PSI - Issue 66

R. Fernades et al. / Procedia Structural Integrity 66 (2024) 49–54 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

50 2

1. Introduction Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) process that enables the use of powders to produce metallic components. The paper uses the AlMgSi1-T6 aluminium alloy which presents good weldability, low density, high strength, and excellent oxidation and corrosion resistance (Wu et al. 2016; Yan et al. 2019). Nowadays, LPBF is widely used to produce complex shapes metallic components. However, crack path and fatigue lifespan of the components is influenced by defect like pores, lack of fusion, residual stresses and high surface roughness (Yang et al. 2018). Regarding to the fatigue crack path of aluminum alloys, it is influenced by microstructural changes after the application of the heat treatments. Fiocchi et al. (2021) concluded that the application of heat treatments with temperature above 260ºC will contribute to the Si precipitation from the supersaturated Al matrix, leading to changes in path and a decrease in the mechanical properties. Also, T6 is widely used, but as concluded by Giovanni et al. (2019) the heat treatment was responsible for a microstructural and residual stresses homogenization that lead to lower crack growth rates (da/dN) for the same ΔK. Maskery et al. (2015) and Aboulkhair et al. (2016) observed a significant improvement in fatigue strength, with an increase achieved through solution treatment and ageing. These findings were also independently reported by Brandl et al. (2012) and Bagherifard et al. (2018).

Nomenclature AB

As-built specimens Additive manufacturing Compact tension Fatigue crack growth

AM CT FCG HIP

Hot isostatic pressing LPBF Laser Powder Bed Fusion ORL Overload ratio SR Stress relief treatment

2. Material, experimental procedures and methodology Compact Tension (CT) specimens were produced using a Renishaw machine, AM 400 model, with the following process parameters: a laser power of 350 W, a layer thickness of 30  m, and a scanning speed of 1.8 m/s. The nominal chemical composition of the aluminum alloy is summarized in Table 1. The specimen geometry used in this research was defined in accordance with the ASTM E647 standard. All specimens were built vertically with the layers deposited perpendicular to the loading axis. After the fabrication the specimens were subjected to distinct heat treatments: stress relief treatment (SR) conducted at a temperature of 250ºC for 2 hours followed by water quenching; and hot isostatic pressing (HIP) carried out at the same temperature and duration under atmospheric pressure of 100 MPa, and cooling to room temperature in ambient air. Fig. 1) presents the cross-sectional morphology of the as-built specimens where are observed the boundary between two melted pools. The predominant morphology observed is a supersaturated Si cellular-dendritic microstructure, where the aluminum content is represented by the grey color. Fatigue crack growth tests (FCG) tests were performed at room temperature under mode I loading conditions with constant amplitude (R=0.05), sinusoidal wave, and a cyclic frequency of 10 Hz, using an Instron ElectroPuls E10000, servo-electric testing machine. The crack length was measured by employing a traveling microscope.

Table 1. Chemical composition of the AlSi10Mg aluminum alloy (% wt) (1706 2021)

Al

Si

Mg

Mn 0.45

Cu

Ni

Fe

Zn

Pb

Sn

Ti

Bal.

9-11

0.25-0.45

0.05

0.05

0.55

0.10

0.05

0.05

0.15