PSI - Issue 71

R. Anil Kumar et al. / Procedia Structural Integrity 71 (2025) 302–308

307

dislocation density and the degree of entanglement are higher in coarse-grained zones compared to fine-grained zones (Xiao et al., 2024). AlSi10Mg contains both fine and coarse cellular zones inside melt pools and at melt pool boundaries and in the as-built condition, residual stresses developed during fabrication adversely affected ductility. Post-heat treatment, due to stress relieving, ductility is increased, likely due to the contribution of the coarse cellular zones. While the fine cellular structure and nanoprecipitation enhance the alloy's strength, the stress-relieved coarse cellular zones improve ductility by accommodating larger plastic deformation (Xiao et al., 2024). In case of sample 41, interaction of dislocations with silicon rich network and nano-sized particles lead to better combination of strength and ductility. In sample 44, reduction of strength can be attributed to growth of nano-sized particles during 2 hrs of ageing. Santos Macias et al. observed that significant strengthening comes from Orowan mechanism of strengthening from very fine particles (Santos Macías et al., 2020; Takata et al., 2020; Zhao et al., 2019). They reported that strengthening contribution of 158 MPa from fine particles of 12 nm dropped to just 44 MPa when size increased to 60 nm. This behaviour can explain the decrease in strength of sample 44 compared to 41. Higher strength in as built and sample 41 is also attributed to load bearing of silicon rich interconnected network. It has been reported by Zhang et al. that silicon network’s stress partitioning ratio is about 13.5% whic h proves that interconnected silicon rich network slightly contributes to the overall strengthening (Zhang et al., 2021). In case of sample 44, silicon rich network is broken to some extent which also explains the lower strength compared to that of sample 41. But more in-depth characterisation and analysis is required to explain the reduction of ductility in sample 44. 4. Conclusion In this work, effect of direct ageing at 245 °C and T5 treatment on microstructure, hardness and tensile behaviour has been investigated in AlSi10Mg manufactured by LPBF. Uniaxial tensile testing was carried out on samples in vertical orientation as it is widely reported that tensile strength is slightly lower in this orientation due to anisotropy. The following conclusions are drawn from the present investigation: a) T5 treatment enhanced the ductility at the expense of tensile strength. UTS was decreased to almost 50% that of AlSi10Mg in as-built condition. b) Direct ageing of AlSi10Mg has led to only 8 – 12% reduction in micro-Vickers hardness. c) Direct ageing of AlSi10Mg at 245 °C for 30 minutes imparted better combination of strength and ductility compared to as-built condition than all other treatments analysed in this work. Dislocation strengthening from nano-sized particles precipitated during rapid solidification has significant contribution to overall strengthening. Load bearing effect from continuous silicon network also contributed to strengthening. References Aboulkhair, N. T., Maskery, I., Tuck, C., Ashcroft, I., and Everitt, N. M. 2016. The microstructure and mechanical properties of selectively laser melted AlSi10Mg: The effect of a conventional T6-like heat treatment. Materials Science and Engineering A, 667, 139 – 146. https://doi.org/10.1016/j.msea.2016.04.092 Butler, C., Babu, S., Lundy, R., O’Reilly Meehan, R., Punch, J., and Jeffers, N. 2021. Effects of processing parameters and heat treatment on thermal conductivity of additively manufactured AlSi10Mg by selective laser melting. Materials Characterization, 173, 110945. https://doi.org/https://doi.org/10.1016/j.matchar.2021.110945 Kumar Ramavajjala, A., Dandekar, T. R., Khatirkar, R. K., Joshi, C., Chouhan, R. N., and Agnihotri, A. 2024. 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