Fabrication of Aluminum Foam by Centrifugal Casting Using Calcium Carbonate as Foaming Agent

Abstract

  This study clarifies that high porosity aluminum foam can be produced by combining investment casting and centrifugal casting, using CaCO₃ powder as a foaming agent. The conditions of centrifugal casting for producing high porosity foamed aluminum alloys were investigated through experiments. A master model was obtained by using a stereolithography 3D printer to produce a castable resin, and then a plaster mold was produced using the master model. ADC12 aluminum alloy was melted in an electric furnace at 600℃, and 3 mass% CaCO₃ powder (particle size : under 125 μm) preheated to 600℃ was added to the melt. Centrifugal casting was performed by pouring melt into a plaster mold preheated to 600℃ and rotating the mold at 1100 rpm. The obtained precursor was cut into the specimens of φ15 × 10 mm³ in size, which were then heated in an electric furnace at 800℃ for 8 min to perform foaming tests. A maximum porosity of 51% could be obtained by using a combination of investment casting and centrifugal casting. The specimen cut from near the pouring basin foamed strongly when centrifugal force was not applied. The specimen cut from the position furthest from the pouring basin foamed strongly when centrifugal force was applied at 1100 rpm for 30 s. This is considered to be due to the sedimentation of CaCO₃, whose density is higher than that of the melt, by the centrifugal force. These results suggest that in order to obtain a precursor with uniformly dispersed foaming agent particles by centrifugal casting, CaCO₃ powder with a wide diameter distribution should be used, and sedimentation speed should be varied between the particles.