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。

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.