Preparation method of copper-niobium alloy cast ingot

Abstract

The invention discloses a preparation method of a copper-niobium alloy cast ingot, which comprises the following steps of: 1, stacking an oxygen-free copper foil and a niobium foil, winding and forming, placing in an oxygen-free copper pipe, performing vacuum seal welding on two ends of the oxygen-free copper pipe, and performing hot extrusion to obtain a copper-niobium winding structure composite bar; 2, the copper-niobium winding structure composite bar is subjected to consumable smelting, and a primary cast ingot is obtained; thirdly, the primary cast ingot is sequentially subjected to hot extrusion and consumable smelting, and a secondary cast ingot is obtained; and fourthly, the secondary cast ingot is subjected to hot isostatic pressing after being subjected to vacuum sheathing treatment, and the copper-niobium alloy cast ingot is obtained. According to the preparation method, the oxygen-free copper foil and the niobium foil are made into the copper-niobium winding composite bar, layered distribution of copper and niobium in the bar is achieved, copper and niobium are initially and uniformly distributed, then the ingot casting structure is uniform through two times of consumable smelting preparation, and finally shrinkage porosity and shrinkage cavities in the ingot casting are eliminated through hot isostatic pressing so that the density of the ingot casting can be improved, and the yield of the ingot casting can be improved. The method is suitable for the technical field of high-strength alloys.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength alloys, and in particular relates to a method for preparing a copper-niobium alloy ingot. Background Art

[0002] High-strength and high-conductivity copper alloys are non-ferrous metal composite materials that integrate excellent physical and mechanical properties. They are currently widely used in key materials for high pulse magnetic field conductors, lead frames, tram and electric train conductors and other devices. Among them, for the construction of long-pulse, high-field magnets, magnet winding materials are the hardware core of pulsed strong magnets and a strong support for obtaining pulsed strong magnetic fields. Theoretical and a large number of experimental studies have shown that high-strength and high-conductivity Cu-Nb materials can obtain excellent strength properties through the effective matching of BCC metals (Nb) and FCC metals (Cu) with extremely low solid solubility in each other, and maintain good electrical transport properties through the copper matrix. Therefore, Cu-Nb high-strength and high-conductivity materials have always been the focus of attention in the field of pulse magnets.

[0003] At present, the smelting method of copper-niobium preparation technology (in-situ method) is considered to be promising to break through the bottleneck of material performance, and has become a research hotspot in recent years. For example, in the prior art, Y2O3, ThO2 and graphite are used as smelting crucible materials to prepare Cu-Nb ingots, but there are small pure Nb balls in the ingots; then, by designing three different electrodes to arrange the Nb strips at intervals, the material is melted and alloyed once and the organization is uniform, solving the problem of pure Nb balls in the ingots. However, after low-temperature extrusion of the Cu-Nb ingot, Nb-enriched areas appear locally in the rods, resulting in uneven organization. In addition, some researchers prepared Cu-Nb ingots by arc melting in a high-purity argon atmosphere, and then extruded the ingots into rods with a diameter of 2.5 cm at 750°C, and then cold-drawn the rods to 1.5 cm, but secondary cracks on the interface are prone to occur during this preparation process. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing a copper-niobium alloy ingot. The preparation method realizes the layered distribution of copper and niobium in the ingot by making oxygen-free copper foil and niobium foil into a copper-niobium wound composite rod, so that copper and niobium are initially evenly distributed, and then the uniformity of the ingot structure is further improved by two self-consumable smeltings, and finally the shrinkage and shrinkage cavities inside the ingot are eliminated by hot isostatic pressing, thereby solving the problem that the copper-niobium ingot prepared by the prior art has an uneven structure and is prone to secondary cracks on the interface.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a copper-niobium alloy ingot, characterized in that the preparation method comprises the following steps:

[0006] Step 1: stacking oxygen-free copper foil and niobium foil and winding them into shape, and then placing them in an oxygen-free copper tube, vacuum-sealing and hot-extruding the two ends of the oxygen-free copper tube to obtain a copper-niobium wound structure composite rod;

[0007] Step 2: subjecting the copper-niobium wound structure composite rod obtained in step 1 to consumable smelting to obtain a primary ingot;

[0008] Step 3, hot extruding and consumable smelting are sequentially performed on the primary ingot obtained in step 2 to obtain a secondary ingot;

[0009] Step 4: subjecting the secondary ingot obtained in step 3 to vacuum encapsulation treatment and then hot isostatic pressing to obtain a copper-niobium alloy ingot.

