On the Role of Sc in Powders and Spray Deposits of Hypoeutectic Al–Mg Alloys

• Published in: Journal of phase equilibria and diffusion 2022-02, Vol.43 (1), p.3-14
• Main Authors: Yin, S., Bogno, A-A., Henein, H., Gallerneault, M.
• Format: Article
• Language: English
• Subjects: Aging; Aging (metallurgy); Aluminum base alloys; Atomizing; Ceramics; Chemical precipitation; Composites; Crystallography and Scattering Methods; Dendritic structure; Engineering Thermodynamics; Glass; Heat and Mass Transfer; Heat treatment; Intermetallic compounds; Magnesium; Metallic Materials; Microhardness; Microstructure; Natural Materials; Physics; Physics and Astronomy; Scandium; Solid solubility; Solid solutions; Solidification; Supersaturation; Thermodynamics
• ISSN: 1547-7037; 1863-7345; 1934-7243
• DOI: 10.1007/s11669-021-00934-5

This paper studies the solidification of hypoeutectic Al–Mg–Sc powders and spray deposited (SD) strips, generated by Impulse Atomization. The effects of Mg content in hypoeutectic Al–Mg–Sc was examined with respect to the extended solid solubility of Mg and Sc in α –Al, microstructure refinement and heat treatment. Increasing Mg content from 1.5 to 3wt% yielded a reduction in dendrite cells spacing by 30% in the atomized powders, and up to 10% in SD samples. Melt superheat appeared to yield a finer microstructure. The size of the primary structure in the SD was about five times larger than those of powder samples. However, the supersaturation of the primary phase is similar in both powders and SD samples, and their microhardness values (Hv0.1) are found to be ~45 and ~55 for the 1.5wt%Mg and 3wt%Mg alloys, respectively. Following aging, a significant increase in hardness is observed (75–85 for 1.5wt%Mg samples and ~85 for 3wt%Mg samples). Thus, the scale of the primary structure in both powders and SD did not contribute to the differences in the hardness. Apparently, supersaturation, the precipitation of intermetallics and solid solution of the remaining solute after aging, are the main contributors. The aging effect of liquid droplets falling on an SD layer is similar to a new layer of melted powder solidifying over a former layer in additive manufacturing (AM). Thus, powders and SD samples are a good model for building a microstructure-property database in these class of alloys for other processes such as AM.