Microstructure of high pressure die cast AZ91D modified with Ca and Ce

High pressure die cast (HPDC) AZ91D (Mg–8.8 wt%Al–0.74 wt%Zn–0.29 wt%Mn) modified with Ca and Ce was investigated. Thermodynamic calculations of liquid/solid equilibrium were confirmed by DTA measurements and solid/liquid equilibrium at various temperatures between the liquidus and solidus temperatures.The solidification path of HPDC AZ91 and AZ91 modified with Ca and Ce was calculated using the Termo-Calc program. The microstructure was investigated utilizing optical and electron (SEM) microscopy.The phases Mg17Al12, αMg, Al8Mn5, Al2Ca, and Al4CeMg4 were found. Their volume fractions and the composition of the residual melt as functions of the temperature were determined. The microstructure, the distribution of the alloying elements in the matrix, and the precipitation during exposure to elevated temperatures as well as their effect on creep properties are discussed.