OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 without the use of stabilizer powder. They take Al356 aluminum alloy for making the metallic foam. The aluminum alloy is heated above its melting point. After the aluminum melts (~700 °C), CaCO3 is added to the melt and the decomposition of the foam agent begins and as a result of decomposition gas (CO2) is released. CaCO3 should be mixed uniformly with the help of stirrer. Here controlled parameters are speed of rotation of the stirrer, amount of foaming agents, stirring time, temperature, gas bubbles rise speed and melt viscosity. Stirrer casting setup is shown in fig. 3. These parameters affect the cell size, relative density, porosity of the metallic foam. Pore size and its distribution affect the strength, sound insulation, and thermal properties, etc. By controlling the size of the bubbles formed during the formation of gas inside the melt, the researcher controls the pore size and their distribution [10]. By adding additives into the molten metal, which increase viscosity, stabilize the cell walls and prevent the bursting of bubbles, the correct foam structure is created [11]. Porosity and pore size are controlled by holding time and amount of CaCO3. As the calcium carbonate content increases, the pore size increases, which negatively affects the cell size, porosity, and relative density. It means cell size, porosity and relative density decreased, increasing in the amount it is sure to there is in increment in porosity level but simultaneously reduction takes place in the pore size [12]. Compressive properties of metallic foam depend on the porosity, cell size and relative density. Relative density and cell homogeneity are factors affecting the strength of the metallic foam. Compressive strength and energy absorption capacity increase with increasing cell size. Both of these properties deteriorate as the amount of CaCO3 in the molten metal increases. The porosity of foam metal depends on the foaming temperature, because it affects density; the compressive strength of foam metal depends on it to a lesser extent, but strongly depends on the stirring time [13]. Fig. 3. Stirrer casting setup [12] Two metallic alloys are manufactured by the two different methods: stir casting and inflation; both have the same compressive strength, but less porosity is obtained in case of implementing stir casting method as compared to infiltration one. Metal foam produced by infiltration is used to obtain higher strain rates. The strain rate will be high in the case of high porosity; high porosity is achieved by adding a large amount of foaming agent to the metal – 10 % or 15 % [14]. Researchers are trying to optimize the various parameters to achieve the best mechanical properties and surface structure, pore size, relative density, etc. C.C Yang assumed that that there is no need to control the rate of decomposition, since it is important to control the dissolution of the foaming gas in the molten metal and it should be directly proportional to each other. If this does not happen, the foam structure will be unstable. The efficiency of foaming molten metal with hydrogen gas is 17 %. Therefore, it is necessary to use a foaming agent in an appropriate amount, since
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