A welding agent for live repair of aluminum busbar

Abstract

The present invention belongs to the field of welding materials technology and relates to a welding flux for hot-line repair of aluminum busbars. The welding flux is composed of the following components, measured by mass percentage: 4-6% magnesium powder, 2.5-3.3% calcium silicate powder, 1-2% copper powder, 3-4% nickel powder, 3-4% niobium powder, 1-2% graphene, 2.2-5.4% lanthanum hexaboride powder, 1-2.7% lanthanum powder, 7.3-10.5% potassium fluoroborate powder, 2.5-4% barium sulfate powder, and aluminum powder to make up 100%. The welding flux for hot-line repair of aluminum busbars provided by the present invention exhibits excellent electrical conductivity and strength. The addition of graphene provides a conductive framework for gaps in the aluminum busbar that are not fully covered by the welding flux after melting, thereby reducing the welding flux's effect on the aluminum busbar.

Description

Technical Field

[0001] The invention belongs to the technical field of welding materials and relates to a welding agent for the live repair of an aluminum busbar. Background Art

[0002] As aluminum electrolysis production evolves toward larger electrolytic cells, a single electrolytic series typically consists of dozens or even hundreds of cells connected in series, forming a circuit. This increases the current intensity and series voltage of the cells, making electrolytic cell overhauls increasingly difficult for aluminum producers. Currently, aluminum producers must either shut down the power supply for welding or use cathode square steel crimping to maintain cell maintenance, open slots, or perform partial welding on individual cells. This welding method, when used during a power outage, results in a loss of primary aluminum production and impacts the power grid, resulting in wasted energy. This impacts the stable operation of the electrolytic cells, production safety, and shortens their lifespan. Furthermore, the cathode square steel crimping method, due to its higher crimping resistance than welding, increases over time, leading to increased power consumption.

[0003] Live welding has a high temperature and a short welding time, and is easily accompanied by the entry of impurity elements and other harmful elements, making it difficult to obtain joints with good performance. The main reason is that the instantaneous heat generation of live welding is very large, which easily produces coarse eutectoid metal columns and coarse columnar products growing along the cooling direction in the weld. At the same time, some impurity elements are prone to segregation and accumulate at the boundaries of columnar products, reducing the bonding strength between the particles, causing the plasticity of the weld joint to seriously decrease and the brittleness to increase. It is also easy to introduce impurities such as nitrogen, hydrogen, oxygen, sulfur, and phosphorus during the welding process, causing the joint to become brittle over time and increasing the sensitivity to thermal cracks during the welding process. The shorter solidification time of live welding makes it difficult for hydrogen, oxygen, nitrogen, etc. dissolved in the liquid metal to precipitate, resulting in pores. In addition, since the live welding process cannot effectively protect the joint, it is easy for the alloy elements to be oxidized and burned, which weakens the strengthening effect of the alloy elements and seriously reduces the strength of the weld structure.

[0004] When performing hot welding repairs on aluminum busbars, the choice of welding flux elements is particularly important. CN103286476B discloses a flux for hot repairing aluminum electrolytic cell busbars, containing 18-26% copper powder. The addition of Cu improves the tensile strength, fatigue resistance, and toughness of the weld, as well as surface finish, but also reduces corrosion resistance. Increasing Cu content increases lattice distortion within the Al matrix and the formation of secondary phases, hindering dislocation slip and leading to a decrease in the alloy's electrical conductivity. Furthermore, the addition of Cu refines the grains, increases the grain boundary area, and increases the scattering of directional free electrons, reducing conductivity. The addition of other elements can also significantly affect weld performance. For example, Ti refines the grains and increases the grain boundary area, which in turn increases the scattering of directional free electrons and reduces conductivity. Mn has a high solid solubility in α-Al, and while it can increase strength, it also produces significant lattice distortion within the aluminum matrix, enhancing electron scattering and reducing conductivity. In addition, the use of existing welding materials and welding technology for busbar welding has defects such as insufficient welding heat, inability to fusion the interface, incomplete slag-liquid separation, welding delamination, too long welding preheating time, poor metal strength and tensile properties in the weld, and serious energy loss during operation. Summary of the Invention

[0005] The object of the present invention is to provide an aluminum busbar live repair welding agent, which has better hardness, tensile strength and corrosion resistance while taking into account the conductive performance.

