Influence of thermomechanical processing on superplastic forming of Mg-Al alloys

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 postforming 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 crystallography slip during forming.