Enhanced nucleation of primary silicon in Al–20Si (wt%) alloy inoculated with Al–10Si–2Fe master alloy

Efficient use of iron impurity in Al–Si alloys

“…Since the (AlFeSi) clusters are the building blocks of a-Al 8 Fe 2 Si [18,19] and a-Al 8 Fe 2 Si is the metastable counterpart of b-Al 5 FeSi, a-Al 8 Fe 2 Si is easily stabilised by high cooling rates during solidification in commercial purity Al-Si alloys [13]. Therefore, with temperature decreasing, the amount of (AlFeSi) clusters increases continuously, and this is consistent with our early in-situ XRD characterization of Al-10Si-2Fe melt [12]. Consequently, a low-temperature holding provides an appropriate condition where abundant (AlFeSi) clusters can develop and a lower holding temperature induces a larger amount of these clusters.…”

“…In the silicon matrix, there are two isolated nanoparticles with special crystal structures. The corresponding fast Fourier transforms (FFTs) of these nanoparticles reveal that they cannot be identified as any well-established crystals known in Al-Si-Fe alloy systems, and this agrees well with the nanoparticles earlier reported in Al-Si alloys inoculated with the (AlFeSi) clusters [11,12]. Therefore, it is reasonable to conclude that (AlFeSi) clusters developing in the melts play the dominant role in enhancing the nucleation of silicon phase.…”

“…The first samples of every part were held at 830°C for 20 min before pouring into a graphite mold (inner diameter: 27 mm, wall thickness: 3 mm); the second samples of every part were further cooled to 587 ± 5°C, 600 ± 5°C and 620 ± 5°C and held for 10 min, respectively, and then were heated to 830°C and held for 20 min, followed by pouring into the mold. To determine the effects of this treatment on solidification behavior of these melts, the cooling curves during solidification of some melts were measured using a K type thermocouple, and detailed information can be found in early work [12]. Metallographic samples were prepared through standard routine and further characterized by optical microscopy and scanning electron microscopy (JSM6610-LV, a secondary electron detector and energy dispersive spectroscopy (EDS) detector were used for imaging and composition analysis, respectively).…”

“…Even though extensive studies have focused on the iron-rich phases in Al-Si alloys [7][8][9][10], only few reports have concentrated on the beneficial effects of iron in Al-Si alloys. Recently, an iron-rich particle, b-Al 5 FeSi, was used as an inoculant and found to evolve into a kind of Mackay icosahedral (AlFeSi) clusters, and enhance the silicon phase nucleation [11,12]. Though the inoculating effect is pronounced, it still relies on exogenous addition, i.e., an Al-10Si-2Fe master alloy containing b-Al 5 FeSi.…”

“…Since b-Al 5 FeSi is a natural outcome of solidification in commercial purity Al-Si alloys [13,14], one may ask why the endogenous iron-rich particles do not significantly enhance the nucleation of silicon phase? Theoretically, the Mackay icosahedral (AlFeSi) clusters should occur before the b-Al 5-FeSi phase [12,13], implying that the endogenous iron may show remarkable effect in enhancing the nucleation of silicon. Therefore, it is necessary to investigate the method that can trigger the intrinsic potential of endogenous iron in Al-Si alloys, and this is also the topic of this study.…”