Tin-plated brass and method for producing the same

Abstract

The application provides a tinned brass and a production method thereof. Compared with the prior art, the tinned brass is obtained by spraying tin liquid on the surface of a copper strip, controlling the composition of the tin liquid, the spraying temperature and the like, so that the tinned strip is difficult to grow tin whiskers due to stress change, and the growth of tin whiskers can be inhibited. Moreover, through the synergistic control of the composition of the tin liquid, the temperature and the fan speed, the alloying time of the tin layer and the copper material is reduced, the generation rate of the free alloy layer is reduced, the thickness of the tinned alloy layer is controlled to be 1 / 5-2 / 5 of the thickness of the tinned layer, the optimal alloy layer thickness is obtained, and the anti-aging performance of the product is improved.

Description

Technical Field

[0001] This invention belongs to the field of copper strip production, specifically relating to a tin-plated brass and its production method. Background Technology

[0002] Currently, the most commonly used copper alloys on the market are brass, copper alloys, and bronze. Different types of alloys have different compositions and uses.

[0003] Brass: Copper alloys with zinc as the main additive element, possessing an attractive yellow color, are collectively known as brass. Binary copper-zinc alloys are called ordinary brass or simple brass, while brass with three or more elements is called special brass or complex brass. Brass alloys with less than 36% zinc have good cold-working properties; for example, brass with 30% zinc is often used to make cartridge cases. The most commonly used is brass with 40% zinc. To improve the properties of ordinary brass, other elements are often added, such as aluminum, nickel, manganese, tin, silicon, and lead. Aluminum improves the strength, hardness, and corrosion resistance of brass, but reduces its plasticity, making it suitable for use in marine condenser tubes and other corrosion-resistant parts. Tin improves the strength and seawater corrosion resistance of brass, making it suitable for use in marine thermal equipment and propellers. Lead improves the machinability of brass; this free-machining brass is commonly used for watch parts. Brass castings are often used to make valves and pipe fittings; the explosion-proof crescent wrench for fire hydrants commonly used on ships is cast from brass and aluminum.

[0004] Nickel-plated cupronickel (CPC) is a copper alloy with nickel as the main additive element. Binary copper-nickel alloys are called ordinary cupronickel; cupronickel alloys with added manganese, iron, zinc, aluminum, etc., are called complex cupronickel. Industrial cupronickel is divided into two main categories: structural cupronickel and electrical cupronickel. Structural cupronickel is characterized by good mechanical properties and corrosion resistance, and a beautiful color. This type of cupronickel is widely used in the manufacture of precision machinery, chemical machinery, and ship components. Electrical cupronickel generally has good thermoelectric properties. Manganese bronze, constantan, and copper copper are manganese cupronickel with different manganese contents, and are materials used in the manufacture of precision electrical instruments, rheostats, precision resistors, strain gauges, thermocouples, etc.

[0005] Bronze: Originally referring to copper-tin alloys, later all copper alloys except brass and cupronickel were called bronze, often preceded by the name of the first major added element. Tin bronze has good casting properties, anti-friction properties, and mechanical properties, making it suitable for manufacturing bearings, worm gears, gears, etc. Lead bronze is a bearing material widely used in modern engines and grinding machines. Aluminum bronze has high strength, good wear resistance, and corrosion resistance, and is used for casting high-load gears, bushings, marine propellers, etc. Phosphor bronze has a high elastic limit and good electrical conductivity, making it suitable for manufacturing precision springs and electrical contact elements. Beryllium bronze is also used to manufacture sparkless tools used in coal mines and oil depots. Beryllium copper has good mechanical, physical, chemical, and corrosion resistance properties. In powder metallurgy manufacturing of molds made of tungsten copper, high-carbon copper, and high-temperature resistant superhard alloys, tungsten copper is a more ideal material for electro-erosion due to the high wear and slow speed of ordinary electrodes, with a bending strength ≥667 MPa.

