High-strength materials lack a synergistic combination of mechanical properties and corrosion resistance desired for most structural applications. Phase and grain boundary architecturing is done in the material to attain balance in these properties. A friction stir processed Fe 38.5 Mn 20 Co 20 Cr 15 Si 5 Cu 1.5 (Cu-HEA) exhibited excellent mechanical properties and high corrosion resistance in synergy. The excellent mechanical properties were attributed to the controlled transformation of ultrafine γ matrix and ε twinning; whereas good corrosion resistance was due to homogenized fine grained γ microstructure. In short, Cu-HEA design opens a new pathway towards realizing strong and ductile alloys with tunable corrosion resistance by engineering matrix metastability. © 2019 Elsevier Ltd.