Modelling Crack Behaviour During Formation and Growth of Liquid Metal Embrittlement

模拟液态金属脆化形成和增长过程中的裂纹行为

• 批准号: RGPIN-2019-05649
• 负责人: Biro, Elliot
• 金额: $ 2.04万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=760410
• 关键词: Modelling; Crack; Behaviour; During; Formation

Due to environmental challenges, regulatory bodies are requiring automakers to decrease the greenhouse gas emissions of their vehicles. One way automakers are accomplishing this is by reducing vehicle weight using ultra high strength steels (UHSS). This allows thinner gauges of steel to be used without sacrificing safety. However, UHSS is susceptible to a cracking phenomenon known as liquid metal embrittlement (LME) when joined using resistance spot welding (RSW). LME is an intergranular cracking phenomenon where liquid metal weakens the surface grains of a metal being contacted. Under tensile stress, grain boundaries in the solid metal separate, forming a crack. Much work has been done to understand LME, however, there are still many questions. Although there is some understanding of how LME cracking affects post-welded strength, there is no understanding of how material attributes, temperature and stress states exasperate LME, leading to cracking during welding. Without this understanding, LME cracking cannot be modelled nor can crack-free welding procedures be designed. The proposed research program seeks to understand the role of material composition, microstructure, and strength in the initiation and growth of LME cracking. This knowledge will be used to create a process model capable of predicting cracking to design welding parameters to minimize LME. The program seeks to understand the role of material characteristics on LME by carrying out a series of in-situ observations. Various materials will be observed when heated under tension, so that role of microstructure on crack initiation and growth may be studied. Further understanding will be gained by analyzing the cracked area using electron microscopy. This knowledge will be built on by in-situ observations of weld cross-section during welding, showing how the dynamics of welding affects crack formation and how grain texture results in cracking repeatability. With understanding of how material characteristics, stress, and temperature affect crack formation, a process model will be made to predict cracking during welding. This model will be used to develop new process parameters and machine modification to minimize LME occurrence during spot welding. The proposed research program will develop an understanding of LME that will connect the role of material characteristics such as: microstructure, grain boundary orientation, composition and strength to local weld temperature and stress to LME formation. This knowledge will be used to develop guidelines to design LME resistant steels. Furthermore, the developed welding process model will be integrated into mechanical models so that post-weld properties predictions may account to for the role of LME cracking. The results from this program will offer welding methodologies to help Canadian industries minimize LME formation, allowing automakers to produce crack-free welds in their assembly plants, expanding the use of UHSS.

由于环境挑战，监管机构要求汽车制造商减少其车辆的温室气体排放。汽车制造商实现这一目标的一种方法是使用超高强度钢（UHSS）减轻车辆重量。这允许在不牺牲安全性的情况下使用更薄的钢。然而，当使用电阻点焊（RSW）连接时，UHSS易受称为液态金属脆化（LME）的开裂现象的影响。LME是一种晶间开裂现象，其中液态金属削弱了所接触金属的表面晶粒。在拉伸应力下，固体金属中的晶界分离，形成裂纹。人们对LME的认识已经做了很多工作，但仍存在许多问题。虽然对LME开裂如何影响焊后强度有一定的了解，但对材料属性、温度和应力状态如何加剧LME，导致焊接期间开裂没有了解。没有这种理解，LME裂纹不能建模，也不能设计无裂纹焊接工艺。拟议的研究计划旨在了解材料成分，微观结构和强度在LME裂纹的产生和增长中的作用。这些知识将被用来创建一个过程模型，能够预测裂纹设计焊接参数，以尽量减少LME。该计划旨在通过进行一系列现场观测来了解材料特性对大型海洋生态系统的作用。将观察各种材料在拉伸下加热时的情况，以便研究显微组织对裂纹萌生和扩展的作用。通过使用电子显微镜分析裂纹区域将获得进一步的理解。这方面的知识将建立在焊接过程中的焊缝横截面的原位观察，显示焊接的动态如何影响裂纹的形成，以及晶粒纹理如何导致裂纹的可重复性。通过了解材料特性、应力和温度如何影响裂纹的形成，将建立一个工艺模型来预测焊接过程中的裂纹。该模型将用于开发新的工艺参数和机器修改，以尽量减少点焊过程中LME的发生。拟议的研究计划将发展对LME的理解，将材料特性的作用联系起来，例如：微观结构，晶界取向，成分和强度，局部焊接温度和应力，以形成LME。这些知识将用于制定设计LME钢的指南。此外，开发的焊接工艺模型将被集成到力学模型，使焊后性能预测可能占的作用，LME开裂。该计划的结果将提供焊接方法，帮助加拿大工业最大限度地减少LME的形成，使汽车制造商能够在其装配厂生产无裂纹焊缝，扩大UHSS的使用。