LC4铝合金在NaCl水溶液中应力腐蚀临界破裂电位及裂尖状态的研究

采用控制电位下的恒载荷拉伸试验测得ＬＣ４铝合金在３０℃、５０℃、９０℃的０．５ｍｏｌ／ＬＮａＣｌ水溶液（ｐＨ＝７）中的应力腐蚀临界破裂电位Ｅｃｒｉ分别为－７２０ｍＶ、－７６０ｍＶ、－８５０ｍＶ（ＳＣＥ）．体系电位负于Ｅｃｒｉ时不发生应力腐蚀破裂．Ｅｃｒｉ随介质温度Ｔ升高而向负方向移动，Ｅｃｒｉ与Ｔ大体呈直线关系：Ｅｃｒｉ＝－Ａ１５５－２．１７Ｔ（ｍＶ）．用改进的模拟闭塞电池研究了裂纹尖端化学状态的变化：当通入闭塞区的阳极电流密度为１ｍＡ／ｃｍ２时，其溶液ｐＨ值从７降至３．３，Ｃｌ－浓集倍数高达４．断口呈典型的沿晶应力腐蚀开裂形貌．

AN INVESTIGATION OF CRITICAL SCC POTENTIAL AND CHEMICAL STATES WITHIN CRACKS FOR ALUMINIUM ALLOY LC4 IN NaCl SOLUTIONS

Constant load and potentiostatic techniques were used to study the critical SCC potential of aluminium alloy LC4 in 0.5mol/L NaCl solution. It was found that the critical potentials for this system at 30℃, 50℃, 90℃ are -720mV, -760mV, -850mV (SCE), respectively, below which the SCC will not occur. The dependence of the critical potential upon temperature follows a linear equation: Ecri=-655-2.17t (mV). The simulated occluded corrosion cell was modified and used to investigate chemical changes within stress corrosion cracks. When an anodic currellt of 1mV/cm2 was passed through, the pH value of the occluded cell solution dropped down from 7 to 3.3 and the faCtor of Cl- enrichmeat in the solution could be up to 4. Scanning electron fractographs of SCC of alloy LC4 showed a typical intergranular cracking feature.