Simultaneously minimizing residual stress and enhancing strength of selective laser melted nano-TiB 2 decorated Al alloy via post-uphill quenching and ageing

International audience; Selective laser melting (SLM) of aluminium alloys is of research interest to produce customized or complexshaped metal components for functional or structural applications. In order to palliate the undesirable residual stress developed in the SLM process, traditional post-annealing heat treatment has been widely used to lower residual stress in selective laser melted (SLMed) Al alloys. However, the traditional post-annealing method usually leads to a decrease in strength which is another concern for applications. In this study, we developed and validated a new strategy combining post-uphill quenching and subsequent ageing to simultaneously minimise residual stress and increase the strength of SLMed nano-TiB2 decorated Al alloy parts. The results show that the high as-built residual stress was partly counteracted by the newly-produced residual stress in the opposite direction during the uphill quenching stage and synergistically reduced by dislocation recovery during the ageing stage. The microstructural features of grains and cell structures remain unchanged after the treatment. While substantial new nano-Si particles with dot-like or needle-like morphology precipitate inside the cells. The tensile strength was improved mainly due to effective precipitation strengthening by dispersed nanosized Si precipitates. The proposed strategy is expected to be useful in other materials and components fabricated by SLM in which residual stress is also unwanted.