Study of mechanical effects of probeless friction stir spot surface treatment on 3D-printed AlSi10Mg specimens

Porosity and internal defects currently hinder the applicability of Laser Powder Bed Fusion (LPBF)-manufactured components. Innovative post-process methods specifically designed for the unique characteristics and microstructures of LPBF-manufactured aluminum alloys aim to suppress the porosity originating from the manufacturing process. Therefore, this study introduces a novel thermo-mechanical post-process treatment using flat surface tools – a probeless friction stir spot processing (P-FSST). Our results demonstrate that the imposed treatment plays a significant role in densifying the LPBF-manufactured specimens, while the treatment-induced distortions were highly dependent on the applied process conditions. The identified distortions on the upper surfaces of specimens, correlating with the imposed treatment, were mainly influenced by the dwell time. At the same time, the rotational speed majorly affected the presence of residual porosity in the central regions of the processed specimens. The results demonstrate that the P-FSST treatment significantly densifies the LPBF-manufactured specimens, achieving a reduction in porosity to under 0.4 % in sections treated at a rotational speed of 2000 rpm and various dwell times. The dwell time's influence on porosity was confirmed across treated regions, with significant decreases observable at a dwell time of 5 s, while further reductions correlated with increased dwell time and the thermomechanically affected zone. Distortions in the x-dimension were notably affected by dwell time (p-value = 0.011), whereas the y-dimension reflected the influence to both dwell time (p-value = 0.031) and rotational speed (p-value = 0.031).