Examining the Mechanisms of Dynamic Recrystallization (DRX) in Two-Phase Al Alloys

Second phase particles raise density and stability of strain-induced dislocation boundaries (SIB-HAB high-angle) and also markedly diminish boundary transformability and mobility at high temperature. In deformation of Al-Mg-Mn, large Al₆Mn particles create surroundings of high-density cells that can nucleate particle-stimulated static or dynamic recrystallization (PSN-SRX or PSN-DRX, discontinuous with mobile boundaries, GB) that are valuable for grain refinement (if no pinning by fine Al₆Mn). Particle stimulated nucleation PSN-DRX is only supported in alloys with over 2% Mg that markedly reduces the level of DRV, Hornbogen showed that fine particles in high density after cold working can markedly deter dSRX, but the SIB-HAB reorganize into boundaries that would be mobile if not particle pinned; this is continuous cSRX. After heavy thermomechanical processing (TMP: <300°C,>5s−1), Al-Cu-Mg-Zr, or Al-10Mg-Zr, when subjected to superplastic testing (>400C, <10 −2s−1) SIB-HAB rapidly rearrange into GB capable of rapid shearing, thus supporting very high elongations; a rearrangement that deserves the name continuous cDRX. The dislocation build up into very stable SIB-HAB during TMP is not reasonably classed as cDRX. Initially deformed substructures (IDS) are often present where precipitates hinder SRX. They markedly and diversely affect substructure development in hot working and could lead to a pseudo IDS-DRX that deserves careful investigation but is not a general characteristic of the alloy.