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

doi:10.1016/j.metadv.2026.02.023

Abstract

Abstract:

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 Al₃Ti 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.

Key words: Laser powder-bed fusion, 6061 Al alloy, In-situ alloying, Synergistic strengthening, Mechanical properties

Dezheng Sun, Shuaixian Yu, Siran Wang, Dongdong Zhao, Zhihang Xu, Lihua Dang, Lizhuang Yang, Hao Wang, Chunsheng Shi, Chunnian He, Naiqin Zhao, Junwei Sha. 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[J]. Metals Advances, 2026, 43: 12-20.

Figures/Tables 13

Fig. 1. (a) SEM image and (b1-b6) EDS elemental distribution of AA6061-2Ni-5Ti composite powders.

Table 1. Printing parameters of L-PBF AA6061-Ni-Ti.

Parameters	Setting values
P (W)	250
v (mm/s)	1200
H (μm)	100
L (μm)	30
θ (°)	67

Fig. 2. Schematic of powder preparation and L-PBF processes.

Fig. 3. (a) XRD patterns of powders and as-built bulk sample and (b) the enlarged Al (111) diffraction peak marked by using dashed box in (a).

Fig. 4. (a1-a3) Crystallographic information of the as-built AA6061 and (b1-b3) the as-built AA6061-2Ni-5Ti: (a1, b1) inverse pole figure (IPF) maps on the XOZ planes which parallel to the building direction, (a2, b2) the size distribution of the grain structures, and (a3, b3) the pole figures (PFs) for texture intensities along different planes.

Fig. 5. TEM analysis of as-built AA6061-2Ni-5Ti: (a) bright-field TEM image; (b-f) the EDS elements distribution from (a).

Fig. 6. TEM analysis of as-built AA6061-2Ni-5Ti: (a) HRTEM image, (b) SAED patterns of cubic particle in (a), and (a1-a5) element distribution from (a).

Fig. 7. (a) Engineering stress-strain curves of as-built AA6061‐2Ni‐5Ti; (b, c) the comparison on YS and UTS of different alloys [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44].

Table 2. Mechanical properties of Al-Si, Al-Mg, cast Al-Si, and AA6061‐2Ni‐5T in this work fabricated through L-PBF.

Fig. 8. SEM images of the fracture surface morphologies of (a, b) as-built AA6061 and (c, d) L-PBF AA6061-Ni-Ti; the dimple dimension statistics of (d1, d2).

Fig. 9. (a) Thermal-calc solidification path simulation of as-built AA6061 and AA6061‐2Ni‐5Ti; (b1, b2) Ti hetero nucleation growth and stable stage schematic diagram.

Table 3. Matrix solute concentration of Mg, Si, Ni and Ti at different positions (at.%).

Elements	001	002	003	Average
Si	0.01	0.13	0.13	0.09
Ni	0.09	0.31	0.07	0.16
Mg	0.44	0.67	0.47	0.53
Ti	0.51	0.87	0.62	0.67
Al	Bal.	Bal.	Bal.	Bal.

Fig. 10. (a) HAADF map of the as-built AA6061‐2Ni‐5Ti and (b1-b4) Ti distribution at different states. (b1) Ti element distribution at TEM maps, (b2) Ti particle size statistics by using Nano Measurer, (b3) Image J 8-bit treatment with enhanced contrast and (b4) Image J threshold treatment.

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