Enhancing homogenous precipitation and strengthening effectiveness in AlCuMg alloy

Abstract

Precipitation strengthening is one of the most effective strengthening mechanisms in metallic alloys. Its effectiveness depends on the number density of small precipitates homogenously distributed in the matrix. In this work, an attempt has been made to accelerate precipitation and thus precipitation strengthening in an AlCuMg alloy though a specially designed thermo-mechanical treatment. Solution heat treatment has been carried out before and directly after heavy rolling followed by conventional ageing in order to study homogenous nucleation of GPB zones. It appeared that samples solutionized after plastic deformation feature much higher hardness as well as density of precipitates when compared to ones after conventional treatment. The reasons of this unexpected outcome had been studied by means of differential scanning calorimetry and transmission electron microscopy. It was found that the evolution of GPB zones and further phases vary depending on the pre-ageing history. Diffusion-based phenomena controlling the nucleation seems to be accelerated in samples heat treated directly after the rolling. Based upon the affinity of solutes to the vacancies it has been deduced that magnesium plays a critical role in binding and releasing vacancies during the thermo-mechanical procedure. As a result, GPB zones are present in very early stages of ageing providing nucleation sites for the most strengthening precipitates which are fine and densely distributed within grains. An atomistic model for nucleation of early precipitates is discussed on the basis of DSC measurements, STEM analysis and data available in literature.

Keywords

• Aluminium alloys
• Precipitation strengthening
• (Scanning) transmission electron microscopy
• Differential scanning calorimetry
• Diffusion