A spot welding method for copper-nickel-phosphorus alloy and copper-nickel-phosphorus alloy after welding

Abstract

The present invention discloses a spot welding method for a copper-nickel-phosphorus alloy, comprising obtaining a welding blank having an electrical conductivity of 40% IACS or less, wherein the alloy composition of the welding blank is Cu-Ni-P-Pb; placing the welding blanks on electrodes respectively and clamping them, and then preheating them to 800-850°C, setting the electrode spacing before welding to 30-50mm, advancing the electrodes to a distance between the electrodes of 15-25mm at a welding pressure of 60-100bar, and advancing the electrodes to a distance between the electrodes of 2-4mm at a top forging pressure of 150-250bar; cooling the welded joint obtained after welding at a cooling rate of 300-500°C / s to obtain a post-weld copper-nickel-phosphorus alloy, wherein the temperature of the welded joint before cooling is 750-840°C. Utilizing this method, the welded area can have good mechanical properties and bending properties. The present invention also provides a post-weld copper-nickel-phosphorus alloy obtained by utilizing this method.

Description

Technical Field

[0001] The invention belongs to the technical field of copper alloys, and in particular relates to a spot welding method of a copper-nickel-phosphorus alloy and the copper-nickel-phosphorus alloy after welding. Background Art

[0002] Copper-nickel-phosphorus alloy is a precipitation-strengthened alloy. After solution-aging heat treatment, dispersed nickel-phosphorus compounds precipitate within the material matrix, increasing the alloy's strength and conductivity. The material also exhibits excellent electroplating and corrosion resistance. To enhance the material's machinability, lead is added to further improve its cutting properties.

[0003] Chinese patent publication number CN101113501A discloses a low-lead, boron, free-cutting antimony brass alloy and its preparation method. The low-lead, boron, free-cutting antimony brass alloy comprises 55-65 wt% copper, 0.4-1.2 wt% antimony, 0.1-0.3 wt% lead, 0.0003-0.05 wt% boron, and 0.05-1.5 wt% other elements, with the remaining elements being at least one selected from magnesium, iron, tin, nickel, silicon, bismuth, and phosphorus, and zinc and unavoidable impurities. The preparation method comprises: smelting the low-lead, boron, free-cutting antimony brass alloy using alloying and coating methods to rapidly dissolve the antimony and boron metals in the brass melt to form intermetallic compounds; continuously casting the alloy into brass ingots at 1020°C; extruding the alloy at a high extrusion ratio at 680-750°C; performing intermediate heat treatment, annealing at 450-650°C according to cold working conditions, and performing stress relief annealing at temperatures below 400°C. The advantages of this patented product are its excellent mechanical properties, thermoforming properties, corrosion resistance, and polishing and electroplating properties. It also successfully solves the problem of recycling and comprehensive utilization of single and multiple types of waste and scrap materials, allowing for both single and comprehensive recycling of Cu-Zn-Si, Cu-Zn-Bi, and Cu-Zn-Sb alloy waste and scrap materials, as well as the recycling of some lead brass waste and scrap materials. However, the cutting antimony brass alloy prepared by this patent has poor welding properties due to the presence of high-temperature brittle elements such as lead and phosphorus.

[0004] Among copper-nickel-phosphorus alloys, C19160 is a typical leaded, free-cutting alloy, combining excellent mechanical, electrical, plating, and cutting properties. It is widely used in new energy vehicles, electronic connectors, and other fields. However, current leaded copper-nickel-phosphorus products, such as C19160, face welding difficulties due to the presence of high-temperature brittle elements such as lead and phosphorus.

[0005] Lead-containing copper-nickel-phosphorus (CuNP) products, such as C19160, are prone to hot brittleness during the welding heating process, often experiencing brittle cracking and post-weld tensile fracture. The melting point of elemental lead is 327°C, which is far higher than the high-temperature welding temperature of CuNP alloys. During welding, the lead element, distributed at the grain boundaries, melts and aggregates, forming large brittle zones. This causes cracking during the weld upset process, severely impacting production efficiency and quality. Furthermore, as lead-containing CuNP materials, such as C19160, are precipitation-strengthened alloys, residual heat from welding easily precipitates NiP compounds from the matrix. This precipitation of NiP strengthening phases further increases the strength of the weld joint while reducing its ductility. This makes the weld joint more susceptible to fracture during subsequent high-rate cold deformation, impacting normal processing. Summary of the Invention

[0006] The present invention provides a spot welding method for a copper-nickel-phosphorus alloy. By utilizing the method, the welding area can have better mechanical properties and bending properties.

