Laser powder bed fusion of AlSi10Mg-based composites with graphene and nanodiamond additions

Laser powder bed fusion (LPBF) processing of aluminum matrix composites (AMC) with blends of AlSi10Mg powder and nanodiamond and graphene additives was investigated. AMC with 0.5 wt% nanodiamonds addition was prepared by mechanical mixing, while AMC with 0.5 wt% of multi-layered graphene was prepared by electrochemical deposition. Initial powders for LPBF were thoroughly characterized and optimal LPBF parameters were found based on the relative density analysis and optical microscopy. Processing windows of both AMCs moved towards lower energy density possibly due to the increased total absorptivity of the powders. Raman spectroscopy results, SEM and HRTEM studies of samples after LPBF demonstrated the absence of nano-diamond in the structure after processing which is explained by graphitization of the nanodiamond particles during laser melting. In case of AMC with graphene additives, carbon-containing particles remained in the structure with partial in situ formation of Al4C3, along with a noticeable strengthening effect, which increased material's microhardness by more than 40% compared to the initial AlSi10Mg alloy. The strengthening effect is explained by the presence of a network of graphene and Al4C3 particles across the solidified melt-pool promoting the Orowan strengthening mechanism.