Influence of Mn content on mechanical properties and fatigue behavior of extruded Mg alloys

Effect of manganese addition, which has been known to improve formability during extrusion, on mechanical properties and fatigue strength was investigated to confirm the total performance of the Mn addition to the magnesium alloys. The grain size decreased with increasing Mn content and attained a constant grain size at the Mn contents higher than 0.4 wt%, where the Mn–Al–Mg intermetallic particles were precipitated. The tensile strength and hardness increased with increasing Mn content and attained a constant value at the Mn contents higher than 0.4 wt%, which was consistent with the grain size variation. The fatigue life increased with increasing Mn content and attained a constant value similar to the case of tensile strength. However, the fatigue life was significantly reduced at the Mn content of 0.79 wt%. It is speculated to result from a large number of precipitated intermetallic particles, which would degrade the fatigue crack growth resistance. The magnesium alloys with Mn contents between 0.4 and 0.6 wt% have a good balance of mechanical properties and fatigue strength.