High temperature compressive behavior of closed-cell Al foams

This work deals with the compressive behavior of closed-cell Al foams at high temperature. Al foams have been manufactured with the powder compacted method, mixing together powders of Al, stabilizing agent (SiC) and blowing agent (TiH2). Foams containing 0.4 wt% TiH2 and 2.8 wt% SiC have been manufactured. By pressing (12 t) the mixed powders inside a mold, cylindrical precursors (diameter 16 mm) have been obtained. After that, each precursor has been inserted inside the oven at 700 degrees C in a suitable copper crucible for the time required for liquid foam expansion. Successively the crucible has been water quenched in order to obtain such a porous structure at ambient temperature. Mechanical characterization of the manufactured foams has been performed in compression employing a MTS machine at constant crosshead speed (2 mm/min) up to the maximum load of 35 kN. In thermostatic chamber 25 degrees C, 100 degrees C, 200 degrees C and 300 degrees C have been selected for mechanical testing. For the different temperatures relative density, elastic limit, Young modulus, plateau stress and specific absorbed energy have been compared. At increasing test temperature the reduction of the elastic limit and Young modulus has been evidenced as well plateau stress and the whole stress-strain curve. Consequently also the absorbed energy has been considerably reduced. At the same time it has been found, in correspondence of the same applied load, a greater deformation at increasing temperatures. It can be concluded that compressive behavior and energy absorption decrease as temperature increases.