Controllable microstructure and strength-ductility synergy of selective laser melting Al-Zn-Mg-Cu alloy reinforced with TiSi2 particles

• In this article, Al-Zn-Mg-Cu alloy is modified by TiSi 2 ceramic particles and parametric unfolding experiments are carried out by SLM molding process, and the results of the study show that TiSi 2 particles can effectively avoid crack defects and make the number of porosities greatly reduced. • The Al-Zn-Mg-Cu+TiSi 2 alloy fabricated by SLM process has high tensile strength and elongation after break under the optimal ratio (4 %TiSi 2 ) and optimal process conditions (laser power: 300 W; scanning speed: 800 mm/s; layer thickness: 30 μm; scanning spacing: 80 μm), which can reach 561.2 ± 6.5 MPa and 7.4 ± 0.4 % and the density can reach 98.86 % respectively. This results in a significant increase in both tensile strength and elongation after break. • The strengthening mechanism mainly originates from the fine-crystal strengthening (Δσ Hall-Petch ), the particle-induced Orowan looping strengthening (Δσ Orowan ) and the load-transferring strengthening (Δσ load ) of the precipitated phases, such as L1 2 -Al 3 Ti. The increase in post-break elongation is mainly attributed to changes in the number, angle and size of grain boundaries. • The addition of TiSi 2 decomposes under the instantaneous heating of SLM process, which promotes the nucleation of α-Al. Ti and α-Al form L1 2 -Al 3 Ti phase in the solidification process at the intracrystalline and grain boundaries, which prevents the cross-layer growth of columnar crystals, and the grain size is reduced from 8.847 μm to 1.175 μm, which results in the refinement of the grains. Si to form Al-Si eutectic organization in the solidification process to fill the cracked area, playing a “healing role”. • Under different TiSi 2 content and SLM process conditions, the types, shapes and numbers of defects are different. cracks and irregular pores due to H 2 appear at lower TiSi 2 content and lower energy density. As the energy density and TiSi 2 content increase, the crack defects gradually disappear, the size of the pores becomes smaller, the number decreases, and the shape is mainly circular. When the energy density reaches 156.25 J/mm 3 , the crack defects are completely removed, and the size and number of pores are minimized. The conventional Al-Zn-Mg-Cu alloy is susceptible to hot cracking, limiting its application. To address this issue, we fabricated a TiSi₂-reinforced Al-Zn-Mg-Cu alloy via selective laser melting (SLM) and achieved a crack-free, dense microstructure (relative density: 98.8 %) with fine equiaxed grains (average size: 1.174 μm) composed of α-Al, L1₂-Al 3 Ti, β-Mg 2 Si, and Al-Si eutectic by optimizing the process parameters (laser power: 300 W, scanning speed: 800 mm/s) and content (4 wt.%). The alloy exhibited exceptional mechanical properties, including a tensile strength of 561.2 ± 6.5 MPa, elongation of 7.4 ± 0.4 %, and hardness of 192.9 ± 4.4 HV 0.2 , surpassing those of most reported SLM-processed Al-Zn-Mg-Cu alloys. The strength-ductility synergy was attributed to the combined effects of fine-grain strengthening (Δσ Hall-Petch ≈ 130.8 MPa), Orowan strengthening by L1₂-Al 3 Ti (Δσ Orowan ≈ 26.16 MPa), thermal mismatch-induced dislocation hardening (Δσ CTE ≈ 29.52 MPa), and load transfer from precipitates (Δσ load-transfer ≈ 273.52 MPa). This work provides fundamental insights into the microstructure-property relationships in particle-reinforced aluminum alloys and establishes a practical strategy for manufacturing high-performance Al-Zn-Mg-Cu components via SLM, opening new possibilities for aerospace and automotive applications.