Effects of re-solution, pre-stretching and double re-ageing treatment on mechanical behavior and microstructure of 2195 Al-Cu-Li alloy

The effects of re-solution, pre-stretching and double re-ageing (RPD) treatment on the microstructure and me-chanical performance of 2195 Al-Cu-Li alloy were investigated. The results indicate that RPD treatment en-hances the strength from-567 MPa with a standard T8 temper to-584 MPa. A simultaneous improvement in strength and ductility is attained in a PA-RPD sample processed by 510 degrees C x 1 h re-solution, 7% pre-stretching and 120 degrees C x 12 h + 155 degrees C x 24 h double re-ageing. The improved mechanical properties are ascribed to the re -tailor of microstructures during RPD treatment involving grain morphology, dislocation density, and precipi-tation feature. The PA-RPD samples with varied pre-strains exhibit no evident difference in grain size, but slightly larger than that at T8 state and much smaller than that at re-solution state. The dislocation density is mainly determined by the pre-stretching levels and suffered minor annihilation in double re-ageing. T1 precursor phases are nucleated from first-step re-ageing (120 degrees C), most of which are connected to pre-stretched dislocations, and then grow into well-dispersed T1 plates in second-step re-ageing (155 degrees C). The increased strength is dominantly attributed to the reversible finer precipitation of nano-sized T1 plates, yielding considerable precipitation strengthening, as well as higher dislocation density, producing dislocation strengthening. The improved ductility in the PA-RPD sample is mainly on account of the finer and more uniform distribution of T1 plates which enhance the plastic stability during tensile testing.