Abstract
A powder metallurgical technique for the production of foamed cellular metals with very low apparent densities has been studied. Aluminum powder mixed with a powdered foaming agent, e.g. titanium hydride or zirconium hydride, is extruded at an elevated temperature below the decomposition temperatures of the foaming agents to achieve gas-tight fully densed compacts. Expansion into a porous cellular aluminum is performed by heating the compact to decompose the foaming agent to evolve gas. As the resistance of the aluminum matrix against expansion rapidly decreases by melting, a highly porous cellular aluminum is obtained by heating the compact in a temperature range above the solidus line of the matix. The foamed aluminum produced by free expansion usually shows excessive bulging which is accompanied with a rather large surface roughness and micro-cracks on its bulged surface. A use of a steel sleeve to restrict the bulging of the compacts during expansion is effective both to improve the surface quality and to achieve a higher porosity of the foamed products by preventing the evolved gas to leak.
