Enhancing Mechanical and Corrosion Properties of a Cr₉Fe₄₆Ni₁₅Mn₃₀ Medium-Entropy Alloy through Synergistic Al/Ti Microalloying and Aging

This study systematically investigates the synergistic effects of Al/Ti microalloying and subsequent aging treatment on the microstructure and properties of the Cr₉Fe₄₆Ni₁₅Mn₃₀ high-entropy alloy. The results demonstrate that Al and Ti additions induce pronounced grain refinement, reducing the average grain size from 5.2 μm to 1.52 μm, promote the formation of nanoscale Al/Ti-rich precipitates together with ~0.7 % body-centered cubic (BCC) phase, and decrease the recrystallization fraction to 92.1 %. Subsequent aging at 600 °C further improves microstructural homogeneity, increases the recrystallization fraction to 99.2 %, and reduces the kernel average misorientation (KAM) to 0.07°. Mechanical testing reveals that microalloying enhances the tensile strength to 708 MPa and significantly lowers the hydrogen embrittlement sensitivity index (δH) to 2.6 %. After aging, a pronounced hydrogen-induced plasticity effect is observed, with δH decreasing to −16.8 % and the elongation after hydrogen charging increasing to 29.2 %. In addition, the aged Al/Ti-microalloyed alloy exhibits superior corrosion resistance, characterized by the most positive corrosion potential (−0.279 V), the lowest corrosion current density (6.39 × 10⁻⁷ A·cm⁻²), and the largest capacitive arc radius in electrochemical impedance spectroscopy. These improvements are attributed to the formation of a stable Cr₂O₃ passive film and a reduced defect density.