Lightweight Metal–Polymer Interpenetrating Phase Composites for Mechanical Reinforcement and Absorption‐Dominant Electromagnetic Interference Shielding

The pursuit of multifunctional lightweight materials with electromagnetic interference (EMI) shielding of low reflection, programmable architecture, and robust mechanical performance presents both significant opportunities and challenges. In this work, aluminum (Al)‐alloy lattice with 90% porosity was designed and fabricated using additive manufacturing. Following epoxy infiltration, the resulting Al/epoxy interpenetrating phase composites (IPCs) exhibit not only markedly enhanced compressive strength and exceptional energy‐absorption capability but also superior EMI shielding performance in the X‐band (8.2–12.4 GHz), even under extreme environmental conditions such as elevated temperature and acidic environments. Both single‐phase metal lattices and Al/epoxy IPCs were systematically studied to elucidate their mechanical behavior. Compared with the underlying single‐phase lattices, the Al/epoxy IPCs exhibit constitutive responses characterized by significantly higher peak stress, a more stable plateau stress, and markedly enhanced toughness under compression. Moreover, the Al/epoxy IPCs exhibit effective EMI shielding performance dominated by absorption‐driven attenuation. This behavior arises from the reduced impedance mismatch at the composite surface and multiscale attenuation mechanisms within the porous, interconnected metal framework. Upon incorporating an Al foil as a reflective backing layer, the resulting hybrid IPC systems simultaneously achieve high total shielding effectiveness (exceeding 74 dB) and elevated absorptivity (0.63), effectively suppressing secondary electromagnetic reflections. This design strategy effectively transforms conventional metal‐based EMI shields from reflection‐dominant to absorption‐dominant behavior, offering a promising pathway for multifunctional structural EMI shielding materials with strong potential for aerospace, defense, and advanced electronic applications.