Zhang Jixi, Daun Kyle J, Smith Rodney D L
Department of Chemistry, University of Waterloo, 200 University Avenue W., Waterloo, Ontario N2L 3G1, Canada.
Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue W., Waterloo, Ontario N2L 3G1, Canada.
ACS Omega. 2023 Jul 17;8(30):27002-27009. doi: 10.1021/acsomega.3c01938. eCollection 2023 Aug 1.
Hot-stamped ultrahigh strength steel components are pivotal to automotive light-weighting. Steel blanks, often coated with an aluminum-silicon (Al-Si) layer to protect them from oxidation and decarburization, are austenitized within a furnace and then simultaneously quenched and formed into shape. The Al-Si coating melts within the furnace and reacts with iron from the steel to yield an intermetallic phase that provides some long-term corrosion protection. During the intermediate liquid phase, some of the coating may transfer to the furnace components, leading to maintenance costs and operational downtime. A detailed understanding of the coating transformation mechanism is needed to avoid such production issues while ensuring that final intermetallic coatings conform to specifications. We introduce cross-sectional Raman microscopic mapping as a method to rapidly elucidate the coating transformation mechanism. Raman spectroscopic fingerprints for relevant intermetallic compounds were determined using synthesized Al-Fe-Si ternary and Al-Fe binary compounds. These fingerprints were used to map the spatial distribution of intermetallic compounds through cross sections of Al-Si-coated 22MnB5 specimens that were heated at temperatures between 570 and 900 °C. These chemical maps show that the intermetallic fraction of the coating does not grow significantly until formation of η (AlFe) at the steel interface, suggesting that η facilitates extraction of iron from the steel and subsequent diffusion through the coating. Under the heating conditions used here, a series of reactions ultimately lead to a silicon-rich τ (AlFeSi) phase on top of the binary η phase. The technique presented here simplifies structural analysis of intermetallic compounds, which will facilitate prototyping of strategies to optimize hot stamping.
热冲压超高强度钢部件对汽车轻量化至关重要。钢坯通常涂有铝硅（Al-Si）层以防止氧化和脱碳，在炉内进行奥氏体化，然后同时淬火并成型。Al-Si涂层在炉内熔化并与钢中的铁反应生成金属间相，提供一定的长期腐蚀保护。在中间液相阶段，部分涂层可能转移到炉部件上，导致维护成本和运行停机时间。需要详细了解涂层转变机制，以避免此类生产问题，同时确保最终的金属间涂层符合规格。我们引入横截面拉曼显微镜映射作为一种快速阐明涂层转变机制的方法。使用合成的Al-Fe-Si三元和Al-Fe二元化合物确定了相关金属间化合物的拉曼光谱指纹。这些指纹用于通过在570至900°C之间加热的Al-Si涂层22MnB5试样的横截面绘制金属间化合物的空间分布。这些化学图谱表明，直到在钢界面形成η（AlFe），涂层的金属间部分才会显著生长，这表明η促进了铁从钢中的提取以及随后通过涂层的扩散。在此处使用的加热条件下，一系列反应最终导致在二元η相顶部形成富硅的τ（AlFeSi）相。本文介绍的技术简化了金属间化合物的结构分析，这将有助于优化热冲压策略的原型设计。
