Precipitation hardening and microstructures of rapidly solidified Mg−Zn−Ca−X alloys

Two quaternary magnesium alloys based on ternary Mg-5wt.%Zn-4wt.%Ca containing either Co(2wt.%) or Zr(0.5wt.%) were rapidly solidified using melt spinning. The nano-scale second phase distribution and thermal stability were studied using TEM, STEM and EDS system. Microhardness measurements conducted in the aged condition have identified that the Mg−Ca−Zn−Co alloy presented a peak value at 150°C followed by a hardness decrease. The Mg−Ca−Zn−Co alloy showed refined quaternary precipitates distributed along the cell boundary and a refined grain structure, yielding higher hardness values than the Mg−Ca−Zn−Zr alloy at all aging temperatures.