Constitutive Modelling of Twinning in Magnesium Alloys

镁合金孪晶的本构模型 社会和政府对汽车生产商施加了相当大的立法压力，要求它们减少汽车的燃油消耗和废气排放。实现这一目标的最有效方法之一是减轻车辆重量，这可以通过在结构和车身面板中用镁取代钢和铝来实现。然而，镁合金有一些明显的和实际的技术限制，其中最重要的是与铝和钢相比，它们的成形性降低。人们认为，这可以通过改进合金的开发来消除，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。从开发用于类似应用的铝和钢等其他材料所获得的经验来看，适当的本构模型是开发过程的重要和基础部分。因此，本研究的主要目的是开发、改进和验证描述镁合金在不同变形过程中大应变行为的本构模型。 在麦克马斯特，人们一直致力于镁合金的本构模型研究。2012年，我们提出了镁合金的孪生和去孪生模型(TDT)，并将其应用到我们于2010年发展的多晶材料的有限应变弹粘塑性自洽(EVPSC)模型中。结果表明，EVPSC-TDT模型能够很好地反映镁合金大应变行为的主要特征。虽然EVPSC-TDT模型代表了这一研究领域的最先进水平，但仍然存在一些长期的挑战。特别是，有必要开发一种更基于物理的孪生模型，该模型适当地描述孪生以及孪生孪生和孪晶滑移的相互作用。因此，拟议计划的重点是开发最佳双胞胎模型。 拟议工作的主要影响将是基本科学知识的发展和开展这项研究时出现的培训机会。这项研究的结果将对涉及轻金属制造工艺的关键行业具有重要价值，并最终将导致利用最佳成形性和性能特征的成本效益制造工艺。

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.