JPS6143426B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention maintains sufficient electrical conductivity and tensile strength,
Moreover, the present invention relates to a method for manufacturing a highly heat-resistant aluminum alloy for conductive use that can exhibit high heat-resistant performance. In recent years, the demand for electricity has been increasing year by year. For this reason, for example, there is a need to increase the current carrying capacity of overhead power transmission lines, and conventionally, so-called heat-resistant ACSR
A containing approximately 0.1% Zr as (steel core aluminum stranded wire)
- Zr-based alloys are widely used. However, in this case, normally the allowable temperature for short-term use of IACS with 60% conductivity is specified as 180℃, and even if high heat resistance is required, the allowable short-time use temperature of IACS with 58% conductivity is specified as 230℃. Ta. However, recently, the demand for electricity has been increasing more and more, and there is an increasing need to use existing steel towers to transmit even larger amounts of electricity. In such cases, the temperature rise during energization is significant, requiring the conductor to have an allowable short-term operating temperature of 300°C or higher. Moreover, if the electrical conductivity and tensile strength decrease as a result, it is not practical, and the electrical conductivity also decreases.
It is required to meet the strict conditions of ensuring a tensile strength of 58% IACS or higher and a tensile strength of 16 kg/mm ² or higher. If the purpose is simply to improve heat resistance, it is not difficult to select additive elements, but it is extremely difficult to ensure high electrical conductivity. Zr is one of the few elements that can improve heat resistance and maintain electrical conductivity, but the conventional mechanism for improving heat resistance relies on solid solution of Zr, and high heat resistance is required. In this case, the amount of Zr must necessarily be increased, and as a result, a decrease in electrical conductivity due to an increase in solid solution elements is unavoidable. For this reason, in conventional alloys, as mentioned earlier,
Addition of about 0.1% Zr was the limit, and there was a limit to the improvement of heat resistance. In order to solve these conventional problems, the inventors focused on adding a higher concentration of Zr and finely precipitating it to improve heat resistance and maintain electrical conductivity. However, it is extremely difficult to make these fine precipitates through the conventional process of annealing after solid solution treatment, and if the annealing temperature is high, coarse precipitates will form, making it impossible to obtain the desired heat resistance performance. However, if the temperature is lowered, a long time is required for precipitation, making industrial production impossible. As a result of various experiments, the inventors found that even with the addition of a relatively high concentration of Zr, by adding a third element and providing certain limited processing conditions, it was found that fine precipitation of Zr could be easily achieved industrially. By doing so, they found that it was possible to significantly improve heat resistance, and also maintain the desired electrical conductivity and tensile strength, and found that the solution could be reached all at once. A detailed explanation will be given below. In the alloy according to the present invention, in order to increase heat resistance, a much higher concentration of Zr is added compared to the conventional example, ie 0.2 to 1.5% Zr. 0.2%
The following products are excluded because they cannot achieve heat resistance that satisfies the condition of short-term use temperature of 300°C or higher. If the Zr content exceeds 1.5%, it becomes extremely difficult to obtain conductivity of 58% IACS or higher, and embrittlement during wire drawing becomes significant, so this is also excluded. Therefore, the alloy according to the present invention is added as a third element in a range of 0.1 to 1.0% Si and 0.005 to 0.02% Be. The addition of Si and Be in the above ranges increases the precipitation rate of Zr and exhibits high heat resistance due to the precipitation hardening.
Si is also expected to have the tensile strength of the material itself. It has been known that when Be is added to A, the conductivity and strength increase, and such A alloys are currently in practical use. However, Zr0.2
There is no example of adding Be to an A-Zr alloy with a high concentration of 1.5% to 1.5%. The reason why adding Be to A-Zr alloy accelerates the precipitation rate is still under investigation.
Even the detailed mechanism has not yet been clarified. However, it can be inferred that this is probably due to the following effect. In other words, it is understood that precipitation in an alloy progresses by the generation of nuclei for precipitation and their growth, so in order to accelerate the precipitation rate, it is necessary to facilitate the generation and growth of the nuclei. It turns out. Although dislocations and grain boundaries are generally thought to be places where such nuclei are likely to occur, fine precipitated phases also create distortion in the surroundings and can become places where nuclei can occur. Looking at this in the case of Be addition, we find that
Be has no solid solubility in A, and
Because the bonding force with the impurities inside is strong, there are
