Impact of impurity elements on the corrosion performance of high strength 6xxx aluminium alloys

高强度和高抗压碎性的AA 6xxx AlMgSiCu铝合金目前是汽车工业中用于轻型车辆结构（包括白色车身）以及用于轻型和电动化的公路和越野车辆的优选选择。然而，全球对铝合金不断增长的需求只能在短期内通过二次金属的流通来满足，这不可避免地会给合金带来杂质。铁等杂质的增加或铜和镍等故意添加可能会对耐腐蚀性有害，特别是在用于汽车OEM认证的加速测试中。这意味着有强烈的研究动机来改善锻造AA 6xxx汽车合金的腐蚀性能，以满足这一需求，并从报废的再生铝中配制这些合金，以将嵌入的碳水平降低到低于2吨CO2 e/吨铝作为供应组件，并最终达到净零碳。了解表面微观结构的作用对于理解和控制挤压AA 6xxx合金在汽车应用中的腐蚀性能至关重要，特别是对于由寿命末期废料配制的合金，与由优质铝配制的合金相比，其杂质水平更高。这些高性能汽车合金都是通过故意添加杂质和来自报废废料来源（如车辆残骸和建筑物拆除）而配制的。这项工作将集中在合金微观结构的影响，包括模具线和其他表面特征，成分金属间化合物颗粒和晶界沉淀物，对腐蚀的启动和传播，使用相关的加速实验室测试，电化学分析，原位光学显微镜支持分析电子显微镜。新开发的X射线和基于电子的纳米层析成像技术也将用于空间上确定负责腐蚀引发和传播的微观结构特征。

High strength and high crush resistant AA6xxx AlMgSiCu aluminium alloys are presently the preferred choice for applications in the automotive industry for lightweight vehicle structures, including the body-in-white and for the light-weighting and the electrification of both on- and off-road vehicles. However, the increasing global demand for aluminium alloys will only be met in the near term by the circulation of secondary metals, which inevitably introduces impurities to alloys. Increased additions of impurities like iron or deliberate additions like copper and nickel can be detrimental to corrosion resistance particularly in the accelerated tests used for qualification with automotive OEMs. This means that there is a strong research incentive to improve the corrosion performance of wrought AA6xxx automotive alloys in response to this demand and to formulate these alloys from end-of-life recycled aluminium to reduce embedded carbon level to below 2 tonnes CO2e/tonne of aluminium as a supplied component and eventually to Net Zero carbon. Understanding of the role of surface microstructure is critical for the understanding and control of the corrosion performance of extruded AA6xxx alloys in automotive applications particularly for alloys formulated from end of life scrap with higher levels of impurities compared to those formulated from prime aluminium.The objective of the PhD project is to study the surface microstructure of the HSA6 family of high- performance automotive alloys formulated both with deliberate impurity additions and from end-of-life scrap sources like vehicle hulks and from the demolition of buildings. The work will be focused on the influence of alloy microstructure, including die lines and other surface features, constituent intermetallic particles and grain boundary precipitates, on the initiation and propagation of corrosion using correlative accelerated laboratory testing, electrochemical analysis, in situ optical microscopy supported by analytical electron microscopy. The newly developed X-ray and electron-based nanotomography will also be employed to spatially determine the microstructural features that are responsible for the initiation and propagation of corrosion.