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

Abstract

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.

Texture and mechanical properties of superplastically deformed magnesium alloy rod

“…Since superplastic alloys can attain extensions greater than 200%, the application of superplasticity is expected to be useful for the forming of magnesium alloys [1]. Although the mechanical properties of superplastically deformed alloys are very important in industrial applications, limited data are available for those of magnesium alloys [1][2][3][4][5][6][7].…”

Effect of pressurization profile on the deformation characteristics of fine-grained AZ31B Mg alloy sheet during gas blow forming

“…The maximum average strain rate of 4.77 × 10 −3 s −1 was attained at the apex of the formed cap. Stepwise pressurization profiles for gas blow forming of a hat shaped geometry in Mg-Al alloys have been proposed by Pérez-Prado et al (2007). The aim of their work was to explore the influence of the initial microstructure on the superplastic formability of several Mg-Al alloys.…”

Influence of thermomechanical processing on the grain size, texture and mechanical properties of Mg-Al alloys

“…Indeed, a very fine grain size may be useless if stresses near to 100 MPa are required to carry out a forming process to prevent grain growth. The analysis performed in [108,109] shows that the best strategy to perform superplastic blow forming in magnesium alloys is to use grain sizes in the micron range and high forming temperatures, since then deformation is still controlled by GBS and elongations to failure larger than 200-300 % can be obtained using the moderate flow stresses that can be applied using conventional presses.…”

“…The mere obtaining of the finest possible grain size is not sufficient to ensure the practical feasibility of the process, as significant grain growth might occur already during temperature stabilization prior to forming. Optimization of a form- ing process thus requires a global approach to control microstructure stability and the deformation mechanisms operative under the forming conditions using the capabilities of the presses available [108,109]. Let us first examine the thermal stability of the Mg AZ31 alloy.…”

“…On the other hand, several studies were devoted to practical aspects about the development of microstructures capable of undergoing superplastic deformations. Various efforts have been devoted to investigate the superplastic conditions for sheet processed by LSHR [68,108]. In addition, the thermal stability of the microstructures obtained by severe plastic deformation processes has been discussed with the aim of obtaining the optimum superplastic conditions [67,109].…”