Effect of specimen orientation and welding on the fracture and fatigue properties of 2195 Al–Li alloy

Abstract

In view of the use of 2195 Al–Li alloy in the construction of super-light-weight external fuel tank of space shuttles, bulkheads of reusable single-stage-to-orbit launch vehicles and in combat ground vehicles, the dependence of tensile properties, fracture toughness and fatigue resistance of this alloy on the specimen orientation and welding is very important and was studied. The T8 base alloy, with primary strengthening precipitates of T1 (Al2CuLi) phase, contained mainly brass-type texture. After welding with AA 4043 filler alloy, the fusion zone (FZ) consisted of T (AlLiSi) phase and in the heat-affected zone (HAZ) T1 phase was replaced by TB (Al7Cu4Li) phase, and micro-cracks were observed. The post-weld heat treatment (PWHT) resulted in the spheroidization of primary T phase and the precipitation of more T particles in the FZ, and the dissolution of TB phase and the re-precipitation of T1 phase in the HAZ. The yield strength, fracture toughness and fatigue threshold of the 2195-T8 alloy was observed to depend on the specimen orientation, with the lowest values obtained at 45° to the rolling direction. Welding resulted in a reduction in the tensile properties and fatigue strength. The post-weld heat treatment enhanced the yield strength, but no increase in fatigue strength was observed. Fracture mechanisms in various cases were evaluated by SEM examination of fracture surfaces and are discussed.