PSI - Issue 71

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

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production stages (Montanari et al., 2023; Santos Macías et al., 2020). When it comes to AM applications with light weighting in focus, aluminium alloys are widely used. Out of various AM technologies, laser powder bed fusion (LPBF) is commonly employed and AlSi10Mg is most common aluminium alloy considered for AM applications fabricated through LPBF route (Kumar Ramavajjala et al., 2024). Lot of research was conducted in optimising process parameters of LPBF for producing highly dense and defect free AlSi10Mg parts (Butler et al., 2021; Maamoun et al., 2018; Rao et al., 2016; Tian et al., 2017). In the as-built condition, LPBF AlSi10Mg possesses significantly higher strength compared to its counterparts produced through conventional casting route. However, ductility is low for LPBF AlSi10Mg in as-built condition which necessitates post-processing treatment for improving it. When it comes to post processing treatment of AM parts, heat treatment is the widely accepted non-destructive treatment for relieving the residual stresses accumulated during the rapid solidification and for achieving desirable properties. Conventional treatments like T6, stress relieving, etc., were initially studied for LPBF AlSi10Mg parts and observed to reduce the strength to a very large extent with improvement in the ductility. LPBF AlSi10Mg like any other AM parts needs heat treatment to relieve the residual stresses, which are accumulated during the rapid cooling (Aboulkhair et al., 2016) and improve ductility. But the issue with conventional heat treatments is that they fail to take advantage of the unique microstructural characteristic of the LPBF AlSi10Mg. Microstructure of as-built LPBF AlSi10Mg consists of unique cellular dendritic structures owing to rapid cooling and it is comprised of super saturated α -Al cells surrounded by silicon rich interconnected network which contributes to significantly higher strength. There is a need for optimised heat treatment cycle for relieving the residual stresses without completely degenerating the cellular and cellular dendritic structures. As reported in literature, direct ageing and stress relieving treatments are focussed on temperature ranges of 130°C to 200 °C and 290 °C to 330°C leaving a gap between both the treatments. In this work, direct ageing at 245 °C was investigated for its influence on microstructure, hardness, and tensile behaviour. It is observed that direct ageing at 245°C is superior to aging at 300 °C and it gives optimum combination of strength and ductility. 2. Materials and Methods AlSi10Mg blocks were fabricated through LPBF process using EOS M290 machine in nitrogen atmosphere. The methodology was designed to understand the effect of direct ageing at 245 °C on the microstructure and mechanical properties of the LPBF AlSi10Mg and compare it with conventional T5 heat treatment. Details of heat treatment are given in Table 1. The samples were loaded into the furnace at the beginning of the heat treatment process and were gradually heated to the desired temperature at a rate of 10 °C per minute. All the samples are cooled to ambient

Table 1. Details of heat treatment conditions

Heat treatment condition

Sample code

Temperature (°C)

Time (minutes)

As-built

AB

--

--

Direct Ageing

41 42 43 44

30 60 90

245

120 120

T5

SR

300

temperature after direct ageing and T5 treatments by air cooling in ambient air. Samples were cut in vertical orientation i.e., the longitudinal axis of tensile samples is parallel to the build direction. Microstructures of as-built and heat- treated samples are observed after polishing and etching with Keller’s reagent (95% water, 2.5%HCl, 1.5% HNO 3 and 1% HF) using an optical microscope (Leica DMi8C) and SEM (Jeol IT300).