Introduction

• C70250(CuNi3SiMg), also known as silicon bronze, is a copper alloy that contains nickel and silicon, offering exceptional properties such as high strength, excellent formability, high stress relaxation resistance, excellent electrical conductivity, high elasticity, and superior corrosion resistance. It doesn’t require heat treatment, exhibits good stampability, and is free of beryllium, making it both economical and non-toxic. The alloy boasts an attractive appearance, along with high conductivity, good thermal and oxidation resistance, as well as impressive strength, ductility, hardness, fatigue resistance, and excellent plating and welding capabilities.
• Nickel (Ni) and silicon (Si) can form the compound Ni₂Si, which has a solubility of up to 9% in the solid solution at the eutectic temperature of 1025°C, but its solubility drops to nearly zero at room temperature. Therefore, when the Ni/Si ratio in the alloy is 4:1, Ni₂Si can fully form, leading to significant age hardening, which provides the alloy with excellent overall properties. If the Ni/Si ratio is less than 4, the alloy may have higher strength and hardness, but its electrical conductivity and ductility will decrease, making it less suitable for pressure processing. Adding a small amount of manganese (Mn) (0.1% – 0.4%) to a Cu-Si-Ni alloy can improve its performance, as Mn not only acts as a deoxidizer but also contributes to solid solution strengthening.

Chemical Composition

• Ni: 2.2%~4.2%
• Si: 0.25%~1.2%
• Mg: 0.05%~0.3%
• Cu: min. 96.2%

Alloy Standard

• ASTM: C70250——ASTM B422/ASTM B888
• DIN: CuNi3SiMg——CEN/TS 13388
• EN: CuNi3SiMg——CEN/TS 13388
• JIS: C7025
• Wieland: K55 _{is a trademark licensed by Wieland}

Physical Properties

• Density: 8.83 g/cm³
• Electrical conductivility: 40 IACS%(20°C)*(value for the lowest temper class)
• Modulus of elasticity: 130 GPa
• Coefficient of thermal expansion: 17.7 10^-6/K
• Thermal conductivity: 190 W/(m*K)

Mechanical Properties

Application

• C70250 is widely used in relays, mobile phone components, switches, and headphone jacks. It’s also an ideal substitute for low-beryllium-content beryllium copper.
• Additionally, C70250 is utilized in electronic copper strips, serving as a base material for manufacturing integrated circuits and semiconductor discrete devices. It’s primarily used in electronic and electrical integrated circuits, medium and high-power transistors, measurement devices, LED and diode brackets, telecommunications, and connectors and terminals for testing instruments.

Stress Relaxation Resistance

• Stress relaxation resistance is essential for preserving contact force over long durations or at high temperatures. Figure 4 illustrates how C70250 performs in terms of stress relaxation resistance when compared to phosphor bronzes. It demonstrates that C70250 maintains more than 80% of the original applied stress at 150°C after 1000 hours.

REF1－1 Stress-strain curve for C7025 TM02(Rolling direction)

REF1－2 Stress-strain curve for C7025 TM02(Transverse direction)

REF2－1 Stress-strain curve for C7025 TM03(Rolling direction)

REF2－2 Stress-strain curve for C7025 TM03(Transverse direction)

Bending Properties

Notes

*This article is for general information only and is not subject to revision. No claims can be derived from it unless there is evidence of intent or gross negligence. The data given are no warranty that the product is of a specified quality and they cannot‎ replace ‎expert‎ advice‎ or‎ the‎ customer’s‎ own ‎test. Some data and pictures are quoted from the Internet.