High-strength copper-magnesium alloy contact wire and preparation process thereof

Abstract

The invention provides a high-strength copper-magnesium alloy contact wire and a preparation process thereof, and belongs to the technical field of contact wires, and the preparation process comprises the following steps: uniformly stirring lanthanum nitrate, deionized water and citric acid, slowly dripping into a magnesium powder suspension, simultaneously dripping ammonia water to adjust the pH value, stirring, centrifuging, washing, vacuum drying, putting into a tubular furnace, introducing argon, heating and preserving heat to obtain a high-strength copper-magnesium alloy contact wire; cooling is carried out, such that Mg-La2O3 core-shell particles are obtained; uniformly mixing magnesium carbonate powder with diatomite, pressing into blocks, and baking to obtain a covering agent; a cathode copper plate is baked and melted at a high temperature, the Mg-La2O3 core-shell particles and the boron-doped graphene-silicon material are put into the cathode copper plate and stirred, a covering agent is lightly placed on the surface of melt, cooling and traction are performed to obtain a copper-magnesium alloy casting rod, and cutting, preheating, extrusion and drawing are performed to obtain the high-strength copper-magnesium alloy contact wire. The tensile strength of the contact wire can be improved while the high conductivity is met.

Description

Technical Field

[0001] The present invention relates to the technical field of catenary, and particularly relates to a high-strength copper-magnesium alloy catenary and its preparation process. Background Art

[0002] Currently, the materials generally used for electrified railway catenaries include pure copper, copper-silver alloy, copper-tin alloy, copper-magnesium alloy, etc. Among them, the use of multi-element copper alloys such as copper-tin alloy, copper-magnesium alloy, and copper-chromium-zirconium is gradually increasing, mainly to improve the tensile strength of the catenary to meet the use requirements of increased suspension tension at speeds of 200 km / h and above for high-speed railways. The catenary is responsible for transmitting electricity to electric locomotives and vehicles in the railway electrification system to ensure the normal operation of the railway. In this process, the tensile strength, electrical conductivity, and softening resistance of the catenary become the key indicators for measuring its performance.

[0003] With the introduction of alloying elements such as copper-tin alloy and copper-magnesium alloy, the tensile strength of the catenary has been significantly improved, but this has also led to a significant decrease in electrical conductivity. Taking copper-magnesium alloy as an example, its conductivity is only 62% - 77% IACS (International Copper Association Standard), far lower than 97% IACS of pure copper. The decrease in electrical conductivity means an increase in the impedance of the catenary power supply line, resulting in an increase in power loss, especially under high-current loads, and the phenomenon of significant power loss and a large decrease in electrical conductivity is obvious.

[0004] In the railway industry standard, the tensile strength of the copper-silver alloy catenary is the same as that of the pure copper catenary, and its conductivity is higher than that of the pure copper catenary. In the copper-silver alloy, the addition of silver is mainly to improve the softening resistance of the material, and at the same time, it can ensure that its tensile strength and conductivity are not lower than those of the pure copper catenary. The advantage of the copper-silver alloy is that its softening resistance is significantly improved, which is crucial for the long-term use of the catenary in a high-temperature environment. Although the softening resistance of the copper-silver alloy is improved, the production cost of this alloy has increased significantly. As silver is a precious metal with a high price, the application cost of the copper-silver alloy is much higher than that of the pure copper material, which is also one of the reasons for its limitation in practical applications.

[0005] Therefore, it is necessary to provide a high-strength copper-magnesium alloy catenary and its preparation process to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0006] In view of this, the present invention provides a high-strength copper-magnesium alloy catenary and its preparation process, which can meet high conductivity while improving the tensile strength of the catenary.

