New Insights into Fabrication of Al-Based Foam with Homogeneous Small Pore-Structure Using MgCO3/Zn Composite Powder as a Foaming Agent

The Effect of Foaming Agents on the Thermal Behavior of Aluminum Precursors

Various foaming agents can be used to achieve foaming of the precursors obtained by using the powder metallurgy method. However, the thermal behavior of pure aluminum precursors with different foaming agents has been studied very little in recent times. For the production of aluminum foams with closed cells, 1 wt.% of calcium carbonate (CaCO3), titanium hydride (TiH2), heat-treated TiH2 and zirconium hydride (ZrH2) were used. The foaming capability of the compacted precursors was investigated at temperatures 700, 720 and 750 °C. CaCO3 and TiH2 showed the best foamability at all considered temperatures, while ZrH2 achieved relatively good foaming only at the highest temperature, 750 °C. Due to their low onset temperature of the decomposition compared to the melting point of the unalloyed aluminum, in hydride-based foaming agents the drainage occurred at the bottom part of the foam samples. Among the investigated foaming agents, precursors with heat-treated TiH2 had the worst foaming properties, while CaCO3 showed the best foamability without the occurrence of drainage.

Fabrication and Characterization of Porous Copper with Ultrahigh Porosity

The fabrication of porous copper with ultrahigh porosity by adding 90% spacer content was an unsolved technical problem in the field. In this study, the green compacts placed on a layer wire mesh during the decomposition process of needlelike carbamide as space holder with volume content up to 90% was successfully conducted to fabricate nondestructive porous copper. Compared with the green compacts directly placed on an alumina plate, the use of this support was crucial for manufacturing highly-porous copper. Characterization of macro- and microscopic morphologies as well as quasi-static compressive test for the obtained porous copper samples was carried out. The results show that the porosity of porous copper samples with 87.3% was slightly smaller than the spacer content. The SEM observation indicates that the internal pores of porous copper formed an open-cell structure and its skeleton was very dense. The compressive tests show that the stress–strain curve of a porous copper sample exhibits the typical characteristics of elastic-plastic metal foam. The energy absorption properties of porous copper samples were also comparable. This study provides a possibility for the preparation of porous copper and other metals with ultrahigh porosity by the well-known space holder method.