[0006] To prevent copper from oxidizing when exposed to air, tin-plated copper was developed. This involves plating a thin layer of tin onto the surface of the copper, such as tin-plated copper wire, which has applications in cable manufacturing. Tin plating prevents copper from oxidizing and forming a film called verdigris when exposed to air. Verdigris has poor conductivity, increasing resistance. Verdigris formed on food containers can be harmful to human health. Therefore, the primary purpose of tin plating is to prevent copper from oxidizing. Key features include: 1) Excellent solderability of the solder ribbon, with unique and superior solder additives ensuring solder flowability; 2) High-quality copper substrate with low resistivity, ensuring low solder ribbon resistance and preventing component power loss; 3) Stable chemical properties, good solder flow and low-temperature performance, ensuring attractive appearance, smooth and bright surface, no solder dross, no pinholes, and no exposed copper; 4) Advanced heat treatment process, ensuring the physical properties of the copper substrate and appropriate hardness, allowing adjustment of the solder ribbon's physical properties according to different solar cells, ensuring a low breakage rate of solar cells during welding; 5) Automated soldering process ensures the quality stability and consistency of the solder ribbon products; 6) Powerful experimental and testing equipment and methods, guaranteeing quality at every stage from materials to finished products.

[0007] Currently, the main methods for producing tin-plated copper are electroplating and hot-dip plating, with electroplating being the most widely used. Compared to other tin plating methods, the main advantages of electroplating are uniform and controllable metal thickness. However, its production process is more complex than hot-dip tin plating, requiring stricter operation, higher equipment prices, more complex plating solutions, higher formulation costs, and more severe emissions and environmental pollution. In contrast, hot-dip tin plating offers advantages such as good solderability, a dense and strong coating, less pollution, simpler production process, and shorter delivery time, making it the preferred method for many tin plating manufacturers abroad.

[0008] However, tin whisker growth often occurs during the production process or when the tin-plated strip is used by the customer. This is mainly due to the following reasons: the thickness of the alloy formed by tin and copper is too low or the surface is uneven during the tin plating process; the tin layer thickness is too low; and the stress on the tin-plated copper sheet is too high during use, resulting in high residual stress that damages the original crystal structure. All of these phenomena will eventually lead to the formation of tin whiskers on the tin-plated copper strip. The continuous growth of tin whiskers will inevitably lead to short circuits and orange peel texture in electronic components over a long period of time, ultimately resulting in a significant reduction in the product's lifespan.

[0009] Therefore, suppressing tin whisker growth is an urgent problem to be solved in the production of tin-plated copper. Summary of the Invention

[0010] The purpose of this invention is to provide a tin-plated brass and its production method. In the tin plating process, a tin-ion-containing solution is sprayed, which improves the uniformity of the tin layer on the tin-plated strip, increases the growth rate of the oxide film on the tin layer surface, and avoids phenomena such as tin whisker growth caused by stress changes in the tin-plated strip. Furthermore, through process optimization during production, the optimal alloy layer thickness is obtained, improving the product's anti-aging performance.

[0011] The specific technical solution of this invention is as follows:

[0012] A method for producing tin-plated brass includes tin plating, wherein the tin plating is performed by spraying molten tin onto the surface of a copper strip.

[0013] Furthermore, molten tin is sprayed onto the surface of the running copper strip, which travels at a speed of 8 meters per minute.

[0014] The spraying process involves controlling the spray flow rate to 10-15 liters / minute, the spraying speed to 4-16 meters / minute, and the spraying angle to be vertically downward and fixed, i.e., perpendicular to the copper surface. The nozzle pressure is set at 250KPa-300KPa, and the nozzle diameter is 4-11mm.

[0015] The molten tin comprises the following components by mass percentage: Cu ≤ 1.5%, Zn 0.05-0.20%, and the balance being Sn;

[0016] The temperature of the molten tin is 300–500°C.

[0017] The molten tin is sprayed onto the copper strip surface at an ambient temperature of 80-90℃. The molten tin is heated to a temperature of 300-500℃ and then sprayed onto the surface of the copper strip in operation through a nozzle. During the spraying process, the heat of the molten tin is transferred, and the molten tin is sprayed onto the copper strip surface at an ambient temperature of 80-90℃.