[0007] To achieve the above object, the present invention provides a preparation process for a high-strength copper-magnesium alloy catenary, including the following steps: S1. Stir lanthanum nitrate, deionized water, and citric acid evenly. After forming a sol, slowly drip the sol into the magnesium powder suspension, and at the same time, add ammonia water to adjust the pH to 9 - 10. Continuously stir, perform centrifugal separation, washing, vacuum drying, then place it in a tubular furnace, introduce argon, heat up, keep warm, and cool to obtain Mg-La 2 O 3 core-shell particles; S2. Mix magnesium carbonate powder and diatomite evenly, then press them into blocks and bake to obtain a covering agent; S3. Bake the cathode copper plate, melt it at high temperature, put in Mg-La 2 O 3 core-shell particles and boron-doped graphene-silicon material and stir. Gently place the covering agent on the surface of the melt, cool, draw to obtain a copper-magnesium alloy casting rod, then cut it evenly, preheat, extrude, and draw to obtain a high-strength copper-magnesium alloy contact wire.

[0008] The present invention prepares Mg-La 2 O 3 core-shell particles by the sol-gel method to achieve the gradient release of Mg in the copper melt. Mg-La 2 O 3 In the smelting process of core-shell particles, magnesium will not be immediately evenly distributed throughout the alloy. Instead, through the La 2 O 3 shell layer, its diffusion rate is controlled, and it preferentially aggregates at the copper grain boundaries, effectively reducing the problem of the decline in the mechanical properties of the alloy caused by lattice distortion; magnesium aggregates at the grain boundaries to form a stronger interface, thereby enhancing the high-temperature stability and fatigue resistance of the alloy. And when melting at high temperature and putting in Mg-La 2 O 3 core-shell particles, part of the magnesium reacts with La 2 O 3 at high temperature to generate LaMgO 3 spinel phase, further enhancing the stability of the grain boundaries and preventing the excessive growth of grains; the LaMgO 3 spinel phase can withstand higher temperatures and stresses during the stretching process, further improving the tensile strength and long-term stability of the copper-magnesium alloy; in addition, the presence of La 2 O 3 can refine the grains, reduce the obstacles between grains, and reduce the scattering effect during the electron transport process, further enhancing the conductivity of the alloy.

[0009] The covering agent of the present invention optimizes the quality and efficiency of the melting of copper-magnesium alloy through the synergistic effect of magnesium carbonate and diatomite. The addition of the covering agent isolates the melt from contact with oxygen in the air, and magnesium carbonate decomposes at high temperature to generate carbon dioxide gas, making it more difficult for oxygen to contact the melt, thereby further inhibiting the formation of an oxide film on the surface of the melt and avoiding the problem that the oxide film hinders the flow of current and reduces the conductivity of the alloy; diatomite ensures the stability and durability of the covering agent and avoids the negative impacts brought about by the rupture or failure of the covering layer during the melting process. In addition, it also avoids the problems that the existence of excessive oxides inside the copper-magnesium alloy causes lattice defects and increased brittleness, thereby reducing the tensile strength of the alloy.

[0010] In the present invention, boron-doped graphene-silicon material is added to the melt to improve the conductivity of the contact wire. Among them, boron replaces carbon atoms in the graphene lattice, introducing hole-type carriers, further enhancing the electron mobility and endowing the whole with higher conductivity. At the same time, the interfacial tension is reduced through B-Cu bonding, enhancing the wettability between graphene and copper and avoiding the conductive loss caused by interfacial pores. Silicon nanoparticles serve as the carrier of graphene, bind to graphene through B-Si bonds, and form nano-scale Cu 3 Si phase with the copper matrix, forming a three-dimensional conductive network, promoting the uniform dispersion of graphene and avoiding the loss of conductivity caused by the deformation of the metal lattice.

[0011] Optionally, the magnesium powder suspension is obtained by dispersing pretreated magnesium powder in absolute ethanol and stirring at high speed for 30 min.

[0012] Optionally, the pretreated magnesium powder is obtained by soaking magnesium powder in dilute hydrochloric acid with a mass concentration of 5% for 10 min, washing with deionized water until neutral, then washing 3 times with absolute ethanol, and vacuum drying at 60 °C for 12 h.

[0013] The present invention uses dilute hydrochloric acid soaking to dissolve magnesium oxide and adsorbed impurities on the surface of magnesium powder and improve the purity of magnesium powder.

[0014] Optionally, the continuous stirring time in step S1 is 6 - 10 h, the detergent used for washing is ethanol, the number of washing times is 3 - 5 times, the vacuum drying temperature is 60 - 80 °C, the time is 5 - 7 h, the heating rate is 10 °C / min, heating to 400 - 600 °C, and the holding time is 2 h.

