The aim of this paper is to study the influence of the initial microstructure of several Mg-Al alloys on their superplastic formability and on their post-forming microstructure and mechanical properties. Various thermomechanical processing routes, such as annealing, conventional rolling, severe rolling and cross rolling, were used in order to fabricate AZ31 and AZ61 alloys with different grain sizes. These materials were then blow-formed into a hat-shaped die. It was found that the processing route has only a small effect in the formability of Mg-Al alloys or on the post-forming microstructures and properties due to rapid dynamic grain growth taking place at the forming temperatures. Nevertheless, good formability is achieved as a result of the simultaneous operation of grain boundary sliding and crystallographic slip during forming.

A coarse grained Zr-Hf alloy has been subjected to one rolling pass with different thickness reductions ranging from 10% to 80%. Rolling was performed at three temperatures: 300°C, room temperature (RT) and liquid nitrogen temperature (-196°C). It has been found that, with increasing strain per pass, i.e., with increasing strain rate, the deformation mechanism changes from twinning to dislocation slip. The minimum strain per pass necessary to trigger the transition in deformation mechanism decreases with decreasing temperature. High strain, high strain-rate deformation leads to the development of an ultrafine grained structure. Simultaneously, a basal type rolling texture forms. At the higher temperatures (RT and above) a recrystallization texture component is also present. Thus, nanostructuring of this Zr-Hf alloy during severe rolling is attributed to a combination of grain subdivision by the formation of geometrically necessary boundaries and to nucleation and growth phenomena taking place as a consequence of rapid adiabatic heating.