Low Cycle Fatigue Behavior of Al-Zn-Mg-Cu Alloy Containing Zr and Sc
ZHANG Xiaoyu1,2, LENG Li3, WANG Zhanjun2
1 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083; 2 Beijing Research Institute of Mechanical & Electrical Technology, Beijing 100083; 3 School of Material Science and Engineering, Shenyang University of Technology, Shenyang 110870
Abstract: The single stage aging and RRA treatment on both microstructure and fatigue properties of Al-Zn-Mg-Cu alloy with Zr and Sc content were investigated through the transmission electron microscope and the low-cycle fatigue tests. In the single aging treatment state, the major precipitates inside the grains are η′ phases, the discontinuous equilibrium phase precipitates at the grain boundaries, and there exist the precipitate free zones near the grain boundaries. For the alloy subject to RRA treatment state, the precipitates both inside the grains and at the grain boundaries obviously grow, and the precipitate free zone widens. Under the low-cycle fatigue loading condition, the alloy with different heat treatment states exhibits mainly the stable cyclic stress response behavior at the total strain amplitudes ranged from 0.4% to 0.7%. However, at the total strain amplitude of 0.8%, the alloy shows mostly the cyclic strain softening followed by the cyclic strain hardening. At the total strain amplitudes from 0.4% to 0.6%, the RRA treatment can effectively prolong the low-cycle fatigue lives of the alloy. The relationships between the plastic strain amplitude, elastic strain amplitude and reversals to failure are linear, and can be described separately with the Coffin-Manson formula and Basquin equations. In addition, the fatigue cracks initiate transgranularly at the free surface of fatigue samples and propagate transgranularly.
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2017, Vol. 31 
