Role of inclusions in the nucleation of alpha-aluminum and iron intermetallics in the aluminum-rich corner of the aluminum-silicon-iron ternary system

The aim of this work has been to study the nucleation of iron intermetallics and the alpha-Al phase on inclusions introduced into dilute liquid Al-Si-Fe alloys. Systematic experiments were designed to study the effect of (i) the alloy composition (Fe and Si), (ii) cooling rate (from 0.2°C/s to 15°C/s, similar to those encountered in most commercial casting processes), and (iii) inclusion type (where a variety of inclusions covering the most common oxides, carbides, and borides were used).; Six experimental alloys representative of the Al-rich corner of the Al-Si-Fe system were used in the present study. Gas injection experiments for the addition of a variety of inclusions (alpha- and gamma-Al2O3, MgO, CaO, TiC, SiC, Al4C3 and TiB2) to the alloy melts were carried out using a gas injection technique that successfully introduced the different oxides, carbides and borides into the liquid aluminum alloys.; The results showed that the volume fraction of iron intermetallics obtained increased with the increase in the amount of Fe and Si added, as well as with the decrease in cooling rate. A low cooling rate produces larger-sized intermetallics, whereas a high cooling rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions in producing intermetallics.; The systematic inoculation experiments carried out to study the influence of various inclusions on the nucleation of the alpha-Al phase in Al-Si-Fe alloys at different cooling rates showed that in the dilute alloys (containing less than 1.5 pct Si+Fe), almost all the inclusion types have high percentages of occurrence within the alpha-Al phase, indicating that nucleation is promoted on the surface of such inclusions.; Nucleation of Fe-intermetallic phases (i.e. binary Al-Fe, alpha-Al8Fe2Si, beta-Al5FeSi, delta-Al 4FeSi2 and q1-AlFeSi phases) on the surface of different inclusions in the six experimental Al-Si-Fe alloys was studied. It was found that nucleation of each of the Fe-intermetallic phases was generally observed to be promoted on the surface of several inclusions under the same conditions of alloy composition and cooling rate. However, some inclusions exhibited high potency for the nucleation of particular Fe-intermetallic phases under certain conditions and poor potency under other conditions. (Abstract shortened by UMI.)...