PSI - Issue 71

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

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Micro Vickers hardness test was carried out at 1kgf using a 136° pyramidal diamond indenter. Tensile tests for as built and select heat treated samples were performed using UTM with 10 kN load cell and samples for tensile test were cut using wire-cut EDM (Fig. 1). Tensile specimens are 1 mm thick with gauge length of 5 mm and width of 2.5 mm within the gauge length. All the comparative analyses carried out to determine the effect of heat treatment were done on AlSi10Mg samples whose longitudinal axis is parallel to build direction (Fig. 2c).

Fig. 1. Photograph showing build direction and orientation of tensile samples with respect to the build direction.

3. Results and discussion 3.1 Microstructures

Fig. 2. (a) Optical micrographs and (b & c) SEM images showing microstructures of as-built AlSi10Mg sample.

Fig. 2a shows one of the characteristic features of SLM, fish eye structure which consists of melt pools with a half cylindrical shape due to the locally melted and rapidly solidified regions. Fig. 2b shows cellular-dendritic structure of the AlSi10Mg in the as-built condition which is unique characteristic of LPBF and as reported in literatures, three regions are distinguishable viz., melt pool centres, boundaries and heat affected zones (HAZs) where cell sizes vary significantly (Kumar Ramavajjala et al., 2024; Zhao et al., 2022). Cells are composed of super saturated solid solution of aluminium (α -Al) due to rapid cooling and surrounded by silicon rich interconnected network. Melt pool centres are characterised by fine cellular dendritic structure commonly referred to as fine melt pool zone and melt pool boundaries are characterised by coarse cellular structure, also termed as coarse melt pool zone. In both fine and coarse melt pool zones, silicon rich eutectic network remains interconnected. There is also another zone evident from Fig. 2 b & c, where silicon rich network is broken and is commonly referred to as heat affected zone (HAZ). Coarse melt pool zone along with HAZ (combined) constitutes melt pool boundary.

According to literature, fine cellular dendrites are formed during melting of powder and previously solidified layers and subsequent rapid solidification, which is the characteristic of LPBF as evident in Fig. 2 b and c. This forms the