Understanding plastic instability in next generation magnesium alloys

在高度可成形变形镁合金的合金和工艺设计中，考虑塑性变形过程中发生的材料不稳定性是非常重要的。特别是，应通过了解其在大范围变形条件下的机制来源来避免不必要的关联效应，如应变局部化、过早开裂和表面条纹。因此，本研究建议更好地理解动态回复、动态再结晶和动态析出等动态组织现象与塑性失稳的发生之间的联系，作为不同变形条件和合金成分的函数。该项目的主要目的是研究选定的具有良好强度和成形性的镁-锰-钕和镁-锰-钙合金的塑性流动不稳定性(不连续屈服)，并对所研究的合金中塑性失稳的控制机制提供合理的描述。此外，还将确定由于溶质原子和/或析出物的存在而发生塑性失稳的条件，以及它们与移动位错的相互作用。同样重要的是，与单独添加合金相比，合金元素可能的协同效应在塑性不稳定的发生中是否起着越来越大的作用，以及是否可以利用这种效应来优化织构和微观结构。拟议的研究具有基础性，但对板材成形的前景具有重要影响，特别是在汽车和航空工业，镁合金由于其优异的比强度，正变得越来越重要。深入了解合金成分、主动变形机制与塑性失稳发生之间的关系，有助于提高新一代镁合金的强度和成形能力，从而改善其性能。

In alloy and process design endeavours of highly formable wrought Mg alloys it is utterly important to account for material instability that occurs during plastic deformation. Especially, unwanted associated effects, such as strain localization, premature cracking and surface striations, should be avoided by understanding their mechanistic origins over a wide range of deformation conditions. Therefore, the present research proposal focuses on better understanding the link between dynamic microstructural phenomena, such as dynamic recovery, dynamic recrystallization and dynamic precipitation and the occurrence of plastic instability as a function of varying deformation conditions and alloy compositions. The main aims of the proposed project are to investigate the plastic flow instability (discontinuous yielding) in selected Mg-Mn-Nd and Mg-Mn-Ca alloys showing a good property profile of strength and formability, and provide a sound description of the governing mechanisms of plastic instability in the investigated alloys. Additionally, the conditions under which the plastic instability occurs as a result of presence of solute atoms and/or precipitates, and their interaction with mobile dislocations will be determined. Also of importance is whether possible synergetic effects of alloying elements play an increasing role in the onset of plastic instability, as compared to individual alloying additions, and whether such effects can be exploited to optimise texture and microstructure.The proposed research is of fundamental nature but has significant implications for sheet metal forming perspectives, particularly in the automotive and aircraft industries, where Mg alloys, due to their excellent specific strength, are becoming increasingly important. Acquiring advanced knowledge of the correlation between alloy composition, active deformation mechanisms and the occurrence of plastic instability greatly contributes towards improving the performance of next generation magnesium alloys by increasing their strength and forming capability.