JP2001226754A - Method of manufacturing for heat resistant aluminum alloy and electric cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy which has characteristics well balanced among tensile strength, electric conductivity and short-time heat resistance and suitable for an electric cable such as a power-transmission line. SOLUTION: An aluminum alloy, which has a composition containing, as additives, 0.28-0.5% Zr, 0-1-0.3% Fe, 0.1-0.3% Si, 0.09-0.2% Cu, 0.005-0.03% Ti and 0.002-0.005% B and having the balance Al with impurities, is melted. The resultant molten aluminum alloy is cast at >=5 deg.C/s cooling rate. After the temperature of the aluminum alloy reaches 450-550 deg.C, area reduction working is performed at >=80% reduction of area until a temperature of <=200 deg.C is reached while carrying out cooling at >=5 deg.C/s cooling rate. Subsequently, heat treatment is applied at 300-400 deg.C for 8-48 h, and then cold working is performed at >=80% reduction of area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heat-resistant aluminum alloy suitable as a strand of an overhead power transmission line, and an electric cable using the alloy.

[0002]

2. Description of the Related Art An increase in power demand has led to a demand for laying lighter and higher-capacity electric cables using existing towers. To meet this demand, aluminum alloys containing various additives have been developed (Japanese Patent No. 2582073), and a steel core aluminum stranded wire having high heat resistance and mechanical strength has been provided.

[0003]

However, the above-mentioned prior art has the following problems to be solved. Aluminum alloys used in conventional electric cables have a tensile strength equivalent to that of general electric aluminum alloys. However, for example, when laying a transmission line so as to cross a mountain area or a river, it is necessary to support the transmission line over a longer span (distance between towers) than usual. In this case, there is a problem that the mechanical strength is insufficient and the allowable span is limited. On the other hand, hot working is performed by adding Zr or the like in order to enhance mechanical strength, but it is difficult to adjust the balance between mechanical strength, elongation and heat resistance. It is desired to develop an excellent method for producing an aluminum alloy.

[0004]

The present invention employs the following structure to solve the above problems. <Structure 1> The additive amount of Zr is 0.28% to 0.5%,
e is 0.1% to 0.3%, and the amount of Si is 0.1 to 0.3%.
1% to 0.3%, Cu content is 0.09% to 0.2
%, The addition amount of Ti is 0.005% to 0.03%, the addition amount of B is 0.002% to 0.005%, and the balance is made of an aluminum alloy composed of Al and impurities, and at least 5 degrees Celsius per second. After the temperature of the aluminum alloy reaches 450 ° C. to 550 ° C., the surface is cooled at a cooling rate of 5 ° C. or more per second to reduce the surface area by 80% or more until the temperature reaches 200 ° C. or less. A heat-resistant aluminum alloy, which is subjected to heat treatment at a temperature range of 300 to 400 degrees Celsius for 8 to 48 hours, and then to cold work at a surface reduction rate of 80% or more. Manufacturing method. <Structure 2> The additive amount of Zr is 0.28% to 0.5%,
e is 0.1% to 0.3%, and the amount of Si is 0.1 to 0.3%.
1% to 0.3%, Cu content is 0.09% to 0.2
%, The addition amount of Ti is 0.005% to 0.03%, the addition amount of B is 0.002% to 0.005%, and the balance is made of an aluminum alloy composed of Al and impurities, and at least 5 degrees Celsius per second. After the temperature of the aluminum alloy reaches 450 to 550 degrees Celsius, the aluminum alloy is cooled at a cooling rate of 5 degrees Celsius per second or more while reducing the surface area by 80% or more until the temperature reaches 200 degrees Celsius or less. Alloy wire produced by performing a heat treatment at a temperature range of 300 to 400 degrees Celsius for 8 to 48 hours, and then performing a cold working with a surface reduction rate of 80% or more. Electrical cable consisting of

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below using specific examples. FIG. 1 is a process chart showing an outline of a method for producing a heat-resistant aluminum alloy of the present invention. As shown in the figure, the method of the present invention comprises the following steps:
, Casting step 2, surface reduction step 3, and heat treatment step 4.
And a cold working step 5. The details of each step are described below.

