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

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

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.