Microstructural Evolution and Mechanical Weakening Mechanisms in Pulsed Laser Powder‐Fed Welding of Dissimilar AA2195‐T8/AA7075‐T6 Aluminum Alloy Joints

Reliable joining of dissimilar AA2195‐T8 and AA7075‐T6 high‐strength aluminum alloys is challenged by hot‐cracking susceptibility and pronounced microstructural heterogeneity across the weld zone. In this study, pulsed laser powder‐fed welding combined with a Box–Behnken response surface design was used to establish a stable processing window and clarify the origin of local mechanical weakening. The optimized parameters were a welding speed of 0.003 m/s, a defocus distance of 9.5 mm, a pulse duration of 2.8 ms, and a pulse frequency of 180 Hz, producing crack‐free joints with an average ultimate tensile strength of 252 MPa. The weld exhibited distinct solidification partitioning from columnar grains near the fusion boundaries to coarse equiaxed grains in the weld center. Tensile fracture consistently occurred in the AA2195‐side columnar‐grain region (CGZ), where the minimum hardness reached 72.2 HV and the maximum indentation depth was the largest among the examined regions. This local weakening was attributed to precipitation‐strengthening loss, grain coarsening, Cu‐rich interdendritic segregation, and increased second‐phase connectivity, which promoted strain localization and mixed intergranular/transgranular fracture. These results establish a quantitative process–solidification–local weakening–fracture relationship for dissimilar AA2195‐T8/AA7075‐T6 joints.