Foaming conditions of porous aluminum in fabrication of ADC12 aluminum alloy die castings by friction stir processing

Porous aluminum is expected to be used as a multifunctional material because of its light weight, high energy absorption and high sound- insulating properties. Recently, a precursor method based on FSP has been developed to improve the cost-effectiveness and productivity of fabricating porous aluminum. Aluminum alloy die castings have the advantages of high productivity, low cost and high recyclability. Thus, it is expected that, by using aluminum alloy die castings in the FSP route, the improved cost-effectiveness and productivity of porous aluminum can be realized. In this paper, the most important parameters of the precursor method, i.e., the holding temperature, holding time and the amount of alumina powder added to the precursor as a stabilization agent, were considered. Experiments under two sets of conditions were carried out to fabricate porous aluminum with high porosity and high quality (a uniform pore size distribution with highly spherical pores). It was shown that closed-cell porous aluminum with a porosity of about 65% was successfully fabricated using ADC 12 aluminum alloy die castings. When the holding time during foaming was fixed at 12 min, high-porosity and high-quality porous aluminum was obtained by adding 10 mass% alumina at holding temperatures of 933 K and 963 K (slightly higher than the melting point of ADC 12 aluminum alloy). Whenthe amount of alumina added was restricted to 5 mass% and the holding temperature was fixed at 933 K or 963 K, it was demonstrated that high-porosity and high-quality porous aluminum can be obtained with a holding time of lOmin and a holding temperature of 933 K.