Abstract
A comprehensive consideration based on castability or plastic formability, as well as mechanical properties for development of either cast magnesium alloys or wrought magnesium alloys is a very important issue. To develop new magnesium alloy sheets with high formability at room temperature, the microstructure, texture, ductility and anisotropy of rolled Mg-Zn-Gd alloy sheets were investigated. The sheets exhibit an excellent ultimate elongation of nearly 50% and an uniform elongation greater than 30% with a very low planar anisotropy. The new sheet has a random basal texture and the basal pole is tilted by maximum 40° from the normal direction towards the transverse direction. The majority of grains in the tilted texture have an orientation favorable for both basal slip and tensile twining because of their high Schmid factor. The low planar anisotropy, the large uniform elongations and the high strain hardening rate observed in the Mg-Zn-Gd sheets result in excellent room temperature formability, the Erichsen values reach ~8, well comparable with the conventional aluminum alloys sheets at room temperature. The solidification pathways and phase equilibria of Mg-Al-Ca alloys have been profoundly investigated by using thermal analysis and thermodynamic calculations. The relationship between hot tearing tendency and alloy compositions were discussed in terms of strength of the mushy zone, solidification pathways and feeding mechanisms, et al. Thixoforming refers to as that metal components are formed in their semi-solid state. Criteria for thixoforming are summarized and then the thixoformability of Mg-Al-Ca based alloys (AC alloys) are evaluated using the thermodynamic calculations based on the consideration of metallurgical parameters.
Highlights
Improving fuel efficiency and reducing emissions of vehicles can be achieved through lightweight construction
The relationship between hot tearing tendency and alloy compositions were discussed in terms of strength of the mushy zone, solidification pathways and feeding mechanisms, et al Thixoforming refers to as that metal components are formed in their semi-solid state
Studies by Yong Liu, et al have shown that alloys with the Zn/Gd ratio in the range of 0.25 - 1 consist of α-Mg, w-phase and an unknown phase [17], and the w-phase is a ternary MgZnGd compound with the fcc structure [18]
Summary
Improving fuel efficiency and reducing emissions of vehicles can be achieved through lightweight construction. As the lightest structural metals, offer a remarkable potential in this regard. Their wide use is still restricted by their limited formability and castability. To improve the formability, it is desirable to develop magnesium sheets with weak basal texture and low anisotropy as well as excellent ductility at room temperature. It is feasible to develop new magnesium sheets with high formability at room temperature by addition of RE. Many efforts have been focused on the creep rupture and mechanical behavior of Mg-Al-Ca alloy at elevated temperature [12,13]. We report the texture, ductility, strain-hardening behavior, and stretch formability of rolled Mg-Zn-Gd alloys sheets at room temperature. The semi-solid formability of Mg-Al-Ca alloys at Mg-rich corner is predicted by thermodynamic calculation, which will provide some guide for future alloy composition design for semisolid forming
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