晶粒尺寸对Al-Zn-Mg铝合金应力腐蚀敏感性的影响
Effect of Grain Size on Stress Corrosion Cracking Susceptibility of an Al-Zn-Mg Alloy
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摘要: 采用慢应变速率拉伸试验、扫描电镜断口观察和透射电镜晶界微观结构观察及析出相统计等方法,研究了两种晶粒尺寸的Al-Zn-Mg铝合金在3.5%(质量分数)NaCl溶液(pH=6)中的应力腐蚀行为。结果表明:晶粒度大的Al-Zn-Mg铝合金的应力腐蚀敏感性比晶粒度小的合金要高;透射电镜的统计观察分析表明,小晶粒度小的合金的晶界析出相覆盖率高于大晶粒度合金的晶界析出相覆盖率。在一定的晶界析出相面积范围之内,析出相面积分数高的Al-Zn-Mg合金应力的腐蚀敏感性小于析出相面积分数低的Al-Zn-Mg合金。Abstract: The stress corrosion cracking behaviors of two Al-Zn-Mg alloys with different grain sizes have been investigated using slow strain rate testing (SSRT)in 3.5% (mass fraction) NaCl solution at 50 ℃. The results indicate that the Al-Zn-Mg alloy with larger grain size has higher SCC susceptibility than the small-grain alloy. Statistical investigations by transmission electron microscopy (TEM) reveal that the area fraction of grain boundary (GB) precipitates on GB for the small-grain alloy is higher than that of larger grain alloy. This result implies that the area fraction of GB precipitates is the dominant mechanism for SCC of the Al-Zn-Mg alloy.