In the present invention, first, the amount of Zr added is set to 0.1.
28% to 0.5%, Fe added amount is 0.1% to 0.3%
%, The addition amount of Si is 0.1% to 0.3%, the addition amount of Cu is 0.09% to 0.2%, and the addition amount of Ti is 0.005%.
~ 0.03%, B content is 0.002 ~ 0.005%
Melts an aluminum alloy consisting of Al and impurities. The above [%] indicates the weight ratio of each additive to the weight of the total aluminum alloy.

[0007] Zr is an additive element for improving the strength and heat resistance of the Al alloy. If the addition amount of Zr is less than 0.28%, the precipitation amount of Zr is small and does not contribute to the improvement of the strength and heat resistance of the alloy. When the addition amount exceeds 0.5%, the temperature for melting the alloy becomes too high, and it becomes difficult to industrially manufacture the alloy. Further, when the addition amount exceeds 0.5%, the precipitation of Zr becomes coarse, the alloy becomes brittle, and the electric conductivity also decreases. From the above, the addition amount of Zr is set to 0.
It was selected from 28% to 0.5%.

[0008] Fe is an additive element for improving the strength, elongation and heat resistance of the Al alloy. Further, it is an additional element that prevents casting cracks due to the addition of Si. If the added amount of Fe is less than 0.1%, the effect of the addition is not exhibited, and if the added amount exceeds 0.3%, brittleness due to working of the alloy occurs. Therefore, the addition amount of Fe was selected to be 0.1 to 0.3%.

Si is an additive element that improves the strength of the Al alloy and promotes the precipitation of Zr having a low diffusion rate. If the added amount of Si is less than 0.1%, the effect is small. On the other hand, if the addition amount exceeds 0.3%, the heat resistance and conductivity of the alloy decrease. Therefore, the addition amount of Si is 0.1 to
0.3% was selected.

[0010] Cu is an additive element having a large work hardening ability and improving the strength of an Al alloy. If the amount of Cu is less than 0.09%, the effect is small, and
%, The electrical conductivity and corrosion resistance of the alloy decrease. Therefore, the addition amount of Cu is set to 0.09 to 0.2%.

[0011] Ti is an additional element that refines the cast structure, improves workability, and prevents the occurrence of scratches on the alloy during hot working. If the added amount of Ti is less than 0.005%, the microstructure effect cannot be obtained. On the other hand, the addition amount is 0.03%
If it exceeds, the conductivity will be reduced. Therefore, the addition amount of Ti is set to 0.005 to 0.03%.

B is an additive element that refines the cast structure, improves workability, prevents the alloy from combining with Ti to prevent a decrease in electrical conductivity, and prevents scratches in the alloy during hot working. If the added amount of B is less than 0.002%, the fine effect of the structure of the alloy cannot be obtained. On the other hand, if the added amount exceeds 0.005%, the heat resistance decreases. In particular, when combined with Ti, the effect of preventing ingot cracking is remarkable. The effect becomes remarkable when the weight ratio of Ti and B is around 5: 1. Therefore, the addition amount of B is set to 0.002 to 0.005%.

Incidentally, a small amount of Ni can be added to the above alloy to improve the strength, and a small amount of Be can be added to the alloy to improve the electric conductivity.

Next, casting is performed at a cooling rate of 5 degrees Celsius or more per second. If an aluminum alloy to which Zr is added is cast at a cooling rate of less than 5 degrees Celsius per second, Zr exceeding the solid solubility limit will precipitate without being sufficiently dissolved, and the strength and heat resistance of the alloy will be reduced. Therefore, a cooling rate of 5 degrees Celsius per second or more was selected.

