PSI - Issue 53

Luca Marchini et al. / Procedia Structural Integrity 53 (2024) 203–211 Author name / Structural Integrity Procedia 00 (2019) 000–000

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match the final dimensions of the AM samples. To achieve their ultimate mechanical properties, the specimens were subjected to distinct heat treatment processes. For the forged samples, this process consisted of a one-hour solution treatment at 820 °C, followed by rapid cooling in ambient air, followed by aging for 5 hours and 30 minutes at 490 °C. Conversely, for the AM samples, only an aging treatment was carried out, holding the sample at 490 °C for 4 hours to promote the formation of precipitates. These samples derive from a previous work where additional data can be found (Tonolini et al. , 2022). Furthermore, samples of more conventional die tool steel H11 were also machined and included in the testing. The chemical composition of all investigated samples is reported in Table 1. The actual samples for the hot-corrosion test were machined by wire EDM (Electrical Discharge Machining) from their cylindrical shape to obtain 20x10x5 mm samples with a through hole on the larger face. Prior to the immersion tests, the microstructural characterization was carried out on mirror-polished samples etched with Nital 2% by using a DMI 5000M optical microscope (Leica, Wetzlar, Germany) provided with an image analysis software (Las 4.12). By analyzing 10 images at 500x magnification collected from each sample, the pores fraction area was measured as the ratio of the total area of porosities to the area of the samples that were subjected to analysis.

Table 1 - Samples mean chemical composition: maraging steel additively manufactured (AM) and forged (F); H11 tool steel.

El. (wt%)

C

Si

Mn 0.3 0.03

Cr 0.1 0.1 5.3

Mo

Ni

Co

V

Ti

Fe

AM

0.01

0.2

5

17.9 18.3

13.4 9.75

- -

-

Bal. Bal.

F

0.004

0.02

4.95

1.13

H11

0.37

1

0.4

1.3

-

-

0.4

-

The static immersion test apparatus, schematized in Fig.1 involves the use of an electric furnace equipped with a graphite crucible. The Al alloy used was a primary low iron AlSi7Mg (B356.2). Approximately 1 kg (1020 ± 20 g) of Al alloy was molted for each test and held at 740 ± 3 °C. The quantity of molten Al was defined to guarantee a sufficient volume to cover the sample and to be far from a possible Fe saturation condition for the melt. The temperature was chosen considering that the AlSi7 alloy has a higher melting temperature than conventional AlSi10 alloys typically used for HPDC applications.

Fig. 1 – Schematization of the static immersion test apparatus