Porous aluminum with a porosity of 78% and pore size of 850-1000 mm was fabricated under various sintering pressure, sintering time and raw Al powder size conditions by the spacer method consisting of spark plasma sintering (SPS) and sodium chloride (NaCl) dissolution. The effects of the fabrication conditions on compressive properties of the porous Al were investigated. The sintering pressure of 20 MPa and sintering time of 10 min were needed to fabricate robust porous Al under the sintering temperature of 843 K and raw Al powder size of 3 mm. Also, the porous Al specimen fabricated from Al powder of 300 mm exhibited much lower flow stress than those fabricated from Al powder of 3 and 20 mm when employing the temperature of 843 K, the pressure of 20 MPa and the duration time of 10 min. This indicates that the raw Al powder size is needed to be much smaller than the spacer size. This is because the Al particle cannot touch with adjacent Al particles when the Al powder size is comparable to the spacer size.
Porous aluminum with a porosity of 78% and pore sizes of 850-1000 mm was produced by the spacer method including spark plasma sintering (SPS) at various sintering temperatures of 773-853 K and the dissolution of space-holding sodium chloride particles. The effect of sintering temperature on the compressive properties of porous Al was investigated. The stress-strain curves for the specimens fabricated at 813 K and higher exhibited a plateau region with a nearly constant flow stress to a large strain of about 40%. However, the specimens fabricated at less than 813 K showed no plateau regions, although there were no significant differences in the characteristics of the pores by macroscopic observation between the porous Al specimen fabricated at 843 K and that fabricated at 773 K. Microscopic observation revealed that there were large voids in the cell wall of the specimens fabricated at 773 K, showing that sintering was insufficient and the connection of Al powder was poor. Furthermore, the fully-dense Al specimen fabricated at 793 K exhibited poor ductility in tension. Therefore, poor ductility in tension of cell walls may be responsible for the lack of plateau regions in the specimens fabricated at less than 813 K.
Compressive properties at 573-773 K of porous aluminum produced by the spacer method were investigated and compared with those of bulk reference aluminum with the same chemical compositions. The stress exponent and activation energy for deformation at elevated temperatures in the porous aluminum were in agreement with those in the bulk reference aluminum. In addition, the plateau stress of the porous aluminum was comparable to the stress of the bulk reference aluminum upon compensation by the relative density. Therefore, it is conclusively demonstrated that the mechanism of deformation at elevated temperatures in the porous aluminum is the same as that in the bulk reference aluminum. This is likely due to the homogeneous microstructure in the porous aluminum produced by the spacer method.
Compressive tests at temperatures of 573-773 K with initial strain rates of 8:0 Â 10 À4 -2:0 Â 10 À1 s À1 were carried out on a closed-cell aluminum foam and its bulk reference aluminum (a cell wall material of the aluminum foam). As a result, the stress exponent and the activation energy for elevated temperature deformation of the aluminum foam were in agreement with those of the bulk reference aluminum. In addition, upon compensation by the relative density, the plateau stress of the aluminum foam was comparable to the stress of the bulk reference aluminum. It is concluded that the elevated temperature deformation mechanism in the aluminum foam is essentially the same as that in the bulk reference aluminum.
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