[0018] The spraying is performed using an atomizer with nozzles.

[0019] The production method also includes cooling after tin plating, controlling the cooling fan speed at 800±20m / s, and cooling to room temperature.

[0020] The present invention provides a tin-plated brass, which is produced by the above method and is a tin-plated brass that inhibits the growth of tin whiskers;

[0021] The invention includes a tin-plated brass substrate that inhibits tin whisker growth. The surface of the copper substrate is covered with a tin plating layer, which comprises an alloy layer and a tin layer. The thickness of the alloy layer is 1 / 5 to 2 / 5 of the total thickness of the tin plating layer.

[0022] Compared with existing technologies, this invention sprays molten tin onto the surface of a copper strip and controls the composition and spraying temperature of the molten tin, making it difficult for the tin-plated strip to grow tin whiskers due to stress changes, thus inhibiting tin whisker growth. Furthermore, by coordinating the control of the composition and temperature of the molten tin and the cooling (fan speed) after tin plating, the alloying time between the tin layer and the copper material is reduced, lowering the rate of free alloy layer formation. The thickness of the tin alloy layer is controlled to 1 / 5 to 2 / 5 of the total tin plating thickness, achieving optimal alloy layer thickness and improving the product's anti-aging performance. Attached Figure Description

[0023] Figure 1 It consists of a cross-section of tin-plated copper strip, including a copper substrate, an alloy layer, and a tin layer.

[0024] Figure 2 For material alloy layer under wind speed of 200m / s;

[0025] Figure 3 The material alloy layer is for wind speeds of 800 m / s. Detailed Implementation

[0026] The present invention provides a method for producing tin-plated brass, the method comprising the following process flow: melting and casting → semi-continuous casting → sawing → walking beam furnace heating → hot rolling → double-sided milling → rough rolling → thick edge shearing → bell furnace annealing → thick strip cleaning → pre-finish rolling → intermediate rolling annealing → finish rolling → finished product cleaning → tension bending and straightening → finished product slitting into bare material → tin plating → finished product slitting into tin-plated material.

[0027] The molten tin comprises the following components by mass percentage: Cu ≤ 1.5%, Zn 0.05-0.20%, and the balance being Sn;

[0028] The temperature of the molten tin is 300–500°C.

[0029] The molten tin is sprayed onto the copper strip surface at an ambient temperature of 80-90℃. The molten tin is heated to a temperature of 300-500℃ and then sprayed onto the surface of the copper strip in operation through a nozzle. During the spraying process, the heat of the molten tin is transferred, and the molten tin is sprayed onto the copper strip surface at an ambient temperature of 80-90℃.

[0030] The spraying is performed using an atomizer with nozzles.

[0031] The production method also includes cooling after tin plating, with the cooling fan speed being 800±20m / s.

[0032] The tin-plated brass produced by the above method improves the uniformity of the tin layer in the tin-plated strip, increases the growth rate of the oxide film on the tin layer surface, and avoids phenomena such as tin whisker growth caused by changes in the stress of the tin-plated strip. The thickness of the produced tin-plated brass alloy layer is 1 / 5 to 2 / 5 of the total thickness of the alloy layer and the tin layer.

[0033] Traditional molten tin plating methods suffer from uneven tin plating thickness due to factors such as the contact time of the tin solution with the copper strip surface and the concentration of tin ions. This invention employs a high-temperature spraying method using an atomizer. The tin-ion-containing solution sprayed from the atomizer nozzle is densely distributed into small particles on the copper strip surface. The tin ions gain electrons and form a more uniform tin layer. The molten tin is heated to 300-500℃ and then sprayed onto the operating copper strip surface. During spraying, the heat from the molten tin is transferred to the plating equipment and environment, where the ambient temperature reaches 80-90℃. This temperature accelerates the movement of tin ions. The increased movement of tin ions on the high-density, small-particle atomized surface results in a more uniform, gap-free tin layer on the copper strip surface after energization. Simultaneously, the reaction of the tin layer on the copper strip surface with oxygen in the air to form tin dioxide is accelerated, resulting in a more uniform, gap-free, and thicker tin oxide layer. Ultimately, this prevents the growth of tin whiskers due to stress changes in the tin-plated strip, avoiding short circuits in electrical components.