[0010] The present invention is used to improve the defects such as looseness and shrinkage holes in the ingot after the first consumable smelting by hot extrusion of the first ingot, promote the redistribution of Nb in the Cu matrix, and improve the quality and uniformity of the ingot; at the same time, during the first consumable smelting process, the high heat input will cause the coarsening of some grains in the ingot after smelting, and the grains can be effectively refined after hot extrusion with large plastic deformation; in addition, when the second consumable smelting is carried out, the material to be smelted needs to be welded at the electrode as a consumable electrode for subsequent smelting. The present invention is conducive to the welding of the consumable electrode end by hot extruding the block ingot into a thinner rod, so as to carry out consumable smelting again. Through two consumable smeltings, the uniformity of the distribution of Nb in the copper matrix is ​​greatly improved, and an ingot with uniform structure can be obtained. Finally, by introducing hot isostatic pressing, the defects such as looseness and shrinkage holes in the ingot can be improved, the density of the ingot can be improved, and the quality of the ingot can be improved.

[0011] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the thickness of the oxygen-free copper foil and the niobium foil in step 1 are both 0.09 mm to 0.12 mm, and the thickness of the oxygen-free copper foil and the niobium foil are equal.

[0012] The present invention adopts an oxygen-free copper and niobium foil winding structure, and its copper-niobium interface strengthening effect is remarkable; by controlling the thickness of the foil, it is avoided that when the foil is thick, obvious work hardening is avoided, which is not conducive to subsequent extrusion deformation; it is avoided that the foil is further thinned, which will lead to complicated foil processing procedures and a sharp increase in procurement costs, and a higher requirement for foil surface flatness during winding, thinner foil is not conducive to winding, and the effect after assembly is poor.

[0013] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the winding forming process in step one is: the oxygen-free copper foil and the niobium foil are tightly stacked and then wound around the central copper rod, and the oxygen-free copper foil is bonded to the central copper rod during winding.

[0014] Due to the difference in plastic deformation ability between copper and niobium, copper has excellent ductility but low strength, while niobium has high strength but significant work hardening, and local strain mismatch is prone to occur during deformation. The present invention improves the metallurgical bonding between the foil and the central copper rod during large plastic deformation by bringing the oxygen-free copper foil into contact with the central copper rod, thereby promoting plastic coordinated deformation between the copper rod and the foil.

[0015] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the vacuum sealing welding in step 1 is electron beam sealing welding after vacuum degassing.

[0016] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the temperature of the hot extrusion in step 1 is 600°C to 800°C.

[0017] The present invention controls the temperature at 600°C to 800°C for hot extrusion. At this temperature, copper has a high plastic state and niobium maintains a high strength, which can promote dynamic recrystallization, reduce deformation resistance, and allow the copper matrix to flow while maintaining material stability; avoid low solubility of solid copper in niobium when the temperature is too low, and avoid coarse grains caused by excessively high temperature.

[0018] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the consumable smelting in step 2 and step 3 both adopts a vacuum consumable arc melting furnace, and the consumable smelting temperature is not less than 1900°C.

[0019] The present invention adopts a vacuum consumable arc melting furnace for consumable melting. The vacuum consumable arc melting furnace is equipped with an electromagnetic stirring function, which can stir the molten metal, accelerate the melting and crystallization speed of the melt, avoid the composition and structure segregation of the ingot after the molten metal solidifies, inhibit the coarsening and growth of grains, accelerate the crushing of large-sized grains, promote the grain size to be smaller, and obtain an ingot with more uniform composition and structure; by controlling the temperature of the consumable melting, it is avoided that the temperature is too low to completely melt the niobium foil, thereby causing the niobium phase to agglomerate and unevenly distribute in the ingot.

[0020] The above-mentioned method for preparing a copper-niobium alloy ingot is characterized in that the temperature of the hot isostatic pressing in step 4 is 650° C. to 800° C. and the pressure is 130 MPa to 150 MPa.

[0021] The present invention sets the hot isostatic pressing temperature at 650°C to 800°C. Since the melting point of copper is about 1085°C and the melting point of niobium is about 2468°C, the copper matrix softens in this temperature range and is in a high plastic state, which can promote diffusion and pore closure and improve the material density; niobium still maintains a high strength, which helps to ensure the mechanical properties of the copper-niobium alloy ingot after hot isostatic pressing. Since copper-niobium alloy requires a high pressure to ensure densification, but too high a pressure will place high demands on the equipment and cause the ingot to deform, the pressure is selected to be 130MPa to 150MPa according to the upper limit of the equipment pressure and the degree of deformation after extrusion.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention realizes the layered distribution of copper and niobium in the rod by winding oxygen-free copper foil and niobium foil, so that copper and niobium are initially evenly distributed, which is beneficial to the even distribution of niobium element in the copper matrix after smelting and improves segregation; at the same time, by winding the copper foil and niobium foil and placing them in an oxygen-free copper tube, and vacuum-sealing and welding the two ends of the oxygen-free copper tube and then performing hot extrusion deformation, the copper-niobium wound structure composite rod undergoes large plastic deformation, the lattice undergoes serious distortion, and the recrystallization temperature and melting temperature of the copper-niobium wound structure composite rod are significantly reduced, avoiding the problem that the solid solubility between copper and niobium at room temperature is extremely small and cannot be effectively smelted.

