Crack growth behaviour of high strength aluminium alloy in 3.5%NaCl solution with corrosion inhibiting pigments

The fatigue crack growth rates of 7075-T76 aluminium alloy were measured in 3.5%NaCl solution with the presence and absence of corrosion inhibiting pigments, including chromate, phosphate, and a kind of nontoxic compound pigment, which was composed of phosphate, molybdate, citrate, and thiazole/imidazole derivatives. Microscopic features of fracture morphology were analyzed with scanning electron microscopy. In order to study the inhibition of these pigments, electrochemical polarization curves were measured in 3.5%NaCl (pH 6.2 and 3) solution with and without these pigments. The results showed that these pigments slowed down the fatigue crack growth rate of aluminium alloy mainly at the early propagation stage, and the retardation was related closely to the inhibition mechanism of the pigments, respectively.