[0007] The present invention provides a spot welding method for a copper-nickel-phosphorus alloy, comprising:

[0008] (1) pre-treating a welding blank so that the electrical conductivity of the welding blank is less than 40% IACS, wherein the alloy composition of the welding blank is Cu-Ni-P-Pb;

[0009] (2) butt welding the welding blanks obtained in step (1), comprising: setting the electrode spacing before welding to 30-50 mm, placing the welding blanks obtained in step (1) on the electrodes respectively, clamping and preheating to the welding temperature, pushing the electrodes at a welding pressure of 60-100 bar until the distance between the electrodes is 15-25 mm, and then pushing the electrodes at a forging pressure of 150-250 bar until the distance between the electrodes is 2-4 mm, thereby completing the butt welding;

[0010] (3) Cooling the welded joint obtained after the butt welding in step (2) at a cooling rate of 300-500° C. / s to obtain a post-weld copper-nickel-phosphorus alloy, wherein the temperature of the welded joint before cooling is 750-840° C.

[0011] The present invention reduces the conductivity of the welding blank in advance to ensure a relatively uniform temperature distribution inside the welding blank during the subsequent heating process, thereby avoiding uneven temperature distribution that causes lead particles to melt and aggregate rapidly at high temperatures. At the same time, by reducing the conductivity, the resistance is increased, so that the temperature can be raised quickly to avoid long-term heat preservation during the welding process, which allows the molten Pb to have sufficient time to aggregate and form brittle areas, thereby causing material cracking during the welding process.

[0012] During welding, the resistance heat generated by the copper-nickel-phosphorus-lead alloy at the very front end of the weld, i.e., from the weld joint to the electrode clamp, shows a decreasing trend. Generally, the temperature is highest at the very front end, where the material layer is brittle, while the temperature in the middle portion is moderate. Therefore, using the middle portion as the welding area can achieve a weld with high plasticity. The present invention controls the pre-welding electrode spacing, welding pressure, upset pressure, and post-welding electrode spacing, ensuring that the primary welding area occurs in the middle portion. Specifically, the electrode spacing is between 15-25mm and 2-4mm. This squeezes out the brittle region while avoiding welding in the lower temperature region, significantly improving the welding success rate of the copper-nickel-phosphorus-lead alloy.

[0013] If the electrode spacing before welding provided by the present invention is too large, the resistance increases, the resistance heat rate generated increases, it is difficult to effectively control the welding temperature, and overburning or insufficient heating problems are very likely to occur. The welding stability is poor and it is easier to form a brittle area where Pb accumulates. If the electrode spacing before welding provided by the present invention is too small, the high-temperature brittle area at the front end of the welding cannot be effectively squeezed out during the forging pressure advancement stage, resulting in loose welding and brittle welding areas.

[0014] If the welding pressure provided by the present invention is too high, the advancement speed will be too fast. The faster the speed, the more likely the material will crack during thermal deformation, affecting the welding quality. If the welding pressure is too low, the debris in the high-temperature brittle zone at the front end of the weld cannot be effectively squeezed out, resulting in a loose weld and brittle weld. Further, the electrodes are advanced at a advancement speed of 2-5mm / s until the distance between the electrodes is 15-25mm. The top forging pressure provided by the present invention mainly controls the tightness of the weld area after welding. If the top forging pressure is too low, the weld force is not tight and it is very easy to cause the subsequent processing welding head to break. If the top forging pressure is too high, the deformation of the weld end material is too large and cracks appear.

[0015] The present invention controls the distance between electrodes after welding is completed, squeezes out the miscellaneous materials in the high-temperature brittle zone and avoids welding in the lower temperature area, so that the welded material provided by the present invention is more compact and has better toughness.

