Improvement in electromagnetic shielding effectiveness and mechanical properties of ultrafine Mg98.5Zn0.5Y alloy via friction stir processing

• Achieved simultaneous enhancement in mechanical properties and EMI SE of Mg 98.5 Zn 0.5 Y alloy through FSP. • Refinement of LPSO phases and grain size is a key factor for strength and EMI performance improvement. • Mg 98.5 Zn 0.5 Y alloy sheets show a promising combination of lightweight, high strength, and full-spectrum EMI shielding effectiveness. • Provides a new strategy for designing Mg-based alloys with optimized mechanical and shielding properties for advanced electronic and automotive applications. • The study reveals the key role of multi-pass FSP in microstructure control and enhancement of EMI shielding materials. A novel Mg 98.5 Zn 0.5 Y alloy sheet with ultrafine grains and exceptional electromagnetic shielding performance has been fabricated using friction stir processing (FSP). This study investigates the impact of FSP on the microstructure, mechanical properties, and electromagnetic interference (EMI) shielding effectiveness (SE) of the alloy, specifically across three distinct layers within the stir zone (SZ): Top, Middle, and Bottom. The results reveal that the Mg 12 YZn long-period stacking ordered (LPSO) phase is the predominant structure, undergoing significant grain refinement. The grain size is drastically reduced from 1.5 mm in the as-cast state to 12.6 µm, 10.0 µm, and 7.1 µm in the Top, Middle, and Bottom, respectively. This grain refinement and fragmentation of the LPSO phase into nanoscale particles result in a substantial enhancement of mechanical properties. The ultimate tensile strength (UTS) reached 358.2 MPa with an elongation (EL) of 15.1%, reflecting a 344% increase in strength and a 733% improvement in ductility compared to the as-cast material. Simultaneously, the EMI SE was maintained between 70 and 110.4 dB over a broad frequency range (30–4500 MHz). Despite the nanoscale LPSO particles contributing minimally to EMI shielding, the lamellar LPSO structure demonstrated excellent performance through multiple electromagnetic wave reflections within the matrix. These findings underscore the dual benefits of FSP in improving both mechanical strength and electromagnetic shielding effectiveness, positioning this Mg 98.5 Zn 0.5 Y alloy for advanced applications in the electronics and telecommunications sectors.