Phase Transformations in the AlMg Alloys Driven by High‐Pressure Torsion

Abstract

As‐cast aluminum–magnesium alloys with 3, 5, and 10 wt% Mg are subjected to high‐pressure torsion (HPT) at room temperature: 5 GPa, five turns with rotation speed of 1 rpm. HPT leads to the strong grain refinement for both (Al) solid solution and intermetallic β‐phase. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) are used to characterize the phase transitions under heating of the HPT‐treated alloys. The decomposition of the solid solution in the ultrafine‐grained Al–10 wt% Mg alloy obtained by HPT does not follow the equilibrium diagram. The results of DSC, XRD, and TEM show that the Mg‐rich intermetallic phases appear during heating in the following sequence: GP zones → β → ε → β → γ → β. The (Al)/(Al) grain boundaries (GBs) in the fine‐grained Al–10 wt% Mg alloy after HPT and annealing up to 400 °C (i.e., in the solid solution area, far from solvus and solidus lines) contain the Mg‐rich areas. This can be the result of possible GB phase transitions with the formation of Mg‐rich GB phases. The GBs in the binary AlMg can contain the thin layers of a GB phase far away from the solvus line.