[0015] Optionally, in step S1, after cooling, it is loaded into a fluidized bed CVD reactor, hydrogen is introduced, the temperature is raised to 800 °C, held for 30 min, the temperature is adjusted to 950 °C, methane is introduced, grown for 30 min, methane is turned off, cooled to 200 °C in a hydrogen atmosphere and then switched to argon, and cooled to room temperature, and finally Mg-La 2 O 3 core-shell particles are prepared.

[0016] The present invention uses methane as a carbon source. Through chemical vapor deposition, after the carbon source in methane decomposes, it is deposited in the form of gas on the surface of Mg-La 2 O 3 core-shell particles to uniformly generate graphene on the surface, forming a dense layered structure to form a physical barrier to isolate oxygen penetration. The outer-layer graphene ruptures at a high temperature above 600 °C to release magnesium, delaying the release of magnesium and further reducing the magnesium burning loss rate; and the ruptured graphene can be dispersed in the melt to further increase the conductivity.

[0017] Optionally, in the step S2, the baking temperature is 100 °C to 150 °C, and the time is 3 to 5 h.

[0018] Optionally, the boron-doped graphene-silicon material is obtained by mixing boric acid, graphene oxide and silicon, ball milling for 30 to 60 min, and sintering at 900 °C for 3 to 5 h in an argon and hydrogen atmosphere.

[0019] Optionally, in the step S3, the cathode copper plate is baked for 10 to 20 min, put into a crucible melting furnace, kept in a nitrogen atmosphere, melted at 1200 °C to 1400 °C, and Mg-La 2 O 3 core-shell particles and boron-doped graphene-silicon material are kept stirred for 2 to 4 h, and the covering agent is gently placed on the surface of the melt, then cooled through a crystallizer, and drawn at a speed of 200 to 500 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 20 to 30 mm.

[0020] Optionally, after the copper-magnesium alloy casting rod is obtained by drawing, it is evenly cut into 5 to 10 pieces, preheated at 650 °C to 750 °C, introduced into a continuous extruder, extruded at 500 °C to 600 °C and 1000 to 1500 MPa to obtain a copper-magnesium alloy extrusion rod with a diameter of 25 to 30 mm, and then obtained through multi-pass drawing a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2 ².

[0021] Preheating treatment of the copper-magnesium alloy casting rod in the present invention can effectively reduce the internal stress of the copper-magnesium alloy casting rod, making it have better ductility in the subsequent extrusion process and avoiding the occurrence of cracks or excessive stress concentration phenomena.

[0022] Optionally, the high-strength copper-magnesium alloy contact wire comprises the following raw materials in parts by mass: 42 to 70 parts of cathode copper plate, 1.7 to 3.2 parts of Mg-La 2 O 3 core-shell particles, 0.5 to 0.8 part of boron-doped graphene-silicon material, and 1.9 to 2.3 parts of covering agent.

[0023] By adopting the above-mentioned mass fraction matching ratio, the present invention can improve the overall performance of the copper-magnesium alloy in multiple aspects, and the electrical conductivity, tensile strength, and thermal stability of the copper-magnesium alloy are all optimized.

[0024] The above technical solution of the present invention has at least the following beneficial effects: 1. The present invention prepares Mg-La 2 O 3 core-shell particles by the sol-gel method, realizing the gradient release of magnesium in the copper melt, controlling the diffusion rate of magnesium, making it preferentially aggregate at the copper grain boundaries, enhancing the high-temperature stability and fatigue resistance of the alloy. Part of the magnesium reacts with La 2 O 3 to form LaMgO 3 spinel phase, stabilizing the grain boundaries, preventing excessive grain growth, and enhancing the tensile strength and long-term stability. In addition, La 2 O 3 refines the grains, reduces the scattering effect, and improves the electrical conductivity of the alloy.

