Effect of Zn on the Structure and Mechanical Properties of Mg-Ca Foams

Mg-3Ca alloys with varying Zn concentration (0 to 5 wt pct) were foamed using CaCO₃ via liquid processing route and their compressive and energy absorption behavior were investigated. The Mg-Zn-Ca alloy foams revealed a uniform cell structure with minimum defects and improved expansion in comparison to Mg-3Ca foams without zinc. The cell wall microstructure of Mg-3Ca alloy foam revealed micro-cracks and MgO particle agglomerates at the gas-solid interfaces. Upon Zn addition, the micro-cracks were diminished to larger extent and finely MgO particles were dispersed homogenously at the gas-solid interface. Pore diameter of the foams decreased from 2.29 to 2.06 mm, while circularity improved from 0.60 to 0.72 with increasing Zn content from 0 to 5 wt pct. The peak compressive stress also improved from 1.64 to 5.09 MPa with 5 wt pct Zn addition to Mg-3Ca foam. The ductility number improved from 0.66 to 0.75 while retaining energy absorption efficiency ~ 60 pct in the plateau region. The improved mechanical properties of Mg-Zn-Ca foams are due to elimination of brittle Mg₂Ca and increase in the Mg₆Zn₃Ca₂. The reduced pore diameter, circular and equiaxed pores and crack-free interfaces in the foams were also contributed to the better mechanical properties.