Microstructure, Mechanical Property and Thermo-Stability of Traditionally and Severely Deformed Al–Mg–Sc–Zr Alloy

The effect of annealing temperature on microstructure and mechanical property of rolling and equal channel angular pressing Al–Mg–Sc–Zr alloy were studied. The ECAP passes were set as 2, 4 and 6, and the rolling deformation was set as 75%. Then, the samples were annealed at different temperature (from 100 °C to 550 °C). Results show that with the increase of the ECAP strain, the grain size becomes finer and finer, and the microstructure becomes more and more uniform. According to the XRD result, the average dislocation densities are 8.02 × 1014/m2, 1.67 × 1015/m2, 2.12 × 1015/m2 and 2.21 × 1015/m2 for CR, 2P, 4P and 6P sample. The Vickers hardness also increases with the ECAP strain. The yield strengths of CR, 2P, 4P, and 6P samples are 384 MPa, 420 MPa, 449 MPa and 462 MPa, respectively. Different samples have different degrees of hardness reduction after annealing. When the annealing temperature is over 400 °C, the hardnesses of samples are upside down. The strength of 6P samples are the lowest among all samples, while the those of CR samples are the highest. This is because the extreme high dislocation density leads to drastic recrystallization, making the grains grow up and many Al3(Sc, Zr) particles become large and incoherent, undermining the pinning effect.