[0025] 2. The covering agent of the present invention improves the melting quality and efficiency of the copper-magnesium alloy through the synergistic effect of magnesium carbonate and diatomite. Magnesium carbonate decomposes at high temperature to generate carbon dioxide gas, making it more difficult for oxygen to contact the melt, and avoiding the influence of excessive surface and internal oxides on the electrical conductivity and tensile strength of the alloy. Diatomite ensures the stability and durability of the covering agent, and avoids cracking or failure during the melting process.

[0026] 3. The present invention adds boron-doped graphene-silicon material to the melt to improve the conductivity of the contact wire. Boron replaces carbon atoms in graphene, introducing hole-type carriers, enhancing the electron mobility, and improving the overall conductivity. The B-Cu bonding reduces the interfacial tension, enhances the wettability between graphene and copper. Silicon nanoparticles serve as the carrier of graphene and combine with graphene through B-Si bonds to form a nanoscale Cu 3 Si phase, constructing a three-dimensional conductive network, ensuring the uniform dispersion of graphene and avoiding the decrease in conductivity caused by the deformation of the metal lattice. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the cross-sectional metallographic diagram of the product of Example 1 of the present invention; Figure 2 is the cross-sectional metallographic diagram of the product of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are some of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0029] Preparation work: Immerse 5 kg of magnesium powder in 5% dilute hydrochloric acid by mass for 10 min, wash it with deionized water until neutral, then wash it 3 times with absolute ethanol, and vacuum dry it at 60 °C for 12 h to obtain pretreated magnesium powder; Disperse 4 kg of pretreated magnesium powder in 40 L of absolute ethanol and stir at high speed for 30 min to obtain a magnesium powder suspension.

[0030] Example 1 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of the magnesium powder suspension, and at the same time dropwise add ammonia water to adjust the pH to 9.6. Continuously stir for 7 h, centrifuge and separate, wash 5 times with ethanol, and vacuum dry at 80 °C for 6 h to obtain Mg-La(OH) 3 Precursor; Place the precursor in a tubular furnace, introduce argon, heat it to 500 °C at a rate of 10 °C / min, keep it warm for 2 h, naturally cool to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, keep it warm for 30 min, adjust the temperature to 950 °C, introduce methane as a carbon source, with a growth time of 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 Core-shell particles.

[0031] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, and bake them at 130 °C for 4 h to remove the moisture therein to obtain a covering agent. After mixing boric acid, graphene oxide, and silicon, ball mill for 60 min, and sinter at 900 °C for 5 h in a mixed atmosphere of argon and hydrogen to obtain a boron-doped graphene-silicon material.

[0032] Hang 10 cathode copper plates at the furnace mouth of the melting furnace and bake for 20 min, then put them into the crucible melting furnace, keep it under a nitrogen atmosphere, melt at 1400 °C, and put in 2.6 kg of Mg-La 2 O 3The core-shell particles and 0.8 kg of boron-doped graphene-silicon material were stirred for 4 h, and 2 kg of covering agent was gently placed on the surface of the melt. Then it was cooled through a crystallizer and drawn at a speed of 300 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 25 mm. Among them, the covering thickness of the covering agent shall not be less than 100 mm, and the covering agent shall be cleaned every 12 h.

[0033] Take 2500 mm of copper-magnesium alloy casting rod and evenly cut it into 10 pieces. After preheating at 750 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 600 °C and 1500 MPa, a copper-magnesium alloy extrusion rod with a diameter of 30 mm was obtained through extrusion. The extrusion rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2

[0034] Example 2 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of magnesium powder suspension, and at the same time add ammonia water to adjust the pH to 9. Continuously stir for 10 h, centrifuge and separate, wash 3 times with ethanol, and vacuum dry at 60 °C for 7 h to obtain Mg-La(OH) 3 Precursor; place the precursor in a tubular furnace, introduce argon, heat it to 400 °C at a rate of 10 °C / min, keep it warm for 2 h, naturally cool to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, keep it warm for 30 min, adjust the temperature to 950 °C, introduce methane as a carbon source, with a growth time of 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 Core-shell particles.

[0035] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, and bake at 150 °C for 3 h to remove the moisture in them to obtain a covering agent. After mixing boric acid, graphene oxide and silicon, ball mill for 50 min, and sinter at 900 °C for 5 h in a mixed atmosphere of argon and hydrogen to obtain boron-doped graphene-silicon material.

