A study on Sc- and Zr-modified Al–Mg alloys processed by selective laser melting

In this study, Al-4.6Mg-0.66Sc-0.42Zr-0.49Mn (wt.%) alloy was processed by selective laser melting (SLM). The relative densities of SLM-processed Al–Mg-Sc-Zr-Mn alloy reached up to 99.92%. The optimal energy density range is 60–80 J/mm3. The optimal laser power, scanning speed and hatch distance is 200–250 W, 800–900 mm/s and 135–165 μm, respectively. The two factors that have the greatest effects on relative densities are laser power, and the interaction between laser power and scanning speed. The effect of hatch distance on relative densities is comparatively small. During the SLM process, fine equiaxed grains were formed inside the melt pool and coarse columnar grains were formed at the melt pool boundary. A large number of nano-scale Al3(Sc, Zr) phases were precipitated and uniformly dispersed in the matrix, which effectively improved the mechanical properties and high temperature stability of the material. The samples were aged at an isothermal temperature of 350 °C for 8 h. After aging treatment, some of the low-angle grain boundaries were transformed into high-angle grain boundaries, which improved the hindering effect on dislocations. The mechanical properties of the heat-treated samples were excellent, with the maximum tensile strength and elongation reaching 510 MPa and 11%, respectively. The samples were mainly fractured by a mixture of brittle and ductile cracking mechanism, with brittle fracture in the columnar grain region and ductile fracture in the equiaxed grain region. The equiaxed grains have better effects on the mechanical properties of the alloy than the columnar grains.