Microstructure and mechanical properties of D023-Al3Zr modified Al-Zn-Mg-Cu alloys fabricated by laser powder bed fusion

Unweldable high-strength aluminum alloys have limited applications in additive manufacturing due to their hot-crack-sensitivity. In this study, the addition of D0 23 -Al 3 Zr particles significantly improved the formability of Al-Zn-Mg-Cu alloy for laser powder bed fusion (LPBF) process. The D0 23 -Al 3 Zr particles served as an excellent carrier for introducing Zr elements into LPBF-fabricated high-strength aluminum alloys due to their excellent oxidation resistance and thermal stability. The L1 2 -Al 3 Zr phases generated through in-situ reactions promoted heterogeneous nucleation of α-Al grains. Moreover, the residual D0 23 -Al 3 Zr particles inhibited grain growth by pinning grain boundaries. These particles functioned as both effective grain refiners and reinforcement particles . When the content of D0 23 -Al 3 Zr particles reached 5 wt%, the coarse columnar grains and hot cracks in the Al-Zn-Mg-Cu alloy were completely eliminated. And the microstructure of alloy was replaced by fine equiaxed grains with an average size of ∼1.4 μm. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the as-built samples reached ∼322 MPa, ∼354 MPa, and ∼12.9 %, respectively. T6 heat treatment further enhanced YS and UTS to ∼641 and ∼654 MPa, respectively, while reduced EL to ∼7.2 %. The high densities of η' phase and secondary L1 2 -Al 3 Zr phase were the primary contributors to the strength improvement. This study offers new insights into enhancing the formability and strength of hot-crack-sensitive high-strength aluminum alloys for additive manufacturing. • The addition of D0 23 -Al 3 Zr refines the grains of LPBF-prepared Al-Zn-Mg-Cu alloys. • The L1 2 -Al 3 Zr phase promotes heterogeneous nucleation of α-Al grain. • The residual D0 23 -Al 3 Zr particles hinder grain growth by pinning grain boundaries. • The transformation mechanism from D0 23 -Al 3 Zr to L1 2 -Al 3 Zr is discussed. • T6 heat treatment further enhances the alloy's strength.