Effects of tool rotating rate and pass number on pore structures of ADC12 porous aluminum fabricated by friction stir processing

Closed-cell porous aluminum is expected to be used in automobile components, because porous aluminum has good lightweight properties and can realize the improvement of fuel efficiency. Recently, a new processing route for fabricating porous aluminum, in which friction stir processing (FSP) is used, has been developed. In the FSP route, a precursor is fabricated by mixing blowing agent powder and stabilization agent powder into aluminum alloy plates by the significant stirring action of FSP. In this contribution, ADC12 porous aluminum is fabricated by the FSP route using high recyclability ADC12 aluminum alloy die castings and the effect of the tool rotating rate and the number of passes on the porosity and morphology of the pores is investigated. It is shown that groove-like defect was formed because of abnormal stirring action at any tool rotating rate. However, by applying multi-pass FSP, the defect disappeared at 800 and 1000 rpm. On the other hand, the defect remained at 1200 and 1400 rpm instead of carrying out 4 pass FSP. The porosity and the morphology of pores of obtained porous aluminum were affected by these defects. It is shown that closed-cell porous aluminum with uniform pore size distribution and with porosity of about 50-60% is successfully fabricated using ADC12 aluminum alloy die castings at the tool rotating rate of 800-1000 rpm and a holding time of 10 minutes and a holding temperature of 933 K.