High strength Al-Cu-Mg based alloy with synchronous improved tensile properties and hot-cracking resistance suitable for laser powder bed fusion

Abstract

• A high-strength Al-Cu-Mg based alloy with improved hot-cracking resistance was developed for SLM. • Duplex microstructure evolution caused by the precipitated behavior of D0 22 -Al 3 Ti was investigated. • The orientation relationship of [1 1 ¯ 2 ¯ ] α-Al //[ 1 ¯ 11 ] D022-Al3Ti , (1 1 ¯ 1) α-Al //( 1 ¯ 1 2 ¯ ) D022-Al3Ti predicted by E2EM model was firstly verified by TEM. • Dual-nanoprecipitation of Q’ and S’ phases was firstly introduced to enhance the mechanical properties. 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 D0 22 -Al 3 Ti 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 D0 22 -Al 3 Ti. There are two orientation relationships (ORs) between α-Al and D0 22 -Al 3 Ti, i.e. [001] α-Al //[001] D022-Al3Ti , (200) α-Al //(200) D022-Al3Ti and [1 1 ¯ 2 ¯ ] α-Al //[ 1 ¯ 11 ] D022-Al3Ti , (1 1 ¯ 1) α-Al //( 1 ¯ 1 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%.