Process-driven evaluation of laser-assisted pre- and post-heating in laser welding of Al-Cu dissimilar materials

The laser welding of different metals such as Al and Cu is severely limited due to the formation of uncontrollable elemental transitions, which leads to significant mechanical degradation. Therefore, in this study, laser-assisted pre-heating and post-heating strategies were systematically evaluated from a process-driven perspective to clarify their effects on interfacial reactions and joining performance. In conventional welding, increasing the laser power (1150, 1200, 1250 W) concentrated the heat input, causing excessive intermetallic compound (IMC) growth at the interface on the Cu-side and an increase in Cu concentration in the region on the Al-side. High laser power caused significantly greater brittleness, resulting in approximately 45 % reduction in tensile lap shear strength and approximately 90 % reduction in elongation. Laser pre-heating altered the molten pool behaviour, increasing penetration at low laser power (P1150) and limiting excessive intermetallic growth on the Cu-side at higher laser powers, thereby regulating the Cu concentration on the Al-side. Despite localised cracks at the Cu interface due to thermal expansion mismatch and the presence of porosity in the weld zone, tensile lap shear strength improved in all pre-heated joints, achieving higher strength compared to conventional welding at the same power level. The combination of pre/post-heating strategies reduced crack formation at low laser power but promoted porosity formation and a more compact intermetallic structure formation at higher heat inputs. However, values close to the mechanical properties in the laser pre-heating process were obtained. Overall, the laser pre- and post-heating system provided better penetration, balanced microstructural stability, and mechanical performance at low laser power.