High-Porosity Closed-Cell Aluminum Foams Produced by Melting Method Without Stabilizer Particles
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00528-w
Abstract Closed-cell A356 aluminum foams have been produced by the addition of calcium carbonate (CaCO3) powder as a foaming agent to the molten aluminum without any stabilizer particles. The foaming process is performed by the addition of 2.5–3.5 wt% CaCO3 and has relative density ranges of 0.12–0.44 and cell sizes of 1.5–3.1 mm with uniform cell structures. The foaming stabilizing mechanism and effect of foaming conditions such as the amount of foaming agent, casting holding and mixing time at the furnace on the foamed samples were investigated. The stabilizing mechanism is because of the foaming gas (CO2)/ melt reaction during the foaming procedure and producing
some solid particles such as CaO, Al2O3 and MgO. The optimum foamed aluminum with uniform cell size distribution was obtained at 4-min mixing time and 10-min holding time with 3 wt% CaCO3 foaming agent. The porosity of aluminum foam increased as the holding time increased from 60 to 86%. Also, the average cell size increased from 1.5 to 3.1 mm when the amount of CaCO3 increased from 2.5 wt% to 3.5 wt%, respectively.
Introduction
cost.4–6 Therefore, there is a need for another foaming agent having a slower decomposition rate and lower cost. An alternative foaming agent suitable was calcium carbonate (CaCO3), which was used in the FOAMCARP process previously.7–9[ Gergely et al. reported that the decomposition characteristics of CaCO3 are suitable for foaming of aluminum melts.7 Haesche et al. also studied the foaming of Al–Mg alloy with CaCO3 foaming agent.8 They showed that aluminum foams with high porosity levels and finer cell sizes than TiH2 can readily be produced.7,8
Metal foams are structural materials in which gas bubbles are separated by thin walls and volume fraction of matrix alloy is very low. In recent years, there have been strong demands for lightweight aluminum foams to be used in automotive and aerospace applications, where weight reductions and energy absorption are needed.1–3 Closed-cell aluminum foams can be produced by adding a foaming agent to the molten aluminum and simultaneous stirring. The most commonly employed foaming agent for aluminum alloys is titanium hydride (TiH2), owing to its high specific hydrogen content, a reasonably good correspondence between its decomposition temperature and typical alloy melting temperatures and rapid kinetics of the decomposition reaction. But there are three problems in foaming with TiH2 particles: premature gas release during hydride dispersion in the melt, presence of solid particles such as SiC and Al2O3 to stabilize molten foam and high
International Journal of Metalcasting
Keywords: A356 aluminum foam, calcium carbonate, cell size, inhomogeneity, stabilizer particle
Generally, solid particles were employed in the foaming process to stabilize the aluminum foams. Many researchers have investigated the effects of ceramic particles on the stabilization of aluminum foams and reported that these solid par
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