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

该项目旨在促进对纳米颗粒增强高强度铝合金可焊性的机理的基本理解。由于其优异的机械性能，高强度铝合金被广泛应用于各种结构应用中。例如，通过焊接将轻质结构部件整合到功能组件中，对于减少运输应用的燃料消耗和排放至关重要。然而，这些高强度合金大多因裂纹而难以焊接，这严重阻碍了它们的广泛使用。最近，为了改善铝合金的弧焊性能，人们尝试了一种纳米技术焊接方法，即在熔池中添加纳米颗粒，但缺乏控制和基础知识的缺乏阻碍了这种方法的实际应用。为了克服高强铝合金焊接性差的问题，本项目研究了一种基于纳米技术的新型弧焊工艺，该工艺包括一种特殊制造的纳米复合送丝。这有助于制造用于航空航天、汽车和生物医学应用的大型、轻质结构和部件，从而影响美国工业并促进国家繁荣。该项目有丰富的教育、培训和外展内容，包括新课程开发、多样化的K-12和大学生参与、外展和技术转让活动。本研究的目的是了解纳米颗粒在高强铝合金弧焊过程中如何提高焊接性和消除热裂纹。由于热应力、柱状晶生长和填充不完全等原因，导致弧焊接头产生热裂纹。本研究采用Al-锌-铜-镁(AA7075)铝合金为模型铝合金，以钨极气体保护焊(GTAW)为模型焊接工艺。该项目首先专注于通过助熔剂辅助的液态纳米颗粒掺入和分散工艺对铸造的钢锭进行挤压和拉丝来制造纳米复合消耗丝。其次，进行了实验和分析研究，以了解纳米颗粒如何影响AA7075在弧焊过程中的凝固行为。在凝固过程中进行了标准的裂纹敏感性测试、显微组织研究和热分析。这项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和次级相的细化/变质。该项目研究纳米颗粒如何在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接组织和机械性能的影响，建立了工艺-组织-性能的相关性，并为纳米颗粒对传统难以焊接的铝合金的焊接性的影响产生了新的知识。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。

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.