[0036] Hang 6 cathode copper plates at the furnace mouth of the melting furnace and bake for 10 min, then put them into a crucible melting furnace, keep it under a nitrogen atmosphere, melt at 1400 °C, and put in 2.1 kg of Mg-La 2 O 3 ​The core-shell particles and 0.8 kg of boron-doped graphene-silicon material were kept stirred for 3 h, and 1.9 kg of covering agent was gently placed on the surface of the melt. Then it was cooled through a crystallizer and drawn at a speed of 500 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 20 mm. Among them, the covering thickness of the covering agent shall not be less than 100 mm, and the covering agent shall be cleaned every 12 h.

[0037] Take 2000 mm of copper-magnesium alloy casting rod and evenly cut it into 5 pieces. After preheating at 650 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 600 °C and 1200 MPa, an extrusion rod of copper-magnesium alloy with a diameter of 25 mm was obtained through extrusion. The extrusion rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2

[0038] Example 3 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of magnesium powder suspension, and at the same time drop ammonia water to adjust the pH to 10. Keep stirring for 6 h, centrifuge and separate, wash 5 times with ethanol, and vacuum dry at 80 °C for 5 h to obtain Mg-La(OH) 3 Precursor; place the precursor in a tube furnace, introduce argon, heat it to 600 °C at a rate of 10 °C / min, keep it warm for 2 h, naturally cool to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, keep it warm for 30 min, adjust the temperature to 950 °C, introduce methane as the carbon source, with a growth time of 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 core-shell particles.

[0039] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, and bake at 150 °C for 3 h to remove the moisture in them to obtain the covering agent. After mixing boric acid, graphene oxide and silicon, ball mill for 30 min, and sinter at 900 °C for 3 h in a mixed atmosphere of argon and hydrogen to obtain boron-doped graphene-silicon material.

[0040] Hang 7 cathode copper plates at the furnace mouth of the melting furnace and bake for 10 min, then put them into the crucible melting furnace, keep it under a nitrogen atmosphere, melt at 1200 °C, and put in 1.7 kg of Mg-La 2 O 3 ​The core-shell particles and 0.5 kg of boron-doped graphene-silicon material were stirred for 2 h, and 2 kg of covering agent was gently placed on the surface of the melt. Then it was cooled through a crystallizer and drawn at a speed of 200 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 25 mm. Among them, the covering thickness of the covering agent should not be less than 100 mm, and the covering agent was cleaned every 12 h.

[0041] Take 2400 mm of copper-magnesium alloy casting rod and evenly cut it into 8 pieces. After preheating at 700 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 500 °C and 1000 MPa, an extrusion rod of copper-magnesium alloy with a diameter of 28 mm was obtained through extrusion. The extrusion rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2 of.

[0042] Example 4 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of magnesium powder suspension, and at the same time add ammonia water to adjust the pH to 9.2. Continuously stir for 7 h, centrifuge and separate, wash 4 times with ethanol, and vacuum dry at 65 °C for 6.5 h to obtain Mg-La(OH) 3 precursor; Place the precursor in a tubular furnace, introduce argon, heat it to 500 °C at a rate of 10 °C / min, keep it warm for 2 h, naturally cool to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, keep it warm for 30 min, adjust the temperature to 950 °C, introduce methane as a carbon source, grow for 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 core-shell particles.

[0043] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, and bake at 120 °C for 3.5 h to remove the moisture in them to obtain a covering agent. After mixing boric acid, graphene oxide and silicon, ball mill for 40 min, and sinter at 900 °C for 4 h in a mixed atmosphere of argon and hydrogen to obtain boron-doped graphene-silicon material.

[0044] Hang 8 cathode copper plates at the furnace mouth of the melting furnace and bake for 15 min, then put them into the crucible melting furnace, keep it under a nitrogen atmosphere, melt at 1300 °C, and put in 3.2 kg of Mg-La 2 O 3The core-shell particles and 0.7 kg of boron-doped graphene-silicon material were stirred for 3 h, and 3.2 kg of covering agent was gently placed on the surface of the melt. Then, it was cooled through a crystallizer and drawn at a speed of 400 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 30 mm. Among them, the covering thickness of the covering agent shall not be less than 100 mm, and the covering agent shall be cleaned every 12 h.

