Retrogression characteristics of a novel Al-Cu-Li-X alloy

Abstract

Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ′ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ′ and θ′ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ′ and θ′ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T₁, T₂, δ′, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.

Keywords

retrogression / artificial aging / aluminum-lithium alloy / microstructure

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