13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- from the melt that has been degassed in the furnace. The chemical composition of the alloy is given in Table 1. Table 1. Chemical composition of AA7050. Main alloying elements, wt pct Zn Cu Mg Zr Ti Al 6.15 2.2 2.1 0.13 0.03 balance The specimens were tested using a set-up developed at SINTEF Materials and Chemistry with an Instron 5944 series tensile test machine equipped with a 2-kN load cell. The specimen was heated up using an induction heating coil system which was controlled by a Eurotherm™ temperature controller. A quartz-glass tube coated with boron nitride aerosol on the inside, was used to enclose the center part of the sample in order to avoid liquid breakout during the fully melt phase. The coating was intended to prevent the sticking of the liquid aluminum onto the quartz tube which might affect the force measurement due to the added friction resistance. The experimental cycle (for both re-melt and mechanical testing temperature) is shown in Figure 1. Figure 1. Experimental cycle of the tensile test. The test cycle that we used in our experiment was as follows. First, we heated up the sample from room temperature up to Tmax = 635 °C, which is the liquidus of an AA7050 alloy based on the JMat-Pro software (Figure 2). Then we held the sample at Tmax for 60 seconds to assure that the central part of the specimen is fully liquid. Subsequently, we cooled down the sample to the test temperature with a cooling rate of 1 °C/s. We then held the sample at this test temperature for approximately 90 seconds to let the temperature in the specimen stabilize. Then we performed the mechanical tensile testing of the sample at a certain displacement rate until the force value was approximately zero after the fracture.
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