Electrochemical conditions for environment-assisted cracking of 6061 Al alloy

We have investigated the influence of electrochemical conditions on environment-assisted cracking (EAC) of 6061 aluminum alloy in acidic chloride solutions. An EAC test was conducted by means of potential-controlled slow strain rate technique. In addition, thermal desorption spectroscopy (TDS) was employed to determine amount of hydrogen absorbed in the specimens under the same electrochemical conditions as those in the EAC tests. As a result, almost no EAC and very small amount of hydrogen absorption were found in a potential range lower than the film breakdown potential, while the higher potential induced severer EAC and much larger hydrogen absorption. The specimen pre-immersed in the chloride solution of pH 1, which derived voluntary breakdown of the oxide film, suffered preferential grain boundary attack. When the tensile test was conducted in air for the specimen with pre-immersion, the fracture strain became slightly smaller than that without pre-immersion. Moreover, the fracture strain drastically decreased and deep cracks was observed, namely the EAC occurred, when the pre-immersed specimen was examined by the EAC test under the cathodic condition which induced no EAC and very small hydrogen absorption for the specimen without pre-immersion.