Microstructure and mechanical properties of an Al-Mg alloy solidified under high pressures

Phase formation, the microstructure and its evolution, and the mechanical properties of an Al-42.2 at.% Mg alloy solidified under high pressures were investigated. After solidification at pressures of 1 GPa and 2 GPa, the main phase is the gamma phase, richer in Al than in equilibrium condition. When the pressure is further increased to 3 GPa, the main phase is the supersaturated Al(Mg) solid solution with Mg solubility up to 41.6 at.%. Unlike in similar alloys solidified at ambient pressure, the beta phase does not appear. Calculated high-pressure phase diagrams of the Al-Mg system show that although the stability range of the beta phase is diminished with pressure, it is still thermodynamically stable at room temperature. Hence, the disappearance of the beta phase is interpreted as kinetic suppression, due to the slow diffusion rate at high pressures, which inhibits solid-solid reactions. The Al-42.2 at.% Mg alloy solidified under 3 GPa has remarkably enhanced ultimate tensile strength compared to the alloy solidified under normal atmospheric pressure. (c) 2013 Elsevier B.V. All rights reserved.