Effects of Er on microstructure and corrosion resistance of degradable Mg-Al-Zn-Mn magnesium alloy

• Er addition promotes grain refinement during solidification by increasing nucleation rate and forming Al3Er secondary phase. • A dense MgO/Er2O3 composite oxide layer is formed, suppressing loose magnesium hydroxide/basic magnesium carbonate. • Mn interacts with Fe impurities to form AlFeMn phase, reducing micro-galvanic corrosion driving force. • The corrosion rate of AZ31Mn-1.2Er in 3.5% NaCl solution decreased from 10.46 mm/a to 0.44 mm/a, approaching the 0.2–0.5 mm/a target for bone-repair implants.