Ultrafast electromagnetic annealing for cold-deformed sandwich shaped copper/steel/copper composite material

Conventional annealing of copper/steel/copper laminates faces a fundamental thermal conflict, as the required recrystallization temperature for steel exceeds the melting point of copper. Here, pulsed current treatment (500 V, 330 Hz, 65 μs, 180 A/mm²) applied at 700 °C for 2 min results in a simultaneous increase in elongation from 15% to 54% while retaining a tensile strength of 713 MPa. Microstructural analyses reveal that accelerated copper/steel interdiffusion widens the interface by 35.7%, transforming the bonding from mechanical to metallurgical, while reduced dislocation activation energy alleviates strain accumulation and residual stress, shifting the steel-side grain-size distribution from bimodal to normal. In addition, this treatment promotes carbide phase transformation, such as the transformation from metastable CrO₂ to stable Cr₂₃C₆ and CrC, thereby enhancing microstructure stability and reducing interface energy. This work demonstrates that pulsed current treatment enables precise regulation of microstructure and mechanical properties in multi-material systems, offering a viable pathway to overcome conventional annealing limitations.