Microstructure evolution during hot working of an Al-Li-Cu-Mn alloy

The 2090 experimental alloy was deformed in torsion in the temperature range of 300oC through 500oC at strain rates of 0.01 to 5 s-1. The torsion results were analyzed using the equation A (sinh α σ)n Z = ε exp (QHW/RT), where Z is the Zener-Hollomon parameter. For the stress multiplier α = 0.052 kJ/mol, an activation energy of 219 kJ/mol was determined. During hot working, the mechanism of dynamic recovery was operating. The average subgrain size (d) changed with the conditions of deformation according to the relationships: d-1 = 0.057 lnZ - 1.619 and σm = 155.036 d-1 - 5.33. The need to reduce the anisotropic behaviour through a better understanding of deformation mechanisms was the overall goal of this research. Studies using transmission electron microscopy (TEM) were performed with the aim of understanding the difference in deformation mechanisms at 500oC, 400oC, and 300oC. Electron microscopic analyses have revealed a large number of helical dislocations after deformation at 500oC. The nature and density of precipitates depends on deformation temperature and strain rate. The properties of a material during hot working are influenced by heterogeneous precipitation, which occur on dislocations and grain boundaries. Dynamic precipitation, especially T, phase, influences mechanical properties of 2090 alloy. (author)