[0024] 2. The present invention adopts copper-niobium wound structure composite rods as the initial structure configuration and prepares copper-niobium alloy ingots through two consumable smelting processes, which greatly shortens the preparation cycle while achieving grain refinement and uniform composition and organization. It avoids the need for cold drawing, secondary assembly and other processing processes when the prior art uses multi-core assembled composite rods for consumable smelting, effectively reduces costs, and is conducive to the engineering preparation of copper-niobium alloys.

[0025] 3. The present invention can eliminate most of the loose and shrinkage defects inside the ingot by introducing the hot isostatic pressing process, so that the densification degree of the copper-niobium alloy ingot is close to 100% of the theoretical density of the solid material; at the same time, by using a sleeve for hot isostatic pressing, it can effectively eliminate the holes inside the secondary ingot and the open defects that are connected to the outer surface and in contact with the external gas medium, which is beneficial to further improve the quality of the copper-niobium alloy ingot.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of the copper-niobium winding structure obtained in Example 1 of the present invention.

[0028] Figure 2This is the metallographic structure diagram of the copper-niobium wound structure composite rod obtained in Example 1 of the present invention.

[0029] Figure 3 This is the metallographic structure diagram of the secondary ingot obtained in Example 1 of the present invention.

[0030] Figure 4 This is the metallographic structure diagram of the copper-niobium alloy ingot obtained in Example 1 of the present invention.

[0031] Figure 5 This is the metallographic structure diagram of the secondary ingot obtained in Example 2 of the present invention.

[0032] Figure 6 This is the metallographic structure diagram of the copper-niobium alloy ingot obtained in Example 2 of the present invention.

[0033] Figure 7 This is the metallographic structure diagram of the secondary ingot obtained in Comparative Example 1 of the present invention.

[0034] Figure 8 This is the metallographic structure diagram of the secondary ingot obtained in Comparative Example 2 of the present invention.

[0035] Fig. 9 This is the metallographic structure diagram of the copper-niobium alloy ingot obtained in Example 3 of the present invention.

[0036] Fig.10 This is the EDS result diagram of the copper-niobium alloy ingot obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] Example 1

[0038] The preparation method of this embodiment comprises the following steps:

[0039] Step 1: stack oxygen-free copper foil and niobium foil with a thickness of 0.09 mm and a mass purity of more than 99.99% tightly, and use automatic winding equipment to wind the oxygen-free copper foil and niobium foil around the central copper rod to form a shape, and the oxygen-free copper foil is bonded to the central copper rod during winding, and then placed in an oxygen-free copper tube with an outer diameter of 120 mm to obtain the following Figure 1 The copper-niobium winding structure shown in the figure is that the oxygen-free copper tube is vacuum degassed and then electron beam sealed at both ends, and then hot extrusion deformation is performed at 600°C to obtain a copper-niobium winding structure composite rod;

[0040] Step 2: The copper-niobium wound structure composite rod obtained in step 1 is subjected to surface mechanical polishing and chemical pickling treatment, and then placed in a vacuum consumable electrode arc furnace for consumable smelting to obtain a primary ingot; the consumable smelting temperature is 1900° C., and the vacuum degree in the vacuum consumable electrode arc furnace is less than 10 -3 Pa;

[0041] Step 3: hot extrusion deformation of the primary ingot obtained in step 2 at 800° C. to form a rod, and after surface mechanical polishing and chemical pickling treatment, placing it in a vacuum consumable electrode arc furnace for consumable smelting to obtain a secondary ingot;

[0042] Step 4: Use stainless steel to encase the secondary ingot obtained in step 3, evacuate the two ends, seal and weld, perform hot isostatic pressing for 3 hours at a temperature of 650° C. and a pressure of 130 MPa, remove the stainless steel encasement after furnace cooling, and obtain a copper-niobium alloy ingot; the consumable smelting temperature is 1900° C., and the vacuum degree in the vacuum consumable electrode arc furnace during the consumable smelting is less than 10 -3 Pa.

