Highly ductile and mechanically strong Al-alloy/boron nitride nanosheet composites manufactured by laser additive manufacturing

Laser metal deposition (LMD) is one of the prospective additive manufacturing (AM) processes to fabricate metal-based nanocomposites. In this study, aluminum alloy (AlSi10Mg) was reinforced by boron nitride nanosheets (BNNSs) via LMD method. High speed ball-milling was used to mix AlSi10Mg powder with BNNSs at fraction range 0.05–0.2 wt%. Comprehensive morphology analysis as well as structure-property relations were investigated. The study showed that adding BNNSs into Al-alloy via LMD process not only promoted the hardness (40 %) and mechanical properties of the matrix (24 %, 100 % and 96 % increments in ultimate tensile strength, yield strength and Young's modulus, respectively), but also significantly improved its ductility (∼300 % increase). This has been observed clearly in fracture analysis where ductile fracture features were the dominant mode for all prepared samples. According to the observations by optical microscopy and electron backscattered diffraction, BNNSs have a crucial effect on grain refinement; grain size reduced from ∼30.4 to 17.5 μm upon the addition of 0.2 wt% of BNNSs. In addition, during LMD process, hard mesophase of aluminum nitride was formed which assisted BNNSs in reinforcing the Al-alloy. The results helped to understand the microstructure changes and mechanical properties improvements when LMD method was used.