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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=738427
• 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较薄的钢量表。但是，当使用电阻点焊接（RSW）连接时，UHSS易受一种称为液态金属含量（LME）的破裂现象。 LME是一种晶间开裂现象，其中液体金属削弱了接触的金属的表面晶粒。在拉伸应力下，固体金属中的晶界分开形成裂缝。为了了解LME，已经做了很多工作，但是，仍然有很多问题。尽管人们对LME开裂如何影响后焊后强度有一些了解，但对物质属性，温度和应力状态如何激怒LME，导致焊接过程中的破裂。没有这种理解，LME开裂就无法建模，也无法设计无破解的焊接程序。拟议的研究计划旨在了解材料组成，微观结构和力量在LME开裂的启动和增长中的作用。这些知识将用于创建一个过程模型，能够预测破裂以设计焊接参数以最大程度地减少LME。该计划试图通过进行一系列原地观察来了解材料特征对LME的作用。在张力下加热时，将观察到各种材料，以便可以研究微观结构对裂纹开始和生长的作用。通过使用电子显微镜分析破裂区域，将获得进一步的理解。这些知识将由对焊接过程中焊接横截面的原位观察结果建立，这表明焊接动力学如何影响裂纹形成以及谷物纹理如何导致重复性开裂。了解材料特性，压力和温度如何影响裂纹的形成，将制定过程模型以预测焊接过程中的裂纹。该模型将用于开发新的过程参数和机器修改，以最大程度地减少LME在点焊接过程中的发生。拟议的研究计划将对LME的理解发展，该计划将连接材料特征的作用，例如：微结构，晶界边界方向，组成和强度与局部焊接温度和应力与LME形成。这些知识将用于制定设计LME抗性钢的准则。此外，开发的焊接过程模型将集成到机械模型中，以便焊接后的性能预测可能解释了LME开裂的作用。该计划的结果将提供焊接方法，以帮助加拿大行业最大程度地减少LME的形成，从而使汽车制造商能够在其装配厂中生产无裂缝的焊接，从而扩大了UHSS的使用。