Investigation of the connection between the microstructure and thermomechanical properties in structured AlCu-based alloys

Abstract

A description is given of the structure and precipitation sequence of AlCu_4.5 alloys with a magnesium content between those of binary AlCu and quasi-binary AlCuMg alloys. For alloys with a small magnesium content (0.23 wt%) these are the coherent copper-like Guinier-Preston zones and the incoherent Θ' and Θ phases with an adequate content of dissolved magnesium, so the precipitation sequence can be essentially realized without any difficulty. In the case of higher magnesium concentration, a re-orientation occurs because it requires both time and energy. An undisturbed transition to the Θ (Mg) phase is impossible. The phase structure becomes more similar to that of the S phase but it is unsafe to describe it as a quasi-binary structure. The different sizes which develop between the AlCu_4.5 and AlCuMg_0.98 alloys are discussed.