[0043] The internal structure of the copper-niobium wound composite rod obtained in step 1 of this embodiment is analyzed. Figure 2 As shown in FIG. 1 , the copper strip and the niobium strip in the copper-niobium wound structure composite rod are tightly combined; the metallographic structure of the secondary ingot obtained in step 3 of this embodiment is as shown in FIG. Figure 3 As shown in Figure 1, there are casting defects such as holes, and some holes are connected to the outer surface; compared with the copper-niobium alloy ingot after hot isostatic pressing, as shown in Figure 1 Figure 4 As shown, the originally existing holes were effectively improved, especially the holes connected to the surface were effectively filled, indicating that the introduction of hot isostatic pressing can effectively improve the casting defects produced in vacuum consumable melting.

[0044] Example 2

[0045] The preparation method of this embodiment comprises the following steps:

[0046] Step 1, tightly stacking oxygen-free copper foil and niobium foil, both of which have a thickness of 0.09 mm and a mass purity of more than 99.99%, and using an automatic winding device to wind the oxygen-free copper foil and the niobium foil around a central copper rod to form a shape, wherein the oxygen-free copper foil is bonded to the central copper rod during winding, and then placed in an oxygen-free copper tube with an outer diameter of 120 mm to obtain a copper-niobium winding structure, vacuum degassing the oxygen-free copper tube, and then electron beam sealing welding is performed at both ends, followed by hot extrusion deformation at 700° C. to obtain a copper-niobium winding structure composite rod;

[0047] Step 2: The copper-niobium wound structure composite rod obtained in step 1 is subjected to surface mechanical polishing and chemical pickling treatment, and then placed in a vacuum consumable electrode arc furnace for consumable smelting to obtain a primary ingot; the consumable smelting temperature is 1900° C., and the vacuum degree in the vacuum consumable electrode arc furnace is less than 10 -3 Pa;

[0048] Step 3: hot extrusion deformation of the primary ingot obtained in step 2 at 800°C to form a rod, and then placing it in a vacuum consumable electrode arc furnace for consumable smelting to obtain a secondary ingot; the consumable smelting temperature is 1900°C, and the vacuum degree in the vacuum consumable electrode arc furnace is less than 10 during the consumable smelting. - 3 Pa;

[0049] Step 4: Use stainless steel to encase the secondary ingot obtained in step 3, evacuate the two ends, seal and weld, perform hot isostatic pressing for 3 hours at a temperature of 750° C. and a pressure of 130 MPa, remove the stainless steel encasement after furnace cooling, and obtain a copper-niobium alloy ingot; the consumable smelting temperature is 1900° C., and the vacuum degree in the vacuum consumable electrode arc furnace during the consumable smelting is less than 10 -3 Pa.

[0050] The secondary ingot obtained in step 3 of this embodiment was subjected to microscopic analysis. Figure 5 As shown in FIG. 1 , the composition and microstructure of the secondary ingot are uniform, the grains are refined, but there are tiny holes. The copper-niobium alloy ingot obtained in this embodiment is subjected to microscopic analysis, as shown in FIG. Figure 6 As shown in the figure, niobium grains are dispersed in the copper matrix, the grain size is effectively refined, and there is no obvious agglomeration and segregation phenomenon; compared with the secondary ingot without hot isostatic pressing, its internal shrinkage, shrinkage holes and other casting defects are significantly improved.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 2 is that the consumable melting temperature in step 2 and step 3 is both 1700°C.

[0053] The secondary ingot obtained in this comparative example was subjected to microscopic analysis. Figure 7 As shown, due to the low consumable smelting temperature, part of the niobium strip melts to form dendrites, and there is niobium that has not been completely melted inside the secondary ingot, resulting in niobium phase agglomeration and uneven distribution.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 2 is that the thickness of the oxygen-free copper foil and the niobium foil in step 1 are both 0.14 mm, and the hot extrusion temperature is 600°C.

[0056] The secondary ingot obtained in this comparative example was subjected to microscopic analysis. Figure 8 As shown in the figure, due to the thick copper foil and niobium foil, although the niobium strip is melted and spheroidized, the niobium grains cannot be further refined. The niobium phase is agglomerated inside the secondary ingot and the niobium grain size is large.

[0057] Example 3

[0058] The difference between this embodiment and embodiment 1 is that the temperature of hot isostatic pressing in step 4 is 800° C. and the pressure is 150 MPa.

