Foaming of aluminum foam precursor during friction stir welding

Al-Si-Cu alloy ADC12 precursor, fabricated by the friction stir welding (FSW) route, was foamed during the traversing of an FSW tool along a steel plate. The ADC12 precursor can be sufficiently foamed at a tool traversing rate of v = 10 mm/min. The precursor began to foam as the tool approached the precursor and gradually foamed as the tool traversed. There is an optimum tool traversing rate to induce sufficient foaming of the precursor. ADC12 foam obtained with v = 10 mm/min sufficiently foamed, had a porosity of around p = 75%, and had pores throughout the entire foam with almost constant porosity along the traversing direction. ADC12 foam obtained with v = 20 mm/min did not sufficiently foam, had a porosity below p = 50%, and had dense parts without pores throughout the entire sample. The temperatures of the steel during FSW for v = 10 mm/min and v = 20 mm/min exhibited a similar tendency. The temperature of the ADC12 precursor during FSW for v = 20 mm/min was much lower than that for v = 10 mm/min. This is because the temperature of the precursor was not sufficient for the precursor to surpass the solid-liquid coexistence state because the high tool traversing rate resulted in insufficient heat input. v = 10 mm/min was sufficiently slow to provide the heat required for the precursor to surpass the solid-liquid coexistence state and to exhibit a higher temperature than the liquidus temperature, resulting in sufficient expansion of the ADC12 foam.