Foaming behavior of aluminum foam precursor induced by friction heat generated by rotating tool used for spot friction stir welding

摘要

A precursor foaming process can be used to fabricate aluminum (Al) foam. In this study, Al foam precursors were foamed by a friction heat foaming process (FHFP), i.e., the precursors were foamed only by the friction heat generated between a rotating tool used for spot friction stir welding (FSW) and a Cu plate, and the transmission of the generated friction heat in the Cu plate. The effect of the distance between the precursor and the rotating tool on the foaming behavior in the FHFP during spot FSW was investigated to determine whether the precursor can be foamed if the rotating tool is apart from the precursor. Two Al alloys with different melting points, ADC12 Al-Si-Cu alloy and A1050 commercial purity Al were used. The foamable precursors were fabricated by the FSW route. It was found that a precursor can be foamed by the FHFP involving spot FSW even when it is some distance apart from the tool. For ADC12 foam, a high expansion ratio was achieved owing to the achievement of a much higher temperature than the solidus temperature. In addition, each pore was small, especially in the upper part above the Cu plate. Although increasing the distance between the rotating tool and the precursor decreased the rate of increase in the temperature and the maximum temperature for a given foaming time, the precursor can be sufficiently foamed by increasing the foaming time. For A1050 foam, although the expansion ratio was lower than that of ADC12 owing to its higher melting point, an expansion ratio of around 3.5-4.0 was achieved when the distance between the rotating tool and the precursor was appropriate. In addition, pores with almost the same size were distributed over most of the foam. It was found that Al foam can be fabricated using only energy-saving FSW from the fabrication of the precursors to the foaming of the precursors. (C) 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.