PSI - Issue 42

Teresa Morgado et al. / Procedia Structural Integrity 42 (2022) 1545–1551 Morgado et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. RM zone where the sample was cut (a) One of the RM samples; (b) multiple pictures from inverted microscope taken in one sample zone; (c) one of the sample pictures obtained by inverted microscope; (d) picture with threshold obtained with Image J software.

3.3. Fatigue tests

The fatigue tests were carried out using the universal servo-hydraulic equipment of mechanical tests Instron 8802, which has a maximum load capacity of up to 100 kN. For the implementation and treatment of test data, it was associated with the Instron 8800 controller and a computer with the Instron SAX V7.0 software. It used a sinusoidal wave on the fatigue tests with a constant amplitude and stress ratio of R=0.05. It also applied a frequency ƒ= 10 Hz during each test and considered a room temperature of 25ºC. The tests were performed until complete failure of the specimens or after 6.0x10 6 of load application. 4. Results and discussion Table 1 presents the results of the Vickers’s hardness values and total manufacturing defect areas. From the manufacturing defects study, all defects detected were porosities. The Vickers microhardness tests showed that the hollow rectangular cross-section extruded piece in 6060 T4 (RO) presents the highest Vickers hardness value; nevertheless, the RO piece did not present the lower value of total defect area. The CO and the RM pieces, with the same material and thermal treatment (6060 T1 aluminium alloy), present a discrepancy value of approximately 5 HV. This discrepancy can be justified by the different cross-section geometry of the pieces since area of the total defects is approximately double. On the other side, the Billet piece, obtained by die-casting process, presents the lowest Vickers hardness value but not the highest value of the total defect area. Therefore, independently of the heat treatment (T4 and T1) the area of the total defects decreases comparatively with the Billet piece. The piece that presented the highest value of total defects area was hollow circular cross-section in 6060 T1 (CO); this proves that the pieces cross section geometry is essential for the appearance of manufacturing defects. In addition, the cross-section geometry of