Explosive-welding–induced matrix microstructural gradient: role in strength prediction and structural response

Heterogeneous laminated metallic composites are widely applied in aerospace, defense, and energy equipment. However, most existing studies have mainly focused on interfacial bonding characteristics, while systematic investigations on the gradient evolution of base microstructures induced by explosive welding and their effects on material deformation and failure behavior remain limited. In this study, a TA1/Q235B laminated composite fabricated by explosive welding was investigated. Using multiscale characterization techniques including EBSD, TEM, nanoindentation, and in-situ μCT tensile testing, it was revealed that a gradient structure in grain size and dislocation density was formed within the base material. This microstructural gradient not only significantly enhances the tensile strength of the laminated composite but also influences, to some extent, its deformation behavior and fracture mechanism. Accordingly, a modified rule of mixtures (MROM) considering the gradient characteristics of the base microstructure was constructed. Compared with the traditional method, it can significantly improve the predictive accuracy of strength for laminates with different thickness ratios. During the tensile process, the material response exhibits a four-stage evolution mechanism of “elastic stage—early yielding of Q235B—interfacial instability caused by strain incompatibility—crack propagation into TA1 and final failure.” Among them, the multiscale structural heterogeneity of the base material governs the distribution of interfacial shear stress, the crack propagation path, and the transition of fracture modes. Fracture surface analysis shows that the TA1 side evolves from an early mixed ductile–brittle fracture into a ductile fracture dominated by intervoid necking, while the Q235B side mainly exhibits ductile fracture characterized by intervoid shearing and coalescence. The results of this study promote the development and application of explosive welding technology in high-performance heterogeneous laminated composites.