Keyhole mode induced simultaneous improvement in strength and ductility of Sc modified Al–Mn alloy manufactured by selective laser melting

The effect of melting modes on microstructure evolution and tensile properties of selective laser melted (SLM-ed) Sc modified Al–Mn alloy (Al–5Mn-0.6Sc) is investigated in this work. With the transition of melting mode from conduction to keyhole by coinstantaneous increasing the laser power from 200 W to 380 W and the scanning speed from 800 mm/s to 1400 mm/s, the columnar grain width significantly decreases by 88% from 34.9 μm to 4.2 μm. Consequently, the yield strength and the elongation increase simultaneously from 266 MPa and 10% to 308 MPa and 17%, which increase by 16% and 70%, respectively. The refinement and orientation diversification of the grains caused by keyhole mode simultaneously improve the strength and elongation by inducing the Hall-Petch effect and enhancing the crack path tortuosity. This work reveals the feasibility and the mechanism of changing melting mode acts as a method to regulate the SLM-ed microstructure and mechanical properties.