[0016] The present invention controls the temperature of the weld joint before cooling, allowing the NiP compound, a strong brittle phase, to dissolve in the weld structure after cooling. If the temperature of the weld joint before cooling is lower than 750°C, the NiP compound in the weld material begins to precipitate, increasing strength while reducing plasticity, increasing the risk of fracture during subsequent stretching. The present invention achieves a good quenching effect by cooling to room temperature in a short period of time through an appropriate cooling rate, thereby achieving as much NiP compound as possible in the copper-nickel-phosphorus-lead alloy after welding, thereby preventing the copper-nickel-phosphorus-lead alloy from cracking during subsequent high-processing rate stretching.

[0017] Furthermore, the welding blank is composed of the following mass percentages: Ni: 0.8-1.2%, P: 0.15-0.35%, Pb: 0.8-1.2%, and the balance is Cu and other inevitable impurities.

[0018] Furthermore, in step (1), the pretreatment of the welding blank is performed, and the pretreatment is solution treatment, quenching or induction heating quenching, etc.

[0019] Furthermore, in step (1), the electrical conductivity of the welding blank is below 30% IACS. By further optimizing the electrical conductivity, the subsequent welding success rate of the welding blank is increased to above 95%.

[0020] Furthermore, the welding temperature is 800-850°C and the welding power is 50-60 kW. The present invention provides a suitable welding temperature, which allows the copper-nickel-phosphorus-lead alloy to have good fluidity at the initial high temperature and high forging plasticity after the temperature drops during welding, thereby facilitating effective welding while preventing Pb aggregation. If the welding temperature is too low, the welding power can be controlled to 50-60 kW to achieve a welding temperature of 800-850°C.

[0021] Furthermore, in step (2), a clamping pressure of 200-300 bar is applied to the welding blank placed on the electrode. The workpieces are brought into close contact with each other by the set clamping pressure.

[0022] Furthermore, in step (2), the clamped welding blank is preheated, and the preheating power is 20-40 kW and the preheating time is 2-4 seconds. Preheating allows the welding blank to be heated evenly and stably to reach the required welding temperature. If the preheating power is too large, on the one hand, it is not conducive to stable and uniform heating and thus a smooth transition to the required welding temperature range, resulting in overburning; on the other hand, too fast a temperature rise causes the temperature in the structure to be too high. Excessive temperature can aggravate the aggregation of brittle phases such as Pb, significantly increasing the brittleness of the weld end material. If the preheating power is too low, the preheating effect is not obvious under room temperature air cooling conditions, and the efficiency is reduced. At the same time, a low preheating power means an increase in preheating time. Since the preheating temperature is also higher than the melting point of Pb, long preheating provides sufficient time for Pb to aggregate, thereby increasing brittleness. Therefore, the preheating power and time need to be strictly controlled.

[0023] The present invention also provides a copper-nickel-phosphorus alloy after welding prepared by the copper-nickel-phosphorus alloy spot welding method. The average diameter of the Pb particles in the welding area of the copper-nickel-phosphorus alloy after welding is 0.1-5 μm.

[0024] Furthermore, the copper-nickel-phosphorus alloy has a tensile strength of 220-350 MPa, a yield strength of 50-100 MPa, and an elongation of 35-50% in the welded area after welding. The welded area has good plasticity and moderate strength, and can achieve a high processing rate of 40-60% cold deformation and stretching without cracking.

[0025] Compared with the prior art, the present invention provides the following beneficial effects:

[0026] The present invention reduces the electrical conductivity of the welding blank so that the welding blank is heated uniformly and the temperature is rapidly raised to a suitable welding temperature, thereby avoiding the aggregation of molten Pb to form a large-area brittle phase.

[0027] The present invention controls the electrode spacing, welding pressure and upset pressure, so that the high-temperature brittle area of the welding front end is squeezed out during the welding process and welding in a lower temperature area is avoided, thereby improving the welding quality.

[0028] The present invention increases the appropriate cooling rate and controls the temperature of the weld joint before cooling, so that the NiP phase can be dissolved in the copper-nickel-phosphorus alloy after welding as much as possible, avoiding the precipitation of a large amount of NiP phase and thus reducing the plasticity, thereby making the weld area have better mechanical properties and bending properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a distribution diagram of lead particles in the welding area of the copper-nickel-phosphorus alloy after welding prepared in Example 1 of the present invention;

[0030] Figure 2 This is a distribution diagram of lead particles in the welding area of the copper-nickel-phosphorus alloy after welding prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0032] The specific ingredients of Examples 1-10 and Comparative Examples 1-5 provided by the present invention are shown in Table 1.

