Microstructural and mechanical enhancement of AA2024 via multi-pass friction stir processing with HEA (FeNiCrAlCu) particle reinforcement

Friction stir processing (FSP) is an effective solid-state technique for fabricating aluminum-based metal matrix composites (MMCs) with refined and homogeneous microstructures. In this study, HEA (FeNiCrAlCu) powders were incorporated into AA2024 aluminum alloy via multi-pass FSP using 1, 2, and 3-passes. The effects of pass number on microstructural evolution, mechanical properties, tribological behavior, and corrosion resistance were investigated using SEM, XRD, hardness, tensile, wear, and electrochemical corrosion tests. Increasing the FSP pass number promoted progressive fragmentation and more uniform dispersion of HEA particles, as supported by SEM observations and ImageJ-based measurements, resulting in a more homogeneous composite structure. This microstructural improvement directly enhanced the mechanical, wear, and corrosion performance of the composites. For the 3-pass FSPed composite, hardness increased from 155 to 258 HBN, tensile strength from 188 to 246 MPa, and uniform elongation from 3.0 ± 0.5 to 3.6 ± 0.3 mm compared with the base AA2024 alloy. In addition, corrosion current density decreased from 6.94 to 1.36 µA, corrosion potential shifted from − 703 to − 548 mV, and corrosion rate decreased from 14.79 to 3.11 mpy. The 3-pass FSPed composite also exhibited the lowest volumetric wear rate and a more stable friction response.