Analyzing the influence of the investment casting process parameters on microstructure and mechanical properties of open-pore Al–7Si foams

Abstract

Aluminum alloy foams with high specific compressive strength and good energy absorption capacity are widely used as structural materials and shock absorbers. The investment casting process offers an interesting opportunity for the production of open-pore aluminum foams. However, foam casting differs from casting of solid parts, and there is a lack of practical knowledge about the microstructure tuning of the ultra-thin cast struts. Our study focuses on the influences of the casting conditions such as mold temperature on the microstructure and consequently on the mechanical properties of aluminum-silicon alloy foams. We investigated microstructural features using various metallography techniques and defined mechanical properties under uniaxial compression test. Here, we observed improvements in the strut microstructure together with decrease of the mold filling by reduction of the mold temperature. Microstructure improvements involve transformation of a single dendritic aluminum grain in each strut to globular grains along with a more homogeneous distribution of the silicon particles across the strut cross-section. These changes bring higher ductility and energy absorption efficiency to the foams, which are evident from the smoother plateau of the stress-strain curves. Decline of the mold filling, on the other hand, has negative effect on the overall mechanical properties.