KR20100073730A - Method of producing cu-sn-zr alloy for improving hot workability and strength - Google Patents

Abstract

PURPOSE: A Cu-Sn-Zr alloy manufacturing method with superior hot workability and intensity is provided to prevent the generation of delta phase by miniaturizing crystallite. CONSTITUTION: A Cu-Sn-Zr alloy manufacturing method with superior hot workability and intensity comprises: a step of preparing Cu-Sn-Cr melted alloy in a tundish; a step of spraying gas to the Cu-Sn-Cr melted alloy while discharging the melted alloy to the lower part of the tundish; a step of stacking Cu-Sn-Cr alloy solution on the upper part of a substrate; and a step of descending the substrate to the height of the Cu-Sn-Cr alloy solution and manufacturing a billet by consecutively pouting alloy solution on the substrate.

Description

Method of Producing Cu-Sn-Zr Alloy For Improving Hot Workability and Strength}

The present invention relates to a method for producing a Cu-Sn-Zr alloy, which increases the solid-solution content of Sn through the spray casting process and the addition of a small amount of Zr to increase the strength by increasing the aging reinforcement and the solid-solution content of Sn during the subsequent aging treatment. The present invention relates to a method for producing a Cu-Sn-Zr alloy having excellent hot workability and strength for improving workability.

Due to the industrial development, the weight reduction and miniaturization of parts are being made rapidly. Due to this tendency, high functionality and high strength of copper alloy materials are required. Representative high strength copper alloys currently produced or studied include phosphor bronze, Cu-Be alloys, Cu-Ni-Sn alloys, and Cu-Ni-Si alloys. Current high strength copper alloy is mainly produced by a continuous casting process.

However, copper alloy is not easy to implement functionality because the microstructure or precipitate shape is greatly affected by the casting and processing heat treatment conditions. In the case of phosphor bronze alloys, cracks are easily generated during hot working after casting, so mass production is impossible. Therefore, only cold working is carried out to produce the final product. The reason why the subsequent heat treatment of the copper alloy is not easy is due to coarse casting structure and segregation of grain boundaries.

Cu-Be alloys, which are used as high-elastic spring materials, have excellent strength and resistance to corrosion and fatigue, but they are increasingly used in recent years because Be elements are expensive, very harmful to the human body, and cause serious environmental problems. It is decreasing. Due to the demand for the development of new alloys, various copper alloys were studied as alternative alloys, among which Cu-Ni-Sn alloys and Cu-Ni-Si alloys were most actively studied.

In the Cu-Ni-Sn alloy, the spinodal decomposition strengthening effect and the composition of (Cu _X Ni _{1 -X} ) ₃ Sn, Al ₃ Ti It shows the precipitation strengthening effect in a matching relationship with the γ 'mother phase, which is a quasi-stable phase with a DO ₂₂ type regular structure. In order to exhibit the reinforcing effect, the content of Sn should be 3wt% or more, the heat treatment temperature should be in the range of 300 ~ 400 ℃, heat treatment time should be limited to 3 to 5 hours.

Among the Cu-Ni-Sn alloys, the Cu-9Ni-6Sn alloy is the most excellent in terms of ductility and strength. However, tin-containing bronze alloys segregate during solidification to form α + β vacancies between dendritic phases of α-solids. In addition, the α solid solution also changes in concentration due to crystal segregation, resulting in the formation of organic tissue. Therefore, the general microstructure of tin-containing copper alloys is nonuniform as described above and tends not to be removed even by solution treatment. [Ref. C. Brooks, "Heat treatment, Structure and Properties of Nonferrous Alloy" American Society for Metals, Metals Park ,, Ohio 44073 pp. 275] It will adversely affect.

In the Cu-Ni-Si alloy, the strength is improved by precipitation of intermetallic compound particles mainly composed of δ-Ni ₂ Si during aging treatment after solution treatment. In the Cu-Ni-Si alloy, the content of Si is determined by the content of Ni, and it is generally known that an ideal Ni / Si ratio of 3 to 6 is ideal. However, the Cu-Ni-Sn alloy has a tensile strength of 800 MPa or less even after aging treatment, which does not meet the recently required mechanical properties.

Therefore, the present invention increases the solid solution content of Sn compared to the existing alloy, and by adding a small amount of Zr to produce a Cu-Sn-Zr alloy which can further improve the strength and hot workability through the solid solution strengthening and aging strengthening effect To provide.

