Effect Of Liquid NaK On Crack Propagation In Aluminium Alloys

Many Al-Li alloys exhibit low fracture toughness, particularly in the T-L direction. One mechanism proposed to account for this is liquid metal induced embrittlement (LMIE) resulting from the presence of a liquid NaK (impurity) phase. In this study, the effect of test temperature on the impact behaviour of an Al-Li alloy containing controlled amounts of NaK is examined. This is compared with the behaviour of the same alloy fractured under quasi-static conditions. Finally, the crack propagation behaviour in the presence of liquid NaK of a similar, non-lithium containing alloy, 2024, is studied using short double cantilever beam (DCB) specimens and a da/dt vs K diagram for the system is developed. It was found that the impact specimens did not show significant signs of embrittlement over the temperature range studied whilst previous studies of the same alloys showed embrittlement at temperatures near ambient. This was attributed to the slow rate at which NaK assisted cracks propagate in such alloys.