Application of High-Performance Copper Alloy Strips in Automotive Connectors

Copper, being the non-precious metal with the highest electrical conductivity, along with its high ductility, moderate strength, and good corrosion resistance, makes it the preferred choice for manufacturing large conductors such as cables, busbars, transformer windings, and motor stators and rotors. However, for connector components and commutators, it is necessary to enhance performance by adding appropriate alloying elements.

At the same time, as the functional requirements of automobiles increase, the application of automotive connectors will become more widespread. The trend towards vehicle integration has led to higher levels of connector integration, demanding more stringent performance requirements. This necessitates that the copper and copper alloy strips used in automotive connectors possess excellent comprehensive properties. This article discusses the performance requirements of copper strips for automotive connectors, introduces the properties of various high-performance copper alloy strips, and provides references for high-performance copper alloys that meet the performance requirements of automotive connectors.

Essential Properties of Copper and Copper Alloy Strips for Automotive Connectors:

The required properties for automotive connectors include high contact force, minimal displacement deformation (limited compression stroke but requiring high contact force), small bending angles (product miniaturization), resistance to failure under alternating stress (high insertion and extraction cycles), low contact resistance, good heat dissipation and low temperature rise, sustained high contact force/high-temperature operation, and compliance with environmental standards. Therefore, copper and copper alloy strips must possess high yield strength, high elastic modulus, high electrical conductivity, excellent bending properties (low r/t), excellent fatigue resistance, high thermal conductivity, high resistance to stress relaxation/high-temperature softening, and be free of environmentally harmful substances/ROHS compliance.

Copper easily forms alloys with other elements, allowing the enhancement of its properties through alloying to meet the performance requirements of copper alloy strips for automotive connectors. Based on the performance requirements of copper alloys for automotive connectors, multiple groups and types of high-performance alloys have been developed for selection.

Typical Performance Comparison of High-Performance Copper and Copper Alloy Strips:

1. Bending Performance:
   Bending performance refers to the mechanical characteristics of a material under bending load. The bending performance of copper and copper alloys is positively correlated with the manufacturability and reliability of connectors.
   This article uses the coefficient R/t (bending radius / strip thickness) to evaluate the bending performance of copper and copper alloy strips perpendicular to (good way) and parallel to (bad way) the rolling direction. Although C103 and STOL80 have superior bending performance compared to other alloys, their strength is lower. STOL76M, STOL78, STOL95, and CuSn5 not only have high strength but also excellent bending performance, meeting the bending performance requirements of copper and copper alloy strips for automotive connectors.

2. Resistance to High-Temperature Softening:
   Resistance to high-temperature softening refers to the ability of a material to resist a decrease in hardness (strength) under high-temperature conditions. The operating environment temperature of automotive connectors, especially in the engine compartment, often exceeds 105°C and can reach several hundred degrees Celsius instantaneously. Therefore, copper and copper alloy strips for automotive connectors must have excellent resistance to high-temperature softening; otherwise, the strength (hardness) of the strips will permanently and significantly decrease under high temperatures, reducing the reliability and lifespan of the connectors.
   After 1 hour, the hardness of C103, CuZn10, CuSn5, and C425 decreased by more than 50%, STOL94 by 20%, STOL76M by 10%, and STOL80 and STOL95 by less than 10%. Considering the strength (hardness) requirements of automotive connectors, STOL76M, STOL94, and STOL95 alloys can meet the resistance to high-temperature softening requirements of copper and copper alloy strips for automotive connectors.

3. Resistance to Stress Relaxation:
   Stress relaxation refers to the phenomenon where stress decreases over time and with increasing temperature in a material under constant deformation. Typically, a material is considered to have a certain resistance to stress relaxation if its yield strength after a period at high temperature (1000 hours for automotive connectors) remains above 70% of its yield strength at room temperature.

4. Fatigue Resistance:
   Fatigue strength refers to the maximum stress at which a specimen does not fail after a certain number of load cycles, known as the fatigue limit. STOL76M, STOL94, and STOL95 maintain high strength even after millions of bending cycles.

As the requirements for automotive connectors become increasingly stringent, it is essential to consider the interrelationship and mutual influence of material properties, design parameters, operating environment, and product performance throughout the product lifecycle when designing automotive connectors. Therefore, during the design and selection of copper and copper alloy strips, it is necessary to choose the appropriate copper and copper alloy strips based on the design requirements of the automotive connectors and the properties of the copper and copper alloy strips.