Low Cycle Fatigue Properties of Sc-Modified AA2519-T62 Extrusion

Abstract

This investigation presents the results of research on low cycle fatigue properties of Sc-modified AA2519-T62 extrusion. The basic mechanical properties of the investigated alloy have been established in the tensile test. The low cycle fatigue testing has been performed on five different levels of total strain amplitude: 0.4%; 0.5%; 0.6%; 0.7% and 0.8% with cycle asymmetry coefficient R = 0.1. For each level of total strain amplitude, the graphs of variations in stress amplitude and plastic strain amplitude in the number of cycles have been presented. The obtained results allowed to establish Ramberg-Osgood and Manson-Coffin-Basquin relationships. The established values of the cyclic strength coefficient and cyclic strain hardening exponent equal to k’ = 1518.1 MPa and n’ = 0.1702. Based on the Manscon-Coffin-Basquin equation, the values of the following parameters have been established: the fatigue strength coefficient σ’f = 1489.8 MPa, the fatigue strength exponent b = −0.157, the fatigue ductility coefficient ε’f = 0.4931 and the fatigue ductility exponent c = −1.01. The fatigue surfaces of samples tested on 0.4%, 0.6% and 0.8% of total strain amplitude have been subjected to scanning electron microscopy observations. The scanning electron microscopy observations of the fatigue surfaces revealed the presence of cracks in striations in the surrounding area with a high concentration of precipitates. It has been observed that larger Al2Cu precipitates exhibit a higher tendency to fracture than smaller precipitates having a higher concentration of scandium and zirconium.

Research on the Properties and Low Cycle Fatigue of Sc-Modified AA2519-T62 FSW Joint

“…Especially, for the highest values of strain amplitude (0.5, 0.6, and, 0.8%), it is difficult to identify the cyclic stabilization period and the samples undergo cyclic hardening until rapid failure. Compared to the base material, the obtained values of stabilized stress amplitude ( Figure 12 a) are lower for about 25% and also the reduction of fatigue life was reported [ 52 ]. At the same time, the registered plastic strain amplitudes of the AA2519-T62 FSW joint are much higher ( Figure 12 b).…”

“…The variations of stress and plastic strain amplitudes with the number of cycles are shown in Figure 12 a,b respectively. Regardless of the strain amplitude, three periods of fatigue life can be distinguished: cyclic hardening, cyclic stabilization, and final rapid drop in the value of stress amplitude until failure, which corresponds to the cyclic properties of the base material [ 52 ]. The length of each period differs depending on the used strain amplitude.…”

The influence of welding parameters on macrostructure and mechanical properties of Sc-modified AA2519-T62 FSW joints

“…12a-d). The fracture surface of Z81 joint is very similar to the fracture surface of base material [30] and it contains typical fatigue striations with occurring secondary cracks (marked with yellow arrows) (Fig. 12a).…”

Fatigue Behaviour of 7N01-T4 Aluminium Alloy Welded by Ultrasonic-Assisted Friction Stir Welding

“…Therefore, researchers mainly focus on the fatigue behaviour and fatigue performance of FSW joints. Generally, the S-N curve and fatigue crack growth behaviour of FSW joints are the effective ways to evaluate the fatigue performance of joints [ 3 , 4 ]. The fatigue performance of FSW joints is mainly related to the surface roughness, micro-defects, stress state and intermetallic compounds.…”