After the temperature of the aluminum alloy reaches 450 ° C. to 550 ° C., it is cooled at a cooling rate of 5 ° C. or more per second to 80% or less until the temperature becomes 200 ° C. or less.
The surface reduction is performed at the above-mentioned reduction ratio. If the starting temperature of the area reduction processing is 550 degrees Celsius or more, cracks and the like occur during the area reduction processing, making the processing difficult. In addition, the starting temperature of the area reduction processing is 45 degrees Celsius.
Even if the angle is less than 0 degrees, cracks and the like occur during the surface reduction processing, making the processing difficult. Therefore, the starting temperature of the surface reduction processing was selected to be 450 degrees Celsius to 450 degrees Celsius or more.

If the processing end temperature is higher than 200 degrees Celsius, Z
The amount of solid solution of r is small and strength and heat resistance are reduced. Therefore,
The working end temperature was selected to be 200 degrees Celsius or less. The reason why the area reduction rate of the area reduction processing is 80% or more is to obtain a sufficient strength of the alloy. This makes it possible to manufacture a power transmission cable using an aluminum alloy wire having high electrical conductivity and sufficient mechanical strength.

Next, heat treatment is performed at a temperature range of 300 to 400 degrees Celsius for 8 to 48 hours. By this heat treatment, Zr is finely precipitated to improve strength and heat resistance. If the heat treatment temperature is less than 300 degrees Celsius or the heat treatment time is less than 8 hours, the amount of deposited Zr is small and sufficient strength and heat resistance cannot be secured. On the other hand, when the heat treatment temperature exceeds 400 degrees Celsius or the heat treatment time exceeds 48 hours, Zr is coarsely precipitated, and strength and heat resistance are reduced. Therefore, the temperature range is set to 300 degrees Celsius to 40 degrees Celsius.
0 degree and the heat treatment time was selected from 8 hours to 48 hours.

After the surface is reduced to a predetermined size, a heat treatment at 250 to 400 degrees Celsius for 3 to 48 hours can improve the conductivity and elongation of the alloy. After the above-mentioned heat treatment, cold working with a surface reduction rate of 80% or more is performed to obtain an aluminum alloy wire. By twisting the aluminum alloy wire, an overhead power transmission cable using a conductor having sufficiently high mechanical strength, electrical conductivity, elongation, and heat resistance and having a well-balanced characteristic can be manufactured.

[0019]

FIG. 2 is a table showing the composition and properties of a heat-resistant aluminum alloy according to the method of the present invention, and the composition and properties of a comparative example. In this table, "sample" is a serial number assigned to each sample having a different composition. Each sample was prepared by dissolving an Al alloy with the composition shown on the right and casting at a cooling rate of 5 degrees Celsius per second.
The rolling process starts at a cooling rate of 15 degrees Celsius per second when the temperature reaches a temperature of 97 degrees Celsius and a finishing temperature of 90 degrees Celsius.
This is a rough drawn wire having a diameter of 9.5 mm.

The obtained rough drawn line was 380 degrees Celsius and 16H
Heat treatment was performed for r (hour), and cold working was performed with a reduction in area of 86% to obtain an aluminum alloy wire. These properties are shown on the right. In this table, the short-term heat resistance is the result of calculating the ratio of the tensile strength before heat treatment to the tensile strength after heat treatment (residual rate%) after heat treatment for 1 hour at 230 degrees Celsius. MPa is the force applied per unit cross-sectional area, and the unit is N
/ M ² . % IACS is the conductivity based on international standard annealed copper, and the unit is percent. The right end is the overall evaluation of each sample, the double circles are the best, and the circles indicate that they are almost usable. Others show poor balance and are unsatisfactory for electrical cables.