[0006] Based on the above objectives, the present application addresses this need in the field by providing an aluminum busbar live repair welding agent.

[0007] On the one hand, the present invention relates to a live repair welding agent for an aluminum busbar, which is composed of the following components, calculated by mass percentage: 4-6% magnesium powder, 2.5-3.3% calcium silicon powder, 1-2% copper powder, 3-4% nickel powder, 3-4% niobium powder, 1-2% graphene, 2.2-5.4% lanthanum hexaboride powder, 1-2.7% lanthanum powder, 7.3-10.5% potassium borofluoride powder, 2.5-4% calcium sulfate powder, and aluminum powder making up to 100%.

[0008] The present invention uses a lower percentage of copper powder. The addition of Cu element can improve the tensile strength, fatigue performance and toughness of the weld and improve the surface finish, but will reduce its corrosion resistance and electrical conductivity. The lower the Cu element, the lower the impact on the weld.

[0009] The present invention selects magnesium powder and calcium silicate powder in a certain ratio. The addition of magnesium element can improve the tensile strength, fatigue performance and toughness of the weld and improve the surface finish, but it will reduce its corrosion resistance and electrical conductivity. Therefore, it is necessary to control the amount of magnesium powder added. However, in the presence of calcium silicate powder, magnesium combines with silicon, which can reduce the adverse effects of magnesium on corrosion resistance and electrical conductivity. Therefore, increasing the amount of magnesium powder to a certain limit is intended to achieve better results.

[0010] The present invention uses graphene. On the one hand, graphene has a different expansion coefficient from aluminum, which produces a dislocation zone at the interface with the aluminum matrix during welding, restricting dislocation movement, thereby achieving a strengthening effect and reducing electron scattering at the interface, thereby improving the conductivity of the weld. On the other hand, niobium can significantly change the distribution of carbon between the carbide phase and the matrix solid solution, making the matrix carbon-poor, and inhibiting the precipitation of weaker carbides, making the carbides more likely to be dissolved in the matrix. It also provides a conductive skeleton for gaps that are not completely covered by the welding agent after melting and the aluminum busbar, thereby improving the influence of the welding agent on the aluminum busbar.

[0011] The present invention uses lanthanum hexaboride powder and lanthanum powder. Lanthanum interacts with alloying elements and has a strong affinity for harmful impurities such as oxygen, sulfur, and phosphorus. This purifies weld joints, improves weld structure, and improves the morphology and distribution of inclusions. It avoids the formation of low-melting eutectic structures between dendrites or at grain boundaries, reducing the weld's tendency to thermal cracking. Lanthanum forms high-melting-point compounds with impurities, providing nucleation sites for weld crystallization, refining grains, and increasing the weld's tensile strength. Lanthanum also effectively reduces hydrogen activity in molten aluminum, lowering the pressure that causes gaseous hydrogen to precipitate, reducing hydrogen-induced pinholes and pores, and to some extent alleviating the adverse effects of the humid environment of aluminum electrolysis production on welding. Furthermore, the present invention avoids the use of other rare metal elements, such as cerium, as co-doping with cerium and lanthanum fails to improve the mechanical properties and electrical conductivity of aluminum.

[0012] Furthermore, in the aluminum busbar live repair welding agent provided by the present invention, the particle size of any of the components is 100-200 meshes.

[0013] Furthermore, in the aluminum busbar live repair welding agent provided by the present invention, the purity of any component is not less than 98% by mass.

