Effect of Exposure Time on Stress Corrosion Cracking Susceptibility of Al-Zn-Mg-Cu Alloys

Abstract

The effect of exposure time on resistance to stress corrosion cracking (SCC) of Al-Zn-Mg-Cu alloys has been investigated. Casted Al-Zn-Mg-Cu alloys were homogenized at 450 degrees C for 24 hours and exposed in 3.5% NaCl solution under the stress of 80% of yield strength (YS) for 10, 20, and 40 days. The specimen were subsequently tested along longitudinal (L) directions in the air at a strain rate of 1x10(-3) s. Grain boundary precipitations (GBP) and pits in the surface can be crack initiation sites for SCC in the environment of anodic dissolution. The reduction on tensile elongation was much higher in the constant load tested specimens comparing to the specimen tested in the air. An interdendritic fracture was observed after the tensile test due to the presence of GBP. The phase boundaries between matrix and nano-phases seemed to serve as initiation sites of pitting corrosion, but reducing the volume fraction of GBP should be preceded to increase the resistance to SCC of Al-Zn-Mg-Cu alloys.