As shown in the table, all the examples have a good balance of each property such that the tensile strength is 242 MPa or more, the conductivity is 55% or more, and the short-time heat resistance is 90% or more. It shows characteristics suitable for such an electric cable. On the other hand, in Comparative Example 1, the amounts of Zr and Fe added were small, and the tensile strength and short-time heat resistance were insufficient. Also,
In Comparative Example 2, the added amounts of Zr, Fe, and Cu were large, and the conductivity was insufficient. In Comparative Example 3, the addition amount of Zr was large, the addition amount of Fe was small, and the electrical conductivity and short-time heat resistance were insufficient. In Comparative Example 4, the amounts of Fe and Si added were large, and the electrical conductivity and short-time heat resistance were insufficient. In Comparative Example 5, the amount of Ti added was large, and the conductivity was insufficient. In Comparative Example 6, the added amount of B was large, and the electrical conductivity and short-time heat resistance were insufficient. Comparative Example 7
Is poor in conductivity because only Ti is added and B is not added. From these results, it is proved that an alloy having a well-balanced characteristic can be obtained by mixing Ti and B in appropriate amounts.

FIG. 3 is a table showing evaluations when the above-described samples were manufactured under various heat treatment conditions. This sample used an alloy having the composition of Example 4 in FIG. All of Examples 11 to 18 treated under the heat treatment conditions according to the present invention have a high level of balance of tensile strength of 254 MPa or more, conductivity of 55% or more, and short-time heat resistance of 95.1% or more. On the other hand, in Comparative Example 11, since the heat treatment temperature was low, the tensile strength and the electrical conductivity were insufficient. Comparative Examples 12 and 13
However, since the heat treatment temperature is high, the tensile strength and short-time heat resistance are insufficient.

[Brief description of the drawings]

FIG. 1 is a process chart showing an outline of a method for producing a heat-resistant aluminum alloy of the present invention.

FIG. 2 is a table showing the composition and properties of a heat-resistant aluminum alloy according to the method of the present invention, and the composition and properties of a comparative example.

FIG. 3 is a table showing evaluations when the above-described samples are manufactured under various heat treatment conditions.

[Explanation of symbols]

 1 Aluminum alloy smelting process 2 Casting process 3 Surface reduction process 4 Heat treatment process 5 Cold working process

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22F 1/00 650 C22F 1/00 650A 660 660Z 661 661A 691 691A 691B 691C 692 692A 692B 694 694A 694B

Claims (2)

[Claims] 1. The amount of Zr added is 0.28% to 0.5%.
%, The addition amount of Fe is 0.1% -0.3%, the addition amount of Si is 0.1% -0.3%, and the addition amount of Cu is 0.09%-
0.2%, the added amount of Ti is 0.005% to 0.03%,
An aluminum alloy containing 0.002% to 0.005% of B and the balance consisting of Al and impurities is melted at a rate of 5 degrees Celsius per second.
After casting at a cooling rate of at least 400 degrees Celsius and the temperature of the aluminum alloy reaches 450 degrees Celsius to 550 degrees Celsius, cooling at a cooling rate of 5 degrees Celsius per second or more while cooling at a cooling rate of 5 degrees Celsius per second or more until the temperature reaches 200 degrees Celsius or less. Reduced area at reduction rate, 300 degrees Celsius
A method for producing a heat-resistant aluminum alloy, comprising: performing a heat treatment in a temperature range of from 400 to 400 degrees Celsius for 8 hours to 48 hours; and then performing a cold working with a reduction in area of 80% or more. 2. The amount of Zr added is 0.28% to 0.5%.
%, The addition amount of Fe is 0.1% -0.3%, the addition amount of Si is 0.1% -0.3%, and the addition amount of Cu is 0.09%-
0.2%, the added amount of Ti is 0.005% to 0.03%,
An aluminum alloy containing 0.002% to 0.005% of B and the balance consisting of Al and impurities is melted at a rate of 5 degrees Celsius per second.
After casting at a cooling rate of at least 400 degrees Celsius and the temperature of the aluminum alloy reaches 450 degrees Celsius to 550 degrees Celsius, cooling at a cooling rate of 5 degrees Celsius per second or more while cooling at a cooling rate of 5 degrees Celsius per second or more until the temperature reaches 200 degrees Celsius or less. Reduced area at reduction rate, 300 degrees Celsius
An electric cable obtained by performing a heat treatment for 8 to 48 hours in a temperature range of 400 to 400 degrees Celsius and then performing a cold working with a surface reduction rate of 80% or more and twisting an alloy wire.