[en] Highlights: • Extrusion improves the discharge activity of Mg–Al–Pb–La alloy. • The relation between grain orientation and electrochemical corrosion behavior is clarified. • The extruded Mg-Al-Pb-La alloy is an appropriate anode for seawater-activated battery. A seawater-activated battery is a disposable reserve battery that is specifically designed to pollute less due to the absence or relatively less use of heavy metals. Mg–Al–Pb–La alloy is a typical anode material that is used in high-power seawater-activated batteries. In this study, we use microstructure characterization to demonstrate that hot extrusion refines the grains of the alloy and leads to the formation of banded structures composed of the lamellar β-Al₁₁La₃ and lump AlMn phases. Our electrochemical measurements reveal that the extruded Mg–Al–Pb–La alloy is a promising anode material that exhibits excellent discharge activity and high anodic efficiency at a large current density. Moreover, we also examine the correlation between the grain orientation induced by extrusion and the electrochemical corrosion behavior of Mg–Al–Pb–La alloy. We believe that our results can significantly contribute to the development of seawater-activated batteries.