High density dislocations enhance creep ageing response and mechanical properties in 2195 alloy sheet

Abstract

The creep strain of conventionally treated 2195 alloy is very low, increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming. Therefore, finding a solution to improve the creep formability of Al-Cu-Li alloy is vital. A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation (LPD) on the creep ageing response in the 2195 alloy sheet at 160 °C with different stresses has been made. The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy. High-quality 2195 alloy sheet largely pre-deformed by 80% without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature, while severe edge-cracking occurs during room temperature rolling. The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10¹⁵ m⁻². At 160 °C and 150 MPa, creep strain and creep-aged strength generally increases by 4–6 times and 30–50 MPa in the LPD sample, respectively, compared to conventional T3 alloy counterpart. The elongation of creep-aged LPD sample is low but remains relevant for application. The high-density dislocations, though existing in the form of dislocation tangles, promote the formation of refined T₁ precipitates with a uniform dispersion.

Keywords

creep ageing / Al-Cu-Li alloy / high dislocation density / cryogenic rolling / dislocation strengthening

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