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 results 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 μm. 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.