Abstract ▼ AI-Helper

Metal foams are very emerging materials as their manufacture involves the simultaneous occurrence of solid, liquid and gaseous phases at varying temperatures and the morphology of the solidified foam is quite complex. And the stabilization mechanism for metal foams has not yet been discussed in the ...

Metal foams are very emerging materials as their manufacture involves the simultaneous occurrence of solid, liquid and gaseous phases at varying temperatures and the morphology of the solidified foam is quite complex. And the stabilization mechanism for metal foams has not yet been discussed in the literature. In this study, Al alloy foams with high porosity were fabricated by melt foaming process. In the melt foaming process, Ca and TiH2 are used to thickening and foaming agent. Ca is reacted with oxygen that form ceramic particle at the thickening period. The molten Al alloys were put in a furnace for a specific period to make it reach the temperature appropriate for foaming. Thickening and foaming agent were added to the molten Al alloys at a specific temperature, which was stirred. For uniform distribution of thickening and foaming agent, the impeller was rotated with high-speed about 400-1000rpm. When left in a furnace for a specific period after uniform dispersion of the foaming agent, gas was generated from the foaming agent and the cell size and distribution inside Al alloys foam could be controlled by the viscosity and surface tension of the molten Al alloys. Silicon carbide, aluminum oxide or other ceramic particles can be used to make aluminum alloys amenable to foaming. Typical volume fractions of the reinforcing particles range from 10 to 20%, mean particle sizes from 5 to 20 ㎛. Mechanism of pore formation is determined to use SEM, XRD apparatus. The compressive experiments were done on Al alloy foam and strain rate is 2 mm/min. Compressive test is conducted by Instron dynamic material tester(INSTRON 8872). The particles present in the melt are collected by the rising bubbles, attach to the metal/gas interfaces and prevent them from bursting when they reach the top surface or the metal. Particle size and volume fraction play an important role to foaming stability. Obviously, a critical concentration of particles is required to stabilize foams made by bubbling gas through a metal melt. The rising bubbles become stale when the critical surface coverage by particles is achieved. The number of particles encountered and picked up by the rising bubbles depends mostly on the distance travelled by the bubbles and the volume fraction of particles in the melt. It was attributed to formation of sub-micron sized magnesium-containing oxide particles in a form of spinel as a result of the interplay of various particles with aluminum oxide film on the surface of pores. The pore diameter was increased with increasing holding time at optimum foaming temperature. It was found that there were a closed relation for kinetic analysis by Ostwald ripening.

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