In-situ synergistic strengthening strategy of Ni eutectic and Ti peritectic phases to high-performance crack-free 6061 Al alloy through laser powder-bed fusion

To address the challenges of coarse columnar grains and solidification cracks in 6061 Al alloy (AA6061) through laser powder-bed fusion (L-PBF), this study proposes an in-situ co-modification strategy by using Ni-induced eutectic reaction and Ti-induced peritectic reaction, resulting in the development of high-performance and crack-free AA6061 based alloys. The in-situ fabrication mechanism, microstructures and mechanical properties of the as-built AA6061-Ni-Ti alloys are investigated systematically. As a result, Ti could in-situ form cubic Al 3 Ti precipitates with low lattice mismatch, acting as heterogeneous nucleation sites to refine grains and promote columnar-to-equiaxed transition. Simultaneously, Ni enriches at grain boundaries to form a continuous network, narrowing the solidification temperature range and suppressing end-of-solidification cracks. The modified alloy achieves a high yield strength (YS) of 413.95±13.37 MPa, ultimate tensile strength (UTS) of 427.77±2.57 MPa and elongation (EL) of 6.40±0.16%, exhibiting superior strength-ductility synergy compared to other L-PBF Al-Si and Al-Mg alloys. Fracture analysis confirms a shift from cleavage fracture (unmodified) to dimple fracture with an average dimple size of ~3.45 μm. This work demonstrates that the dual phases co-modification by combining eutectic and peritectic reaction could effectively enhance laser absorptivity, eliminate un-melted powders, and optimize microstructures for high-performance Al alloys via L-PBF. In-situ generation of Al 3 Ti heterogeneous nucleation particles via Ti-induced peritectic reaction, combined with the construction of grain boundary eutectic networks through Ni-induced eutectic reaction, synergistically modified L-PBF AA6061, achieving excellent ultimate tensile strength (UTS) of 427.77±2.57 MPa and yield strength (YS) of 413.95±13.37 MPa. • Ni-induced eutectic reaction and Ti-induced peritectic reaction synergistically achieve high-performance L-PBF AA6061. • Ti forms cubic Al 3 Ti precipitates to refine grains and promote columnar-to-equiaxed transition. • Ni forms a continuous network, narrowing solidification temperature range and suppressing end-of-solidification cracks. • Excellent mechanical properties are from cooperation of the fine grain, solid solution, and precipitation strengthening.