material (No. 4) in which Si was 14 wt% or more above the upper limit and the comparative material (No. 6) in which Cu was 11 wt% or more above the upper limit. It was confirmed that there was a shortage.

Further, as one method for measuring the castability, a fluidity test was carried out using a fluidity test mold to measure the fluidity during casting. The result is shown in FIG. As shown in Fig. 2, a comparative material in which Si is 5 wt% or less, which is less than the lower limit (No. 3)
It was confirmed that the fluidity was poor and it was not suitable for the production of casting products such as casting defects. The above results are summarized as follows.

If Si is out of the lower limit (No. 3), the castability is poor. On the other hand, when Si is outside the upper limit (No. 4), the elongation is low. When Cu is out of the lower limit (No. 5), the high temperature strength is lowered, while Cu is out of the upper limit (No. 5).
In the case of 6), the growth is insufficient. From the above, it can be seen that when an aluminum alloy cast material, which is a component within the scope of the present invention, is adopted, high heat resistance can be obtained in response to weight reduction of pistons and adaptation to more severe engines. Furthermore, FIG. 4 shows the result of measurement of fatigue strength at 10 ⁷ cycles at 250 ° C. which is another material property, FIG. 5 shows the result of linear expansion coefficient, and FIG. 6 shows the result of thermal conductivity. At 250 ° C., the material of the present invention exhibits higher fatigue strength than the conventional material, and in other characteristics, the material of the present invention shows good results comparable to the conventional material. As for the comparative material, the fluidity test result of the basic characteristics revealed that it was considerably low, and therefore the subsequent tests were not carried out.

[0019]

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a high heat-resistant cast alloy which secures good castability and has higher high-temperature strength than conventional alloys such as AC8A, that is, 300 MPa or more at 200 ° C. and 250 MPa or more at 250 ° C. can get.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between temperature and tensile strength according to the present invention in comparison with a comparative material and a conventional material.

FIG. 2 is a diagram showing the fluidity of the material of the present invention in comparison with a comparative material and a conventional material.

FIG. 3 is a diagram showing the fatigue strength of the material of the present invention in comparison with the conventional material.

FIG. 4 is a diagram showing a coefficient of linear expansion of the material of the present invention in comparison with a conventional material.

FIG. 5 is a diagram showing the heat transfer coefficient of the material of the present invention in comparison with the conventional material.

FIG. 6 is a schematic view of a JIS boat mold used in this example.

Claims (3)

[Claims] 1. The chemical component has a general chemical structural formula: Al.
_{100- (a + b + c)} Cu _a Si _b Mg _C represented by a, b, c
Is 6 wt% ≤ a ≤ 10 wt%, 6 wt% ≤ b ≤ 13 wt%,
A high heat-resistant aluminum alloy, characterized in that it is in a range of 0.5 wt% ≤ c ≤ 1.5 wt%. 2. The compound according to claim 1, which further contains Ti and has a general chemical structural formula: Al _{100- (a + b + c + d)} Cu _a S.
i _b Mg _C Ti _d , where a, b, c and d are 6
wt% ≤ a ≤ 10 wt%, 6 wt% ≤ b ≤ 13 wt%, 0.5 wt
A high heat-resistant aluminum alloy characterized by being in the range of% ≤ c ≤ 1.5 wt% and 0 wt% <d ≤ 0.1 wt%. 3. The method according to claim 1 or 2, wherein 6 wt% ≦ b
A high heat-resistant aluminum alloy characterized by being ≦ 8 wt%.