Fundamental Study on Nanotechnology Enabled Arc Welding of High Strength Aluminum Alloys

该项目旨在推进对纳米颗粒增强高强度铝合金电弧焊接性的基本理解。 由于其优异的机械性能，高强度铝合金被期望用于许多结构应用。 例如，通过焊接将轻质结构部件结合到功能组件中对于减少运输应用的燃料消耗和排放至关重要。 然而，这些高强度合金中的大多数由于裂纹而难以焊接，这显著地阻碍了它们的广泛使用。 最近，纳米技术使焊接方法，包括添加纳米粒子到熔融的焊接池已经进行了实验，以改善电弧焊接的铝合金，但缺乏控制和差的基本理解，阻碍了其实际应用。 在这个项目中，一种新的纳米技术使电弧焊接工艺，涉及一个专门制造的纳米复合材料的进给线，研究克服高强度铝合金的焊接性差的问题。 这有利于制造用于航空航天、汽车和生物医学应用的大规模、轻质结构和部件，从而影响美国工业并促进国家繁荣。 该项目具有丰富的教育，培训和推广组成部分，包括新课程开发，多样化的K-12和大学生参与，推广和技术转让活动。本研究的目的是了解纳米颗粒如何提高高强度铝合金电弧焊接过程中的可焊性和消除热裂纹。 电弧焊中的热裂纹是由于热应力、柱状晶生长和不完全熔化而产生的。 本研究以Al-Zn-Cu-Mg（AA 7075）铝合金为模型，以钨极氩弧焊（GTAW）为模型焊接工艺。 该项目首先侧重于通过挤出和拉丝的铸锭铸造的助熔剂辅助液态纳米粒子的掺入和分散过程的纳米复合材料消耗线的制造。 接下来，进行实验和分析研究，以了解纳米颗粒如何影响AA 7075在电弧焊过程中的凝固行为。 在凝固过程中进行了标准裂纹敏感性测试、显微组织研究和热分析。 该研究涉及研究纳米颗粒如何影响熔融区的凝固时间，凝固过程中的液体分数，以及初级相和次级相的细化/改性。 该项目研究了纳米颗粒如何在整个焊接材料中引起热流和液体分数的变化，影响凝固行为并消除热裂纹。 该项目表征了纳米颗粒对焊缝微观结构和机械性能的影响，建立了工艺-微观结构-性能的相关性，并产生了纳米颗粒对传统难焊铝合金电弧焊可焊性影响的新知识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project seeks to advance the fundamental understanding of nanoparticle-enabled mechanisms for enhancing arc weldability of high strength aluminum alloys. Due to their exceptional mechanical performance, high strength aluminum alloys are desired for numerous structural applications. For example, incorporating lightweight structural components into functional assemblies by welding is critical to reduce fuel consumption and emissions for transportation applications. However, most of these high strength alloys are difficult to weld because of cracking, which significantly hinders their widespread use. Recently a nanotechnology enabled welding approach involving adding nanoparticles to the molten weld pool has been experimented with to improve arc welding of aluminum alloys, but lack of control and poor fundamental understanding have hindered its practical use. In this project, a novel nanotechnology-enabled arc welding process, involving a specially fabricated nanocomposite feed wire, is studied to overcome the problem of poor weldability of high strength aluminum alloys. This facilitates the manufacture of large-scale, light-weight structures and components for aerospace, automotive and biomedical applications, thus impacting US industry and enhancing National prosperity. This project has rich educational, training, and outreach components, including new curriculum developments, diverse K-12 and university student involvement, outreach, and technology transfer activities. The goal of this research is to understand how nanoparticles enhance weldability and eliminate hot cracking during arc welding of high strength aluminum alloys. Hot cracking in arc welds occurs due to thermal stresses, columnar growth and incomplete backfilling. For this research Al-Zn-Cu-Mg (AA7075) is used as the model aluminum alloy while gas tungsten arc welding (GTAW) as the model welding process. The project first focusses on the fabrication of nanocomposite consumable wires via extrusion and wiredrawing of ingots cast by a flux-assisted liquid-state nanoparticle incorporation and dispersion process. Next, both experimental and analytical studies are conducted to understand how nanoparticles influence the solidification behavior of AA7075 during arc welding. Standard crack susceptibility testing, microstructural study, and thermal analysis during the solidification process are performed. The research involves examining how nanoparticles affect the solidification time of the melting zone, liquid fraction during solidification, and refinement/modification of both primary and secondary phases. The project studies how nanoparticles induce changes in thermal flow and liquid fraction throughout the welded material, influence the solidification behavior and eliminate hot cracks. The project characterizes nanoparticle effects on weld microstructures and mechanical properties, establishes process-microstructure-property correlations and generates new knowledge for nanoparticle effects on weldability during arc welding of traditionally hard-to-weld aluminum alloys.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.