Abstract: In present work, a novel crack-free Al-Cu-Mg-Si-Ti alloy with synchronous improved tensile properties and hot-cracking resistance was proposed and successfully manufactured by laser powder bed fusion (LPBF). The microstructure evolution behaviors and the corresponding strengthening mechanisms were investigated in detail. The LPBF-processed Al-Cu-Mg-Si-Ti alloy presents a heterogeneous microstructure consisting of ultrafine equiaxed grains (UFGs) at the boundary and coarse columnar grains (CGs) at the center of the single molten pool. Pre-precipitated D0₂₂-Al₃Ti particles were found to act as the nuclei to refine the grains at the boundary of the molten pool during solidification process, which is attributed to the low cooling rate providing the sufficient incubation time for the precipitation of D0₂₂-Al₃Ti. There are two orientation relationships (ORs) between α-Al and D0₂₂-Al₃Ti, i.e. [001]_α-Al//[001]_D022-Al3Ti, (200)_α-Al//(200)_D022-Al3Ti and [1$\bar{12}$]_α-Al//[$\bar{1}$11]_D022-Al3Ti, (1$\bar{1}$1)_α-Al//($\bar{1}$1$\bar{2}$)_D022-Al3Ti, which are two of the eight ORs predicted with the E2EM model. Refined grains in present alloy, no matter for UFGs or CG, exhibited high critical hot-cracking stress, which means a strong hot-cracking resistance. Dual-nanoprecipitation of Cu-, Mg-, and Si-rich Q' and S' phases was introduced to enhance the mechanical performance of α-Al matrix. The as-built sample exhibits superior tensile properties, with the yield strength (YS) of 473 ± 8 MPa, ultimate tensile strength (UTS) of 541 ± 2 MPa and elongation (EI) of 10.9% ± 1.2%.

Key words: Laser powder bed fusion, High strength Al-Cu-Mg alloys, Duplex microstructure, Precipitation, Tensile properties