[0045] Take 2100 mm of copper-magnesium alloy casting rod and evenly cut it into 7 pieces. After preheating at 650 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 550 °C and 1400 MPa, an extrusion rod of copper-magnesium alloy with a diameter of 26 mm was obtained through extrusion. The extrusion rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2

[0046] Example 5 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of magnesium powder suspension, and at the same time, drop ammonia water to adjust the pH to 9.7. Continuously stir for 8 h, centrifuge and separate, wash 4 times with ethanol, and vacuum dry at 70 °C for 5 h to obtain Mg-La(OH) 3 Precursor; place the precursor in a tubular furnace, introduce argon, heat it to 500 °C at a rate of 10 °C / min, hold for 2 h, cool naturally to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, hold for 30 min, adjust the temperature to 950 °C, introduce methane as the carbon source, with a growth time of 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 Core-shell particles.

[0047] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, and bake at 100 °C for 3.5 h to remove the moisture in them to obtain the covering agent. After mixing boric acid, graphene oxide and silicon, ball mill for 60 min, and sinter at 900 °C for 3 h in a mixed atmosphere of argon and hydrogen to obtain boron-doped graphene-silicon material.

[0048] Hang 9 cathode copper plates at the furnace mouth of the melting furnace and bake for 16 min, then put them into the crucible melting furnace, keep it in a nitrogen atmosphere, melt at 1300 °C, and put in 0.92 kg of Mg-La 2 O 3 ​The core-shell particles and 0.03 kg of boron-doped graphene-silicon material were kept stirring for 3 h, and 1.8 kg of covering agent was gently placed on the surface of the melt. Then it was cooled through a crystallizer and drawn at a speed of 400 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 27 mm. Among them, the covering thickness of the covering agent shall not be less than 100 mm, and the covering agent shall be cleaned every 12 h.

[0049] Take 2500 mm of copper-magnesium alloy casting rod and evenly cut it into 10 pieces. After preheating at 700 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 550 °C and 1500 MPa, an extrusion rod of copper-magnesium alloy with a diameter of 30 mm was obtained through extrusion. The extrusion rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2

[0050] Example 6 Dissolve 1 kg of lanthanum nitrate in 23 L of deionized water and stir evenly. Add 0.8 kg of citric acid and stir until completely dissolved. After forming a transparent sol, slowly drop the sol into 30 L of magnesium powder suspension, and at the same time add ammonia water to adjust the pH to 9. Keep stirring for 9 h, centrifuge and separate, wash with ethanol 3 times, and vacuum dry at 80 °C for 6 h to obtain Mg-La(OH) 3 Precursor; place the precursor in a tube furnace, introduce argon, heat it to 400 °C at a rate of 10 °C / min, keep it warm for 2 h, naturally cool to room temperature, load it into a fluidized bed CVD reactor, introduce hydrogen, heat it to 800 °C, keep it warm for 30 min, adjust the temperature to 950 °C, introduce methane as the carbon source, with a growth time of 30 min, turn off methane, cool to 200 °C in a hydrogen atmosphere and then switch to argon, and cool to room temperature to obtain Mg-La 2 O 3 Core-shell particles.

[0051] Mix 15 kg of magnesium carbonate powder and 5 kg of diatomite evenly, press them into blocks, bake at 110 °C for 5 h to remove the moisture in them to obtain the covering agent. After mixing boric acid, graphene oxide and silicon, ball mill for 50 min, and sinter at 900 °C for 4.5 h in a mixed atmosphere of argon and hydrogen to obtain boron-doped graphene-silicon material.

[0052] Hang 8 cathode copper plates at the furnace mouth of the melting furnace and bake for 20 min, then put them into the crucible melting furnace, keep it under a nitrogen atmosphere, melt at 1400 °C, and put in 1.9 kg of Mg-La 2 O 3 ​The core-shell particles and 0.6 kg of boron-doped graphene-silicon material were kept stirring for 4 h, and 3 kg of covering agent was gently placed on the surface of the melt. Then it was cooled through a crystallizer and drawn at a speed of 400 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 27 mm. Among them, the covering thickness of the covering agent shall not be less than 100 mm, and the covering agent shall be cleaned every 12 h.