[0033] Example 1

[0034] 1) Pre-welding heat treatment: The blanks to be welded undergo solution quenching to reduce the material's electrical conductivity, thereby increasing the material's resistivity. The resulting copper-nickel-phosphorus alloy bar has a controlled electrical conductivity of 35% IACS.

[0035] 2) Butt welding: Use resistance automatic welding machine to butt weld. Copper-nickel-phosphorus alloy bars were fixed to the welding machine electrodes. The electrode spacing before welding was controlled at 40 mm. Pressure was applied to ensure close contact between the workpieces. The clamping pressure was 220 bar, the preheating power was 30 kW, the preheating time was 3 seconds, the welding power was 50 kW, the welding temperature was 815°C, the welding pressure was 75 bar, and the forging pressure was 210 bar. The welding advance speed was 3 mm / s. The electrodes were advanced at a forging pressure of 210 bar until the distance between the electrodes was 3 mm, and then welding stopped.

[0036] 3) Weld end cooling: After completing butt welding, control the temperature of the weld joint at 790℃ and quickly spray water for cooling. The cooling rate is 300℃ / s and the cooling time is 5s.

[0037] like Figure 1 As shown, the Pb particles in the welding area of the copper-nickel-phosphorus alloy prepared by the above steps are evenly distributed without forming a large brittle phase area, and the average diameter of the Pb particles is 4.5 μm.

[0038] Example 2-Example 10

[0039] The preparation steps of Examples 2 to 10 are the same as those of Example 1. For specific processes, please refer to Tables 2 and 3.

[0040] Table 1 Composition / wt% of the welding blanks provided by Examples 1-10 and Comparative Examples 1-5

[0041]

[0042]

[0043] Table 2 Main butt welding process parameters of Examples 1-10

[0044]

[0045]

[0046] Table 3 Process parameters for butt welding and subsequent welding end cooling of Examples 1-10

[0047]

[0048] Comparative Example 1

[0049] Use resistance automatic welding machine to weld A copper-nickel-phosphorus alloy bar was fixed to the welding machine's electrodes. The electrode spacing before welding was controlled at 100 mm. Pressure was applied to maintain close contact between the workpieces. The clamping pressure was 280 bar, the welding power was 80 kW, the welding pressure was 150 bar, and the forging pressure was 300 bar. The welding advance speed was 15 mm / s. The electrodes were advanced at a forging pressure of 300 bar until the distance between them was 20 mm, and welding was stopped.

[0050] like Figure 2 As shown in the figure, the lead particles are obviously aggregated and the lead particles are large in size, forming a large number of brittle areas, which increases the overall brittleness of the material.

[0051] Comparative Example 2

[0052] Use resistance automatic welding machine to weld A copper-nickel-phosphorus alloy bar was fixed to the welding machine's electrodes. The electrode spacing before welding was controlled at 120 mm. Pressure was applied to maintain close contact between the workpieces. The clamping pressure was 300 bar, the welding power was 75 kW, the welding pressure was 100 bar, and the forging pressure was 300 bar. The welding advance speed was 5 mm / s. The electrodes were advanced at a forging pressure of 300 bar until the distance between them was 10 mm, and welding ceased.

[0053] Comparative Example 3

[0054] Use resistance automatic welding machine to weld A copper-nickel-phosphorus alloy bar was fixed to the welding machine's electrodes. The electrode spacing before welding was controlled at 50 mm. Pressure was applied to ensure close contact between the workpieces. The clamping pressure was 200 bar, the welding power was 140 kW, the welding pressure was 40 bar, and the forging pressure was 100 bar. The welding advance speed was 2 mm / s. The electrodes were advanced at a forging pressure of 100 bar until the distance between them was 3 mm, and then welding was stopped.

[0055] Comparative Example 4

[0056] Use ordinary resistance welding machine to weld The copper-nickel-phosphorus alloy rod is fixed on the welding machine electrode. The electrode spacing before welding is controlled to 70mm. Pressure is applied to make the workpieces in close contact. The welding power is 80kW and the welding pressure is 80bar. The electrodes are pushed until the distance between the electrodes is 1mm, and then the welding stops.

