In situ optical diagnostics for characterizing the coating transformation of aluminized steel during hot stamping

科斯玛国际是加拿大最大的汽车零部件制造商之一，通过热冲压生产高强度汽车零部件。在此过程中，超高强度钢坯料首先在辊底炉中进行奥氏体化，然后转移到水冷模具中，在那里零件同时淬火并成形。毛坯有一层薄的铝/硅涂层，可以防止钢在炉中氧化和脱碳。涂层熔化并与钢中的铁反应形成永久的Al-Si-Fe金属间层，提供一些长期的腐蚀保护，但如果涂层太厚也可能损害焊接装配。钢的辐射性能（决定毛坯加热速度）和表面纹理（影响模具淬火速度和油漆附着力）也随着加热时间而变化。目前关于涂层演变的知识几乎完全来自于对在炉中加热、提取和淬火的试样的非原位分析，但是该过程的时间分辨率有限，淬火会改变涂层的织构。这项研究将部署一套新的光学诊断，包括激光散斑分析、傅里叶变换红外光谱和3D拉曼光谱，以提供Al-Si涂层随加热变化的连续原位测量。这些测量将用于推导涂层演变模型，该模型将允许Cosma优化基于炉的热冲压操作，将其技术应用于新材料，并开发全新的制造工艺

Cosma International, one of Canada's largest automotive parts manufacturers, makes high strength automotive parts through hot stamping. In this procedure, ultrahigh strength steel blanks are first austenitized in a roller hearth furnace and then transferred to a water-cooled die, where the parts are simultaneously quenched and formed into shape. The blanks have a thin aluminum/silicon coating that prevents the steel from oxidizing and decarborizing in the furnace. The coating melts and reacts with iron from the steel to form a permanent Al-Si-Fe intermetallic layer that provides some long term corrosion protection, but may also impair welding assembly if it grows too thick. Both the radiative properties of the steel, which determines the blank heating rate, and the surface texture, which affects die quenching rates and paint adhesion, also evolves with heating time. The present state-of-knowledge about coating evolution comes almost entirely from ex situ analysis of coupons that have been heated in the furnace, extracted, and quenched, but the temporal resolution of this procedure is limited and quenching alters the coating texture. This research will deploy a new suite of optical diagnostics, including laser speckle analysis, Fourier-transform infrared spectroscopy, and 3D Raman spectroscopy, to provide continuous in situ measurements of the Al-Si coating as it transforms with heating. These measurements will be used to derive a coating evolution model that will allow Cosma to optimize furnace-based hot stamping operations, adopt their techniques to new materials, and develop entirely new manufacturing processes