Investigating novel forging mechanisms for thin dissimilar copper-aluminum rod weldments via pressure-controlled Joule-heating and interfacial deformation

The novel mechanism of pressure-controlled Joule heating and interfacial deformation offers a route to forging high-strength aluminum-copper weldments, crucial for electrical connections and discharge systems. However, despite their lightweight, rigidity, and high conductivity, differences in melting points, thermal expansion, and strength often hinder effective joining. This study investigates plastic yielding at a controlled temperature while maintaining pressure for high-strength bonding in 5 mm thin aluminum copper rods. A novel experimental setup is developed using an electro-servo press and pneumatically controlled retractable tapered hollow semi-circular copper electrodes for localized heating and mechanical displacement at set pressure for interfacial plastic flow. Finite element-based coupled electric-thermal and dynamic mechanical simulations evaluated the transient heat flux, thermal gradients, and plastic stress that drive the interfacial strain and deformation. Computed and measured results reveal high-strength welds (113–155 MPa) with 2–4.6 interfacial plastic strain, forming thin (0.114–0.176 μm) intermetallic layers under 25–40 MPa applied pressure. The external die enclosures enhance contact and strain concentration. Additionally, the joining behavior under the axial current discharge are investigated and compared. Both copper and aluminum weld interfaces undergo grain refinement via dynamic recrystallization under low-temperature plastic deformation, slightly increasing weld microhardness. Computed lower temperature increment during welding at higher pressure and smaller stroke implies homogeneous interfacial yielding for high-strength welds, enhancing the understanding of forging mechanisms for industrial applications.