Achieving high strength-ductility combination of Al–Mn–Mg-Sc-Zr alloy subjected by laser powder bed fusion and suitable post heat treatment

Post heat treatment is crucial for optimizing the performance of additive manufacturing components, yet it is still challenging to synergistically improve the strength and ductility through simple heat treatment. The present work investigated the microstructure evolution and mechanical properties of laser powder bed fusion (L-PBF) additive manufactured Al-Mn-Mg-Sc-Zr alloy after aging at 300 °C for different durations. All the as-built and aged samples exhibited a typical bi-modal microstructure consisting of coarse columnar and fine equiaxed grain regions. The as-built samples contained a number of primary Al6Mn precipitates distributed along grain boundaries; meanwhile, Mg solutes segregation was visible at grain boundaries, forming "Mg walls". After aging for 4 hours, the Al6Mn and a small content of Al3Sc were precipitated. Two types of Mg-rich precipitates evolved along grain boundaries simultaneously, increasing ultimate tensile strength from 401 MPa to 501 MPa, while the ductility was significantly reduced from 19.6% to 4.6%. When increased to 6 hours, the Mg-rich precipitates disappeared, and the density of Al6Mn and Al3Sc precipitates reached its peak concurrently, providing a dual-precipitate strengthening effect. As a result, an excellent strength-ductility balance with an ultimate tensile strength of 528 MPa and ductility of 14.5% was obtained. The Al6Mn precipitates became coarsening with increasing to 7 hours, resulting in lower ductility. The strategy of modulating elemental distribution and precipitated phases by simple heat treatment is expected to be further developed for high strength and ductility Al alloys prepared by L-PBF.