Understanding the Effect of Be Addition on the Microstructure and Tensile Properties of Al–Si–Mg Cast Alloys

While the findings show the benefits of Be to reduce the deleterious effects of Fe-phases, this work does not promote its use. As noted, care must be taken due to the toxic nature of Be to ensure proper ventilation and environmental controls as well as personnel protection are in place. The present work was carried out on a series of heat-treatable aluminum-based aeronautical alloys containing various amounts of magnesium (Mg), iron (Fe), strontium (Sr) and beryllium (Be). The results show that Be (~300–400 ppm) causes partial modification of the eutectic silicon (Si) particles similar to that reported for Mg addition. Addition of 0.8 wt% Mg reduced the eutectic temperature by ~ 10 °C. During solidification of alloys containing high levels of Fe and Mg, without Sr, a peak corresponding to the formation of a Be–Fe phase (Al8Fe2BeSi) was detected at 611 °C, which is close to the formation temperature of α-Al. The Al–Be–Fe phase precipitates in a script-like morphology. Beryllium addition is beneficial in the case of high Fe contents as it lowers the harmful effects of Fe-phases in Al–Si alloys. In the case of high Fe contents, it seems that the addition of 500 ppm of Be is not sufficient for all interactions with other alloying elements. During the melting process, the formation of Be–Sr phase (probably SrBe3O4 compound) decreases the free Be content and hence the alloy mechanical properties. The role of Be in preventing the oxidation of Mg and in changing the chemistry and morphology of the Fe-intermetallics is observed through improved mechanical properties of Be-containing alloys. The partial modification effect of both Mg and Be appears to improve the alloy tensile properties.