An Innovative Hybrid Ultrasonic Resistance Welding Process for Joining Advanced Lightweight and Dissimilar Materials

在提高燃油经济性和减少碳排放方面，轻量化结构是非常可取的。作为关键的轻量化推动因素，先进的轻质材料和多材料结构的成功利用依赖于经济可靠的连接工艺。电阻点焊作为汽车工业中应用最广泛的技术之一，由于不同材料的物理性能和冶金差异，不适合用于不同材料的连接。此外，RSW在加入最新一代先进的高强度钢和铝合金方面也面临着挑战。相比之下，超声点焊显示了一些优点，但其应用受到了普遍存在的超声波换能器输出功率的限制。该奖项侧重于一种创新的混合超声电阻焊(URW)工艺，该工艺有效地集成了超声波和电阻焊，最大限度地发挥了每种工艺的优势。初步结果表明，与URW联合力学性能得到了很好的改善。这一研究将深入推进对电声耦合复杂机理的科学认识。由于该技术广泛适用于汽车、航空航天和国防工业，该项目直接影响到美国的经济福利和国家安全。成功开发的URW工艺将大大有利于轻量化结构的制造和组装，特别是多材料结构的制造和组装。超声波和RSW系统的内在相似性使其可以很自然地适应现有的RSW机器人和设备，促进了URW的广泛工业应用。所获得的关于超声诱导物理现象的知识将对开发和改进各种先进制造工艺做出深刻贡献。一个具体的例子是超声波电阻添加剂的制造。URW过程和微结构演化模型加强了集成计算材料工程(ICME)在固态制造领域的应用。最后，作为该奖项的结果，多学科教育计划将增强机械、材料、冶金、控制和数据处理领域的下一代工程师和研究人员的能力。本研究的目的是增进对新型混合URW工艺所涉及的多物理热-力-电-声耦合机理的认识，揭示焊接组织演变的基本物理过程，并优化URW用于连接先进的轻质和不同材料。超声振动通过去除表面涂层和污染物来改变接触电阻，通过声流和空化效应影响熔化过程中的热力学和动力学条件，以及在凝固过程中细化组织。本文的研究范围包括：(1)对不同条件下的城市道路钢焊接进行了全面的试验研究，并对焊缝进行了力学性能测试和多尺度表征。将建立工艺-结构-性能关系；(2)通过高速和热成像对城市污水处理过程进行现场分析，并进行多物理模拟，以确定工艺过程中的热机械场。还将建立Al-Fe界面反应模型，通过在受控热机械试验环境下金属间化合物(IMC)的形成和生长的物理模拟来验证该模型。(3)在工艺参数、电极几何形状以及声场和电场之间的同步方面对URW工艺进行优化，以便以最少的输入工艺能量实现理想的联合性能。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Lightweight structures are highly desirable for improving fuel economy and reducing carbon emissions. As key lightweight enablers, successful utilizations of advanced lightweight materials and multi-material structures rely on economical and reliable joining processes. Resistance spot welding (RSW), as one of the most extensively used technologies in the automotive industry, is not suitable for joining dissimilar materials due to their different physical properties and metallurgical differences. In addition, RSW faces challenges in joining the newest generation of advanced high strength steel and aluminum alloys. In comparison, ultrasonic spot welding (USW) shows several advantages, but its applications are limited by the output power of generally available ultrasonic transducers. This award focuses on an innovative hybrid ultrasonic resistance welding (URW) process, which effectively integrates ultrasonic and resistance welding, maximizing the advantages of each process. Preliminary results show promising enhancements of joint mechanical performance with URW. The research will deeply advance the scientific understanding of the complex coupling mechanisms between electrical and acoustic fields. Since this technology has wide applicability to the automotive, aerospace and defense industries, the project directly impacts the economic welfare and national security of the United States. The successfully-developed URW process will significantly benefit manufacturing and assembly of lightweight, and especially multi-material structures. The inherent similarities of ultrasonic and RSW system make it naturally convenient to adapt existing RSW robots and equipment, facilitating widespread industrial applications of URW. The obtained knowledge on ultrasonically induced physical phenomena will deeply contribute to developing and improving various advanced manufacturing processes. One specific example is ultrasonic resistance additive manufacturing. The URW process and microstructural evolution model enhances applications of integrated computational materials engineering (ICME) in the field of solid-state manufacturing. Finally, the multidisciplinary educational program as a result of the award will empower next-generation engineers and researchers in the fields of mechanical, material, metallurgy, control, and data processing. The objectives of this research are to advance the knowledge of multiphysical thermo-mechanical-electrical-acoustic coupling mechanisms involved with the novel hybrid URW process, to reveal the fundamental physics of weld structure evolution and to optimize URW for joining advanced lightweight and dissimilar materials. Ultrasonic vibration is hypothesized to affect RSW in three stages: modifying contact resistance through removal of surface coatings and contaminations, influencing thermodynamic and kinetic conditions during melting through acoustic streaming and cavitation effects, and refining microstructure during solidification. The scope of this research includes: (1) A comprehensive experimental study of URW at various conditions, followed by mechanical testing and multi-scale characterizations of the welds. Process-structure-properties relationships will be established; (2) In situ analysis of the URW process through high speed and thermal imaging, as well as multiphysical modeling to determine the thermo-mechanical field during the process. Al-Fe interfacial reaction model will also be developed, which will be verified through physical simulations of the inter-metallic compounds (IMC) formation and growth under a controlled thermo-mechanical testing environment. (3) Optimization of the URW process in terms of process parameters, electrode geometry along with the synchronization between acoustic and electrical fields for desirable joint performance with the minimum amount of input process energy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.