Modification of open-cell cast aluminum-silicon foams with strontium

Highlights

• Strontium modifies eutectic silicon in cast aluminum foams even at slow cooling rates during solidification below 0.5 °C/s
• Possibility of higher modification efficiency in confined solidification spaces such as micrometer-sized foam struts
• 3D morphology of eutectic silicon phase in Al-Si alloy observed under modified and unmodified conditions
• Sr addition (max 400 ppm) enhances peak/plateau compressive stresses, UTS, and deformation strains in Al-Si foams

Abstract

The mechanical properties of open-cell aluminum foams can be influenced by enhancing the microstructure of the struts. The foams produced by investment casting face slow cooling rates, which makes it challenging to improve the morphology of the phases. In the case of aluminum silicon cast foams, the silicon phase accumulates on the surface of the struts, which leads to brittle fractures. In the present study, we successfully modified the silicon phase in open-cell AlSi7Mg and AlSi10Mg cast foams by adding strontium and investigated the influence of the strontium content on the microstructure and mechanical properties at the foam and strut levels. Despite the cooling rates of less than 0.5 °C/s during solidification, the strontium addition of 200–800 ppm effectively decreased the size of the silicon particles and improved their distribution in the micrometer-sized struts. Improvements in the compressive properties of the foams and the tensile properties of the struts only occurred at the strontium levels of 200 and 400 ppm. The effective modification in this casting condition is due to the limited solidification space, which favors the formation of the atomic clusters responsible for the modification.