PSI - Issue 25

Francesco Leoni et al. / Procedia Structural Integrity 25 (2020) 348–354 Francesco Leoni / Structural Integrity Procedia 00 (2019) 000–000

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The homogenizing of the 95 mm diameter DC cast extrusion billet was carried out at a heating rate of 200 °C/h. The extrusion billet was then held at 540 °C for 2 hours and 15 minutes and subsequently cooled down to room temperature at a cooling rate of 300 °C/h. Prior to extrusion the billets were preheated at a heating rate of 100 °C/min up to 500 °C. The preheated billets were then hot extruded to blank wire of a target diameter of 2.7 mm at a ram speed of 0.6 mm/s. Following extrusion, the blank wire was first shaved and then cold drawn in steps down to the final diameter of 1.4 mm. In the cold-drawn condition the wire displays a Vickers hardness of about 130 HV 0.5 . Besides some minor surface imperfections, the wire surface appeared smooth and contained no cracks. Tensile testing was carried out in steps from RT and up to 500 °C at a constant strain rate of 10 -3 s -1 using an Instron 5985 testing machine equipped with a special heating chamber. Both ultimate tensile strength and elongation were determined. Fracture surfaces of the tested specimens were then analyzed using a scanning electron microscope (FEI Quanta 450 model). 3. Results and discussion The measured engineering stress-strain curves at different temperatures are shown in Figure 2. Note that the results reported here are the average of three independent measurements at each temperature.

Figure 2: Measured engineering stress-strain curves for the 1.4 mm diameter AA6082 filler wire at different temperature.

From these curves the data presented for the fracture strain in Figure 3A and the ultimate tensile strength (UTS) in Figure 3B have been extracted. As expected, the softening of the AA6082 alloy starts already at very low temperatures. The strength then continues to drop with increasing temperatures. At 500 °C the UTS is as low as 24 MPa. In contrast, the fracture strain shows a different temperature response. Up to 200 °C the fracture strain appears to be essentially unaffected by an increase in the testing temperature. However, at 350 °C the material starts to behave more ductile before it becomes brittle again at a temperature of 500 °C.