[0059] The copper-niobium alloy ingot obtained in this example was subjected to microscopic analysis. Fig. 9 As shown in the figure, niobium grains are dispersed in the copper matrix, the grain size is effectively refined, no casting defects are found, and the density is high; the energy spectrum analysis of points a, b, and c is as follows Fig.10 As shown, the compositions of the three points are close, indicating that the internal composition of the copper-niobium alloy ingot prepared in this embodiment is uniform without obvious agglomeration and segregation.

[0060] Example 4

[0061] The preparation method of this embodiment comprises the following steps:

[0062] Step 1, tightly stacking oxygen-free copper foil and niobium foil, both of which have a thickness of 0.10 mm and a mass purity of more than 99.99%, and using automatic winding equipment to wind the oxygen-free copper foil and niobium foil around a central copper rod to form a shape, wherein the oxygen-free copper foil is bonded to the central copper rod during winding, and then placed in an oxygen-free copper tube with an outer diameter of 120 mm to obtain a copper-niobium winding structure, vacuum degassing the oxygen-free copper tube, and then electron beam sealing welding is performed on both ends, followed by hot extrusion deformation at 800° C. to obtain a copper-niobium winding structure composite rod;

[0063] Step 2: The copper-niobium wound structure composite rod obtained in step 1 is subjected to surface mechanical polishing and chemical pickling treatment, and then placed in a vacuum consumable electrode arc furnace for consumable smelting to obtain a primary ingot; the consumable smelting temperature is 1910° C., and the vacuum degree in the vacuum consumable electrode arc furnace is less than 10 -3 Pa;

[0064] Step 3: hot extrusion deformation of the primary ingot obtained in step 2 at 800°C, surface mechanical polishing and chemical pickling treatment, and then placing it in a vacuum consumable electrode arc furnace for consumable smelting to obtain a secondary ingot; the consumable smelting temperature is 1910°C, and the vacuum degree in the vacuum consumable electrode arc furnace is less than 10 during the consumable smelting. -3 Pa;

[0065] Step 4: Use stainless steel to encase the secondary ingot obtained in step 3, evacuate the two ends, seal and weld, perform hot isostatic pressing for 3 hours at a temperature of 750° C. and a pressure of 140 MPa, remove the stainless steel encasement after furnace cooling, and obtain a copper-niobium alloy ingot; the consumable smelting temperature is 1910° C., and the vacuum degree in the vacuum consumable electrode arc furnace during the consumable smelting is less than 10 -3 Pa.

[0066] The copper-niobium alloy ingot obtained in this embodiment has dispersed niobium grains inside, effectively refined grain size, no casting defects, uniform internal composition, no obvious agglomeration and segregation, and high density.

[0067] Example 5

[0068] The difference between this embodiment and embodiment 4 is that the thickness of the oxygen-free copper foil and the niobium foil in step 1 are both 0.12 mm.

[0069] The copper-niobium alloy ingot obtained in this embodiment has dispersed niobium grains inside, effectively refined grain size, no casting defects, uniform internal composition, no obvious agglomeration and segregation, and high density.

[0070] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a copper-niobium alloy ingot, characterized in that: The preparation method comprises the following steps: Step 1: stacking oxygen-free copper foil and niobium foil and winding them into shape, and then placing them in an oxygen-free copper tube, vacuum-sealing and hot-extruding the two ends of the oxygen-free copper tube to obtain a copper-niobium wound structure composite rod; Step 2: subjecting the copper-niobium wound structure composite rod obtained in step 1 to consumable smelting to obtain a primary ingot; Step 3, hot extruding and consumable smelting are sequentially performed on the primary ingot obtained in step 2 to obtain a secondary ingot; Step 4: subjecting the secondary ingot obtained in step 3 to vacuum encapsulation treatment and then hot isostatic pressing to obtain a copper-niobium alloy ingot.

2. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: In step 1, the thickness of the oxygen-free copper foil and the niobium foil are both 0.09 mm to 0.12 mm, and the thickness of the oxygen-free copper foil and the niobium foil are equal.

3. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: The winding forming process described in step 1 is: the oxygen-free copper foil and the niobium foil are tightly stacked and then wound around the central copper rod, and the oxygen-free copper foil and the central copper rod are bonded during the winding.

4. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: The vacuum sealing in step 1 is electron beam sealing after vacuum degassing.

5. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: The temperature of the hot extrusion in step 1 is 600°C to 800°C.

6. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: The consumable smelting in step 2 and step 3 both adopts a vacuum consumable arc melting furnace, and the consumable smelting temperature is not less than 1900°C.

7. The method for preparing a copper-niobium alloy ingot according to claim 1, characterized in that: The temperature of the hot isostatic pressing in step 4 is 650° C. to 800° C., and the pressure is 130 MPa to 150 MPa.

Images