| Fatigue crack growth behavior of various Al-Li alloys was examined with different environments, including air, vacuum and 3.5% NaCl solution, and load ratios. Al 2090 and RSP 644-B showed the better resistance to fatigue crack growth in air than conventional high strength Al alloys such as Al 7075, but MA 905-XL with the fine grain size showed the higher fatigue crack growth rate because of low crack closure level coming from smooth crack path and crack plane. These Al-Li alloys showed the lower fatigue crack growth rate in vacuum and the higher fatigue crack growth rate in 3.5% NaCl solution than in air. But MA 905-XL showed the lower fatigue crack growth rate in 3.5% NaCl solution than in air, which is thought to come from :he corrosion product induced crack closure in 3.5% NaCl solution. In Al 2090 alloys, △K_(th) value decreased linearly in air with increasing the load ratio, but △K_(eff,th) after compensating for the crack closure showed an almost constant value independent of the load ratio. MD345 showed the lowest fatigue crack growth rate in air among the three Al-Cu-Li-Mg-Ag alloys, which is thought to be clue to the highest crack closure level. Weldalite 049 with the highest strength showed the highest △K_(th) among the three alloys, an d also showed the highest fatigue crack growth rate in 3.5% NaCl solution because of the highest corrosion rate. |
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