Multi-length scale studies of early stage precipitation hardening phenomena in Al and Mg alloys

可热处理的AA6xxx(即Al-Mg-Si-(Cu))合金具有良好的综合性能，是应用最广泛的结构材料之一。这些合金用于几类豪华汽车或卡车的面板应用。然而，轻量化的紧迫性也引起了人们对它们在主流汽车上的使用的浓厚兴趣。这些面板通常是通过冷冲压，然后在油漆烘焙循环(PBC)过程中沉淀硬化而制成的。优化PBC的工业趋势是缩短加热时间和使用较低的温度。如果合金成分和/或加工历史没有得到适当优化，这些工艺要求可能会将析出限制在相对较早的阶段，并对硬化产生不利影响。这样的优化和设计更高强度的合金和具有成本效益的加工路线需要对控制溶质聚集和早期析出现象的机制有深入的了解。申请人在这一领域的最新工作突出了对铝合金时效硬化过程中出现的早期现象的主要认识空白。特别是，需要一项全面的原子到宏观尺度的研究，以了解合金成分、变形和早期沉淀硬化动力学之间的关系。 镁是工程金属中密度最低的，在交通运输的结构应用中也具有重要意义。然而，现有变形合金性能上的缺陷严重阻碍了它们的实际应用。最近，申请人和他以前的学生设计了极具吸引力的镁锌钙铈合金，具有良好的综合性能。然而，合金的优化和这些合金的最终使用需要进一步研究它们的沉淀硬化行为的基本原理。 本工作就是在上述背景下开展的，旨在研究合金化学成分、变形和热处理历史对AA6xxx合金和镁锌钙(Ce)合金早期析出和随后硬化的影响。将使用多尺度实验和建模方法来分析上述合金类别的选定集合中的加工-结构-性能关系的基本原理。 这项研究将创造重要的新知识，并为设计新的高强度轻质合金和组件以及具有成本效益的工艺铺平道路。这样的结果对加拿大的制造业和汽车行业将非常重要。它还将导致培训能够很好地为加拿大的教育和工业机构服务的高素质人员。

Heat treatable AA6xxx (i.e., Al-Mg-Si-(Cu)) alloys are among the most widely used structural materials owing to their combination of desirable properties. These alloys are used for panel applications in several classes of luxury automobiles or trucks. However, the urgency for lightweighting has created significant interest in their use in main stream automobiles, as well. These panels are commonly-fabricated by cold stamping and then precipitation hardened during paint bake cycling (PBC). The industrial trend in optimizing PBC is towards shortening heating times and using lower temperatures. These process requirements can limit precipitation to relatively early stages and adversely affect hardening, if alloy compositions, and/or processing histories are not properly optimized. Such optimizations and the design of higher strength alloys and cost effective processing routes requires a deep understanding of the mechanisms that govern solute clustering and early stage precipitation phenomena. The applicant’s most recent work in this area has highlighted the major gaps in knowledge of the early-stage phenomena that occur during age hardening of Al alloys. Particularly, a comprehensive atomic-to-macro length scale investigation is needed to understand the relationships between alloy compositions, deformation and the kinetics of early-stage precipitation hardening. Magnesium, with its lowest density among engineering metals, is of significant interest for structural applications in transportation, as well. However, the shortcomings in the properties of currently-available wrought alloys pose serious obstacles to their practical use. Recently, the applicant and his former student have designed highly attractive Mg-Zn-Ca-Ce alloys with promising combination of properties. However, alloy optimization and the eventual use of these alloys require further investigations into the fundamentals of their precipitation hardening behaviour. The proposed work is built on the above background and aims to investigate the role of alloy chemistry, deformation and thermal processing histories on the early stage precipitation and subsequent hardening in AA6xxx alloys, and Mg-Zn-Ca-(Ce) alloys. Multi-length scale experimental and modeling approaches will be used to analyze the fundamentals of processing-structure-property relationships in selected sets of the above alloy classes. This investigation will create significant new knowledge and pave the way for designing new high strength light alloys and components, as well as cost-effective processes. Such outcome will be highly important for Canada’s manufacturing and automotive sectors. It will also lead to the training of highly-qualified personnel which can well serve Canada's educational and industrial institutions.