Stress corrosion cracking (SCC) behaviors of Al-4.5 Zn-1.5 Mg alloy were investigated in 3% NaCl solution at 30C and 70C, using a slow strain rate technique (SSRT). The effects of crosshead speed (CS), specimen thickness and temperature on the SCC behaviors were studied in this method. The susceptibility to SCC increased with decreasing CS and was independent of specimen thickness at both temperatures. Crack propagation rate showed constant value for the changes of CS or specimen thickness. It

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... as become clear that SSRT method is available for SCC test method of this alloy-corrosive system. The results of tesnile test in laboratory air after exposure to the corrosive at 70C without stress indicated that the loss in ductility of specimens is the results of intergranular hydrogen embrittlement. It has been found by a high voltage electron microscope observation (JEM 1000) of specimens pre-exposed to the corrosive that the strain field contrast revealed hydrogen bubbles was formed in association with the grain boundary precipitates. The results of ion micro analysis for the specimen after SCC test in 3 % NaCI deuterium solution at 70C has shown that the peak of secondary ion intensity corresponding to deuterium (m/e =2) is observed at the oxide-metal interface. From above results SCC of the specimen has been explained by a hydrogen embrittlement mechanism.