Electro-Thermal Activity Coupled Digital Twin-Driven Many-Objective Co-Optimization of Flux-Cored Preform Composition and Segmented Current Schedule for Resistance Brazing of Aluminum Conductors

Aluminum conductor terminations are limited by an alumina film that blocks wetting and raises interfacial resistance. Existing process models absorb flux behavior into a fitted decay factor, so the composition and current schedule are tuned sequentially. Here, flux activity is resolved as a transport–reaction field whose oxide coverage feeds back to the contact resistance, closing the electro-thermal activity loop. An activity–melting synchronization index (AMSI) combining temporal overlap with precedence of film removal over liquid formation is imposed as an explicit constraint. Composition simplexes are mapped to isometric log-ratio coordinates and the segmented waveform to a bounded recursive amplitude map, so the cycle-time budget and slew limit hold structurally without repair or penalty. A coupling-aware multi-fidelity Bayesian optimizer (CAMBO) reads cross-block curvature from a three-level autoregressive surrogate to switch between joint and alternating search, and measured dynamic resistance is assimilated by an unscented Kalman filter. The optimizer reaches the target hypervolume with 26% fewer evaluations at a fully feasible search, and the selected design gains 16.9% shear strength with 13.3% less energy than the incumbent. Equal-heat trials confirm that timing governs strength.