The influence of manganese on the microstructure and mechanical properties of AZ31 gravity die cast alloys

Calculated phase diagrams for the Mg–Al–Zn–Mn system indicate that β-Mn(Al) and Al8Mn5 can primarily crystallize during the solidification of Mn-modified AZ31. Both phases may act as potential heterogeneous nucleants for Mg grains and thus as potential grain refiners in the Mg–Al system. In this investigation three Mg–3Al–1Zn alloys with different Mn content were die cast and hot rolled at 450 °C. The influence of the Mn content on the microstructural evolution and mechanical properties after hot rolling was studied. After casting, β-Mn and Al8Mn5 are present in all three AZ31 alloys without showing a significant influence on the grain size. The potential of β-Mn and Al8Mn5 precipitates for grain refinement in AZ alloys is discussed in detail on the basis of solidification kinetics.