Detection of Phase Transition in Free-Cutting Al-Mg-Si Alloys by Resonant Ultrasound Spectroscopy
The transition temperatures of small amounts of eutectic particles contained in free-cutting aluminum alloys (namely AA6262 and AA6023) are investigated in this paper. Detection of the transition temperatures by conventional differential scanning calorimetry (DSC) measurements is difficult because of the small volume fraction (~ 1wt.%) of the eutectic. On the other hand, the melting of the particles induces small changes of elastic moduli of the alloy, which can be sensitively measured by resonant acoustic methods, for example by resonant ultrasound spectroscopy (RUS). It is shown that the phase transitions of the particles correspond to well-detectable changes of the resonant spectrum, which enables a more detailed characterization of the transition process. A significant thermal hysteresis is observed between the cooling and the heating runs, and also the widths of the temperature ranges in which the transitions occur exhibit a strong melting/freezing asymmetry.
Knut Marthinsen, Bjørn Holmedal and Yanjun Li
J. Nejezchlebová et al., "Detection of Phase Transition in Free-Cutting Al-Mg-Si Alloys by Resonant Ultrasound Spectroscopy", Materials Science Forum, Vols. 794-796, pp. 21-26, 2014