Texture Control Techniques for Improving Room Temperature Formability of Mg Alloys including Pre-twinning: A Review

Magnesium (Mg) alloys are the lightest among the structural metallic materials and have attracted great interest due to their high specific strength and specific stiffness. However, Mg alloys show poor formability particularly at room temperature (RT), due to the development of strong basal texture and thus limiting their structural applications. Therefore, many techniques being constantly proposed to alter the crystallographic texture in Mg alloys, such as microalloying, especially with rare-earth (RE) elements, severe plastic deformation (SPD), thermomechanical processing (TMP), pre-twinning/stretching in the recent past. Pre-twinning remains the most effective technique that controls the crystallographic texture in Mg alloys by introducing {10 (1) over bar2} extension twins (ETs) which work out for alloys prepared through various prior processing conditions and compositions. Interestingly, only a small fraction of ETs during pre-twinning imparts significant improvement in the RT stretch formability. Therefore, this manuscript critically reviews the underlying mechanisms of pre-twinning and texture control via practical pre-twinning methods such as in-plane compression and compares its effectiveness with other texture control methods through alloy design, TMP, and SPD processes. In addition, the effect of initial microstructure and various deformation conditions on the contribution of twin, twin-orientation control during thermal treatment and also their influence on the RT stretch formability are discussed.