长期大气腐蚀对2A12-T4铝合金结构疲劳性能的影响

开展了2A12-T4铝合金平板试验件、螺栓干涉试验件和冷挤压后螺栓干涉试验件在海南万宁大气环境下暴露腐蚀7年、12年和20年后的疲劳试验,进行了试验件腐蚀形貌分析、断口形貌分析和断口附近的侧边损伤形貌分析,并讨论了结构裂纹萌生位置、结构断裂部位和寿命变化规律等疲劳特征的形成原因和机理。研究结果表明:平板试验件和冷挤压后螺栓干涉试验件在腐蚀20年后的疲劳寿命与腐蚀12年相比基本持平,而螺栓干涉试验件的疲劳寿命持续下降;在长期大气腐蚀环境下结构局部强度的衰减速度排序是:螺栓干涉强化部位>未强化部位>冷挤压后螺栓干涉强化部位;2A12-T4铝合金材料在L-S面中部的腐蚀敏感性与L-S面侧边和L-T面相比更弱;L-S面发生的沿晶腐蚀是疲劳开裂的主要萌生源,长期腐蚀后侧面密集损伤导致的能量分散是使腐蚀20年后平板试验件寿命与腐蚀12年相比无明显下降的主要原因。

Effect of long-term atmospheric corrosion on fatigue behavior of 2A12-T4 aluminum structures

Fatigue tests on 2A12-T4 aluminum alloy plate specimens, bolt interference fitted specimens and bolt interference fitted specimens with cold expansion are carried out after the specimens are exposed in Wanning, Hainan Province for 7 years, 12 years and 20 years. Corrosion morphologies, fatigue morphologies of fracture surfaces and side surfaces beside fracture site are analyzed. Furthermore, origins and mechanisms of fatigue characters, such as the positions of cracks initiate, the fracture sites of specimens, the change laws of fatigue lives, etc., are discussed. The results show that the fatigue lives of plate specimens and interference fitted specimens with cold expansion after being exposed for 20 years are almost the same as those of the specimens exposed for 12 years, while the fatigue lives of interference fitted specimens continue to decrease. The decrease of local intensity ranks in the order: section of interference fitted hole > section of untreated material > section of interference fitted hole with cold expansion. The corrosion susceptibility on the mid-area of L-S surface is weaker than that of L-T surface and on the side-area of L-S surface. The sites where intergranular corrosion occurs on the L-S surface become potential sources of fatigue cracking, and dense damage on the L-S surface due to long-term atmospheric corrosion is the main cause that the fatigue lives of plate specimens and interference fitted specimens with cold expansion do not decrease after 20 years of exposure than 12 years.