Constitutive Modelling of Twinning in Magnesium Alloys

镁合金孪生本构模型***社会和政府对汽车生产商施加了相当大的立法压力，要求他们减少汽车的燃料消耗和废气排放。实现这一目标的最有效方法之一是通过在结构和车身面板中用镁代替钢和铝来减轻车辆重量。然而，镁合金有许多可感知的和实际的技术限制，其中最重要的是与铝和钢相比，它们的可成形性降低。人们相信，这可以通过改进合金的发展来消除，或者通过使用新的制造方法来避免。******与钢和铝相比，人们对镁及其合金的成形行为知之甚少。从开发其他材料（如铝和钢）的类似应用中获得的经验来看，适当的本构建模是开发过程中重要的基础部分。因此，本研究计划的主要目的是开发/改进和验证描述镁合金在各种变形过程下大应变行为的本构模型。******在麦克马斯特，一个巨大的努力已经集中在镁合金的本构模型。2012年，我们提出了镁合金的孪生和去孪生模型（TDT）模型，并将其应用于我们在2010年为多晶材料开发的有限应变弹粘塑性自一致（EVPSC）模型。结果表明，EVPSC-TDT模型能够捕捉到镁合金大应变行为的关键特征。尽管EVPSC-TDT模型代表了该研究领域的最新技术，但仍存在一些长期存在的挑战。特别是，有必要建立一个更基于物理的孪生模型，以适当地描述孪生和双孪生和双滑移的相互作用。因此，该计划的重点是开发最佳的孪生模型。******拟议工作的主要影响将是发展基础科学知识和在进行这项研究时产生的培训机会。该研究结果将对涉及轻金属制造工艺的关键行业具有重要价值，并将最终导致利用最佳成形性和性能特征的成本效益高的制造工艺。* * * * * * * *

CONSTITUTIVE MODELING OF TWINNING IN MAGNESIUM ALLOYS***There has been considerable societal and government legislative pressure on automotive producers to reduce fuel consumption and exhaust gas emissions from vehicles. One of the most effective ways to achieve this is by vehicle weight reduction that can be obtained by replacing steel and aluminum with magnesium in the structure and body panels. However, magnesium alloys have a number of perceived and real technological limitations, the most significant of which is their reduced formability as compared to aluminum and steel. It is believed that this could be eliminated by the development of improved alloys, or circumvented through the use of new manufacturing methods.******The forming behavior of magnesium and its alloys is poorly understood compared to that of steel and aluminum. From the experiences gained in developing other materials like aluminum and steel for similar applications, appropriate constitutive modeling is an important and foundational part of the development process. Therefore, the main purpose of this proposed research program is to develop/improve and validate constitutive models for describing large strain behavior of magnesium alloys under various deformation processes.******At McMaster, a great effort has been focused on constitutive modellling of Mg alloys. In 2012 we proposed a twinning and de-twinning model (TDT) model for Mg alloys and implemented it into the finite strain Elastic-Viscoplastic Self-Consistent (EVPSC) model we developed in 2010 for polycrystalline materials. It has been shown that the EVPSC-TDT model is able to capture key features observed in large strain behaviour of Mg alloys. Although the EVPSC-TDT model represents the state-of-the-art in this research area, there remain some longstanding challenges. In particular, it is necessary to develop a more physically-based twinning model which appropriately describes twinning and interactions of twin-twin and twin-slip. The focus of the proposed program is thus on developing the best twinning model. ******The major impact of the proposed work will be the development of basic scientific knowledge and the training opportunities that arise while conducting this research. The results of this research will be of great value to the key industries involved in light metal fabrication processes and will ultimately lead to cost-effective fabrication processes utilizing optimum formability and performance characteristics. ********