[0053] Take 2400 mm of copper-magnesium alloy casting rod and evenly cut it into 8 pieces. After preheating at 750 °C and preheating the surface of the extrusion wheel, the copper-magnesium alloy casting rod was introduced into a continuous extruder. Under the conditions of 600 °C and 1000 MPa, an extruded copper-magnesium alloy rod with a diameter of 25 mm was obtained through extrusion. The extruded rod was introduced into a drawing device and drawn through multiple passes to obtain a high-strength copper-magnesium alloy contact wire with a cross-section of 150 mm 2 ².

[0054] The present invention also carried out comparative examples and related tests.

[0055] Comparative Example 1 Compared with Example 1, the difference is that Mg-La 2 O 3 core-shell particles were not prepared, and Mg powder was directly added. Other preparation steps and components remained unchanged, and finally a high-strength copper-magnesium alloy contact wire was obtained.

[0056] Comparative Example 2 Compared with Example 1, the difference is that the covering agent was not prepared, and carbon black was directly used as the covering agent. Other preparation steps and components remained unchanged, and finally a high-strength copper-magnesium alloy contact wire was obtained.

[0057] Comparative Example 3 Compared with Example 1, the difference is that the boron-doped graphene-silicon material was not prepared, and graphene was directly added. Other preparation steps and components remained unchanged, and finally a high-strength copper-magnesium alloy contact wire was obtained.

[0058] Performance detection test The high-strength copper-magnesium alloy contact wires prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were tested for mechanical properties and electrical conductivity. The measurement conditions were speed grade: 400 - 450 km / h, test tension: 36 - 42 KN. The tests were carried out in accordance with the Chinese railway industry standard TB / T2809-2017 Copper and copper alloy contact wires for electrified railways. The test results of mechanical properties are shown in Table 1, and the test results of electrical conductivity are shown in Table 2.

[0059] Table 1

[0060] As can be seen from Table 1, the high-strength copper-magnesium alloy catenaries prepared in Examples 1 to 6 have higher tensile strength, breaking force and fatigue resistance compared with Comparative Examples 1 to 3, and can all meet the requirements for CTMH in the Chinese railway industry standard TB / T 2809-2017, and are applicable to high-strength and high-conductivity copper-magnesium alloy catenaries for 400 km / h high-speed railway lines.

[0061] Combined with the data in Table 1, in Comparative Example 1, the direct addition of Mg powder led to grain coarsening, which in turn caused a significant decrease in mechanical properties. And in Example 1, the addition of Mg-La 2 O 3 core-shell particles also played an important role in inhibiting the propagation of fatigue cracks; the anti-fatigue performance of Comparative Example 2 using the traditional carbon black covering agent was the worst, probably because carbon black was easy to sinter, resulting in local oxidation and stress concentration of the melt. The finished products prepared by the methods described in Examples 1 to 6 of the present invention have finer grain scales, and the substances inside are evenly dispersed and not easy to agglomerate. As Figures 1-2 shown in the metallographic diagram of the finished product, where Figure 1 is the cross-sectional metallographic diagram of the product of Example 1, Figure 2 is the cross-sectional metallographic diagram of the product of Example 3.

[0062] Table 2

[0063] As can be seen from Table 2, the conductivity of all examples exceeds the standard requirements. In Comparative Example 1, compared with Example 1, the increase in the magnesium burn-off rate led to an increase in impurities in the copper matrix, resulting in a significant decrease in conductivity and a significant increase in resistivity; in Comparative Example 2, due to the residual carbon impurities from the carbon black sintering, the electron mobility was reduced, which also affected the conductivity and resistivity; compared with Comparative Example 3, in Example 1, the addition of boron-doped graphene-silicon material to replace the traditional direct addition of graphene significantly increased the conductivity and resistivity.

