The electrothermal fracture mechanism between aluminum and copper wires

Abstract

This study investigates the energization and high-temperature damage characteristics of pure aluminum and copper wires of 20 mil (500 μm) wire diameter. Due to the wire drawing annealing process, the base of aluminum wire has an equiaxed grain structure, while the base of copper wire has an equiaxed grain structure containing a twin crystal structure.Normally, in terms of mechanical characteristics, copper wire is inherently stronger than aluminum wire, and both are ductile materials. Electrical experiments found that the voltage of the copper wire showed a stable upward trend with the increase in current; it is worth noting that the resistance of aluminum wire increases abnormally when the current increases continuously, resulting in an overload resistance zone, and the resistance overload zone will cause the wire to appear incandescent.This study discusses the characteristics of the overload resistance zone with various wire lengths. Changing the length of copper wire has no obvious effect on the electrical properties, but decreasing the length of aluminum wire decreases the width of the overload resistance zone. When comparing the energized tensile test and the simulated environmental heat treatment experiment, it can be inferred that the surface temperature of the copper wire is about 900 °C when energized, whereas the surface temperature of aluminum wire is about 600 °C when energized.The tensile mechanical properties of the aluminum wire at different energization stages show that the incandescent phenomenon in the overload resistance zone will deteriorate the wire's mechanical properties. It is confirmed that the incandescent phenomenon is dominated by the micro-AlNi eutectic cladding structure in the aluminum wire, and the eutectic phase is formed in overload resistance zone. These eutectic liquid spherical areas will reduce the ductility (embrittlement) of the wire when energized and stretched, and the eutectic liquid spherical phase will then produce holes after solidification, which will affect the aluminum wire's reliability. Incorporating a trace amount of nickel can improve the strength and corrosion resistance in aluminum wire, but the voltage and current need to be controlled during application to avoid the occurrence of incandescence or affecting the electrical and thermal stability.