Retrogression, reaging, and mechanical behaviour of a 1441 Al–Li–Cu–Mg–Zr alloy

Abstract

A 1441 Al-Li-Cu-Mg-Zr alloy was subjected to retrogression treatment and the retrogressed states were immediately reaged to various tempers. Hardness measurement, tensile testing, and SEM fractography have been carried out to conventional peak-aged, retrogressed, retrogressed and reaged (RRA), and over-aged tempers of the alloy. Retrogression treatment applied to peak-aged tempered alloys resulted in a decrease in hardness and tensile strength, an increase of ductility, and a serration phenomenon in the plastic region. These are primarily due to the dissolution of matrix strengthening δ′ precipitates into solid solution upon retrogression treatment. Retrogressed states have been reaged to various under-, peak-, and over-aged tempers. Reaging the retrogressed state to peak-aged temper has resulted in attaining the original peak-aged strength and ductility value. SEM fractography study has been carried out and fracture surfaces exhibited predominantly intergranular fracture in presence of few dimples. TEM and DSC studies have been carried out to observe the microstructural changes upon RRA treatment and to explain the mechanical behaviour of the alloy.