In the present invention, a step of preparing a molten Cu-Sn-Zr alloy molten metal including Sn: 10-16%, Zr: 0.2-0.6%, balance Cu and other impurities in tundish, the alloy molten metal in the tundish Spraying the gas of the Cu-Sn-Zr alloy molten metal into the Cu-Sn-Zr alloy liquid droplets by spraying the gas to the spilled Cu-Sn-Zr alloy molten metal through a gas sprayer located in the lower portion of the tundish Stacking the alloy droplets on the rotating substrate at the bottom of the gas atomizer and successively laminating the alloy droplets on the substrate while lowering the substrate corresponding to the stacking amount of the Cu-Sn-Zr alloy droplets. It provides a method for producing a Cu-Sn-Zr alloy excellent in hot workability and strength comprising the step of preparing a billet.

It is preferable that the temperature of the said molten alloy is 1000-1150 degreeC.

It is preferable that the gas is nitrogen gas.

The injection pressure of the gas atomizer is preferably in the range of 4 ~ 8bar.

The descending speed of the substrate is preferably in the range of 0.8 ~ 1.5mm / s.

According to the present invention, it is possible to immediately perform a subsequent processing step without undergoing an essential solution treatment step in the conventional main alloy. In addition, the solid solution content of Sn is increased and the grains are refined to effectively suppress the formation of a secondary phase such as a delta phase.

A small amount of Zr results in excellent mechanical properties during subsequent isothermal aging. In addition, by providing a uniform microstructure in which the secondary phase is hardly present to minimize the crack in the subsequent processing process, it is possible to improve the plastic working rate and workability.

Therefore, the work process can be shortened and the content of Ni, which is relatively expensive, can be reduced. Increasing Sn content enables high strength and can be used in functional parts manufacturing industry and structural materials.

Spray casting is a technique that can produce a rod-shaped, plate-like or tubular shaped body by spraying molten liquid droplets using a high-pressure gas and laminating them onto a molded substrate before the molten liquid droplets are completely solidified. The rapid solidification effect can be obtained through the formation of fine droplets and a uniform microstructure can be formed through the final reaction solidification process on the substrate surface. Metallurgical can form a characteristic microstructure of fine isotropic grains with a high molding density of more than 99% and no segregation.

 In the spray casting process, the molten metal is first dropped freely through a nozzle having a diameter of several mm, and the molten metal is atomized by spraying a high pressure inert gas using a gas injector. The sprayed droplets reach the substrate while being cooled by the high-speed, low-temperature injection gas while falling. Reached droplets are classified according to size into fully coagulated microparticles, semi-melt droplets and coarse droplets in liquid form.

The droplets in various states react to the lamination surface by lamination and form a thin layer of semi-melt state, and the residual liquid phase is solidified by the thermal conduction with the substrate and the sprayed gas.

As the stacking continues, the substrate is lowered at a constant speed to maintain a constant distance between the nozzle of the molten metal and the laminated surface, thereby controlling the heat capacity and the liquid fraction of the laminated surface.

Through the above process, it is possible to obtain a fine and uniform microstructure through the effect of quench solidification and the reaction solidification process on the substrate surface. In addition, segregation can be minimized and the characteristic microstructure of fine isotropic grains can be formed.

If the temperature of the molten alloy is less than 1000 ° C, the temperature is low and the solidification is rapid, it is difficult to deposit the droplets on the substrate, if the temperature exceeds 1150 ° C, the molten metal is overheated, so that the droplets do not stack on the substrate flows down. Therefore, the temperature of the molten alloy is preferably limited to 1000 ~ 1150 ℃.

When the molten metal flows out from the bottom of the tundish, the gas sprayer injects gas. The injecting gas is preferably inert gas such as nitrogen gas or argon gas, but nitrogen gas is most preferably used in consideration of economical efficiency.

The alloy is sprayed into the molten alloy to form alloy droplets. At this time, when the pressure of the injection gas is less than 4 bar, the size of the droplets is coarse and there is a fear that the alloy structure of the billet is not uniform. On the other hand, if the pressure exceeds 8 bar, back pressure may be formed around the gas sprayer, and operation may not be performed smoothly. Therefore, the pressure of the injection gas is preferably limited to 4 ~ 8bar range.

As the alloy droplets are sprayed onto the substrate, the substrate descends. At this time, when the lowering speed of the substrate is less than 0.8mm / s, the thickness of the alloy layer to be laminated may be formed too thick. On the other hand, when it exceeds 1.5mm / s it may be difficult to easily stack the droplets. Therefore, the lowering speed of the substrate is preferably limited to 0.8 ~ 1.5mm / s range.

In addition, when the content of Sn is less than 10% by weight, there is a problem that the strength is lowered, when it exceeds 16% by weight it is difficult to use the spray casting process and the hot workability is also reduced. In addition, when the Zr content is less than 0.2% by weight, the synergistic effect of strength is small. On the contrary, when the content of Zr is more than 0.6% by weight, it is not dissolved in the alloy and exists in the form of particles. Therefore, the content of Sn is preferably limited to 10 to 16% by weight, the content of Zr to 0.2 to 0.6% by weight.

