Evaluation of Fatigue Properties in Future Aircraft Material, Aluminum-Lithium Alloy

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Wide range of fatigue properties under rotating bending were investigated in two kinds of aluminum Lithium (Al-Li) alloys, 2090 and 8090, which are predicted to be used for the future aircraft. The results were compared with the conventional aluminum alloys, 2024 and 7075. The results obtained are summarized as follows ;1. Tensile strength of the AI-LI alloys were approximately the same as those of 2024 alloy, but were lower than those of 7075 alloy. On the other hand, the elongation and reduction of area were extremely small compared to conventional aluminum alloys. The fatigue strength of Al-Li-alloys was superior to that of conventional Al, alloys in the region of long fatiaue life (more than 10^5 cycles). It is suggested that the excellent fatigue strength of AI-LI alloys is mainly due to their high resistance to crack initiation.2. The fatigue strength was decreased by the underaging and overaging process. This was due to the decrease in both crack initiation and growth resistances. The crack initiation and growth were controlled by the precipitation of delta '-Phase during aging.3. Fatigue strength in 3%NaCl solution is much lower than that in air for both Al-Li alloys and conventional AI alloys. The corrosion fatigue strength of AI-LI alloys is not influenced by aging condition, and it is better than that of AI alloys.4. The notch sensitivity of AI-LI alloys is less than that of conventional AI alloys, especially in 8090 alloy. Non-propagating crack was observed only in 8090 alloy with the highest stress concentrator, whose stress concentration factor is 8.18.