Design of Twinning Induced Plasticity (TWIP) Magnesium Alloys

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Magnesium alloys are the lightest structural metals with densities near 34% lighter than aluminum alloys, and are thus very attractive for automotive and aerospace applications where improved fuel efficiency is urgently needed. However, strengthening magnesium alloys through the conventional alloy design approaches that are effective for aluminum alloys has proved difficult. The ductility of magnesium alloys is also low, which results in poor formability at room temperature. The low strength and ductility have limited the industrial applications of magnesium alloys, and new alloy design and processing strategies are needed to overcome these barriers. This award supports fundamental research for a new scheme for magnesium alloy design that departs from conventional approaches, and has the potential to lead to high-strength, ductile magnesium alloys. Computer simulations and experiments will be combined to identify alloying elements that can lead to high strength and ductility. The outcome of this research will provide guidelines for design of new magnesium alloys, leading to improved fuel efficiency of vehicles and reduced emissions. Educationally, this project provides an opportunity for engineering students to conduct computer simulations and experimental studies for alloy design.Twinning induced plasticity is very effective in achieving high strength and ductility in steels with high manganese concentrations in which mechanical twinning is strain-induced and contributes to the plastic flow and hardening, resulting in superior mechanical properties. In stark contrast, application of twinning induced plasticity is lacking in magnesium alloys, despite the fact that profuse twinning can be activated, because twinning is stress-induced at low stress levels in these alloys. Thus, to introduce twinning induced plasticity into magnesium alloys, the critical stress for twinning must be increased. In this research project, first principles calculations will be performed to identify alloying elements that have significant influences on the c/a ratio of magnesium alloys and the energy barrier for atomic shuffling during deformation twinning. These parameters control the critical stress for twin nucleation and growth. After these alloying elements are identified, alloy synthesis and thermomechanical processing will be conducted to achieve the optimal mechanical properties. This strategy opens a new window for sustainable design and processing of high performance magnesium alloys without resorting to expensive and exotic alloying elements.