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

Cosma International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。在这一过程中，高强度钢坯料首先在辊底炉中进行淬火，然后转移到水冷模具中，在那里零件同时淬火并成形。坯料具有薄的铝/硅涂层，其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金属间化合物层，提供一些长期的腐蚀保护，但如果它生长得太厚，也可能损害焊接组件。决定坯料加热速率的钢的辐射特性和影响模具淬火速率和油漆附着力的表面纹理也随加热时间而变化。 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是有限的，并且淬火改变了涂层纹理。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，和三维拉曼光谱，提供连续原位测量的铝硅涂层，因为它与加热转换。这些测量将被用来推导出一个涂层演变模型，这将使Cosma优化基于模具的热冲压操作，采用他们的技术，以新材料，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