Microstructural features and mechanical properties of a novel Ti- and Zr- modified Al-Mn alloy processed by laser powder bed fusion

The expansion of the material library for the laser powder bed fusion (LPBF) process is essential for the further establishment of the process in areas such as the aerospace and automotive industries. In this study, we designed a high-strength and low-cost Al-Mn-Ti-Zr alloy specifically tailored to the unique conditions of the LPBF process. Gas-atomized pre-alloyed powder was prepared and used as feedstock to fabricate LPBF specimens for microstructural examination and mechanical testing. By taking advantage of the high solidification rate, unconventionally large amounts of Mn (3.7 ± 0.5 wt%) are metastably frozen within the α-Al matrix, contributing significantly to solid solution hardening (~104 MPa ≙ 37% share of yield strength). The as-built specimens exhibit a yield strength of 284 ± 3 MPa, an ultimate tensile strength of 320 ± 1 MPa, and an elongation at fracture of 16.9 ± 0.2%. This new alloy exhibits a bimodal microstructure consisting of alternately distributed fine equiaxed and coarse columnar grain regions. Further microstructural analyses reveal a high number of primary L12 cubic Al3(Tix Zr1 - x) nanoparticles within the equiaxed α-Al grains near the bottom of the melt pool. A highly coherent interface with the α-Al matrix confirms high efficiency for heterogeneous nucleation during solidification. In addition to the Al3(Tix Zr1 - x) nanoparticles, an AlxMn(Fe, Si) phase with a quasi-crystalline structure is observed along the grain boundaries and interdendritic areas.