[0034] The inventors discovered that during high-temperature aging experiments, the free alloy layer in the free tin layer grows, causing the entire free tin layer to harden and thus reducing the solderability of hot-dip tin-plated materials. This free alloy layer is mainly due to the incomplete overflow of Cu ions from the substrate, which remain within the free tin layer of the tin plating. This application demonstrates through experiments that the free alloy layer is primarily related to the temperature and chemical composition of the tin melt. Different tin melt compositions correspond to different tin melt temperatures. When the tin melt composition is constant, if the tin melt temperature is below a certain value, the overflow rate is too slow, and Cu ions have not completely overflowed, resulting in surface defects in the product. Conversely, if the tin melt temperature is too high, the number and speed of Cu ions overflowing from the copper material increase, leading to a similar increase in the number of free alloy layers in the tin layer. Therefore, this application controls the tin melt temperature range to be 300–500°C.

[0035] During hot-dip tin plating, a tin plating layer is formed on the surface of a copper substrate. The tin plating layer includes a tin layer and an alloy layer (such as...). Figure 1As shown in the diagram, an alloy layer and a tin layer are sequentially formed on the surface of the copper substrate. Due to the reaction between molten tin and copper, a hard and uniform alloy layer (Cu6Sn5) is formed between the copper substrate and the tin plating layer, ensuring excellent adhesion and improving frictional characteristics. The thickness of the alloy layer is extremely important for the quality of the hot-dip tin plating layer and is a key parameter for controlling the tin plating process. If the alloy layer is too thin, the adhesion of the tin plating layer is weak, making it easy to peel off; if the alloy layer is too thick, the tin plating layer will harden, reducing the material's weldability and corrosion resistance, and increasing the material's contact resistance. Obtaining a suitable alloy layer thickness is crucial for ensuring product performance. This application achieves optimal alloy layer thickness by synergistically controlling the tin liquid composition and temperature, and controlling the post-plating cooling fan speed, thereby reducing the alloying time between the plating layer and the copper material, lowering the rate of free alloy layer formation, and controlling the alloy layer thickness to 1 / 5 to 2 / 5 of the total tin plating layer thickness, thus improving the product's anti-aging performance. Through extensive research, the inventors discovered that the main factor affecting the thickness of the alloy layer is the cooling fan speed. Increasing the cooling fan speed shortens the solidification time of the molten tin, thereby reducing the alloying time between the tin layer and the copper material, and thus reducing the thickness of the alloy layer. This application reveals that, under the tin plating method and plating solution composition described in this application, the alloy layer thickness accounts for approximately 1 / 2 of the total tin plating thickness at a wind speed of 200 m / s; under a wind speed of 800 m / s, the alloy layer thickness reaches its optimal level, accounting for approximately 1 / 5 to 2 / 5 of the total tin plating thickness.

[0036] The following examples further illustrate this application.

[0037] Example 1

[0038] A method for producing tin-plated brass, wherein the tin-plated brass, taking grade C2600 as an example, comprises the following components by mass percentage: copper 69.36%, tin 0.03%, phosphorus 0.002%, nickel 0.006%, lead 0.004%, iron 0.018%, aluminum 0.0014%, and zinc 30.5786%; the method includes the following process flow: melting and casting → semi-continuous casting → sawing → walking beam furnace heating → hot rolling → double-sided milling → rough rolling → thick edge shearing → bell furnace annealing → thick strip cleaning → pre-finish rolling → intermediate rolling annealing → finish rolling → finished product cleaning → tension bending and straightening → finished product slitting into bare material → tin plating → finished product slitting into tin-plated material.

