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Keywords
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High-strength aluminum alloys, Low-cycle fatigue, Stress aging, Microstructure, Mechanical properties
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Abstract
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The effect of a novel heat treatment, i.e., aging under superimposed external stress, on the fatigue performance and microstructural evolution of EN AW-7075 alloy is presented. Stress aging, a combination of heat treatment and superimposed external stress, can enhance the mechanical properties of EN AW-7075 alloy under monotonic loading due to the acceleration of precipitation kinetics. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) revealed that a longer aging time and the presence of superimposed stress both promote the formation and growth of precipitates, i.e., the precipitation of a higher fraction of strengthening η´ precipitates. This has been confirmed by differential scanning calorimetry (DSC) heating experiments of stressless and stress aged states. In case of stress aging this is combined with a reduction of dimensions of precipitate-free zones near grain boundaries. Cyclic deformation responses (CDRs) and half-life hysteresis loops were evaluated focusing on the low-cycle fatigue (LCF) performance of the different conditions. A Non-Masing behavior and the noticeable cyclic hardening seen in case of the specimens aged for a short time of 2 h indicate the occurrence of dynamic strain aging (DSA) during cyclic deformation. Stress aging allows the enhancement of the monotonic mechanical properties of EN AW-7075 without degrading the alloy performance in the LCF regime. Results obtained herein will be of importance for the development of stress-aged aluminum components with superior properties.
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