The Anisotropy of Serrated Flow Behavior of Al-Cu-Li (AA2198) Alloy

The serrations in tensile stress-strain curves for Al-Cu-Li-based AA2198 alloy sheets were studied in various temper conditions. The alloy exhibited typical Portevin-Le-Chatelier effects with intense serrations in the stress-strain curves. This was observed in the solution-treated condition, while the intensity and frequency of serrations decreased upon aging. Detailed microscopic examination together with thermal stability studies showed the absence of delta' (i.e., metastable Al3Li) precipitate in the alloy. As a result, the shearing of d' precipitates by dislocations during plastic deformation did not occur in the present alloy. The quasistatic tensile testing as a function of test temperature, strain rate and temper condition and the acoustic emission study confirmed that the combined interaction of copper and lithium atoms with mobile dislocations is the underlying mechanism for the plastic instability in this alloy. The alloy displayed significant anisotropic behavior in terms of mechanical properties and serration characteristics, and these observations are related to the difference in the effective grain size of the samples in various orientations. (C) The Minerals, Metals & Materials Society and ASM International 2019