The copper-aluminum bond strength of a new copper-aluminum transition clamp is a core indicator determining its performance stability and service life. Ensuring its quality requires a comprehensive approach encompassing material selection, process optimization, structural design, heat treatment control, quality inspection, and maintenance.
Material selection is fundamental. Copper and aluminum have significantly different physical properties, such as a 36% difference in their coefficients of thermal expansion. Direct welding can easily lead to thermal stress due to the different cooling contraction rates, causing cracking at the bond surface. Therefore, it is necessary to select a copper alloy with a coefficient of thermal expansion matching that of aluminum, or to refine the copper-aluminum grains by adding rare earth elements to improve interfacial compatibility. For example, in the process of double-sided copper plating on one end of an aluminum plate, using a high-purity copper plate combined with the aluminum plate can significantly reduce interfacial resistance and increase the bond strength to more than 10 times that of traditional processes.
Process optimization is crucial. Traditional friction welding or arc welding is prone to insufficient strength due to irregular weld surfaces and residual porosity. New processes, such as integral pressure fusion welding technology, use high pressure to cause copper and aluminum atoms to diffuse and fuse together, forming a metallurgical bond that cannot be separated by mechanical stress, effectively solving the fracture problem. Furthermore, the casting-rolling composite process integrates molten aluminum and copper strip into a single unit through high-temperature, high-pressure oxygen-free casting. This results in a smooth, flat, and tightly bonded interface, eliminating electrical intermittents and preventing electro-corrosion and burn-off.
Structural design requires innovation. Traditional copper-aluminum transition clamps often employ symmetrical welded structures, which are prone to cracking due to stress concentration. New designs, such as hand-like grippers, increase the copper-aluminum bonding area, dispersing stress and improving fatigue resistance. Simultaneously, segmented designs separate the copper-aluminum transition section from the conductive contact surface, preventing localized overheating caused by current concentration. For example, a new type of clamp, by incorporating a protrusion in the middle of the aluminum plate and securing it with bolts, ensures uniform stress distribution on the bonding surface, significantly improving strength.
Heat treatment control can eliminate internal stress. During the copper-aluminum composite process, residual stress arises due to differences in cooling contraction rates, affecting bonding strength. Vacuum heat treatment promotes element migration between the two metals, forming a diffusion region at the interface and enhancing bonding force. Simultaneously, heat treatment eliminates internal stress caused by differences in thermal expansion coefficients during furnace cooling, improving bonding performance. However, temperature control is crucial to prevent the formation of intermetallic compounds at the interface, which could widen the transition layer and reduce bonding performance.
Strict quality control is essential. New copper-aluminum transition clamps must undergo multiple tests to ensure adequate bonding strength. For example, ultrasonic testing is used to detect internal weld defects such as incomplete fusion and slag inclusions; tensile tests are conducted to measure the tensile strength of the bonding surface, ensuring it reaches 90-159 MPa; and peel tests are performed to verify the peel strength of the bonding surface, ensuring it is ≥12 N/mm. Furthermore, contact resistance must be tested to ensure it is ≤10 μΩ to prevent oxidation due to heat during operation.
Usage and maintenance are also critical. Excessive bending or stress should be avoided during installation to prevent micro-cracks on the aluminum plate side. For example, during construction, the aluminum wire end should be secured first before tightening the copper end to avoid damage to the weld surface. Regular inspections are necessary during operation, and any corrosion or loosening should be addressed promptly. In heavily polluted areas, such as coastal regions, anti-corrosion coatings or sealing structures are required to prevent electrolyte intrusion and electrochemical corrosion.
Ensuring the copper-aluminum bond strength of the new copper-aluminum transition clamp requires consideration of the entire process, including material selection, process optimization, structural design, heat treatment control, quality inspection, and maintenance. Through technological innovation and meticulous management, its mechanical performance and reliability can be significantly improved, meeting the power system's requirements for high-strength, long-life copper-aluminum transition devices.
