An investigation of the fatigue behaviour of the aluminium alloy AA 6013 T6 in a corrosive medium

The aluminium alloy AA 6013 T6 is considered to be a possible alternative f or the alloy AA 2024 T3 used currently in aircraft construction. In order t o prove the material for use, an extensive series of tests were carried out to establish the fatigue behaviour of the material compared with that used currently. The materials were tested both in air and in artificial sea wat er Specific metallographical investigations of the area surrounding the cra ck tip of specimens of the alloy AA 6013 T6 fatigue tested in simulated sea water revealed that the presence of hydrogen contributed significantly to the damage of the material. The presence of coarse precipitates is shown to play an important role in this process. Under cyclic loading in a corrosiv e medium the interface between the matrix and these particles is found to u ndergo significant changes resulting in the initiation of cracks emanating from the particles and their subsequent fracture. If the number of particle s is plotted against the loading frequency used in the fatigue tests a surp rising dependency is discovered. The results of micro-hardness measurements and investigations into the hydrogen absorption are also found to exhibit a similar frequency dependency. The corrosion mechanism taking place during cyclic loading in a corrosive medium is discussed and found to correlate w ell with the processes occuring during crevice corrosion.