It exists as a precipitate as a compound with Fe, Zr, etc. When this precipitate is rapidly solidified as in the treatment method according to the present invention, it becomes a very fine precipitate, and Zr or a compound of Zr and Si is precipitated as a nucleus along with the finely precipitated Be compound. It can be considered that this allows the time required for precipitation to be significantly shortened. Therefore, the range of these additive elements to exhibit the above-mentioned effects has its own optimum range. As for Si, if it is less than 0.1%, it has no effect of accelerating the precipitation of Zr, and precipitation hardening due to precipitation is also small, making it impossible to secure a predetermined tensile strength. However, when the amount exceeds 1.0%,
Wire drawing becomes difficult, embrittlement occurs, and the conductivity decreases significantly, so it is excluded. As for Be, if it is less than 0.005%, compounds of Be and Fe, Be and Zr, and Be and other impurities, which can become precipitation nuclei, are not formed to the extent that they are effective in accelerating the precipitation of Zr. Moreover, if it is 0.02% or more, a compound of Be and Zr is formed too much, and Zr, which contributes to heat resistance, decreases, resulting in a decrease in heat resistance. Also, since Be is expensive, 0.02%
In this case, the cost of the product increases. In the manufacturing method according to the present invention, an aluminum alloy within the above composition range is melted and subjected to the following steps to provide, for example, a strand of steel-core aluminum stranded wire. (1) First, the melted aluminum alloy in the above composition range is cast, and after casting, the ingot is
Processing is applied while cooling at a cooling rate of ℃/sec or higher, and the area reduction rate of 80% or more is processed until the material temperature drops to 200℃ or less, and it is made into a rough drawing line. The main objectives of this step are to obtain a supersaturated solid solution of Zr and to introduce dislocations into the matrix. Therefore, if it is not cooled at a rate of 5°C/sec or more, the added elements of Zr, Si, and Be will not be sufficiently dissolved and will precipitate during solidification, or will form coarse crystallized substances. It no longer contributes to heat resistance and precipitation hardening. It is preferable to cool at a cooling rate of 15° C./sec or higher. Adding the above-mentioned cooling and processing until the material temperature drops to 200℃ or less is too high for processing that finishes at 200℃ or higher, and coarse Zr,
Si and Be compounds precipitate and solid solution is not sufficient, and machining occurs only in the high temperature range, resulting in subsequent 300~
In heat treatment of 450×20 to 100 hours, effective introduction of dislocations is insufficient. Similarly, if the degree of working is less than 80%, the introduction of dislocations will be insufficient, and the subsequent heat treatment will not work effectively. (2) Following processing during the above cooling, the material is 65%
It is cold worked. This is to sufficiently introduce the dislocation density, which is still insufficient in (1) above, through this cold working. Therefore, if the cold working is less than 65%, the dislocation density will be insufficient, fine precipitation with hardening ability will not occur in the subsequent heat treatment, and the tensile strength after the heat treatment will also be insufficient. (3) The material is then heated at a temperature of 20 to 450℃.
Heat treated for 100h. Needless to say, this is to cause fine precipitation of Zr, and since Zr precipitation is very slow at temperatures below 300℃, there is little increase in conductivity.
At temperatures above ℃, coarse Zr compounds precipitate and do not contribute to improving heat resistance, and the tensile strength of the material decreases, and although the electrical conductivity increases, the tensile strength after wire drawing is insufficient. If it is less than 20 hours, sufficient precipitation of Zr cannot be obtained, and if it is more than 100 hours, the precipitates become coarse, resulting in so-called over-aging, which is not effective in improving heat resistance. Note that this heat treatment only requires a total heat treatment time of 20 to 100 hours in the range of 300 to 450°C, and there is no difference in the effect even if the heat treatment is performed in stages. It is manufactured through the steps described above. The aluminum alloy according to the present invention is used for conductive purposes and has excellent heat resistance performance, as will be clarified by the following examples.
It has a wide range of applications beyond just overhead power transmission lines. Example (1) The alloy shown in Table 1 was melted and cast at a cooling rate of 15°C/sec, and a 9.5φ rough drawn wire (hereinafter referred to as WR) was made at a finishing temperature of 125°C by adding a working degree of 95%.
And so. This WR was cold drawn into a 4.5φ wire, which was then heat treated at 350°C for 40 hours. Its performance is the first priority.
Shown in the table. As a measure of heat resistance, the residual rate of tensile strength after heating at 400°C for 4 hours (hereinafter simply referred to as residual rate) was determined. As can be seen from this result, when Zr is 0.2% or less, tensile strength and heat resistance are insufficient, and when Zr is 1.5% or more, tensile strength and heat resistance are sufficient, but electrical conductivity is low. In addition, in this case, Si, which was extremely difficult to cast,
If it is less than 0.1%, precipitation is slow and the tensile strength, electrical conductivity,
Low heat resistance. If it is 1.0% or more, the tensile strength is sufficient, but the heat resistance and electrical conductivity decrease. Further, in this case, wire drawing was extremely difficult. When Be is 0.005% or less, tensile strength, electrical conductivity,
It can be seen that both heat resistance is low and precipitation is slow. Also
If it is 0.02% or more, the heat resistance decreases due to too much Be. Also, in this case the wire would be quite expensive.

