Effects of scandium addition on microstructure, mechanical and thermal properties of cast Be-Al alloy

The microstructure modification, mechanical property reinforcement, and thermal behaviors of arc-melted casting beryllium-aluminum (Be-Al) alloys with the addition of various contents of scandium (Sc) were studied in this work. The addition of 0.2wt% Sc shortened the secondary dendritic arm spacing (SDAS) of Be dendrites; the addition of 0.4wt% Sc further decreased the SDAS, weakened the dendritic structure of Be, and afforded equiaxed/cellular alloy microstructure with the finest Be grain size; however, higher additions of Sc till 3.0wt% enlarged the SDAS of Be and coarsened the Be grains. An explanation for the microstructure variation was proposed. The addition of Sc resulted in the formation of intermetallic compounds Be13Sc and Al3Sc distributed in the Be and Al matrices and along the Be/Al grain boundaries. It was observed that Sc preferentially formed Be13Sc and rendered the Be phase less plastic. The addition of Sc increased the hardness and elastic modulus of Be-Al alloys while strengthening the Be phase to a higher extent than Al. Thermal analysis showed that the Al phase had the highest latent heat of 167.6 J/g during melting and a low nucleation undercooling of 16.4 °C during solidification with the addition of 0.4wt% Sc. Heat treatment and water quenching changed the relative contents of Be13Sc and Al3Sc and further strengthened the alloys.