Shan Zhaojun, Liu Shengdan, Ye Lingying, Li Yiran, He Chunhua, Chen Jin, Tang Jianguo, Deng Yunlai, Zhang Xinming
School of Materials Science and Engineering, Central South University, Changsha 410083, China.
Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China.
Materials (Basel). 2020 Jul 22;13(15):3248. doi: 10.3390/ma13153248.
The effect of different precipitate microstructures obtained by different heat treatments on fatigue behavior of 7020 aluminum alloy was investigated. The fine Guinier Preston I (GPI) zones in the under-aged alloy can be repeatedly sheared by dislocations produced in cyclic loading, making the fatigue crack initiate difficultly and fatigue crack path propagate tortuously. Fatigue strength and fatigue crack propagation resistance of the alloy with shearable precipitates are much higher than those of the alloy with unshearable precipitates. The peak-aged alloy with continuous grain boundary precipitate (GBP) and narrow precipitate free zone (PFZ) is prone to initiate fatigue cracks and reduce fatigue strength. With the growth of unshearable precipitates, the fatigue strength of the alloy firstly increases and then decreases. Precipitates with moderate size in the over-aged alloy improve the roughness-induced crack closure (RICC) effect. Soft matrix with appropriate width between the precipitates can promote the slip reversibility and relax the crack tip stress. The fatigue strength of the moderately over-aged alloy reaches to 122.1 MPa at 10 cycles of loading, and the fatigue crack growth rate (FCGR) is 35.6% slower than that of the peak-aged alloy at Δ of 10 MPa·m.
研究了不同热处理获得的不同析出相微观结构对7020铝合金疲劳行为的影响。欠时效合金中的细小Guinier Preston I（GPI）区可被循环加载产生的位错反复剪切，使疲劳裂纹难以萌生且疲劳裂纹扩展路径曲折。具有可剪切析出相的合金的疲劳强度和抗疲劳裂纹扩展能力远高于具有不可剪切析出相的合金。具有连续晶界析出物（GBP）和狭窄无析出带（PFZ）的峰时效合金易于萌生疲劳裂纹并降低疲劳强度。随着不可剪切析出相的长大，合金的疲劳强度先增加后降低。过时效合金中尺寸适中的析出相改善了粗糙度诱导裂纹闭合（RICC）效应。析出相之间具有适当宽度的软基体可促进滑移可逆性并松弛裂纹尖端应力。在10次加载循环时，适度过时效合金的疲劳强度达到122.1MPa，在Δ为10MPa·m时，其疲劳裂纹扩展速率（FCGR）比峰时效合金慢35.6%。