[Table] Example (2) A-0.3%Zr-0.1%Si alloy and A-0.3%Zr-
Figure 1 shows the changes in electrical conductivity and tensile strength when a 0.1%Si-0.01%Be alloy was cast, rolled and drawn as in Example (1) and heat treated at 350°C. In alloys to which Be is added, the increase in conductivity and tensile strength due to heat treatment is much faster than in alloys to which Be is not added. Example (3) A-0.3%Zr-0.1%Si-0.01%Be alloy as the second
Casting was performed at the cooling rate shown in the table. The cooling rate was adjusted by the amount of water cooling shower. After starting rolling at 520℃ without reheating this ingot and finishing rolling at 125℃ to produce WR, cold wire drawing was performed to 4.5φ.
The performance was investigated by performing heat treatment at 350°C for 40 hours. It can be seen that the heat resistance is particularly low when the cooling rate is 5° C./sec or less.

[Table] Example (4) A-0.3% Zr-0.1% Si-0.01% Be alloy was cast at a cooling rate of 15°C/sec. WR was manufactured by starting rolling at 520° C. without reheating this ingot, and changing the rolling end temperature as shown in Table 3.
This WR was cold drawn to 4.5φ, heat treated at 350°C for 40 hours, and its performance was investigated. The results are shown in Table 3. It can be seen that heat resistance is low when the finishing temperature is 200℃ or higher.

[Table] Example (5) A-0.3% Zr-0.1% Si-0.01% Be alloy was cast at a cooling rate of 15°C/sec, and rolling was started at 520°C without reheating the ingot. Rolling was completed at 125°C to produce a 9.5φWR. This WR was cold drawn to the wire diameter shown in Table 4 and then heat treated at 350°C for 40 hours to investigate its performance. If the working degree is not 65% or more, hardening and recovery of conductivity due to heat treatment are slow.

[Table] Example (6) A-0.3%Zr-0.1%Si-0.01%Be alloy was cast at a cooling rate of 15°C/sec, and the ingot was rolled at 520°C without reheating. The rolling was completed at ℃ to produce a 9.5φWR. After cold wire drawing of this WR to 4.5φ, heat treatment was performed under the conditions shown in Table 5, and its performance was investigated.
Heat treatment at 300°C for 20 hours or less does not result in sufficient precipitation, resulting in insufficient tensile strength, electrical conductivity, and heat resistance. 450
℃, over 100 hours, it becomes over-aged and the tensile strength,
Heat resistance is insufficient.

[Table] Example (7) A-0.3% Zr-0.1% Si-0.01% Be alloy was manufactured using an actual operating machine, and it was made with the conventional heat resistance A.
Its performance was compared with CT-A (0.04% Zr).
The manufacturing conditions at that time were as follows. Casting speed 160mm/sec, temperature during rolling 520~125℃, WR
Dimensions: 9.5φ, cold wire drawing rate: 74.5%, finished wire diameter
4.8%, heat treatment 350°C x 50h after wire drawing, the results are shown in Table 6. Figure 2 shows the isochronous softening curve after heating for 1 hour. As can be seen from Table 6 and Figure 2, conventional heat resistance A
It has similar tensile strength and electrical conductivity, and has extremely superior heat resistance.

[Table] Through the above examples, it was revealed that the aluminum alloy according to the present invention maintains high electrical conductivity and tensile strength, as well as extremely excellent heat resistance performance. The inventors did not limit themselves to the embodiments shown above, but conducted experiments in various fields regarding the composition and conditions, and thoroughly investigated the excellent effects of the present invention. Since the manufacturing conditions according to the present invention can be achieved by a normal continuous casting method, it is extremely economical from an industrial perspective and mass production is possible. However, as long as the conditions are met, it goes without saying that a hot extrusion rolling method based on semi-continuous casting may be used. Although the alloy according to the present invention has an abnormally high concentration of Zr added, it can be improved by taking special consideration to the conditions of hot working and warm working, and also taking into account the conditions of cold working. By focusing on the introduction of dislocations and discovering that a certain amount of Si and Be had the effect of promoting Zr precipitation, we discovered that fine Zr precipitation could be produced extremely efficiently in a short time. As a result, we were able to provide an aluminum alloy that satisfies the strict conditions of short-term use temperatures of 300 degrees or more while maintaining a conductivity of 58% IACS or higher and a tensile strength of 16 kg/mm ² . be. Therefore, it is expected to be widely applied not only as a conductor for large-capacity power transmission as described above, but also in the conductive field where heat resistance is required, and its industrial effects will be immeasurable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in electrical conductivity and tensile strength under isothermal heat treatment conditions at 350° C., and FIG. 2 is a diagram showing an isochronous softening curve for 1 hour.

Claims (1)

[Claims] 1 Zr0.2~1.5%, Si0.1~1.0%, Be0.005~0.02
An alloy consisting of the remainder A and unavoidable impurities is melted and cast, and processed while being cooled at a cooling rate of 5°C/sec or more, resulting in an area reduction of 80% or more while the finishing temperature is 200°C or less. 300-450℃ after 65% or more cold working
1. A method for producing a highly heat-resistant aluminum alloy for conductive use, which comprises performing heat treatment at a temperature of 20 to 100 hours.