抄録
Stress-corrosion cracking behaviors of Al-Zn-Mg alloys in 3%NaCl aqueous solutions (room temperature to 70°C) with or without oxidizers were examined by means of optical and electron microscopy, and the mechanisms of the stress-corrosion cracking were discussed.
The results obtained from a constant total strain test for Al-2.64%Mg-4.63%Zn alloy in 3%NaCl+3%K2Cr2O7+3.6%CrO3 aqueous solution (70°C) showed that cracks initiated at the edges of three adjacent grains at a relatively low applied stress, and that cracks also initiated at both sites of the three adjacent grains and the normal grain boundaries which have a large angle against the stress direction at a high applied stress. The precipitates at grain boundaries accelerated an intergranular cracking, and even if the condition wherein the precipitates were not observed in grain boundaries through a transmission electron microscope, the intergranular cracking could occur. Although the stress-corrosion cracking propagated predominantly along grain boundaries, some transgranular cracks, which appeared to be mechanically ductile fracture, were also observed in the fractographs. The effects of Cl− ion concentration, pH, oxidizers and temperature on stress-corrosion cracking were also examined, and it was found that the susceptibility to stress-corrosion cracking was strongly affected by the above factors. The results of stress-corrosion cracking tests obtained from a constant total strain method, a constant load method and a constant strain rate method did not show good coincidence.
