3.5%NaCl腐蚀环境下2种航空铝合金材料疲劳性能试验研究

RELATIVE TESTS ON FATIGUE PROPERTIES OF ALUMINUM ALLOYS IN 3.5% NaCl CORROSION ENVIRONMENT

腐蚀环境下的疲劳性能是航空金属结构疲劳寿命设计的重要前提,为此,试验测定了2种航空铝合金材料(2E12-T3、7050-T7451)的光滑试样和缺口试样在干燥大气和3.5%Na Cl腐蚀环境下的疲劳性能,在试验数据的基础上进行性能对比,并对试样断口进行扫描电镜(SEM)分析,研究了3.5%Na Cl腐蚀环境与载荷联合作用对腐蚀疲劳性能的影响机理,研究结果表明:3.5%Na Cl腐蚀环境对2种铝合金材料的疲劳性能均产生不利影响,且腐蚀与疲劳载荷的交互作用随着应力水平的降低而增强,疲劳性能下降更明显;与光滑试样相比,腐蚀环境对铝合金2E12-T3缺口试样疲劳性能的影响更大,但对铝合金7050-T7451缺口试样疲劳性能的影响却变小;在腐蚀环境下,裂纹尖端易发生电化学反应产生腐蚀产物和[H]离子,腐蚀产物的存在会阻碍裂纹闭合,同时,[H]离子导致裂纹尖端的氢脆效应,加快裂纹扩展,使疲劳性能降低。

Fatigue properties in typical corrosion environments are the preconditions of fatigue life design for metallic structures in aircrafts. Fatigue tests were performed on smooth and notched specimens subjected to constant amplitude loading in two environments of dry air and 3.5% NaC1 sodium chloride solution respectively to determine the pure and corrosion fatigue properties of two categories of aluminum alloys 2E12-T3 and 7050-T7451. Corrosion fatigue properties in the two environments were analyzed and compared with each other. The interaction mechanisms between corrosion and fatigue were deduced from fractographical studies by using scanning election microscope （SEM）. The results show that the 3.5% NaC1 sodium chloride solution has a detrimental influence on fatigue properties of both aluminum alloys. The interaction between corrosion and fatigue loading increases with the decreasing of stress level, and ultimately decreases the fatigue strength. The effect of 3.5% NaC1 sodium chloride solution on fatigue behavior is more significant for the notched specimen of aluminum alloy 2E12-T3 than for the smooth specimen, but it is insignificant for the notched specimen of aluminum alloy 7050-T7451 as against for the smooth specimen. The crack closure is prevented by the corrosion products produced from the electrochemical attack at the crack tip in corrosion environment. Furthermore, the hydrogen embrittlement effect resulted from the electrochemical attack enhances the crack propagation to cause the degradation of fatigue properties.