[0064] The above are the preferred embodiments of the present invention. Without departing from the principle of the present invention, those of ordinary skill in the art can also make several improvements and refinements, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A process for preparing a high-strength copper-magnesium alloy contact wire, characterized in that: The steps include: S1. Stir lanthanum nitrate, deionized water and citric acid to form a sol, then slowly drip the sol into a magnesium powder suspension, and simultaneously drip ammonia water to adjust the pH to 9-10, continue stirring, centrifuge, wash, vacuum dry, place in a tube furnace, introduce argon, heat, keep warm, and cool to obtain Mg-La2O3 core-shell particles; S2, mixing magnesium carbonate powder and diatomaceous earth evenly, pressing into blocks, and baking to obtain a covering agent; S3. Bake the cathode copper plate, melt it at high temperature, add Mg-La2O3 core-shell particles and boron-doped graphene-silicon material and stir, and lightly place the covering agent on the surface of the melt. After cooling and pulling to obtain the copper-magnesium alloy casting rod, evenly cut, preheat, extrude and draw it to obtain a high-strength copper-magnesium alloy contact wire.

2. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: The magnesium powder suspension is obtained by dispersing the pretreated magnesium powder in anhydrous ethanol and stirring at high speed for 30 minutes.

3. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 2, characterized in that: The pretreated magnesium powder is obtained by soaking the magnesium powder in dilute hydrochloric acid with a mass concentration of 5% for 10 minutes, washing with deionized water until neutral, then washing with anhydrous ethanol for 3 times, and vacuum drying at 60° C. for 12 hours.

4. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: In the step S1, the stirring time is 6 to 10 hours, the detergent used for washing is ethanol, the number of washing times is 3 to 5 times, the vacuum drying temperature is 60 to 80° C., the time is 5 to 7 hours, the heating rate is 10° C. / min, the temperature is raised to 400 to 600° C., and the insulation time is 2 hours.

5. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: In the step S1, after cooling, the mixture is loaded into a fluidized bed CVD reactor, hydrogen is introduced, the temperature is raised to 800°C, the mixture is kept warm for 30 minutes, the temperature is adjusted to 950°C, methane is introduced, the mixture is grown for 30 minutes, the methane is turned off, the mixture is cooled to 200°C in a hydrogen atmosphere, and then switched to argon gas, and the mixture is cooled to room temperature to finally obtain Mg-La2O3 core-shell particles.

6. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: In step S2, the baking temperature is 100° C. to 150° C. and the baking time is 3 to 5 hours.

7. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: The boron-doped graphene-silicon material is obtained by mixing boric acid, graphene oxide and silicon, ball milling for 30 to 60 minutes, and sintering at 900° C. for 3 to 5 hours in an argon and hydrogen atmosphere.

8. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 1, characterized in that: In the step S3, the cathode copper plate is baked for 10-20 minutes, put into a crucible melting furnace, kept in a nitrogen atmosphere, melted at 1200-1400°C, Mg-La2O3 core-shell particles and boron-doped graphene-silicon material are put in and stirred for 2-4 hours, and a covering agent is gently placed on the surface of the melt, and then cooled through a crystallizer and pulled at a speed of 200-500 mm / min to obtain a copper-magnesium alloy casting rod with a diameter of 20-30 mm.

9. The process for preparing a high-strength copper-magnesium alloy contact wire according to claim 8, characterized in that: After the copper-magnesium alloy casting rod is obtained by pulling, it is evenly cut into 5-10 rods, preheated at 650-750° C., introduced into a continuous extruder, and extruded at 500-600° C. and 1000-1500 MPa to obtain a copper-magnesium alloy extruded rod with a diameter of 25-30 mm, and then drawn through multiple passes to obtain a cross-sectional area of ​​150 mm. 2 High-strength copper-magnesium alloy contact wire.

10. A high-strength copper-magnesium alloy contact wire, prepared by the preparation process of a high-strength copper-magnesium alloy contact wire according to any one of claims 1 to 9, characterized in that: The invention comprises the following raw materials in parts by weight: 42-70 parts of cathode copper plate, 1.7-3.2 parts of Mg-La2O3 core-shell particles, 0.5-0.8 parts of boron-doped graphene-silicon material, and 1.9-2.3 parts of covering agent.

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