Microstructure and mechanical properties of Al-Fe-Sc-Zr alloy additively manufactured by selective laser melting

An Al-5Fe-1Mg-0.8Sc-0.7Zr (wt%) alloy was specifically designed for selective laser melting (SLM) additive manufacturing and atomized powder prepared. The design of this non-equilibrium alloy is based on: first, solid solubility of Fe element in Al alloy can be significantly enlarged during laser rapid solidification; second, Sc and Zr elements are used to refine the microstructure so as to prevent micro-crack and improve strength. At an optimized printing parameters, the SLM printed Al-Fe-Sc-Zr samples exhibited a highest density of 99.2% with rare intergranular cracks. Besides, a bimodal grain structure was observed, consisting of ultrafine equiaxed grain at molten pool boundary and coarse columnar grain inside the molten pool. At the boundary of molten pool, many intermetallic particles (Al6Fe and Al13Fe4) appeared around supersaturated α-Al grains; while the inside of molten pool presented eutectic of α-Al and Al6Fe/Al3(Sc, Zr). Interestingly, a large number of stacking faults were observed around the precipitated particles by HRTEM, which are also conducive to strengthening of SLM printed Al-Fe-Sc-Zr sample. Thus, excellent tensile strength of 489 MPa was obtained at an optimized volumetric energy density (VED) of 70 J/mm3. The current research results have a certain guiding significance for the composition design and microstructure control of additive manufacturing aluminum alloys.