Approaching an ultrafine microstructure and excellent tensile properties of a novel Er/Zr modified Al-7Si-0.6 Mg alloy fabricated by selective laser melting

In order to improve the mechanical properties of Al-Si alloys fabricated by selective laser melting process, the microstructure and mechanical properties of Er/Zr modified A357 (Al-7Si-0.6 Mg) alloy in as-built and stress relief annealing conditions were studied. The re-sults show that adding 0.15 wt.% Er helps to refine the cellular size, which is formed by eutectic Si network. The (Al,Si)3(Er,Zr) phases were precipitated during the solidification of Er-Zr composite modified sample, which could act as inoculants to promote the formation of equiaxed grains and refine the grain size. The average grain size of 0.8Er-0.4Zr sample was only 3.1 +/- 1.4 mm. The yield strength, tensile strength and elongation reached 333 +/- 2 MPa, 454 +/- 1 MPa and 12.5 +/- 1%, respectively. After stress relief annealing, eutectic Si was spheroidized and its size was increased, resulting in a decrease of strength and an increase of elongation. At the same time, the nano-sized L12-structure particles were precipitated in the Er-Zr composite modified sample, which would make up for the loss of strength and level it up to a certain extent. Therefore, Er-Zr composite modification could be an effective method to improve the comprehensive mechanical properties of SLM processed Al-Si alloys. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).