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: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=682580
• 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方法之一是使用超高强度钢 (UHSS) 减轻车辆重量。这使得可以在不牺牲安全性的情况下使用更薄的钢材。然而，当使用电阻点焊 (RSW) 连接时，UHSS 很容易出现称为液态金属脆化 (LME) 的开裂现象。******LME 是一种晶间开裂现象，液态金属会削弱金属的表面晶粒。联系过。在拉应力作用下，固体金属中的晶界分离，形成裂纹。为了理解 LME 已经做了很多工作，但仍然存在许多问题。尽管人们对 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 从而导致焊接过程中开裂尚不了解。 如果没有这种理解，就无法对 LME 裂纹进行建模，也无法设计无裂纹焊接程序。拟议的研究计划旨在了解材料成分、微观结构和强度在 LME 裂纹萌生和扩展中的作用。 这些知识将用于创建能够预测裂纹的工艺模型，以设计焊接参数，以最大限度地减少 LME。******该计划旨在通过进行一系列现场观察来了解材料特性对 LME 的作用。 各种材料在张力下加热时都会被观察到，因此可以研究微观结构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了解。 这些知识将建立在焊接过程中焊缝横截面的现场观察的基础上，显示焊接动力学如何影响裂纹的形成以及晶粒织构如何导致裂纹的重复性。 了解材料特性、应力和温度如何影响裂纹形成后，将建立一个过程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改造，以最大限度地减少点焊过程中 LME 的发生。******拟议的研究计划将加深对 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、成分和强度对局部焊接温度的影响以及对 LME 形成的应力的影响。 这些知识将用于制定耐 LME 钢的设计指南。 此外，开发的焊接工艺模型将集成到机械模型中，以便焊后性能预测可以解释 LME 裂纹的作用。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 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。**