[0057] Comparative Example 5

[0058] Use ordinary resistance welding machine to weld The copper-nickel-phosphorus alloy rod is fixed at the welding machine electrode. The electrode spacing before welding is controlled to 40mm. Pressure is applied to make the workpieces in close contact. The welding power is 70kW and the welding pressure is 80bar. The electrodes are pushed until the distance between the electrodes is 8mm, and then the welding stops.

[0059] Performance Analysis:

[0060] Mechanical properties, microstructure and welding quality tests were conducted on the welded copper-nickel-phosphorus alloys obtained in Examples 1-10 and Comparative Examples 1-5. Specific test indicators and standards are as follows:

[0061] 1) Tensile strength, yield strength, and elongation test: GB / T 228.1-2010 Tensile tests on metallic materials—Part 1: Room temperature tensile test method.

[0062] 2) Lead particle size detection: YS / T 449-2002 Microstructure examination method of copper and copper alloy castings and processed products.

[0063] 3) Welding Tip Bending Performance Test: After welding, polish off any excess material from the welding tip, ensuring the outer diameter of the weld end matches that of the parent material. Bend the weld tip on a bending machine with one end fixed and the other bent at a speed of 0.5-1 rad / s. After a 180° bend, inspect the weld tip for cracks or breakage. If no breakage or cracks form, the weld quality meets the standards.

[0064] As shown in Table 4, the lead particles in Comparative Examples 1-5 were larger than those in Examples 1-10, indicating large-scale aggregation of brittle lead and increased material brittleness. Furthermore, the material strength and plasticity of the weld zone in the Examples were significantly higher than those in the Comparative Examples, with superior tensile and bending resistance. The welding heads in the Examples did not break or crack after bending 180°, while the welding heads in the Comparative Examples immediately broke upon bending, demonstrating that the welding quality in the Examples was superior to that in the Comparative Examples.

[0065] Table 4 Properties of the welding zone materials obtained in Examples 1-10 and Comparative Examples 1-5

[0066]

Claims

1. A spot welding method for copper-nickel-phosphorus alloy, characterized in that: include: (1) Pre-treating the welding blank so that the electrical conductivity of the welding blank is less than 40% IACS, and the alloy composition of the welding blank is Cu-Ni-P-Pb; (2) butt welding the welding blanks obtained in step (1), including: setting the electrode spacing before welding to 30-50 mm, placing the welding blanks obtained in step (1) on the electrodes respectively and clamping them and then preheating them to the welding temperature, pushing the electrodes at a welding pressure of 60-100 bar at the welding temperature until the distance between the electrodes is 15-25 mm, and then pushing the electrodes at a forging pressure of 150-250 bar until the distance between the electrodes is 2-4 mm, thereby completing the butt welding; (3) Cooling the welded joint obtained after the butt welding in step (2) at a cooling rate of 300-500°C / s to obtain a welded copper-nickel-phosphorus alloy, wherein the temperature of the welded joint before cooling is 750-840°C; The welding blank is composed of the following mass percentages: Ni: 0.8-1.2%, P: 0.15-0.35%, Pb: 0.8-1.2%, and the balance is Cu and other inevitable impurities.

2. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (1), the pretreatment is solution treatment.

3. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (1), the electrical conductivity of the welding blank is less than 30% IACS.

4. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (2), the welding temperature is 800-850°C, and the welding power is 50-60kW.

5. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (2), the electrodes are advanced at a speed of 2-5 mm / s until the distance between the electrodes is 15-25 mm.

6. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (2), a clamping pressure of 200-300 bar is applied to the welding blank arranged on the electrode.

7. The spot welding method of copper-nickel-phosphorus alloy according to claim 1, characterized in that: In step (2), the clamped welding blank is preheated with a preheating power of 20-40 kW and a preheating time of 2-4 s.

8. A welded copper-nickel-phosphorus alloy prepared by the spot welding method of copper-nickel-phosphorus alloy according to any one of claims 1 to 7, characterized in that: The average diameter of the Pb particles in the welding area of the copper-nickel-phosphorus alloy after welding is 0.1-5 μm.

9. The welded copper-nickel-phosphorus alloy according to claim 8, characterized in that: The tensile strength of the welded area of the copper-nickel-phosphorus alloy after welding is 220-350 MPa, the yield strength is 50-100 MPa, and the elongation is 35-50%.

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