A study of the effect of precipitation aging on the deformation mechanisms, ductility response, and fracture behavior of an aluminum-lithium alloy

The effect of microstructure as a consequence of precipitation aging on the fracture behavior, deformation mechanisms, mechanical properties, and microstructures of alloy aluminum-lithium was studied. An aluminum alloy containing 2.6wt. %Li, 0.09wt.% Zr, and 0.11wt.%Cu was found to have very low tensile ductility consistently prior to the peak-aged strength condition independent of the thermal treatment. A transition was characterized by very low ductility in the slightly underaged condition up to the near peak-aged condition, then followed by a substantial increase in ductility with aging after the peak-aged treatment In order to better understand the deformation and fracture, a scanning electron microscopy study of the fracture surfaces of the Al-2.6wt. %Li-0.09wt. %Zr-0.11wt. %Cu tensile samples solution heat treated and artificially aged was performed to relate the mechanical behavior to microstructure in the precipitation hardened AI-Li alloy. SEM analysis of the surface features and fracture morphology of the alloy was performed to understand the mechanisms of fracture in relation to the ductile to brittle transition that resulted in the alloy from precipitation hardening. TEM analysis was also performed to characterize the deformation behavior, and revealed the distribution of precipitates, including Al3Li (delta') and Al3Zr-Al3Li, in the microstructure at very high magnifications. It was found from this study that the ultra-low ductility occurred immediately prior to the peak-aged temper. It was also found that a substantial increase in the ductility of the alloy occurred immediately after peak-aging occurred and continued with further precipitation aging of the alloy.