Novel isotropic mechanical properties of laser powder-bed fusion Sc/Zr modified Al alloy

To explore the mechanical anisotropy of high-strength Al alloys for laser powder bed fusion (LPBF) additive manufacturing, the Al-Mn-Mg-Sc-Zr alloys were built along X, Y, Z axial and 45 degrees directions by LPBF subjecting to a series of different heat treatments. All the printed and heat treated components displayed a columnar/ equiaxed bimodal microstructure, where the secondary Al6Mn and nano-size Al3Sc precipitates ubiquitously dispersed in the columnar and equiaxed grain regions, respectively. The Al-Mn-Mg-Sc-Zr alloy exhibited a continuous strength increase from 453 MPa to 577 MPa after the heat treatment through the synergistic effect of the solid solution strengthening, grain boundary strengthening and Orowan dislocations strengthening from Al6Mn as well as Al3Sc precipitates. But its ductility suffered from a decrease from 14.1% to 2.3%. Especially, the optimal collaboration between hard equiaxed grain and soft columnar grain contributed to the mechanical properties isotropy of the printed and heat-treated alloy components along different tensile directions with strength difference only 1.3-2%. Thus, the synergetic effects of hierarchical bimodal microstructure and secondary precipitations could provide the effective avenues to tune the mechanical property and anisotropy of LPBF Al alloys.