Effect of pre-corrosion on crack initiation behavior of friction stir welded aluminum alloy 2024-T3 in high and low cycle fatigue regimes

The effect of microstructural inhomogeneity and pre-corrosion in 3.5% NaCl solution is investigated on the fatigue crack nucleation behavior of welded AA2024-T3. The localized corrosion affects the heat-affected zone more than the weld nugget zone. The formation of corrosion pits often occurs in the region between the adjacent Al-matrix and intermetallic particles due to the reverse polarity behavior of S-phase precipitates (Al2CuMg) in the saltwater environment. Further, the long-term stability of the welded joint is examined by immersing the specimens in 3.5% NaCl solution for different time intervals ranging from 10 hrs to 200 hrs. After 100 hrs of immersion in the salt water, high and low cycle fatigue behavior of the corroded samples has been examined. Long-term exposure to the saltwater environment results in intergranular corrosion due to localized pitting. The micro-mechanism of the pitting process under salt water and its effect on fatigue lives is studied.