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

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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. ************ **