Hereinafter, the present invention will be described in detail through examples.

(Example)

To prepare a billet according to the manufacturing method and the composition ratio according to Table 1 to perform a high temperature compression test to evaluate the workability of the prepared billet, the results are shown in Table 1 below. In addition, the microstructured photograph was observed for Example 1 of the invention, and the results are shown in FIG. 1.

division Manufacturing method Composition of alloys Hardness (Hv) Breakdown temperature (℃) Machinability Inventive Example 1 Spray casting Cu-13Sn-0.4Zr 115 ± 4 900 Very good Comparative Example 1 Spray casting Cu-12Sn 107 ± 2 800 Good Comparative Example 2 casting Cu-12Sn 192 ± 11 X Bad

As shown in Table 1, Comparative Example 2 is a conventional casting method, it can be seen that the crack occurred at room temperature. In addition, Comparative Example 1 prepared by the spray casting process was uniformly deformed up to 750 ° C., but was rapidly destroyed at 800 ° C. On the other hand, Inventive Example 1 showed uniform deformation without cracking up to a compression temperature of 850 ℃. However, it was destroyed at 900 ° C, but this is a fracture caused by partial melting inside the specimen because it is a temperature beyond the solid-liquid boundary.

Inventive Example 1 in the range that satisfies the conditions of the present invention can be seen that the hardness, fracture temperature, workability is superior to Comparative Examples 1 and 2.

On the other hand, as shown in FIG. 1, the invention example 1 has a grain size greatly reduced to 20 to 30 μm, the precipitation of the delta phase is effectively suppressed, and a uniform microstructure having almost no pores and segregation can be obtained. X-ray diffraction analysis showed no formation of secondary phases other than the α- (Cu, Sn) phase.

In addition, in order to evaluate the tensile strength and elongation due to cold rolling and isothermal aging, after the cold rolling and isothermal aging treatment of the alloy prepared according to the alloy composition and production method shown in Table 2 below, the tensile strength and elongation were measured and The results are shown schematically in FIG.

division Manufacturing method Composition of alloys Inventive Example 1 Spray structure Cu-13Sn-0.4Zr Comparative Example 3 Vacuum ingot casting Cu-1.9Be-0.3Co Comparative Example 4 Spray casting Cu Comparative Example 5 Continuous casting Cu-4Sn Comparative Example 6 Continuous casting Cu-5Sn Comparative Example 7 Continuous casting Cu-6Sn Comparative Example 8 Continuous casting Cu-8Sn Comparative Example 9 Continuous casting Cu-13Sn

As shown in FIG. 2, Inventive Example 1 exhibited a maximum tensile strength of 1050 MPa or more at a 20% elongation level, which shows better physical properties than a conventional Cu-Be alloy.

1 is a microstructure photograph of a billet Cu-13Sn-0.4Zr (Invention Example 1) prepared by the spray casting process according to the present invention;

Figure 2 is a graph showing the tensile strength and elongation for the inventive examples and comparative examples.

Claims (5)

In the copper alloy manufacturing method, Preparing a Cu-Sn-Zr alloy molten metal including, by weight, Sn: 10-16%, Zr: 0.2-0.6%, balance Cu and other impurities in tundish; While the alloy molten metal in the tundish flows out to the bottom of the tundish, the gas is sprayed onto the spilled Cu-Sn-Zr alloy molten metal through a gas sprayer located below the tundish to inject the Cu-Sn-Zr alloy molten metal into Cu-Sn. -Atomizing with Zr alloy droplets to deposit the alloy droplets on the substrate rotating underneath the gas atomizer; And Preparing a Cu-Sn-Zr billet by continuously depositing the alloy droplets on the substrate while lowering the substrate corresponding to the deposition amount of the Cu-Sn-Zr alloy droplets; Cu-Sn-Zr alloy manufacturing method excellent in hot workability and strength, comprising. The method of claim 1, The temperature of the molten alloy of the Cu-Sn-Zr alloy manufacturing method excellent in hot workability and strength, characterized in that the range of 1000 ~ 1150 ℃. The method of claim 1, The gas is a Cu-Sn-Zr alloy manufacturing method excellent in hot workability and strength, characterized in that the nitrogen gas. The method of claim 1, The gas spray pressure of the gas sprayer is a Cu-Sn-Zr alloy manufacturing method excellent in hot workability and strength, characterized in that 4 to 8 bar range. The method of claim 1, Cu-Sn-Zr alloy manufacturing method excellent in hot workability and strength, characterized in that the falling speed of the substrate is in the range of 0.8 ~ 1.5mm / s.

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