Analysis of the characteristics and uses of copper-nickel alloys

Copper-nickel alloy, is a copper-based alloy with nickel as the main added element. It exhibits a silvery-white metallic luster, hence the name copper-nickel alloy.

Copper and nickel are infinitely soluble in each other to form a continuous solid solution, and are always alpha single-phase alloys, regardless of their proportions. When nickel is dissolved in red copper and the content exceeds 16%, the colour of the alloy becomes as silvery white. Generally the higher the content of nickel, the whiter the colour. And the nickel content in copper-nickel alloys is generally 25%.

The advantages of copper-nickel alloy can effectively improve the strength, corrosion resistance, hardness, resistivity and thermoelectric properties of copper alloy, and reduce the temperature coefficient of resistivity. Therefore, compared with other copper alloys, copper-nickel has good mechanical and physical properties, good ductility, high hardness, beautiful colour, corrosion resistance and deep-drawn properties.

Copper-nickel alloys are widely used, not only for shipbuilding, petrochemical, electrical appliances, instruments, medical equipment, daily necessities, handicrafts and other fields, but also an important resistance alloy and thermocouple alloy.

Abstract: The rapid development of marine industry puts forward higher and higher requirements for materials used in marine engineering, including white copper, which is widely used in ships, some power plants and desalination. Because it is suffered from long-term sea water erosion, corrosion failure will occur if the corrosion resistance does not meet the requirements, resulting in huge losses. Therefore, white copper has attracted more and more attention because of its good seawater corrosion resistance (especially good erosion corrosion performance) and corrosion fatigue resistance, excellent cold and hot workability, high tensile strength, yield strength and so on. In this paper, the composition, application and manufacturers at home and abroad of different white copper alloys are reviewed, and the research progress of corrosion resistance of copper-nickel alloys is summarized.

Classification of copper-nickel alloys

White copper alloy grades and elemental composition, white copper can be divided into manganese white copper, iron white copper, ordinary white copper, aluminium white copper and zinc white copper, due to the different content of the Ni element in it, so that the performance of the difference, the application of different occasions. Due to its irreplaceable corrosion resistance and many properties superior to traditional alloys, it has a greater potential for application.

 The performance of copper-nickel alloy and its application

Ordinary white copper is generally structural copper-nickel alloy, in addition to high corrosion resistance, in addition to high temperature and low temperature has a better comprehensive mechanical properties, that is, plasticity and toughness are better, generally as a bar or strip. At the same time, on the basis of ordinary copper alloy elements such as Fe, Mn, Zn and Al, etc., can be added to achieve the actual application of special performance requirements, to better meet the industrial needs.

The most widely used Fe white copper is BFe10-1-1 (C70600) and BFe30-1-1 (C71500), when the mass fraction of Ni is 30% and 10%, the alloy has a wider passivation zone and the best corrosion resistance. And the alloy also has a strong resistance to seawater scouring corrosion performance, known as "marine engineering alloys", copper and copper alloys in the field of marine engineering in the main applications.

BFe10-1-1 and BFe30-1-1 alloys have good seawater scouring corrosion resistance, high heat transfer coefficient, excellent mechanical/welding properties, inhibit the adhesion of marine microorganisms, etc., and are widely used in the cooling water pipes of main and auxiliary engines of ships, fire fighting pipelines of offshore oil platforms, heat exchangers of power plants, condensers of coastal nuclear power plants, and brine heaters of multi-stage flash steamers of seawater desalination plants. Meanwhile, BFe30-1-1 alloy has higher strength and is also used in some high strength structural parts such as shafts, fasteners, valve stems and flanges of marine devices. Resistance to seawater scouring corrosion and better resistance to sand corrosion performance of BFe30-2-2 alloy was developed to cope with the East China Sea waters seawater sandy problem.BFe10-1-1 and BFe30-1-1 alloy tubing in the hard state of mechanical properties should be met: tensile strength ≥ 370 MPa, yield strength ≥ 150 MPa, elongation ≥ 18%, Vickers hardness ≥ 85; corrosion resistance: Corrosion (50 ℃, 3.5% NaCl seawater) ≤ 0.025 mm / a, does not allow pitting phenomenon.

Manganese white copper (BMn3-12 alloy) has moderate resistance coefficient, small and stable resistance temperature coefficient, because of its good electrical properties, BMn3-12 alloy can be used to make standard resistors and other precision instruments and meters resistance components. With the development of the times, the precision requirements of instruments are getting higher and higher, so the research of this alloy can not stop at changing the composition and content of the alloy [6]. Qin Fangli et al [7] through the annealing, horizontal extrusion failure and drawing process so that the BMn3-12 alloy has a special common lattice twin grain boundaries, can not affect the conductivity of the material to improve the strength of the material in the case of the BMn40-1.5 alloy is the application of earlier than the BMn3-12 alloy of copper-nickel alloys for electrician, because of its resistance to temperature coefficients of smaller, so the heat resistance is better, can be used in a wide range of temperatures. It can be used in a wide temperature range. Compared with BMn3-12 alloy, BMn40-1.5 alloy has a higher thermal potential for copper, so it is suitable for precision resistors, sliding resistors, starting and regulating transformers and resistance strain gauges for AC applications.

Aluminium copper has both high strength, also has good plasticity and toughness. Among them, BAl13-3 alloy is often used to make high strength corrosion-resistant parts, BAl16-1.5 alloy is used to make flat springs with important uses. For a long time, in order to improve the performance of copper aluminium alloy, often adding a small amount of trace elements to make copper aluminium alloy to produce a strengthened matrix, in order to maintain high strength under the premise of good electrical conductivity to meet the requirements of practical applications. Due to its high strength, high conductivity and good wear resistance, copper aluminium alloy can be used as a potential material for lead frames and wear parts.

Copper-nickel alloy performance requirements

With the rapid development of China's marine shipbuilding industry, marine oil and gas industry, marine mining, marine power and desalination industry, the requirements for materials are getting higher and higher. Among them, copper-nickel alloy tubes are used more, naval copper alloy condenser tubes for long periods of time in the high temperature, high pressure and corrosive very high cooling medium - seawater environment. Therefore, only the chemical composition of the product, mechanical properties, seawater corrosion resistance to meet the requirements is not enough, but also strict requirements for geometric dimensional accuracy, process performance and internal organisation and other indicators, but also requires copper-nickel alloy tube with better corrosion resistance, high heat transfer coefficient, large diameter, high precision, excellent mechanical welding technology, better inhibition of marine microbial adhesion and other characteristics.

Copper-nickel alloy corrosion resistance research

In order to meet the performance requirements of the marine industry materials, to improve the corrosion resistance of copper-nickel alloys people have done a lot of research. The tensile strength and elongation of white copper with the addition of rare earth Ce are improved, the grain organisation is more dense, and the addition of rare earth Ce can improve the typical tendency of nickel removal corrosion of the alloy in sulphur-containing media. It was found that the corrosion resistance showed a trend of increasing and then decreasing with the increase of Fe content, but no further research was done on the corrosion resistance mechanism. Zhang Jiaining [21] of Beijing Nonferrous Metals Research Institute (BNMRI) found the optimum alloy ratio to improve the corrosion resistance of B10 by controlling the Fe/Mn ratio, and found that the alloy has the best corrosion resistance at this time when Fe/Mn=3:2.