[0039] 1) Smelting: Add cathode copper and other metals to the smelting furnace in sequence and proportion → melt → heat up → let stand for 10-15 minutes to degas → remove slag → take samples for analysis → adjust the composition to meet the requirements → heat up to the converter temperature (1080~1100) → converter → after the converter, stir evenly, take samples for analysis, and let stand for no less than 15 minutes. The analysis results must meet the furnace discharge range before the furnace can be discharged for casting.

[0040] 2) Semi-continuous casting: The furnace chamber is tilted to allow the molten copper to flow into the crystallizer (the casting temperature is 1070-1110℃), and then the copper ingot is pulled out by the ingot puller. The initial casting speed is 30mm / min, the initial water flow rate is 15L / min, the water pressure is 0.01-2Mpa, the normal casting speed is 160mm / min, the normal water flow rate is 80L / min, and the covering agent used during casting is borax.

[0041] 3) Sawing: Use a flat ingot saw to remove surface defects at the head and tail, and cast ingots to ensure that the length after sawing is 5500-7000mm.

[0042] 4) Walking beam furnace heating: Material can be added only after the furnace temperature reaches 740℃. The atmosphere adopted in the furnace is a slightly oxidizing atmosphere. The heating temperature of the walking beam furnace is 870~950℃, and the walking cycle is controlled between 540~720s.

[0043] 5) Hot rolling: After the billet exits the furnace, it is rolled to a thickness of 15-16 mm through 9 passes using a two-roll reversible rolling mill. The rolling force is 600-1000 KN and the rolling speed is controlled at 90-130 m / min. After rolling, it is coiled in the cooling section.

[0044] 6) Double-sided milling: The chip amount of single-sided milling is 0.8-1.0mm, the chip amount of single-sided milling is 2-4mm, and the equipment running speed is controlled at 4-8m / s.

[0045] 7) Rough rolling: A 4-roll mill is used to roll the copper strip to 1.5mm in multiple passes. Emulsion is used as lubricant and coolant during rolling. The speed of the first pass is less than 60m / min, and the speed of subsequent passes is less than 180m / min.

[0046] 8) Thick shearing edge: The brass strip is sheared with a width of 30-40mm through thick longitudinal shearing, and the shearing speed is controlled at 60-90m / s.

[0047] 9) Bell-type furnace annealing: The cut copper strip is placed in a bell-type furnace for annealing at a temperature of 420℃ for 6 hours. The annealing atmosphere is 75% H2 + 25% N2.

[0048] 10) Thick strip cleaning: The copper strip is cleaned by alkaline washing to degrease and acid washing to remove the oxide layer. The cleaning speed is 30-35 m / min.

[0049] 11) Pre-finishing: The cleaned copper strip is processed in multiple passes through a 20-roll finishing mill, with a rolling thickness of 0.42 mm. The roughness of the rolls is controlled at 0.3 μm. The rolling is carried out by full oil rolling, and the rolling speed is controlled below 180 m / min.

[0050] 12) Intermediate rolling annealing: The rolled copper strip is annealed in an air cushion furnace at a temperature of 650℃ and an air atmosphere at a speed of 69 m / min. The copper strip is first degreased in an alkaline washing zone, then annealed in a heating zone. The fan speed in heating zones 1, 2, and 3 is 1200 rpm, and the fan speed in heating zone 4 is 1200 rpm. Then it is cooled in a cooling zone. The fan speed in cooling zones 1, 2, and 3 is 1200 rpm, and the fan speed in cooling zone 4 is 500 rpm. Finally, it is pickled, polished, passivated, and dried. The concentration of the alkaline solution is controlled at 2.5-6%. The polishing brush used is 3000 mesh, the polishing current is 2A, the concentration of acid solution is controlled at 8% to 13%, the concentration of passivation solution is controlled at 0.02% to 0.06%, and the tension setting ratio of each strip section is as follows: Loop I: Furnace area: Post-treatment: Loop II: Rewinding = 12:12:1.3:12:12:20.

