Foaming behavior of blowing- and stabilization-agent-free aluminum foam precursor during spot friction stir welding

ADC12 die-casting precursors containing many gas pores were fabricated by the friction stir welding (FSW) route and were foamed by the FSW foaming process only using the friction heat during the indentation of the tool used for spot FSW. ADC12 precursors can be foamed by the friction heat generated during spot FSW without using TiH₂ as a blowing agent. ADC12 foams can be obtained without using Al₂O₃ as a stabilization agent. This is considered to be due to impurities contained in the ADC12 die-castings. ADC12 foams with Al₂O₃ exhibited a larger expansion ratio than those without Al₂O₃. ADC12 foams with Al₂O₃ had significantly finer pores than those without Al₂O₃. The pore diameters of the ADC12 foams with Al₂O₃ were approximately half of those of the foams without Al₂O₃. This is considered to be due to the higher viscosity of the ADC12 substrate containing Al₂O₃.