The Influence of Calcium on the Primary Mg₂Si Phase in the Hypereutectic Mg-Si Alloys

Abstract

The microstructure of Mg-5Si alloy consists of the primary coarse Mg2Si phase, α-Mg solid solution and eutectic α-Mg + Mg2Si, in which eutectic Mg2Si phase solidifies in the form of Chinese script particles. When 0.2 wt.% of Ca was added to the Mg-5Si alloy the size of primary Mg2Si phase remained unchanged. The modification effect of calcium on the primary Mg2Si phase was effective only in the Mg-5Si-0.5Ca alloy. The morphology of the primary Mg2Si phase is changed from the coarse dendrite shape to polyhedral shape and the size of primary crystals is significantly reduced. The addition of 0.6 wt.% Ca to Mg-7Si alloy did not cause the modification of primary Mg2Si phase.

Compressive Deformation Behavior of Closed-Cell Micro-Pore Magnesium Composite Foam

“…It can be seen that cracks mainly propagate along the area where Ca and Si elements are enriched, suggesting the poisoning effect of the segregation of Ca atoms at the growth front of the Mg 2 Si [ 42 , 43 ]. Meanwhile, the addition of Ca refines the Mg 2 Si phase [ 44 , 45 ] and increases the amount of the Mg 2 Si phase, resulting in the increase of the cracks’ source during the compression process. Thus, compared with the magnesium alloy foam, the amount of cracks increases and the compressive stress applied to the matrix is dispersed, leading to a higher yield strength and energy absorption capacity of the magnesium composite foam.…”