Varieties and Limitations of Dynamic Recrystallization Mechanisms in Al Alloys

摘要

Aluminum and its alloys are generally noted for dynamic recovery (DRV) during hot working to such a high level that they do not usually undergo dynamic recrystallization (DRX); although if held at or above the working temperature they do statically recrystallize. Among the exceptions to be discussed here is particle stimulated nucleation (PSN) of DRX in Al-Mg-Mn alloys due to large particles and the dense substructure. In alloys, such as Al-Cu-Zr, which have been processed to develop medium particles pinning a substructure with high misorientation walls, continuous DRX takes place during the initial stages of superplastic forming at low strain rates. In Al 99.999 the grain boundaries are highly mobile so that discontinuous DRX takes place in the classical manner. At very high strains where the elongated grains have a thickness of only 2 or 3 subgrain diameters, the opposite serrated boundaries begin to meet, pinching off the grains into short segments; this gives the appearance of DRX so is called geometric DRX. Finally in the warm end of the hot range, a noticeable density of boundaries misoriented over 10 deg develop inside the grains; this could be attributed to the gradual transition from hot to cold working; however some researchers maintain this is continuous DRX in which all subboundaries are continually rising in misorientation.