Method for the Depletion of the Basal Texture in Rolled AZ31 Magnesium Sheets

Abstract

The deformation and hardening mechanisms of magnesium usually lead to a typical basal orientation of crystals during a production of sheets by forming techniques. The basal texture related anisotropic property behavior and especially the further decrease in formability at room temperature is disadvantageous and undesired for subsequent rolling and final forming processes.The objective of this work is to find methods to improve these texture-related properties and the cold forming ability of magnesium sheets. Firstly, rolling at different temperatures and pass reductions, with the goal of weakening the basal texture component in semi-finished products is investigated, based on the advantageous initial texture and microstructure of twin-roll-cast (TRC) magnesium strips. In this context, texture and microstructure development is examined after a particular multi-pass rolling and heat treatment processes. Twin-roll-cast magnesium strips of alloy AZ31, with an initial thickness of 4.5 mm, rolled to a final thickness of 1.2 mm, are used as feedstock.Secondly, a new thermo-mechanical magnesium strip treatment has been developed in order to completely disintegrate the basal texture and intentionally generate only non-basal orientations with high Schmid-factors for the easy-to-activate basal slip systems. This process, which is designed as a final strip treatment, has been investigated regarding its texture change effect on rolled 1.2 mm AZ31 sheets, which also originate from TRC feedstock.It has clearly been found that the developed rolling technology for TRC feedstock leads to a significantly reduced basal texture due to grain boundary rotation and recrystallization at those rotated regions. The application of the separately developed strip treatment effects a complete elimination of the basal texture in a large volume of the sheet. Applying both technologies on magnesium sheets results in a tremendous increase in formability at room temperature as a consequence of the altered texture.