[0014] Compared with the prior art, the present invention has the following beneficial effects or advantages:

[0015] The present invention provides a live repair welding agent for aluminum busbars, which can be used to repair busbars when the aluminum electrolytic cell is energized. The reaction between the self-fluxing welding agent and the ignition powder is relatively stable, with high safety and a high fusion rate of the weld side walls. While taking into account the conductive properties, it has better hardness, tensile strength and corrosion resistance. DETAILED DESCRIPTION

[0016] The technical solutions of the present invention are described below with reference to the following embodiments; however, the present invention is not limited to the following embodiments.

[0017] The experimental methods and detection methods in the following examples are all conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified; the indicator data are all based on conventional measurement methods unless otherwise specified.

[0018] Example 1

[0019] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0020] Take 4kg of magnesium powder, 2.5kg of calcium silicate powder, 1kg of copper powder, 3kg of nickel powder, 3kg of niobium powder, 1kg of graphene, 2.2kg of lanthanum hexaboride powder, 1kg of lanthanum powder, 7.3kg of potassium borofluoride powder, 2.5kg of calcium sulfate powder, and 72.5kg of aluminum powder. The particle size range of all raw materials conforms to 100-200 mesh, and the purity of all raw materials is not less than 98%. Dry them, mix them evenly using a powder mixer, and obtain an aluminum busbar welding agent.

[0021] Example 2

[0022] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0023] Take 4.5 kg of magnesium powder, 2.8 kg of calcium silicate powder, 1.2 kg of copper powder, 3.2 kg of nickel powder, 3.2 kg of niobium powder, 1.2 kg of graphene, 2.5 kg of lanthanum hexaboride powder, 1.2 kg of lanthanum powder, 8 kg of potassium borofluoride powder, 3 kg of calcium sulfate powder, and 69.2 kg of aluminum powder. The particle size range of all raw materials conforms to 100-200 mesh, and the purity of all raw materials is not less than 98%. Dry them, mix them evenly using a powder mixer, and obtain an aluminum busbar welding agent.

[0024] Example 3

[0025] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0026] Take 5kg of magnesium powder, 3kg of calcium silicate powder, 1.5kg of copper powder, 3.5kg of nickel powder, 3.5kg of niobium powder, 1.5kg of graphene, 3kg of lanthanum hexaboride powder, 1.6kg of lanthanum powder, 8.5kg of potassium borofluoride powder, 3.5kg of calcium sulfate powder, and 65.4kg of aluminum powder. The particle size range of all raw materials conforms to 100-200 mesh, and the purity of all raw materials is not less than 98%. Dry them, mix them evenly using a powder mixer, and obtain an aluminum busbar welding agent.

[0027] Example 4

[0028] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0029] Take 5.5kg of magnesium powder, 3kg of calcium silicate powder, 1.8kg of copper powder, 3.8kg of nickel powder, 3.8kg of niobium powder, 1.8kg of graphene, 4kg of lanthanum hexaboride powder, 2kg of lanthanum powder, 9kg of potassium borofluoride powder, 3.8kg of calcium sulfate powder, and 61.5kg of aluminum powder. The particle size range of all raw materials conforms to 100-200 mesh, and the purity of all raw materials is not less than 98%. Dry them, mix them evenly using a powder mixer, and obtain an aluminum busbar welding agent.

[0030] Example 5

[0031] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0032] Take 6kg of magnesium powder, 3.3kg of calcium silicate powder, 2kg of copper powder, 4kg of nickel powder, 4kg of niobium powder, 2kg of graphene, 5.4kg of lanthanum hexaboride powder, 2.7kg of lanthanum powder, 10.5kg of potassium borofluoride powder, 4kg of calcium sulfate powder, and 56.1kg of aluminum powder. The particle size range of all raw materials conforms to 100-200 mesh, and the purity of all raw materials is not less than 98%. Dry them, mix them evenly using a powder mixer, and obtain an aluminum busbar welding agent.

[0033] Comparative Example 1

[0034] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0035] The preparation and welding methods refer to Example 1 of CN103286476B.

