Process of Simultaneously Fabricating and Foaming Precursor Using Frictional Heat Generated During Friction Stir Welding

Precursor foaming is one of the processes used to produce aluminum (Al) foam. This process fabricates a foamable precursor by mixing a blowing agent powder with solid Al. Then, the fabricated precursor is foamed by heat treatment. In this study, the process of simultaneously fabricating and foaming the precursor was attempted by friction stir welding (FSW). A double-sided FSW was used. Al plates and a blowing agent powder were set in the groove of a steel plate, and the precursor was fabricated using a preceding upper tool. Simultaneously, the fabricated precursor was foamed by pressing and traversing a lower tool from the back of the steel plate slightly behind the upper tool. It was shown that FSW was successfully conducted on Al–Si–Cu ADC12 alloy plates using the upper tool, and the precursor was gradually foamed with the traversal of the lower tool. It was indicated that the blowing agent and stabilization agent powders were thoroughly distributed in the stirred region regardless of the tool traversing rate in the range v = 30–50 mm/min. The tool traversing rate of v = 30 mm/min was appropriate for sufficient foaming and to obtain Al foam with good pore structures of the entire Al foam. From these results, it was shown that fabricating of precursor and foaming of the obtained precursor can be simultaneously conducted by FSW in a single process.