Corrosion-Fatigue Interactions for High Strength Aluminium Alloys

Regarding the interactions between fatigue and corrosion phenomena, one generally distinguishes between those for which fatigue occurs after the environmental exposure of the material (fatigue after corrosion) and those for which fatigue and corrosion occur simultaneously (fatigue-corrosion). This paper firstly proposes a succinct literature review on this subject, based on a rather practical approach. Regarding experimental results, it is shown that the fatigue performance of casting alloys is not susceptible to a prior corrosion exposure: the effect of corrosion is of the same order as the effect of surface (as-cast versus machined). On extruded 6xxx alloys, a 20-30% degradation of the fatigue strength on smooth specimens has been observed. This degradation nevertheless remains moderate when the relatively high exposure duration is considered (up to 11 years). On 6056 for fuselage skin, it was shown that the degradation in fatigue strength (30-50%) depended on both the sheet thickness and the temper. Finally, it was demonstrated that the increase of the stress concentration factor (K sub t) of the fatigue specimens or the presence of a weldment significantly decreases the influence of corrosion pre-exposure.