Flow behaviour and microstructural stability in an Al-3Mg-0.2Sc alloy processed by high-pressure torsion at different temperatures.

Abstract

Experiments were performed to examine the flow behaviour at room temperature (RT ≈ 300 K) and the microstructural stability of a solution-treated Al-3Mg-0.2Sc alloy processed through 10 turns of high-pressure torsion (HPT) at either RT or 450 K and further annealed for 1 h at temperatures (T) up to 773 K. The results revealed that the Al-3Mg-0.2Sc alloy achieved yield strengths of ~590 and 540 MPa after HPT at RT and 450 K, respectively. This followed from the higher dislocation densities achieved after processing at RT since both microstructures had average grain diameters of ~320 nm. After annealing at T ≥ 523 K, there was evidence for the onset of dynamic strain ageing (DSA) during tensile testing at RT and this occurred concurrently with increases in the elongations to failure. The grain structures developed during HPT at 450 K exhibited superior microstructural stability than after HPT at RT for comparable heating conditions. A model derived for materials having second-phase particles was applied to understand the microstructural evolution observed during heating. It is shown that the values calculated for the driving and restraining pressures for boundary migration and the boundary stability factors are consistent with the experimental results.