[0051] 13) Finishing rolling (FRM-2): The annealed copper strip is processed in multiple passes through a six-roll finishing mill. The rolling thickness is 0.3 mm, the roll roughness is controlled at 0.12 μm, the rolling is done with full oil rolling, and the rolling speed is controlled below 120 m / min.

[0052] 14) Finished Product Cleaning: The rolled copper strip is cleaned using a thin strip degreasing machine. Before cleaning, check the condition of the squeeze rollers; if there are no problems, proceed with cleaning. If the rollers have been used for a long time, replace them before cleaning. First, perform alkaline washing for degreasing, with the alkaline concentration controlled at 4-5% and the working temperature at 65-75℃. After alkaline washing, perform acid washing and polishing, with the acid concentration controlled at 6-10% and the working temperature at room temperature. After acid washing, perform polishing using a 3000-mesh polishing brush and a polishing current of 2.1A. After polishing, perform passivation treatment, with the passivation solution concentration controlled at 0.03-0.09%.

[0053] 15) Stretch straightening: The cleaned copper strip is straightened in a plate shape. Stretch straightening adopts the elongation mode, with the elongation controlled at 3%. Surface inspection is also activated to check the surface quality.

[0054] 16) Finished slitting of bare material: Slitting is carried out according to the quality inspection results of bending and straightening and the specifications required by the customer. The slitting speed is less than 70m / min.

[0055] 17) Tin plating: Spray molten tin onto the surface of a running copper strip at a speed of 8 m / min. The molten tin used has the following mass percentage composition: Cu 1.4%, Zn 0.06%, with the balance being Sn. The temperature of the molten tin is 320–360℃. The molten tin is sprayed using an atomizer with nozzles, controlling the spray flow rate at 13 liters / min, the spray speed at 8 m / min, the spray angle perpendicular to the copper strip surface, the nozzle pressure at 250 kPa–260 kPa, the nozzle diameter at 4–6 mm, and the ambient temperature of the molten tin on the copper strip surface at 80–90℃. After spraying, cooling is performed by controlling the cooling fan speed at 800 m / s to cool to room temperature.

[0056] 18) Finished tin-plated materials are slit according to customer specifications, with a slitting speed of less than 70m / min.

[0057] The alloy layer of the tin-plated brass produced in Example 1 is as follows: Figure 3 As shown, the thickness of the alloy layer is 1 / 5 to 2 / 5 of the total thickness of the tin plating layer.

[0058] Comparative Example 1

[0059] Following the same method as in Example 1, except that after the molten tin was sprayed, it was cooled to room temperature using a cooling fan at a speed of 200 m / s. The resulting tin-plated brass alloy layer is as follows: Figure 2 As shown, the alloy layer is relatively thick, accounting for about 1 / 2 of the total thickness of the tin plating layer.

Claims

1. A method for producing tin-plated brass, characterized in that, The production method includes tin plating, wherein tin plating is performed by spraying molten tin onto the surface of a copper strip; The molten tin comprises the following components by mass percentage: Cu≤1.5%, Zn 0.05-0.20%, with the balance being Sn; The temperature of the molten tin is 300–500°C; The spraying process involves spraying molten tin onto the surface of a copper strip at an ambient temperature of 80-90°C. The spraying is performed using an atomizer with nozzles; Molten tin is sprayed onto the surface of the running copper strip, which travels at a speed of 8 ± 0.5 meters per minute. The spraying process is controlled with a flow rate of 10-15 liters / minute, a spraying speed of 4-16 meters / minute, a spraying angle perpendicular to the copper strip surface, and a nozzle pressure of 250 kPa-300 kPa. The production method also includes cooling after tin plating, controlling the cooling fan speed at 800±20m / s, and cooling to room temperature; The tin-plated brass includes a copper substrate, and a tin-plated layer is formed on the surface of the copper substrate. The tin-plated layer includes an alloy layer and a tin layer, and the thickness of the alloy layer is 1 / 5 to 2 / 5 of the total thickness of the tin-plated layer.

2. Tin-plated brass produced by the production method of claim 1.

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