High-entropy alloy reinforced Al-Si alloy with isotropically high strength processed by laser powder bed fusion

In this study, isotropically high strength AlCrCuFeNi high-entropy alloy (HEA) reinforced Al12Si composites were successfully fabricated by laser powder bed fusion (L-PBF) process. The results indicated that the HEA powders were dissolved within the melt pool due to the elevated temperature, thus a substantial quantity of nano size α-Al(Fe, Cr)Si phase formed both at the boundaries and in the interior of the melt pool in the as-built samples. With increasing the content of HEAs from 0 wt % to 5 wt %, the eutectic Si at the melt pool boundaries transformed from lamellar to network structure, and the formation of α-Al(Fe, Cr)Si phase filled up the gaps of Si network, leading to a continuous cell wall of entire microstructure. The formation of α-Al(Fe, Cr)Si phase satisfies the transient nucleation theory. For Al12Si-1 wt.% HEA, the formation of the α-Al(Fe, Cr)Si phases in the melt pool interior was suppressed due to the high cooling rate in the melt pool interior, which exceeded the critical nucleation cooling rate of α-Al(Fe, Cr)Si phase. The finely continuous cell structure within melt pool enables dislocations to accumulate at a large scale of whole melt pool with the addition of HEA powders, rather than small-scale and localized dislocation storage at melt pool boundary for Al12Si. Therefore, the uniform strain/stress distribution within the entire melt pool occurs with the addition of HEA particles, and the as-built Al12Si-HEA samples exhibited nearly isotropic mechanical properties with significant enhancement. The ultimate tensile strength (UTS) of Al12Si-3 wt.% HEA samples reached 500 MPa for both the horizontal and vertical directions, by comparison, that without HEA was 430 MPa at the horizontal and 390 MPa at the vertical, respectively. The findings of this investigation provide a novel perspective on the design of advanced aluminum matrix composites.