[0036] Comparative Example 2

[0037] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0038] The preparation is similar to Example 1 of the present application, except that graphene is not included.

[0039] Comparative Example 3

[0040] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0041] The preparation was carried out with reference to Example 5 of the present application, except that the amount of copper powder added was 20 kg.

[0042] Comparative Example 4

[0043] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0044] The preparation was carried out with reference to Example 5 of the present application, except that the amount of magnesium powder added was 20 kg.

[0045] Comparative Example 5

[0046] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0047] The preparation was carried out with reference to Example 1 of the present application, except that no calcium silicate powder was added.

[0048] Comparative Example 6

[0049] This embodiment provides an experiment for preparing a welding agent for live repair of aluminum busbars.

[0050] The preparation was carried out with reference to Example 5 of the present application, except that the amount of magnesium powder added was 2 kg.

[0051] Example 6

[0052] This embodiment provides an experiment on using the above-mentioned welding agent for welding aluminum busbars.

[0053] Take the following steps to perform welding:

[0054] Step 1: Vertically cut downward from the top of the aluminum busbar to form a weld joint approximately 16 cm deep. Step 2: Polish and lubricate the inner surface of the weld joint. Step 3: Measure the dimensions of the weld joint and calculate the amount of flux to be added based on the dimensions. Step 4: Install a sealing mold to cover the weld joint and insert a funnel-shaped charging mold into the sealing mold. A small hole at the bottom of the charging mold is provided with a baffle. The aluminum busbar flux is loaded into the charging mold. Pyrotechnic powder is sprinkled on the surface of the flux. A lead is inserted and ignited to trigger an exothermic reaction. Step 5: After the baffle at the bottom of the charging mold melts, hot molten metal flows through the small hole at the bottom of the charging mold into the weld joint. After the molten metal cools, the sealing mold and charging mold are removed. Step 6: After cooling, clean the metal surface of the weld and any excess weld slag. The surface is then ground and polished to obtain the repaired aluminum busbar. The electrical conductivity of the sample is measured using an eddy current conductivity meter. The tensile strength of each specimen was determined using a universal tensile testing machine at a rate of 2.0 mm / min. Three tests were performed on each specimen, and the average value was used as the tensile strength. Hardness was measured using a Rockwell / Leeb hardness tester. The coefficient of friction was measured using a flat-surface friction coefficient meter. The electrical corrosion rate was measured according to GB / T 24196-2009. The test results are shown in Table 1.

[0055] Table 1, Performance test results

[0056]

[0057] As shown in Table 1, the welding agent for live aluminum busbar repair provided by the present invention combines electrical conductivity with superior hardness, tensile strength, and corrosion resistance. The incorporation of graphene enhances the electrical conductivity of the weld, while increasing the amount of copper and magnesium significantly impacts electrical conductivity. In the presence of calcium silicate powder, magnesium combines with silicon, increasing the amount of magnesium powder to a certain extent and achieving better performance. Without calcium silicate powder, maintaining a high amount of magnesium powder significantly impacts electrical conductivity and corrosion resistance.

[0058] As described above, the present invention can be better implemented. The above embodiments only describe the preferred implementation methods of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various changes and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the protection scope determined by the present invention.

Claims

1. A welding agent for repairing live aluminum busbars, characterized in that: Calculated by mass percentage, it is composed of the following components: 4-6% magnesium powder, 2.5-3.3% calcium silicate powder, 1-2% copper powder, 3-4% nickel powder, 3-4% niobium powder, 1-2% graphene, 2.2-5.4% lanthanum hexaboride powder, 1-2.7% lanthanum powder, 7.3-10.5% potassium borofluoride powder, 2.5-4% calcium sulfate powder, and aluminum powder making up 100%.

2. The aluminum busbar live repair welding agent according to claim 1, characterized in that: The particle size of any of the components is 100 to 200 meshes.

3. The aluminum busbar live repair welding agent according to claim 1, characterized in that: Calculated by mass percentage, the purity of any of the components is not less than 98%.

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