Enhanced strength and ductility in Al-Zn-Mg-Cu alloys fabricated by laser powder bed fusion using a synergistic grain-refining strategy

Grain refinement is critical to surpassing the bottlenecks of inherent hot tearing of high-strength aluminum alloys fabricated by additive manufacturing (AM). In this study, a synergistic grain-refining strategy including heterogeneous nucleation, solute-driven growth restriction and nanoparticle-induced growth restriction was introduced to control the microstructure of Al-Zn-Mg-Cu alloys during the laser powder bed fusion (LPBF) process. Crack-free Al-Zn-Mg-Cu alloys with significantly refined grains were safely fabricated via LPBF by coincorporation of TiC and TiH2 particles. In-situ L12-Al3Ti particles were produced to promote the heterogeneous nucleation. The grain growth was restricted by adding Ti solute, while introduced TiC nanoparticles (NPs) improved the density of heterogeneous nucleation sites and blocked grain growth physically. The resultant elimination of columnar grains and hot cracks in the (1 wt.%) TiC- and (0.8 wt.%) TiH2-modified Al-Zn-Mg-Cu alloy resulted in excellent ultimate tensile strength (UTS) of 593 ± 24 MPa, yield strength (YS) of 485 ± 41 MPa and elongation (EL) of 10.0% ± 2.5% under the T6 condition. This study provides new insights into improving the grain microstructure and mechanical properties of high-strength aluminum alloys during LPBF.