# Selective Laser-Melted Alloy 625: Optimization of Stress-Relieving and Aging Treatments
## 2 Materials and Method  
The selective laser-melted alloy 625 was provided in the as-built condition in the form of bars printed horizontally, as shown in Figure 2. The dimensions of the transversal section were 12.5 mm \(\times\) 12 mm, and the length was equal to 100 mm. The adopted bars were manufactured for each layer using the island scanning strategy, thus forming a chessboard pattern with a layer thickness of 30 \(\upmu\)m, and the laser parameters are summarized in Table 3. The printing parameters were optimized by the producer aiming to minimize the residual porosity and improve the mechanical characteristics.  
Figure 2: As-built selective laser-melted bars made of alloy 625 adopted in this work. (**a**) View of some of the printed rods; (**b**) details of the island scanning strategy adopted for the inner chessboard pattern.  
The aging treatments were carried out in a laboratory furnace. The tensile specimens were machined along the longitudinal direction of the bars. The samples for microstructural analyses and hardness tests were prepared according to the conventional metallographic technique. In particular, cutting was performed using silicon carbide wheels with a Remet (model TR100 EV) cutting machine (Bologna, Italy). The mounting of the metallographic samples was performed in hot thermo-setting phenolic resin using a mounting machine. The grinding and polishing operations were performed using a Struers machine (Ballerup, Denmark). Chemical etching was carried out in five parts HCl diluted in one part 30% H\({}_{2}\)O\({}_{2}\) for 10 s [5; 39; 40]. Microstructural analyses were carried out via a Leica light optical microscope (Wetzlar, Germany) and a Zeiss scanning electron microscope (Oberkochen, Germany). The HV30 Vickers hardness tests were conducted using a Wolpert Testor 930 hardness tester (Ludwigshafen am Rhein, Germany) according to the EN ISO 6507 standard [41]. The hardness tests of the selective laser-melted material were performed on the ZX plane. In each tested condition, five hardness measurements were carried out. Tensile tests were performed in selected conditions according to the EN ISO 6892 standard using round proportional specimens (6 mm gauge length and diameter) with an INSTRON 4507 testing machine (Norwood, MA, USA) [42]. The intergranular corrosion tests were carried out in a solution of ferric sulphate and sulfuric acid for 120 h, according to the ASTM G28--Method A standard [38]. The size of the corrosion specimens was 12 mm \(\times\) 12.5 mm \(\times\) 8 mm. They were cut along the longitudinal direction of the printed bars; then, they were prepared and polished according to the ASTM G28--Method A standard [38]. The mechanical strength requirements are reported in the ASTM B446 standard [12]. For corrosion resistance, a maximum corrosion rate of 1.20 mm/year was considered since it represents a typical prescription for most of the industrial applications of this grade.  
The experimental data on the conventional forged and soft-annealed (1038 \({}^{\circ}\)C) alloy 625 were elaborated for comparison purposes from the literature data already published by [PERSON] et al. [11; 43; 44]. In this case, the material was taken from an as-forged 60 mm diameter rod. All the soft-annealing and aging treatments were carried out on the metallographic samples and the tensile and corrosion specimens using a laboratory furnace. The samples for metallographic analyses and hardness tests were cut from the received rod with dimensions of 10 mm \(\times\) 10 mm \(\times\) 10 mm. The tensile specimens were machined from the longitudinal direction of the received rod. Hardness, tensile, and corrosion tests were carried out considering the same procedure and the reference standards adopted for the tests on the selective laser-melted material [38; 41; 42].